U.S. patent application number 14/618337 was filed with the patent office on 2015-06-04 for billet, method of working a billet, and ferrous product produced from a billet.
The applicant listed for this patent is Cladinox International Limited. Invention is credited to Antonino Giorgio CACACE.
Application Number | 20150151512 14/618337 |
Document ID | / |
Family ID | 43499937 |
Filed Date | 2015-06-04 |
United States Patent
Application |
20150151512 |
Kind Code |
A1 |
CACACE; Antonino Giorgio |
June 4, 2015 |
BILLET, METHOD OF WORKING A BILLET, AND FERROUS PRODUCT PRODUCED
FROM A BILLET
Abstract
A billet includes a solid steel body and an alloy cladding. The
cladding may include a square tube in which the body is inserted
with an interface at which the cladding becomes bonded to the body
when the billet is heated and rolled or otherwise worked into a
ferrous product. At least one element composed of a mass of finely
divided scavenging aluminium, titanium or magnesium, is placed in
the tube adjacent the body and separate from the interface. The
elements are advantageously compressed into briquettes which
scavenge oxygen from residual air at the interface to prevent
oxidation of the cladding at the interface. The tube may be closed
to prevent gases outside the billet from penetrating to the
interface. Alternatively, reliance may be placed on the briquettes
to scavenge oxygen from the residual air and also from atmospheric
air and furnace gases before they can penetrate to the
interface.
Inventors: |
CACACE; Antonino Giorgio;
(West Glamorgan, GB) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Cladinox International Limited |
Seychelles |
|
AU |
|
|
Family ID: |
43499937 |
Appl. No.: |
14/618337 |
Filed: |
February 10, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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13501937 |
Apr 13, 2012 |
9005767 |
|
|
PCT/GB2010/001934 |
Oct 19, 2010 |
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14618337 |
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Current U.S.
Class: |
428/576 ; 29/505;
428/683; 428/685 |
Current CPC
Class: |
C21D 8/06 20130101; C21D
2251/00 20130101; Y10T 428/12979 20150115; B21C 33/004 20130101;
C22C 9/06 20130101; B32B 15/011 20130101; B32B 15/01 20130101; Y10T
428/12965 20150115; C21D 2251/02 20130101; Y10T 428/12229 20150115;
Y10T 428/12778 20150115; Y10T 428/12924 20150115; Y10T 428/12222
20150115; B32B 15/015 20130101; Y10T 29/49908 20150115; Y10T
428/12937 20150115; Y10S 428/933 20130101 |
International
Class: |
B32B 15/01 20060101
B32B015/01; B21C 33/00 20060101 B21C033/00 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 22, 2009 |
AU |
2009-905130 |
Oct 22, 2009 |
AU |
2009-905132 |
Claims
1. A billet comprising: a solid steel body; a cladding member at
least a portion of which is comprised of an alloy selected from the
group consisting of stainless steel, nickel-chrome, nickel-copper
and copper-nickel alloys; and scavenging metal located in a
position that is separate from an interface between at least a
portion of the steel body and said portion of the cladding member;
the billet being configured so that, upon being sealed, evacuated
and heated, the billet is adapted to be worked to form a ferrous
product in which said portion of the solid steel body and said
portion of the cladding member are bonded together at the
interface.
2. The billet according to claim 1, wherein the cladding member
forms at least a part of a sealed housing in which the solid steel
body and the scavenging metal are enclosed.
3. The billet according to claim 1, wherein the scavenging metal is
selected from the group consisting of aluminum, titanium, magnesium
and an alloy of magnesium and aluminum.
4. The billet according to claim 1, wherein the scavenging metal
comprises a first portion comprised of aluminum, magnesium or an
alloy thereof and a second portion comprised of titanium.
5. The billet according to claim 1, wherein the scavenging metal is
located adjacent at least one end of the solid steel body.
6. The billet according to claim 1, wherein the billet is
configured so that the scavenging metal scavenges oxidizing gases
that evolve in the billet when the billet is heated.
7. The billet according to claim 1, wherein the alloy of which the
cladding member is composed is stainless steel.
8. The billet according to claim 2, wherein the housing is
comprised of a first part in which the body is located, and a
second part in which the mass of scavenging metal is inserted
before the two parts are joined together.
9. The billet according to claim 2, wherein the scavenging metal is
selected from the group consisting of aluminum, titanium, magnesium
and an alloy of magnesium and aluminum.
10. The billet according to claim 2, wherein the scavenging metal
is located adjacent at least one end of the solid steel body.
11. The billet according to claim 2, wherein the billet is
configured so that the scavenging metal scavenges oxidizing gases
that evolve in the billet when the billet is heated.
12. The billet according to claim 1, wherein the cladding member is
comprised of at least two parts which are joined together to form a
sealed housing in which the solid steel body and the scavenging
metal are enclosed.
13. The billet according to claim 1, wherein, upon heating, the
scavenging metal scavenges nitrogen initially present in the billet
before the billet is worked.
14. A ferrous product produced by heating and working a billet as
claimed in claim 1.
15. A ferrous product produced by heating and working a billet as
claimed in claim 2.
16. A method of working a billet comprising: a solid steel body; a
cladding member at least a portion of which is comprised of an
alloy selected from the group consisting of stainless steel,
nickel-chrome, nickel-copper and copper-nickel alloys, and
scavenging metal located in a position that is separate from an
interface between at least a portion of the steel body and said
portion of the cladding member; the method including the steps of
evacuating the billet, sealing the billet, heating the billet and
working the billet to form a ferrous product in which said portion
of the solid steel body and said portion of the cladding member are
bonded together at the interface.
17. The method according to claim 16, wherein the cladding member
forms at least a part of a sealed housing in which the solid steel
body and the scavenging metal are enclosed.
18. The method according to claim 16, wherein the scavenging metal
is selected from the group consisting of aluminum, titanium,
magnesium and an alloy of magnesium and aluminum.
19. The method according to claim 16, wherein the scavenging metal
comprises a first portion comprised of aluminum, magnesium or an
alloy thereof and a second portion comprised of titanium.
20. The method according to claim 16, wherein the billet is
configured so that the scavenging metal scavenges oxidizing gases
that evolve in the billet when the billet is heated.
21. The method according to claim 17, wherein the billet is
configured so that the scavenging metal scavenges oxidizing gases
that evolve in the billet when the billet is heated.
22. The method according to claim 16, wherein the scavenging metal
is located adjacent at least one end of the solid steel body.
23. The method according to claim 16, wherein the cladding member
is comprised of at least two parts which are joined together to
form a sealed housing in which the solid steel body and the
scavenging metal are enclosed.
24. The method according to claim 16, wherein, upon being heated,
the scavenging metal scavenges nitrogen initially present in the
billet before the billet is worked.
25. A ferrous product produced by a method as claimed in claim 16.
Description
FIELD OF THE INVENTION
[0001] This invention relates to a process for the manufacture of
corrosion resistant metal products and to products produced from
the process. The invention has particular but not exclusive
application to products comprising a body of corrosion susceptible
steel bonded to a cladding comprised of stainless steel, or
nickel-chrome alloy, or nickel-copper alloy or copper-nickel
alloy.
DESCRIPTION OF THE RELATED ART
[0002] The susceptibility to corrosion of what are commonly simply
called "steels" that are most often used in industry should not
require further discussion. Conversely, the corrosion resistant
properties of stainless steels and the aforementioned alloys are
equally well known. This invention applies, in principle, to any
product that is composed of a body of steel that is significantly
more susceptible to corrosion than stainless steel or the
aforementioned alloys and that is susceptible of having applied to
it a cladding of these materials by the techniques described
herein. In this specification, the term "steel" used by itself will
refer to such a steel unless it is clear from the context that this
is not intended. In particular, it is intended that the term
"steel" should cover what are commonly called carbon steels.
According to convention, and as used herein, the term "carbon
steels" covers various grades of carbon steel, including mild
steels, low alloy engineering steels and micro-alloy steels.
