U.S. patent application number 10/470486 was filed with the patent office on 2004-05-20 for steel article.
Invention is credited to Jonsson, Lennart, Sandberg, Odd.
Application Number | 20040094239 10/470486 |
Document ID | / |
Family ID | 20283212 |
Filed Date | 2004-05-20 |
United States Patent
Application |
20040094239 |
Kind Code |
A1 |
Sandberg, Odd ; et
al. |
May 20, 2004 |
Steel article
Abstract
A steel article consists of an alloy which consists in weight-
%: 1.7-2.5; 0.1-2.0 Si; 0.1-2.0 Mn; max 0.2 N; max 0.2 S; 12 16 Cr;
2.1-3.5 (Mo+W/2); 5-8 V; max 0.1 Nb, balance essentially only iron
and unavoidable impurities. The steel has a micro-structure
obtainable by a manufacturing of the steel which comprises spray
forming of an ingot, the micro-structure of which contains 14-25
vol-% carbides of mainly MC-type, where M substantially consists of
vanadium, of which carbides at least 80 vol-% have a substantially
rounded shape and a size in the longest extension of the carbides
amounting to 1-10 .mu.m, and M.sub.7C.sub.3-carbides, where M
substantially consists of chromium, which carbides typically have a
more elongated shape than the MC-carbides, of which MC-carbides at
least 80 vol-% have a maximal extension amounting to 3-50
.mu.m.
Inventors: |
Sandberg, Odd; (Uddeholm,
SE) ; Jonsson, Lennart; (Karlstad, SE) |
Correspondence
Address: |
NIXON & VANDERHYE, PC
1100 N GLEBE ROAD
8TH FLOOR
ARLINGTON
VA
22201-4714
US
|
Family ID: |
20283212 |
Appl. No.: |
10/470486 |
Filed: |
July 30, 2003 |
PCT Filed: |
March 5, 2002 |
PCT NO: |
PCT/SE02/00372 |
Current U.S.
Class: |
148/324 ;
420/12 |
Current CPC
Class: |
C22C 38/36 20130101;
C22C 38/26 20130101; C21D 6/002 20130101; C22C 38/24 20130101; C22C
33/0285 20130101; C21D 2211/004 20130101; C22C 38/02 20130101; B22F
2998/00 20130101; C22C 38/001 20130101; C22C 38/04 20130101; C22C
38/22 20130101; B22F 2998/00 20130101; B22F 3/115 20130101; B22F
2998/00 20130101; B22F 9/10 20130101; B22F 3/17 20130101 |
Class at
Publication: |
148/324 ;
420/012 |
International
Class: |
C22C 038/36; C22C
037/06 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 6, 2001 |
SE |
0100737-6 |
Claims
1. Steel article, characterised in that it consists of an alloy
which contains in weight-% 1.7-2.5 C 0.1-2.0 Si 0.1-2.0 Mn max 0.2N
max 0.2 S 12-16 Cr 2.1-3.5 (Mo+W/2) 5-8 V max 0.1 Nb balance
essentially only iron and unavoidable impurities, and that the
steel has a micro-structure obtainable by a manufacturing of the
steel which comprises spray forming of an ingot, the
micro-structure of which contains 14-25 vol-% carbides of mainly
MC-type, where M substantially consists of vanadium, of which
carbides at least 80 vol-% have a substantially rounded shape and a
size in the longest extension of the carbides amounting to 1-10
.mu.m, and M.sub.7C.sub.3-carbides, where m substantially consists
of chromium, which carbides typically have a more elongated shape
than the MC-carbides, of which MC-carbides at least 80 vol-% have a
maximal extension amounting to 3-50 .mu.m.
2. Article according to claim 1, characterised in that the
micro-structure contains 3-8 vol-% MC-carbides and 10-20 vol-%
M.sub.7C.sub.3-carbides.
3. Article according to claim 2, characterised in that it after
hardening and tempering has a hardness of 55 to 64 HRC.