[0003] The terms "stainless steel", "nickel-chrome alloy" and
"nickel-copper alloy" are names that are well known in the metal
industry and are generally applied to a range of alloys containing,
respectively, significant amounts of chrome, nickel and chrome, and
copper and nickel. In nickel-copper alloys there is more nickel
than copper, in contrast to "copper-nickel alloys" in which the
proportions of nickel and copper are reversed. Ranges of alloys
under each of the four names appear in lists available from the
major producers thereof including Outokumpu, Allegheny Ludlum,
Special Metals Corporation (owners of the trade marks Monel for
nickel-copper alloys and Inconel for nickel-chrome alloys), Haynes
International Inc (owners of the trade mark Hastelloy for
nickel-chrome alloys) and Columbia Metals Ltd. Furthermore the
alloys in each range are covered by standards issued under the
names of the respective alloys and set up by international
standards bodies such as ASTM (American Society for Testing
Materials) and JSA (Japanese Standards Association) and material
classification systems such as UNS (Unified Numbering System). As
will become clear, an essential aspect of the invention is the
provision of means to avoid oxidation of the named metals in the
respective alloys when they are heated in the course of producing
ferrous products that are clad with the alloys. As used herein, the
three terms are intended to cover such of these alloys in which
oxidation of the named metals is avoided or at least reduced in the
course of production of such ferrous products according to the
techniques of the present invention. For avoidance of doubt, it is
intended that the alloys to which this invention applies include,
but are not limited to:
Stainless steel: austenitics including ASTM A304 (UNS S30400), ASTM
316 (UNS S31600), ASTM XM-29 (UNS S24000), ASTM XM-28 (UNS S24100);
duplexes including UNS S32101, S32304, S32205, S32760 and 32750.
Nickel-chrome alloys: ASTM B637 (UNS N06002) and ASTM B564 (UNS
N10276) Nickel-copper alloys: ASTM B865 (UNS N05500) and ASTM B166
UNS N06600) Copper-nickel alloys: UNS C70600 and UNS C71500
[0004] In this specification, the following abbreviations are used
in order to avoid excessive repetition: [0005] SS=stainless steel
[0006] NiCr=nickel-chrome [0007] NiCu=nickel-copper [0008]
CuNi=copper-nickel [0009] RT=Starting Rolling Temperature Range
[0010] RTa=RT for: austenitic SS/NiCr: 1230-1280.degree. C. [0011]
RTd=RT for: duplex/ferritic SS/NiCu/CuNi: 1100-1200.degree. C.
[0012] FD="finely divided" in the sense defined below.
BACKGROUND OF THE INVENTION
[0013] In discussing the background of the invention, it is useful
to refer to a series of inventions covered by patents applied for
by Cacace et al. These patents and the processes described therein
are referred to herein as the "earlier Cacace" patents and
processes. The most recent of these appears to be the family of
patents that include U.S. Pat. No. 6,706,416.
[0014] The earlier Cacace patents deal essentially with the
production of long products such as reinforcing bars (hereinafter
referred to as "rebars") comprising a core of mild steel and having
a stainless steel cladding. These rebars are produced from billets
comprised of a stainless steel jacket filled with briquettes of
mild steel swarf. The billets can be heated and rolled into
finished rebars having the desirable properties and low cost of
mild steel but which have a stainless steel cladding for
substantially increased corrosion resistance. On perusal of these
patents it is clear that the achievement of a satisfactory
metallurgical bond at the interface between the stainless steel
cladding and the steel core has been problematical. The root of the
problem is the occurrence of oxidation at elevated temperatures of
the chrome in the stainless steel at the interface. There are
several potential sources of the oxygen that causes this oxidation.
One source is the residual oxygen in the air that remains in the
briquettes and in the jacket after the billet is formed. A second
source is atmospheric oxygen that enters the billet through its
ends, particularly after the billet is heated. This can happen when
the billet cools after it is removed from the furnace, causing the
gas pressure inside the billet to drop below atmospheric pressure.
It can also happen as the billet is heated due to the thermal
gradient between the core and the much hotter cladding. As a
result, a gap develops between the core and the cladding and this
is further exacerbated by the thermal expansion of the stainless
steel, which is greater than that of mild steel. A third potential
source of oxygen is the residual oxidation (rust) that is present
on the surface of the particles of mild steel swarf that make up
the briquettes. In the absence of preventive measures, this
oxidation reacts with carbon that, as the temperature increases,
diffuses out of the mild steel to form CO (carbon monoxide) and/or
CO.sub.2 (carbon dioxide). Both CO and CO.sub.2 can cause
significant oxidation of the stainless steel at elevated
temperatures.
[0015] In the process described in U.S. Pat. No. 6,706,416 this
problem has been addressed by the use of dual additives which are
mixed with the swarf particles before the briquettes are formed.
The working examples of the first of these additives are powdered
ammonium chloride (NH.sub.4Cl) and urea. When the billet is heated,
these evidently break down into gaseous form at a temperature below
which the oxidation of the stainless steel is significant. These
gases are under pressure in the hot interior of the billet and act
to displace the residual oxygen. This first step is employed in
conjunction with the action of the second additive. This second
additive, the working example of which is aluminium, becomes
increasingly reactive as the temperature increases above that at
which the ammonium chloride or urea has completely broken down. The
aluminium reacts with oxygen in the rust to form aluminium oxide
and also with any oxygen that enters the billet from the
atmosphere, thus preventing oxidation of the chrome.
[0016] In U.S. Pat. No. 6,706,416 it is stated that "both
NH.sub.4Cl and urea generate considerable volumes of reducing gases
in the temperature range from 200.degree. C. up to about
500.degree. C.". A similar statement appears in U.S. Pat. No.
5,676,775 in which the use of a single additive such as NH.sub.4Cl
and urea is suggested. These statements are inaccurate insofar as
they suggest that NH.sub.4Cl and urea generate gases that reduce Cr
oxides in the billet. In fact the named agents evolve nitrogen
(N.sub.2), hydrogen (H.sub.2) and chlorine (Cl.sub.2). The
Ellingham diagram for the reaction of metals to form oxides
indicates that these substances should not be reducing to Cr oxides
in the conditions existing in the billet. The applicant now
believes that it is more likely that their evolution creates a
positive gas pressure in the billet. The gases are thus carried out
of the billet and, in the process, drive residual air out of the
billet. So, from a temperature well below 500.degree. C., the
quantity of residual atmospheric oxygen in the billet would
diminish until it is probably close to zero. The remaining sources
of oxygen in the billet would be the iron oxide on the surface of
the swarf and air that enters through the ends of the billet after
the NH.sub.4Cl and urea are spent.
[0017] As stated in U.S. Pat. No. 6,706,416, the iron oxide from
the swarf combines with carbon derived from the mild steel swarf to
form, first CO.sub.2 and then, at higher temperatures, CO. This
process starts to take place on a significant scale at quite a low
temperature, perhaps 300.degree. C. CO.sub.2 is oxidising to Cr
and, contrary to what is stated in U.S. Pat. No. 6,706,416, the
Ellingham diagram shows that CO should be reducing to Cr oxides
only above about 1225.degree. C. Temperatures in the billet at the
interface between the core and jacket may not always uniformly
exceed this transition temperature because it is very close to the
temperatures (1260-1280.degree. C.) at which billets clad with
austenitic SS normally exit the furnace. This could be due to
temperature variations inside the billet or because the soaking
times in the furnace are insufficient. The reducing reaction of CO
may therefore not always be strong enough to bring about complete
reduction, resulting in a micrographically visible layer of Cr
oxides dispersed about the surface of the SS. A more concentrated,
or even continuous, oxide layer would occur if the transition
temperature is not reached at all, resulting in even less bonding
at the interface and possibly product failure.
[0018] In U.S. Pat. No. 6,706,416, aluminium, the second metal that
is added to the billet, is therefore relied on to ensure the
reduction or prevention of Cr oxides as the temperature rises after
the NH.sub.4Cl or urea are spent.
[0019] Having regard to the disclosures in the earlier patents, it
is clear that, in the processes described therein, each reducing
agent on its own is insufficient to prevent the formation of Cr
oxides that impede subsequent bonding of the SS jacket to the
core.
[0020] It also seems clear that, for an open ended billet comprised
of granulated mild steel briquettes, as used in the earlier
process, it is essential that both additives, i.e. NH.sub.4Cl or
urea, and aluminium should be well dispersed through the granules.
In any case, it may be concluded that, for an adequate bond between
the SS jacket and the carbon steel core, it is necessary is to
avoid, as far as possible, the formation of Cr oxides at the
interface from the commencement of heating until the jacket becomes
bonded to the core.
[0021] There are significant potential disadvantages to using swarf
as a feedstock for the core in the earlier process described
above.
[0022] In a full scale manufacturing operation, it may be difficult
to maintain a reliable source of swarf of a particular grade in a
situation in which it is necessary that the end product comply with
an international standard and specification.
[0023] Furthermore, it is self-evident that costly specialised
machinery, some of which is described in U.S. Pat. No. 5,088,399,
is required for preparing the swarf and the billets in the earlier
process. In addition, because of their furnace design, most
established rolling mills cannot roll from round billets. It is not
easy to envisage machinery that will be capable of producing
billets that comprise compressed swarf and have a cross sectional
shape that is not round. Further, the size, and especially the
length, of the billets, at least those described in the earlier
patents, is quite small. There are only a limited number of
existing rolling mills that are able to roll billets of such short
length and even fewer that can also roll from a round billet. This
is partly because existing furnaces are of the pusher type designed
for handling square billets. Round billets require furnaces of the
walking beam type. The use of small billets is likely to result in
the rolling process being inefficient because modern rolling mills
are designed to roll ever-longer billets to enhance productivity.
Although in principle the size and length of billets that comprise
compressed swarf could be increased, and the shape changed, the
technical problems involved in achieving suitable machinery for
this purpose might well be insuperable.
[0024] Another problem inherent in the earlier process described
above, again self evident, is that the gases evolved by the
NH.sub.4Cl and urea must necessarily be vented. Apparently the
billet is open-ended for this reason. This is stated in U.S. Pat.
No. 5,124,214, notwithstanding that it suggests the use of a cap to
enclose the ends of the billet. However, this patent is dated prior
to the use of any additives as described above. Furthermore,
although this patent also contains a suggestion that the tube can
be sealed by applying a graphite paste to the ends of the core,
this would be unworkable.
[0025] The paste would rapidly become friable and porous with the
moisture in the paste rapidly being driven off. This would cause
the graphite to collapse and therefore no longer form the barrier
intended. Moreover, the graphite would react with the steel in the
briquettes at a temperature of about 1000.degree. C., effectively
forming molten cast iron and would be completely ineffective in
reducing Cr oxides.
[0026] U.S. Pat. No. 5,676,775 discloses only an open-ended billet.
In U.S. Pat. No. 6,706,416, an experimental billet is disclosed
which contains only aluminium as an additive. Although this billet
is described as closed, it is provided at each end with a vent hole
to allow gases to escape from the billet. The vent holes were
welded closed after the billet was removed from the furnace. Having
regard to what has been said above, the applicant believes that
that these vent holes would not prevent residual atmospheric oxygen
causing oxidation of Cr in the billet at lower temperatures, before
the aluminium additive becomes active.
[0027] One object of the invention is to provide a billet
comprising a solid steel body and a cladding composed of stainless
steel, or a nickel-chrome, nickel-copper or copper-nickel alloy in
which oxidation which interferes with the bond between the cladding
and the steel body in the finished product is reduced, at least to
the extent of providing a commercially acceptable finished
product.
SUMMARY OF THE INVENTION
[0028] In this specification the term "scavenge" implies the
removal of gaseous oxygen, as opposed to "reduction" which implies
the removal of oxygen from a compound that contains oxygen as one
of its components.
[0029] According to the invention, there is provided a billet
comprising a body of solid steel, a cladding member that is
comprised of an alloy selected from the group comprising stainless
steel, nickel-chrome, nickel-copper and copper-nickel alloys and
that is positioned so that there is an interface between the body
and the cladding member at which the cladding member and the body
become bonded together when the billet is heated and worked to form
a ferrous product, and preventive means for excluding from the
interface gases that are capable of causing oxidation of chrome,
nickel or copper in the cladding member at the interface, the
preventive means including a mass of scavenging metal arranged to
scavenge oxidising gases at the interface.
[0030] Further according to the invention, there is provided a
method of producing a ferrous product, including the steps of
providing a billet comprising a body of solid steel, a cladding
member that is comprised of an alloy selected from the group
comprising stainless steel, nickel-chrome, nickel-copper and
copper-nickel alloys and that is positioned so that there is an
interface between the body and the cladding member, and preventive
means for excluding from the interface gases that are capable of
causing oxidation of chrome in the cladding member at the
interface, the preventive means including a mass of scavenging
metal arranged to scavenge oxidising gases at the interface, the
method including the step of heating the billet in such manner that
the scavenging metal is heated to a temperature at which it becomes
active to scavenge oxidising gases at the interface before the
alloy at the interface reaches a temperature at which oxides of
chrome, nickel or copper can form, and working the billet so that
the cladding member and the body become bonded together at the
interface.
[0031] In one form of the invention the cladding member forms at
least a part of a closed housing in which the body and the mass of
scavenging metal are located and which prevents gases outside the
billet from penetrating to the interface.
[0032] In one aspect of the invention the scavenging metal is
selected from the group comprising aluminium, titanium, magnesium
and an alloy of magnesium and aluminium.
[0033] In one form of the invention, the scavenging metal is
comprised of aluminium, magnesium or an alloy thereof that melts
before the billet reaches a temperature at which it is worked, and
an element is provided that comprises a mass of finely divided
steel located in the housing between the body and the mass of
scavenging metal.
[0034] In another aspect of the invention, the cladding member
forms at least part of a housing in which the body and the mass of
scavenging metal are located, and an element is provided that
comprises ammonium chloride or urea located in the housing between
the steel body and the mass of scavenging metal.
[0035] In one aspect of the invention, the mass of scavenging metal
comprises a first portion comprised of aluminium, magnesium or an
alloy thereof and a second portion comprised of titanium.
[0036] In one aspect of the invention, the housing is comprised of
a first part in which the body is located, and a second part in
which the mass of scavenging metal is inserted before the two
portions are joined together.
[0037] In one aspect of the invention, the mass of scavenging metal
is located in a position that is separate from the interface.
[0038] The mass of scavenging metal is advantageously in the form
of a briquette or similar element of compacted metal in finely
divided form such as particles, granulate, ribbon, turnings or the
like. Equally, the elements composed of steel, ammonium chloride
and urea are also in the form of briquettes or similar compacts.
The advantages of using a metal in such form rather than solid is
that the ratio of surface area to weight thereof is increased, thus
increasing the effectiveness of the metal to react with, or
scavenge, any oxygen in the billet. If compressed to a high
density, such briquettes are relatively impermeable to air or gases
when cold. However, when they are heated up to below their melting
point, they become porous and reactive to hot gases, thereby more
effectively scavenging internal gases or air that enters the
billet. They thus function as what may be called scavenging filters
located in the billet in a position adjacent to parts of the
cladding member and the steel body that become bonded together.
[0039] The invention further includes a ferrous product that is
produced by a method, or from a billet, as described and claimed
herein.
[0040] It is useful in this description to refer to the "free
energy of oxide formation" (hereinafter FEOF). Useful discussions
of this term are available on the Internet and elsewhere. In the
present context, the FEOF provides a measure of whether, at any
given temperature, the metal of which an element in the billet is
composed, will be oxidised in preference to the chrome, nickel or
copper in the cladding member and thus prevent oxidation thereof. A
diagrammatic illustration of the FEOF of various metals appears in
the Ellingham diagram for the reaction of metals to form oxides,
also available on the Internet and elsewhere. On the Ellingham
diagram it can readily be seen that metals that have a lower FEOF
than chrome, nickel or copper up to the rolling temperatures of
billets clad with any of the selected alloys of these metals
include calcium (Ca), magnesium (Mg), lithium (Li), uranium (U),
aluminium (Al), titanium (Ti), silicon (Si), vanadium (V),
Zirconium (Zr) and manganese (Mn). Because of such considerations
as danger in handling, radioactivity etc., many of these may not be
useful for the purposes of the present invention except perhaps in
specialised applications. Many of the named metals might also be
too expensive to be economically useful. However, the applicant
believes at present that magnesium, aluminium and titanium in
particular, and also possibly lithium, could be industrially useful
for manufacturing products according to the present invention. Use
of the other named metals is not however necessarily
discounted.
BRIEF DESCRIPTION OF THE DRAWING FIGURES
[0041] The invention is further discussed with reference to the
accompanying drawings in which:
[0042] FIGS. 1 to 5, 11 and 12, and 14 to 24 show cross sectional
views of one or both ends of a billet;
[0043] FIG. 6 is a schematic view of a heating arrangement for the
billets;
[0044] FIGS. 7 and 8, 25 to 27, and 29 are cross sectional view of
examples of products that can be produced from the billets
[0045] FIGS. 9, 10 and 28 are cross sectional views of billets in
the course of preparation.