4. Article according to claim 3, characterised in that the
martensitic matrix of the steel after hardening and tempering
contains 0.2-0.7 weight-% C in solid solution.
5. Article according to any of claims 1-4, characterised in that
the total content of C in the steel is at least 1.8%.
6. Article according to any of claims 1-4, characterised in that
the total content of C in the steel is max 2.3%.
7. Article according to any of claims 1-6, characterised in that
the steel contains 0.2-1.0% Si.
8. Article according to any of claims 1-7, characterised in that
the steel contains 0.2-1.0% Mn.
9. Article according to any of claims 1-8, characterised in that
the steel contains at least 13% Cr.
10. Article according to any of claims 1-9, characterised in that
the steel contains max 15.5% Cr.
11. Article according to claim 10, characterised in that the steel
contains 13.2-14.5% Cr.
12. Article according to any of claims 1-10, characterised in that
the steel contains at least 6.1% V.
13. Article according to any of claims 1-11, characterised in that
the steel contains max 7.5% V.
14. Article according to claims 12 and 14, characterised in that
the steel contains 6.3-7.3% V.
15. Article according to any of claims 12-14, characterised in that
the steel does not contain more than max 0.04 Nb.
16. Article according to any of claims 1-15, characterised in that
the steel contains at least 2.3% Mo.
17. Article according to any of claims 1-15, characterised in that
the steel contains max 3.0% Mo.
18. Article according to any of claims 1-17, characterised in that
the steel does not contain more than max 1.0% W, preferably max
0.5% W.
19. Article according to any of claims 1-18, characterised in that
the steel does not contain more than max 0.1% S, preferably max
0.05% S.
20. Article according to any of claims 3-19, characterised in that
it after hardening and tempering at a temperature between
180-220.degree. C. has a hardness of 55-62 HRC, preferably at least
59 HRC.
21. Article according to any of claims 3-19, characterised in that
it after hardening and tempering at a temperature between 380 and
450.degree. C. has a hardness of 55-62 ARC, preferably at least 59
ARC.
22. Article according to any of claims 3-19, characterised in that
it after hardening from a temperature between 480 and 520.degree.
C. has a hardness of 60-63 HRC.
23. Article according to any of claims 3-19, characterised in that
it after hardening from a temperature between 510 and 530.degree.
C. has a hardness between 61 and 64 HRC.
Description
TECHNICAL FIELD
[0001] The invention concerns an article made of steel having
features which are desirable for plastic mould steels intended to
be used for any of the following fields of application:
[0002] elements, e.g. screws and barrels for feeding and conducting
plastic masses in machines for the manufacturing of plastic
components, e.g. elements in injection moulding and extrusion
assemblies, and
[0003] mould tools and tool parts for injection moulding of plastic
materials.
[0004] Particularly the invention concerns objects of steel having
excellent wear resistance, good corrosion resistance,
hardenability, and tempering resistance as well as adequate
toughness; features which make the steel suitable to be employed
within said fields of application. The use of steel articles
according to the invention, however, is not limited to said fields
of application but can be employed also for a variety of other
applications, where said features are necessary or desirable, e.g.
details in pumps for feeding wearing media and for wear parts in
machines and other equipments, just to mention some.
BACKGROUND OF THE INVENTION
[0005] For parts of the above mentioned fields of application there
is today used a steel which is known under the trade name
ELMAX.TM., which is a high alloyed, powder metallurgy manufactured
chromium-vanadium-molyb- denum steel having good wear resistance
and corrosion resistance. The steel has the following nominal
chemical composition in weight-%: 1.7 C, 0.8 Si, 0.3 Mn, 18.0 Cr,
1.0 Mo, 3.0 V, balance iron and impurities. The steel has a high
wear resistance and corrosion resistance, which makes a
manufacturing of moulds for plastic moulding having a long working
life possible. The steel is used e.g. in the electronic industry
for the manufacturing of couplings, contacts, resistances, and
integrated circuits, but can also be used in the food industry,
where corrosion resistance is required from sanitary reasons, at
the same time as the wear resistance is an essential factor.