DETAILED DESCRIPTION OF THE INVENTION
[0046] In the work carried out by the applicant up to the present
time in connection with the development of the invention, the
billets have been comprised of core bodies of carbon steel and a
cladding of A304 SS and UNS S32101 and S32304 duplex stainless
steels. The embodiments of the invention described herein are
therefore focussed on such billets. However, considering that
nickel and copper have a higher FEOF than chrome, the applicant
believes that the techniques of this invention can be successfully
applied without significant modification to producing products
comprising a steel core body that is clad with nickel-chrome,
nickel-copper or copper-nickel alloys.
[0047] In the drawings, except as hereinafter explained, each
billet B comprises a solid body or core C of carbon steel or any
suitable grade of steel that is ordinarily more susceptible to
corrosion than stainless steel. The core C is housed in a cladding
member which, in the present examples, is in the form of a jacket
J, that, in some cases, may comprise a central portion J1 that is
composed of stainless steel and an outer portion 12 that is
composed of mild steel. In other cases, the jacket may be entirely
comprised of SS. The SS can be of any suitable grade, including
ASTM 316, A304 or one of the stainless steels in the duplex range.
There is thus in each billet a zone Z in which there is an
interface between juxtaposed parts of the core C and the jacket
that become bonded together when the billet is heated.
[0048] Each billet is provided with preventive means for excluding
from the interface at zone Z gases that are capable of causing
oxidation of chrome in the jacket J. The preventive means includes
a mass comprised of at least one scavenging metal. The metal is
usually but not essentially provided in the form of an element such
as a briquette which is generically labelled E in the examples that
follow and which is located in the jacket adjacent to at least one
end of the core C and is thus displaced from the interface between
the juxtaposed parts in zone Z.
[0049] In relation to the metals that make up the elements
discussed herein, the abbreviation `FD` refers to such metals in
finely divided form including, as appropriate, turnings, ribbon,
powder, wire and so-called wire wool, shot and grit, as well as
swarf in the sense in which the latter term is commonly understood
by those skilled in the art and as used in the earlier patents.
[0050] In the examples hereinafter discussed, a typical billet will
be square in cross section and 150 mm.times.150 mm in cross
sectional size and could be between 6 metres and 14 metres long.
However, all of these dimensions are by way of example only and the
billets could be of any suitable length and size. These might
typically be determined by the length and size of commercially
available bars and tubes that are used for the cores and
jackets.
[0051] Various techniques are known, or have been suggested, for
applying metal cladding to a steel core. Prior to being treated
according to the methods disclosed herein, a billet may be prepared
by any suitable such technique. In the present case, one or more
plates, advantageously but not essentially of duplex SS, can be
wrapped around a steel core bar and the abutting edges of the
plates welded together. An example of such a billet is shown in
cross section in FIG. 28 and is considered at present to be the
optimum arrangement for preparing billets in a production situation
and at the same time keeping capital expenditure on specialised
plant to a minimum. Here, a square core C has been placed in a
channel shaped member 100 of SS that has been bent or rolled
beforehand from a single plate. Initially, the member 100 is in
juxtaposition with three faces of the core. After placement of the
core, the flanges 101 of the member 100 are bent around the fourth
face of the core so that the edges 102 are in mutual abutment.
These edges are welded together as indicated at 103. In a high
production situation, a strip of SS can be fed from a coil through
a conventional pipe mill which forms the strip into a channel shape
having a profile that is essentially similar to that of the member
100. The bar is placed in the channel and the two flanges are
folded around the bar and welded together in further stages in the
pipe mill.
[0052] The core may also be inserted in a preformed SS tube by any
suitable technique including, advantageously, one or other of the
techniques disclosed in the specification that accompanies the
international patent application filed pursuant to Australian
provisional patent application no. 2009 905 130 and entitled
"Billets for the Production of Metal Products".
[0053] FIG. 1 shows one end of a billet B1 in which the ends of the
jacket overlie the ends 10 of the core. A single element Et is
placed against the end of the core. A plate 14 is located in the
tube 12 against the outer end of the element Et and welded in place
to seal the tube. In this example, the opposite end of the billet
is similarly arranged so that the jacket J forms a closed metal
housing in which the core and Et are located and which acts as a
preventive means that excludes gases outside the billet from
penetrating into the zone Z. These gases include furnace gases and
atmospheric gases. In the present example, the element Et is
composed of titanium (Ti) in any suitable FD form and compacted
into a briquette prior to insertion in the billet. In FIG. 2, the
plate 14 is not used. Instead, a preformed cap or dome is used. The
cap can be fabricated by deep drawing from plate. The element Et is
conveniently compacted or inserted in the cap prior to welding the
cap to the end 12 of the jacket. Such a cap is less prone to
failure during rolling than the welds on the end plate 14.
[0054] Referring to FIG. 6, the furnace Fn is provided with
induction coils including a first set, indicated schematically at
11 and 12, that in a first stage quickly heat the ends of the
billet until the element Et reaches a temperature of at least
500.degree. C. and preferably 800.degree. C. while the rest of the
billet, and in particular the part comprising the stainless steel
portion J1, remains below a temperature below which chrome oxides
form in the surface of the jacket in the zone Z. Even at the lower
temperature, the Ti bonds strongly with both nitrogen and oxygen,
the principle gases of which air is composed, forming stable oxides
and nitrides. The Ti thus actively scavenges these atmospheric
gases from the zone Z to form their equivalent solid oxides and
nitrides at each billet end, leaving only minute quantities of
inert gases such as argon (Ar). Considering the amount of Ar
normally present in the air, a partial vacuum, probably of around
19 mm Hg, results at this stage.
[0055] A second set of induction coils 13 are then activated
together with the coils I1 and I2 to heat the whole billet to RT.
During this phase, the heating of the carbon steel in the core
causes it to decarburise. In the absence of the Ti, the carbon so
released would react with any iron oxides on the surface of the
core, initially forming CO.sub.2 and then, at higher temperatures,
CO together with some C. Both CO.sub.2 and CO would be oxidising to
the chrome in the SS. The Ti however has a lower FEOF than Cr so it
is reducing to Cr. The Ti thus combines with any oxygen, including
that from the iron oxide, and either prevents oxides of Cr forming
or reduces any that have formed.
[0056] In this specification, any suggestion that oxidation is
`prevented` or `reduced` is intended to imply that oxidation is
prevented or reduced to the extent that the process results in a
product that is industrially useful. Persons skilled in the art
will recognise that it is probably impossible to expect that
oxidation will be prevented or reduced in an absolute sense.
[0057] In an alternative arrangement, the elements Et can be heated
by several high capacity gas- or oil fired burners that are located
adjacent the main furnace in which the whole billet is subsequently
heated. The main furnace may be an induction furnace as already
described or may also be a gas- or oil fired furnace.
[0058] The heated billet B1 is taken to a mill for rolling into a
long product such as a rebar shown in cross section at R in FIG. 7
or a flat bar F shown in FIG. 8. Clearly, products of other
suitable shapes and sizes could be produced by the processes and
from the billets disclosed herein.
[0059] Referring again to FIG. 1, as long as the jacket remains
completely intact and therefore sealed against ingress of
atmospheric air, there is no chance therefore that atmospheric air
can enter the billet B1 through its ends as a result of the cooling
that occurs when the billet is removed from the furnace. After the
billet has passed through as many roll stands as are needed to
ensure that the jacket is bonded to the core, the ends of the now
more elongated billet incorporating the parts that house the
remains of Et are cropped off.
[0060] One reason that Ti is selected for Et in this initial
example is because it has a melting point that is higher than the
RT. There is therefore no need to make any provision to keep it
separate from the core as is the case with Al and Mg and some of
the other metals that could be used, as discussed below.
Notwithstanding the high melting point of Ti, the oxides that it
forms in the billet are absorbed into the Ti metal so that the
formation of further oxides is not inhibited. Unlike the case when
Al and Mg are in the solid phase, Ti is thus able to react
continuously with any oxygen that is formed in the billet while it
is being heated. Ti therefore does not need to melt in order to
function as an efficient oxygen scavenger. Furthermore, Ti is
reactive even at low temperatures. As is the case with Al and Mg,
dried and cleaned titanium turnings (suitable for briquetting) are
readily available due to their high intrinsic value. This avoids
the need for a scrap-processing plant to clean and dry swarf such
as is required in the processes described in the earlier
patents.
[0061] One advantage of the present process is that the core steel
can be round, square, rectangular or of any other suitable shape. A
billet with a core enables the process to be used with billets of
any suitable cross sectional size and length. In particular, the
billet size can be chosen to suit an existing rolling mill.
[0062] The core could also be a steel hollow preform and the billet
used to produce a steel pipe having either an internal or external
SS cladding. The ability to make rectangular billets enables them
to be used to roll SS clad plates as well as long products.
Examples of such products are discussed below with reference to
FIGS. 25 to 27 as will be discussed.
[0063] To enable a steel core to be more easily fitted into a
stainless steel jacket, the bar that is to be used for the core may
first be mechanically ground. This would also have the result of
descaling the bar. All bars that are commercially produced for the
present purpose will need to be descaled, a process normally
carried out by shot blasting. Such shot blasting would be
unnecessary if the bar is ground.
[0064] In order to assist the removal of atmospheric oxygen from
any of the billets described herein, it may be advantageous to
evacuate the billet by connecting one or both ends of the billet to
a vacuum pump P prior to any heating. This is shown schematically
in FIG. 9. Before the billet is transferred to the furnace, the
pump is disconnected from the billet, and the apertures in the
billet by which the pump is connected are closed. The means of
evacuating the billet in this way are well known and need not be
described in detail.
[0065] Instead of evacuating the billet, or in addition thereto,
the pump P could be of a type arranged to pump an inert gas such as
Ar into the billet to displace the residual air.
[0066] FIG. 3 shows another example of one end of a billet B3. The
billet B3 and those still to be described, and the preparation and
processing thereof into rolled products, will be discussed only
insofar as they have features which differ significantly from those
already described with reference to billet B1.
[0067] Two elements Es, Ea are inserted in each end of billet B3.
Es is sandwiched between Ea and the end 10 of the core C. Es is a
briquette that, in this example, comprises FD carbon steel but
could alternatively comprise FD titanium. In either case Es could
be formed by compressing the FD steel or Ti either directly into
the tube 12 or into a briquette before it is pressed into the tube.
Ea is similar to Et but is composed, not of Ti, but of FD aluminium
(Al) or FD magnesium (Mg) or an alloy of these. It is convenient to
discuss the properties of these three scavenging metals together.
The scavenging function of each in the present process is similar
to that of Ti in Et.
[0068] Of all of the metals named herein as being suitable for use
in connection with the present invention, aluminium is the most
widely available and the least expensive. It is perceived as being
safe to handle. As noted in U.S. Pat. No. 6,706,416, it is an
aggressive oxygen scavenger but, in the context of the present
invention, its usefulness in this regard may be limited by the fact
that its oxide, Al.sub.2O.sub.3, once formed, remains in the solid
state on the surface of the Al metal and forms a barrier to
scavenging. This barrier disappears when the metal melts at about
660.degree. C. This temperature is easily achieved by induction
pre-heating the end of the billet. This is one advantage of using
Al. The boiling point (hereinafter "BP") of aluminium is well above
RT and is thus too high to make aluminium in the gaseous state
useful as an oxygen scavenger.
[0069] On the other hand, the melting point ("MP") of Mg is about
650.degree. C. and its BP is about 1100.degree. C. In addition, it
is a more aggressive oxygen scavenger than Al. Mg is however
commonly perceived as being unsafe to handle. This view is
expressed in U.S. Pat. No. 6,706,416. Contrary to this view
however, information that has been provided by industrial suppliers
of Mg suggests that, provided simple, easily achievable, safety
steps are taken, the use of Mg for Ea, in the working conditions in
which the present invention is put into practice, is unlikely to
prove so hazardous as to render the use of Mg unacceptable. It
appears that this will certainly be the case when the Mg is in the
form of turnings or ribbon and is likely to be the case even when
the Mg is in powder form.
[0070] Both aluminium and magnesium form stable oxides, nitrides,
hydrides and carbides and, as noted, are active scavengers of
atmospheric and other gases. They also have the advantage of low
cost. In addition, Al and Mg turnings are widely available. They
are most reactive on melting, at which point the surface oxide
layers cease to inhibit their scavenging action. The FEOF of each
is lower than that of titanium and of course much lower than that
of Cr.
[0071] For a billet such as B3, there are some disadvantages to the
use of an element Ea comprising Al or any of the other metals named
herein, including Ti, that do not boil below RT. In this case, the
gas pressure inside the billet at the commencement of rolling will
be lower than atmospheric so that air would enter the billet if an
end of the tube 12 was to fail before the jacket is bonded to the
core during rolling or through pinhole leaks in the welding of
plate 14. In this case however, oxygen in the air would still be
scavenged by the elements Es and Ea and only atmospheric Ar would
penetrate past the elements to the interior of the billet.
[0072] Conversely, a significant advantage of the use of Mg for Ea
is that, when Mg is raised above its boiling point, a positive gas
pressure is created inside the billet, replacing the partial vacuum
that it creates in the billet as a result of forming solid oxides.
Mg vaporises at 1100.degree. C. at atmospheric pressure but at a
lower temperature under the partial vacuum. At RTd the pressure of
the vapourised Mg in the billet is close to atmospheric. At RTa the
pressure of the vapourised Mg in the billet is above atmospheric.
The possibility of entry of air during rolling if the jacket fails
is thereby much diminished. The vaporised Mg acts as a strong
reducing gas for any CO and CO.sub.2 that might occur in the
billet. CO starts to form from about 780.degree. C. and reduces Cr
only at above 1225.degree. C.
[0073] The element Ea may also comprise an alloy of aluminium and
magnesium. As is known, the BP of such an alloy can be controlled
by adjusting the proportions of the constituent metals. Thus the BP
of the alloy can be made higher or lower than RT, as desired. One
way of making use of this is discussed below.
[0074] Because Mg and Al melt at temperatures lower than RT, it is
desirable to prevent molten Mg and/or Al, when used for Ea in
billet B3, from reaching the interface of the core and the SS
jacket. This is achieved by the presence of Es which, whether it is
comprised of FD steel or Ti, does not melt below RT and acts as a
barrier to the molten metal. This is one function of Es. If FD
steel is used for Es, it is preferably of medium- to high-carbon
grade, which typically contains 0.4.degree.%-1% of carbon. Graphite
could be added to the FD steel to increase the carbon content if
necessary. At elevated temperatures, CO will be evolving from the
FD steel and any graphite present. At RTa, CO is reducing to any
oxides in the chrome according to the Ellingham diagram. Even at
RTd, CO may be reducing to Cr in the presence of Al or Ti.
[0075] When Es is formed from Ti, Es not only acts as a scavenger
to oxygen that is initially present, or that evolves, inside the
zone Z, but also helps to scavenge atmospheric oxygen before it
gets into the zone Z through the welding or jacket failure as
already noted.
[0076] FIG. 4 shows the end of a billet B4 that comprises at each
end an assembly of three elements Es, Ea and Et. Typically
therefore, Es will be composed of FD steel, Ea will be composed of
Al, Mg or an alloy thereof, and Et will be composed of FD Ti. In
this assembly, the metal of which Ea is composed is thus molten at
RTd as well as RTa. Es, Ea and Et in B4 serve the same respective
functions as in B1 and B3 and therefore need not be further
explained other than to point out that Et in B4 serves as a further
means to scavenge oxygen, particularly from atmospheric air that
may get into the billet in any of the ways previously described.
The potential for oxidation of the Cr to occur as a result of such
failure is exacerbated if the temperature of the interior of the
billet and the incoming air is lower than 1225.degree. C. The
modification to the billet, shown in FIG. 11, addresses this
problem.
[0077] FIG. 11 shows one end of a billet B11 that is provided at
each end with three elements Es, Ea and Et that, subject to what is
said below about Ea, are comprised of the same metals, and serve
the same functions as, the identically named elements in B4. The
ends of B1 are initially sealed by plates 40a but each plate is
provided with a temperature-dependent plug 46 that melts and allows
the billet to be vented inside the furnace at a temperature which
can be preselected but is in any case not less than 1225.degree. C.
A suitable material for such a plug is 30% copper-nickel which
fully melts at 1237.degree. C. When the plug melts, the vacuum
conditions in the billet cause hot oxidising furnace gases, which
are normally at temperatures of around 1300.degree. C. and in any
event well above 1225.degree. C., to be rapidly sucked into the
billet. These furnace gases would pass through Es, Ea and Et and
thus through three layers of reducing and scavenging metals. First
through the outer element Et which is composed of Ti, the
scavenging effectiveness of which, as already noted, is not
impaired by the formation of any oxide or nitride coatings as these
are absorbed into the metal itself on heating above 500-800.degree.
C. The furnace gases then pass through Ea which, if composed of Al
and thus melting at around 650.degree. C., is retained between Es
and Et. Ea can also be composed of an alloy of Al and Mg to provide
an even more powerful scavenging action. Any remaining oxygen or
CO.sub.2 when passing through the final element Es is converted
into CO. This is accompanied by an increase in pressure due to the
formation of two CO molecules for every molecule of CO.sub.2 or
O.sub.2. The CO entering the zone Z at temperatures well above
1225.degree. C. will have a reducing effect on any Cr oxide traces
still present at the interface.
[0078] The three elements pressed into each end of billet B11 also
provide additional protection as a precaution against the
occurrence of oxidation in the core and jacket in the zone Z in the
event of failure of the jacket ends during rolling. The elements
therefore serve a dual purpose as CO converters when the plug melts
and if the ends of the jacket should fail during rolling.
[0079] The fact that a relatively large initial gap 50 can be left
between the steel core and the jacket would enable agents such as
powdered Al or NH.sub.4Cl to be sprinkled on the top of the core C
as it is being inserted in the jacket J1. This is illustrated
schematically at 120 in FIG. 10.
[0080] FIG. 12 shows one end of a billet B12 that is a variation of
billet B11 and is provided with three elements Es (or Et), Em and
Et. The middle element Em would be composed of Mg. The outer
element Et would again be composed of Ti. Here, the billet again
vents through a temperature-dependent plug 46 as already described
whilst in the furnace. In this example, reliance is placed on Mg
vapour to be present inside the billet before and during
rolling.
[0081] It is convenient first to consider Em as being composed of
pure Mg. As with all of the other billets shown in the drawings,
the ends of billet B12 are first heated up rapidly, until the Mg in
Em becomes molten. In essence, the Mg ignites as it reaches melting
point, rapidly scavenging all of the N.sub.2, O.sub.2, CO.sub.2 and
CO creating a vacuum in the billet. At this stage the entire billet
is heated to RTa or RTd. The Mg vaporises at 850.degree. C. due to
the vacuum. The Mg vapour increases in pressure with further rising
temperature, generating a positive pressure.
[0082] As in the previous example, the billet vents whilst still in
the furnace by the provision of the plug 46 of copper-nickel which
is designed to melt close to either RTa or RTd as required.
Copper-nickel 10% fully melts at 1145.degree. C., above the boiling
point of Mg. The positive pressure provided by the Mg vapour
prevents the entry of furnace gases as well as preventing the
ingress of air, once removed from the furnace for rolling.
[0083] It may alternatively be advantageous to design the end
compartments to vent or break during initial rolling and allow the
Mg vapour to escape. Being under pressure, this would help to
prevent the entry of air until the jacket and core are bonded.
[0084] The ratio of Al to Mg could be chosen to cause the alloy to
vaporise anywhere between 850.degree. C. and 1260.degree. C. In
essence, this process relies on the Mg vapour, rather than CO, to
reduce Cr oxides.
[0085] It may prove unacceptable in practice to use elements
composed of a metal such as magnesium or an alloy thereof that
vaporises below RT of the billet concerned, because the vapour that
penetrates into the zone Z may leave unacceptable inclusions at the
interface in the finished product. On the other hand, the same
elements may be acceptable for use in billets whose RT is below the
temperature at which the elements vaporise. Experience will
determine the circumstances in which such elements can be used.
[0086] In the course of tests carried out in connection with the
present invention, it has been observed, surprisingly, that the
ends of billets prepared as shown in FIG. 3 and passed through a
particular conventional pusher type furnace have become adequately
heated (for the purposes of the invention) before the centre parts
without special arrangements being made in the furnace for
preheating the ends. The reason for this is not entirely clear but
it may be due to any one of several factors or perhaps a
combination thereof.
[0087] In most pusher type furnaces the billets are placed on the
furnace floor and eventually exit when they are hottest. The
furnace gases can heat the billets only through their top faces and
their two end faces since other faces of the billets are not
exposed to the furnace gases. The top faces of the billets together
however present as a continuous flat mass of steel which acts as a
heat sink. The ends therefore heat up more quickly than the central
parts of the billets, which initially remain relatively cool. In
addition, the heat conductivity of both Ti and Al, as well as Mg,
is much greater than that of steel or SS.
[0088] The rolling sequence can be arranged so that gas flows in a
controlled manner through the billet. For example, where an in-line
rolling mill is used, the end of the billet that enters the rolls
can be closed and the back end designed to vent during rolling. Mg
vapour and other gases will be pushed towards the vent at all times
under considerable pressure, thereby also serving to flush out any
minute quantities of solid Mg oxides and/or nitrides that have not
already been driven into the end compartments. This technique
ensures that all Mg vapour has been expelled at over 1100.degree.
C. before it cools below its BP. If this was to happen, the oxides
and nitrides might remain in the billet as solid, non-metallic
inclusions.
[0089] In what follows, it is not considered necessary to repeat in
every instance the description of the elements or some arrangements
thereof specifically and such elements may be identified by the
simple letter E.
[0090] Notwithstanding that a billet contains elements comprising
the metals, particularly aluminium and titanium, that have so far
been suggested, it is possible that, after the ends are preheated,
conditions in the interior of the billet may still allow some
oxidation of the Cr, despite the fact that the atmospheric air has
been scavenged or evacuated from the billet prior to heating.
[0091] FIG. 5 shows the end of a billet B5 that addresses this
issue. B5 comprises an assembly of four elements Eu, Es, Ea and Et.
The latter three can be identical to those already described and
serve the same respective functions. The plate 14 can be omitted
or, alternatively, a plate 40 with a vent hole 42 may be provided
to help hold the elements in place during rolling. Eu is sandwiched
between Es and the end 10 of the core and is a briquette comprising
NH.sub.4Cl or urea. The usefulness of this assembly is that the
NH.sub.4Cl or urea dissociates at a low temperature, as described
in the earlier patents, and forms large volumes of gas that are
able to escape from the billet through vent hole 42, since Es, Ea
and Et can be made sufficiently porous to allow this to happen.
These gases displace residual air in zone Z of the billet. The
dissociation of NH.sub.4Cl or urea commences at a temperature below
200.degree. C. and continues until the temperature reaches
somewhere below 600.degree. C. at which point the NH.sub.4Cl or
urea are spent and the flow of gases out of the ends of the billet
ceases. The billet B5 does not therefore need to be evacuated or
purged to remove the atmospheric gases inside the billet. Although
the porosity of Es, Ea and Et also allows atmospheric air to be
drawn into the billet when the ends are being heated, Es, Et and
the molten constituents of Ea scavenge any oxygen that may remain,
or evolve, in the billet and also scavenge oxygen and other gases
in the air before they can penetrate into the interior of the
billet.
[0092] A modified element E30 is shown in FIG. 13. This element
comprises Ti in a suitable FD form such as shavings shown
schematically at 80, mixed with carbon steel, also in the form of
wire or swarf or other suitable FD form as shown schematically at
82.
[0093] In the billets B1-B4, the jacket J that houses the core body
and is closed to the atmosphere provides means for preventing
oxidising gases from outside the billet penetrating the zone Z
until the interfacing parts of the core and SS jacket become bonded
together. In a billet such as B5, this means is effectively
provided by the element Eu in combination with an array of
scavenging elements such as Es, Ea and Et. Eu is active in the
lower temperature ranges to scour oxidising gases from the zone Z
and the scavenging elements not only allow these gases to escape
but also provide a sufficient sealing action at the lower
temperatures to stop atmospheric or furnace gases from penetrating
to the zone Z. As the temperature rises, the scavenging elements
become more active and, although atmospheric and furnace gases may
be able to penetrate to the zone Z, any oxygen in these gases is
scavenged by Es, Ea and Et before they do so. The elements also act
to scavenge oxidising gases that evolve in the zone Z until the
interfacing parts become bonded together.
[0094] It may be found unnecessary to provide as many as three
scavenging elements in a billet such as B4. For example, the
element Et may be active enough to allow the middle element Ea to
be omitted. Since Et does not melt, the barrier element Es may also
not then be needed.
[0095] The elements might typically be 10-150 mm thick. This is
however by way of example and they could be of any suitable
thickness.
[0096] It will probably always be necessary to prevent the raw
scavenging metals from the elements E being present in the zone Z
before the billet is heated. The residue of any significant
quantity of these metals is likely to be deleterious to bonding
between the faces of the core and jacket and the parts of the
billet that contain such residue after rolling are in any case
discarded. It is therefore thought that the scavenging elements E
should initially be located in a position that is separate from the
faces of the core and jacket. In this regard, a mass of any of the
FD scavenging metals, particularly Ti, could be mixed with FD steel
and inserted, advantageously in briquette form in the billet ends.
The FD steel would serve as a matrix to hold the scavenging metal
in place.
[0097] When a preformed tube is used for the centre part J1 of the
jacket, the core must be smaller than the jacket to allow the core
to enter the jacket. The billet of 14 m length with a 150
mm.times.150 mm jacket J11 of 7 mm wall thickness, as exemplified
herein would house a 122 mm.times.122 mm square steel core. In this
example, at room temperature, there would be a 14 mm gap between
the core and the jacket. This gap would represent some 501 of
atmospheric air, i.e. 78% nitrogen and 21% oxygen.
[0098] On a gram molecular basis: Igm of Mg could scavenge 320 cc
of free air: [0099] 1 gm of Ti could scavenge 250 cc of air and
[0100] 1 gm of Al could scavenge 480 cc of air.
[0101] In a sealed billet containing 501 of air, only 104 gm Al
would therefore be required to create a partial vacuum to leave 1%
Ar. Similarly 156 gm of Mg or 200 gm of Ti would be required to
scavenge the 501 of air from a billet of the same size and leave
the same partial vacuum. However in the case of a billet of the
same size with open ends, 5000 l of internal air and/or external
atmospheric air would have to be scavenged in order to create 501
of Ar inside the billet as described above; i.e. 50,000
cc/0.01=5,000,000 cc.
[0102] The following calculations are provided for the purposes of
illustration and assume that a billet such as B4 is to be produced.
It is also assumed that the element Ea is made up of aluminium,
this being the metal that is most to be used in industrial
practice. Al has a density of 2.7 g/cc. Roughly 10.4 kg of FD
aluminium (on a weight basis) would be required, or about 5.2 kg at
either end. This represents 0.5% by weight of the total billet
weight of 2000 kg. Aluminium briquettes with relative densities of
70% of solid aluminium would weigh 5.2 kg each and have a length of
170 mm to fit tightly into each end of a jacket having internal
dimensions of 136 mm.times.136 mm.
[0103] Inside and outside gas pressure equilibrium is eventually
reached when the interior of the billet is filled with Ar. Any
displacement of the pressure equilibrium that occurs as a result of
the expansion or contraction of gases in the billet as the furnace
heats up to RT or variations in furnace temperature, would adjust
automatically. The elements E at each end thus provide a
self-regulating mechanism for the pressure equilibrium.
[0104] There are other metals that have a lower FEOF than Cr and
that therefore might be used instead of Al, Mg or Ti. Although it
appears at present that these other metals are less likely to be
used, this is not discounted. These other metals include zirconium,
lithium, calcium, silicon, vanadium, manganese and uranium.
[0105] Yet another possibility is illustrated in FIG. 14. The
billet B14 contains one or more elements in substantially the same
arrangements as any heretofore described. However, the elements are
not placed directly in the jacket ends but are prepacked instead in
a cartridge 60 of mild steel. In this example, three such elements
Es, Ea, Et are illustrated which are identical to those previously
described. The cartridge is a close fit in the tube 12 and
comprises a longitudinally extending, tubular outer body 62 with
end plates 64, 66 at its inner and outer ends. The end plates are
welded to, or integral with, the body 62 so that the joints between
the plates and body 62 are sealed. The end plate 64 is located
against the end of the core C and is provided with a central
aperture 68. After the cartridge is inserted in the billet end, it
is fixed in place by a plate 70 welded to the tube 12. The function
of the plate 70 is similar to that of the plate 14 so that, as
necessary and depending on the nature of the element or elements E
inserted in the cartridge, the plate 70 may have an aperture or may
be provided with a plug that melts at a predetermined temperature
or alternatively (as shown) may have no aperture, all as previously
described. In the first two of these cases, the end plate 66 will
be provided with an aperture 72 (as shown in FIG. 14a) that is
aligned with the aperture 74 in the plate 70 and is similar to the
aperture 68 in the end plate 64. The inner end plate 64 serves, in
the first place to hold the element or elements in place in the
cartridge. It is one aspect of the invention that the elements E,
in any of the arrangements described herein, can be packed into
cartridges and transported separately from the billets. This could
have the result that simpler machinery might be required for
assembling the billets. Where one of the elements E that is
inserted in the cartridge is composed of a scavenging metal that
melts below RT as previously described, each end plate 64, 66 also
acts as a barrier for holding the molten metal. The quantity of
metal could be chosen so that, when molten, its upper surface lies
below the apertures 68, 72, 74. This would help prevent molten Al
or other metal from spilling out of the cartridge and finding its
way into the gap between the core and the jacket when the hot
billet is being handled.
[0106] By using the multiple elements as described herein with a
billet comprising a core of solid steel, it may be possible to
avoid the expense of closing the ends of the jacket J from the
atmosphere. It may be sufficient merely to close the billets by
crimping the ends as described in the earlier patents. FIGS. 15 and
16 show the ends of billets B15, B16 crimped in this way. Both of
these billets contain elements E as already described. In the case
of the billet B15, the elements are contained in a cartridge 60a,
similar to that already described. In the case of the billet B16,
the cartridge is not used and the elements are inserted directly in
the end of the billet before is it crimped. In this case it may be
necessary to insert a carbon steel plate 90 in the billet end
before it is crimped. The plate 90 is not provided to close the
jacket and so is not welded in place. The plate 90 may help to
prevent the elements E from being crushed by the pipe 12 during
crimping.
[0107] FIG. 15a shows that the end 98 of the core C can be provided
with a peripheral recess 92 that accommodates the end 98 of the
body of the cartridge 60b. This would tend to promote welding of
the cartridge end to the core end when rolling is commenced and
thereby help to prevent the cartridge becoming separated from the
core and the consequent possible failure of the jacket at the
junction between the core and the cartridge.
[0108] In any of the foregoing examples, it may be preferable to
omit the use of carbon steel pipe ends 12 welded to the SS jacket.
Instead, the elements E are inserted in the ends of the SS jacket,
which is made longer for the purpose. A billet B17 so made is shown
in FIG. 17, the SS jacket J extending beyond the plate 14d to the
end 110 of the billet. FIG. 18 shows one end of a billet B18 in
which a cartridge 60c is inserted in the end of a SS jacket J. As
in the case of the billets B15 and B16, the end of the jacket can
be crimped over the cartridge (as shown) or closed by a plate.
[0109] In the case of the billets B17 and B18, relatively large
proportions of the SS jackets J will be wasted as a result of the
fact that the ends are cut off after the billet is rolled. The
expense of this may be reduced by providing a billet B19 or B20
(respectively shown in FIGS. 19, 20) in both of which, in the first
place, the end of the core C is located close to the end of the
jacket J and is provided with a peripheral recess 92d, 92e
respectively similar to the recess 92. Again, no carbon steel tube
is welded to the end of the SS jacket. Instead, cartridges 60d, 60e
respectively are provided. These are similar to the cartridge 60b
in that the bodies of both have identical inner ends 94d, 94e, each
of which is accommodated in a respective recess 92d, 92e and is
fillet welded to the jacket J. However, the bulk of each cartridge
60d, 60e is located outside, and projects clear of the end of, the
jacket J. It may be noted that, in these examples, the outer end of
each cartridge is closed and the billet is thus closed to the
furnace gases and the outside atmosphere.
[0110] In the billet B19, the body of the cartridge is formed by a
cylindrical pipe the cross sectional size of which is substantially
equal to that of the core C. The end of the pipe is closed by a
plate 66d welded in place. In the billet B20, the body of the
cartridge is cup-shaped. The body can be formed by deep drawing.
The provision of a welded-on end plate is thus avoided. In the case
of a jacket that is made up of a square pipe, the part of the
cartridge that projects clear of the jacket and core must be
smaller than the square pipe so as to permit the cartridge to enter
the guides of the rolling mill. These guides will have been shaped
to precisely guide the entry of the (square) billet and will allow
any smaller shapes to enter the guides and thereafter enter the
rolls.
[0111] One advantage of using a cartridge of the type as shown in
FIGS. 19 and 20 is that a portion 80d, 80e of the inner end of the
cartridge projects into the billet and is sandwiched between the
end of the jacket and the end of the core. The joint between the
cartridge and billet may therefore be less likely to cool and crack
during the rolling process. Furthermore, this type of joint may be
structurally stronger as pressure welding between cartridge, core
and SS jacket occurs during rolling thus serving as a back-up
connection system in case of failure of the outer weld.
[0112] Further variation of the billets B19, B20 are shown in FIGS.
21a and 21b. In FIG. 21a, a portion 96 of the billet that comprises
the ends of the core and jacket J and that might typically be 50 mm
long, is swaged down so that its overall cross sectional size is
less than, or at most equal to, the original cross sectional size
of the core. For this purpose, a swaging machine can be used that
is of the type commonly used for swaging metal fittings onto the
ends of flexible hydraulic hoses. Such machines typically have four
or eight concentrically actuated closing and opening jaws. A
cartridge 60f is provided the inner end 80f of which fits snugly
over the outside of the swaged down portion 96 of the jacket and
core. The cartridge 60f, which can have the same outer dimensions
as the original jacket and can be closed by a welded-on plate as in
FIG. 19 or cup-shaped as in FIG. 20, is fillet welded onto the
jacket. A cartridge of this design also helps to protect the
portion of the jacket end that projects into the cartridge from
excessive heat loss during rolling.
[0113] In FIG. 21 b, the cartridge 60g is of larger cross sectional
size than cartridge 60f but is otherwise identical. The cartridge
60f has a skirt that fits over the end portion of the billet B21b,
which is not swaged down.
[0114] In all cases the cartridge can be formed of carbon steel
which is less prone to cracking than SS if the cartridge cools
excessively during rolling.
[0115] The cores and jackets of the billets heretofore described
and shown in the drawings are typically, but not essentially, of
square cross sectional shape. This is because it is thought that it
will be most practical to form a square shaped core with the
requisite degree of longitudinal straightness and uniformity of
cross sectional dimensions. Clearly, however, billets of other
cross sectional shapes (including round and rectangular shapes) may
be used.
[0116] FIG. 22 shows a billet B22 comprising a hollow block of
steel 110 that comprises a round passage 111 in which a SS tube 112
is inserted. The ends 113 of the tube project clear of the block.
An array of annular elements E arranged similarly to any that have
been heretofore described, are mounted over each end 113 and are
housed in a closed steel casing 114 that is also annular and is
welded to the end face of the block. The elements prevent oxidation
of the zone Z at the interface between the tube and block in the
passage 111. The billet B22 is suitable for producing an internally
SS clad, seamless steel pipe 115 shown in FIG. 25 by a known
piercing and rolling technique. The steel body of the pipe and the
cladding are shown at 110' and 112' respectively.
[0117] FIG. 23 shows a billet B23 that is similar to B22 except
that the steel block 110a is housed in a SS tube 112a. Again, B23
is suitable for producing an externally SS cladded, seamless steel
pipe 115a shown in FIG. 26. The steel body of the pipe and the
cladding are shown at 110'' and 112'' respectively.
[0118] FIG. 24 shows a billet B24 that comprises a rectangular
steel slab 116 to the upper face 118 of which a SS plate 119 is
applied. The plate is preformed with each of its four edges being
folded downwardly at 900 to the face 118 to form flanges two of
which are located at the front and back ends of the billet and are
shown at 120. The remaining two flanges (which are not visible in
the drawing) are welded to the side edges of the plate. After the
plate 119 has been placed in this position, the visible flanges are
again folded inwardly as shown at 121 so that the free edges of
these flanges are respectively positioned for welding to the lower
face 122 of the plate at the front and back edges thereof. The
visible flanges 120 enclose arrays of elements E arranged similarly
to any that have been heretofore described. The billet B24 should
be suitable to be heated and rolled into a steel plate 123 shown in
FIG. 27 having one face clad with SS. The steel body of the plate
and the cladding are shown at 118' and 119' respectively.
[0119] FIG. 29 shows a product in the form of square, externally SS
clad pipe 120 comprising a steel body 122 that, in this case, is
tubular and is bonded to a SS cladding tube 124. The pipe could be
produced from a billet that is assembled in essence similarly to
the billet B23, due allowance being made for the differences in
dimensions and shape of all of the components.
[0120] FIG. 29 could equally be viewed as an internally SS-clad
pipe 120 comprising a steel body 124 bonded to an inner cladding
tube 122. This pipe 120 could be produced from a billet that is
assembled in essence similarly to the billet B22, due allowance
again being made for the differences in dimensions and shape of the
components.
[0121] In a first trial, four billets were prepared, each
comprising square core bar of carbon steel with outside dimensions
of 100 mm.times.100 mm and 2 m long. Two cladding plates were
provided for each bar. For two of the billets, the plates were of 6
mm thick UNS S32101 duplex SS and for the other two billets the
plates were of UNS S32304 duplex SS, also 6 mm thick. Each plate
was preformed into a U shape having a base and two upstanding
flanges that closely covered half of the bar. The plates were
applied to opposed sides of the bar so that there were welding gaps
between the abutting edges of the plates that extended along the
centrelines of opposed faces of the bar. The plates were welded
together along the abutting edges without the welds penetrating to
the core bar to form a SS casing around the bar.
[0122] Cartridges 170 mm long were prepared. These contained three
elements composed respectively of compacted masses of Ti turnings,
Al turnings and carbon steel turnings, each approximately 35 mm
long. The three elements were pressed into a carbon steel casing
fabricated from 8 mm thick carbon steel plate as exemplified in the
billet B19. One such cartridge was welded to the cladding plates at
each end of the billet, again as exemplified in the billet B19.
Each billet was thus closed to the atmosphere.
[0123] The ends of each billet were preheated to around 800.degree.
C. leaving the central part of the billet at ambient temperature.
After this the entire billets were heated in a rolling mill furnace
to 1200.degree. C.
[0124] The billets were then rolled through the first six roughing
passes of a conventional rolling mill in a diamond-square roll pass
configuration. In this procedure, the billets were reduced in size
to 70 mm.times.70 mm and the partially rolled product was sectioned
and examined. In all billets, there was no sign of significant
oxidation in the SS casing at the interface with the core bar at a
distance of more than 50 mm from the billet ends. Furthermore,
there appeared to be complete bonding between the core bar and the
casing at the interface. No finning was observed which would have
resulted from de-bonding of the SS casing from the core bar into
the roll gaps. In commercial production, the ends of the billets
containing the remnants of the end pieces would be cropped off as
soon as bonding is known by experience to be complete. In the
present case, it was therefore concluded that, in practice, the
ends could be safely cropped off after the sixth pass.
[0125] In a further trial, two commercially produced carbon steel
core bars 84 mm.times.84 mm in size and 2 m long were descaled. The
bars were inserted into square tubes, also commercially produced,
of ASTM A 304 grade SS 100 mm.times.100 mm in outside size and 6 mm
wall thickness. Initially, there was thus a nominal clearance gap
of 4 mm between the core bar and the tube. After insertion of the
bars, the tubes were stretched beyond the elastic limit of the SS
to result in a 12% elongation of the tube. In this procedure, the
tube was shrunk tightly over the core bar to the point that the
rounded corners of the tube distorted to adapt to the different
radii of curvature of the core bar. The tube became longer than the
core bar and shrank to a size of 91 mm.times.91 mm at its
projecting ends where they were not restrained by the core bar.
[0126] After the stretching procedure, tubular carbon steel end
pieces 70 mm long were welded to the ends of the SS casing using
the same Inertfil 309.TM. welding wire. A single element 35 mm long
and composed of a compacted mass of Ti turnings was pressed into
each end piece before a closing plate was inserted in the end piece
and welded thereto as exemplified in billet B1.
[0127] The billets were rolled using the same procedure as for the
first four billets with the same results.
[0128] In conclusion the processes of the present invention enable
the production of products that have a cladding of ferritic, duplex
or austenitic SS or a nickel-chrome, nickel-copper or copper-nickel
alloy. These new products can be made compatible with modern
rolling mills, including those that employ induction heating. The
new cladding technology should reduce the capital costs including
the cost of specialist plant that is required to make and roll the
billets. Overall, it should be easier for the new process to be
adopted internationally.
* * * * *