[0006] However, there is a demand for a steel having a still better
combination of excellent wear resistance, hardenability, tempering
resistance, and corrosion resistance, particularly for elements
such as screws and barrels for feeding and conducting plastic
masses in equipments for injection moulding of plastic
materials.
DISCLOSURE OF THE INVENTION
[0007] It is the purpose of the invention to provide steel articles
which satisfy the above mentioned demands. This can be achieved
therein that the article is manufactured of a spray formed steel
material having a chemical composition in weight-% and with a
micro-structure which are stated in the appending patent
claims.
[0008] Further, as far as the alloy elements which are included in
the steel are concerned, the following applies.
[0009] Carbon shall exist in a sufficient amount in the steel in
order, in the hardened and tempered condition of the steel, to
form, in combination with vanadium, 3-8 vol-% MC-carbides, in which
M substantially is vanadium and, in combination with chromium,
10-20 vol-% M.sub.7C.sub.3-carbides, in which M substantially is
chromium, the total amount of MC-carbides and
M.sub.7C.sub.3-carbides amounting to 14-25 vol-%, and also exist in
solid solution in the martensitic matrix of the steel in the
hardened condition in an amount of 0.2-0.7 weight-%, preferably
0.3-0.6 weight-%. Suitably the amount of dissolved carbon in the
matrix of the steel is about 0.5%. The total amount of carbon in
the steel, i.e. carbon which is dissolved in the matrix of the
steel plus the carbon that is bound in carbides shall be at least
1.7%, preferably at least 1.8%, while the maximum content of carbon
may amount to 2.5%, preferably not more than 2.3%.
[0010] The article of the invention is manufactured by a technique
which includes spray forming, in which drops of molten metal are
sprayed against a rotating substrate on which the drops rapidly
solidify to form a successively growing ingot. The ingot then can
be hot worked by forging and/or rolling to desired shape. At the
solidification of the drops said carbides are formed, which are
evenly distributed in the ingot and thence in the final product.
Due to the controlled rate of solidification of the drops, which is
slower than during manufacturing of metal powder by atomising a
stream of molten metal and rapid cooling of the formed droplets,
but essentially more rapid than during conventional ingot
manufacturing, continuous casting and/or ESR-remelting, the
carbides have sufficient time to grow to a size which has turned
out to be very favourable in the article according to the
invention. Thus the MC-carbides can be caused to achieve an
essentially rounded shape, such that at least 80 vol-% of the
MC-carbides obtain a size in the longest extension of the carbides
amounting to 1-10 .mu.m, preferably at least 5 .mu.m, while the
M.sub.7C.sub.3-carbides typically achieve a more elongated shape
than the MC-carbides, such that at least 80 vol-% of the
MC-carbides get a maximum extension which amounts to 3-50 .mu.m,
preferably at least 10 .mu.m.
[0011] Nitrogen optionally may be added to the steel in connection
with the spray forming to a maximal amount of 0.20%. According to
the preferred embodiment of the invention, however, nitrogen is not
intentionally added to the steel but will nevertheless exist as an
unavoidable element in an amount of max 0.15%, normally max 0.12%,
and is then not a harmful ingredient. To the contrary, the nitrogen
may have a favourable effect by forming vanadium and chromium
carbonitrides in combination with carbon. Thus a minor fraction of
carbonitrides may be included in the above mentioned volume
contents of MC- and M.sub.7C.sub.3-carbides.
[0012] Silicon is present as a residue from the manufacturing of
the steel and exists normally in an amount of at least 0.1%,
preferably at least 0.2%. The silicon increases the carbon activity
in the steel and therefore contributes to affording the steel an
adequate hardness without causing embrittlement problems. Silicon,
however, is a strong ferrite former and must therefore not exist in
amounts above 2.0%. Preferably, the steel does not contain more
than max 1.0% silicon.
[0013] Manganese also exists as a residue from the manufacturing of
the steel and binds the low amounts of sulphur which may exist in
the steel by forming manganese sulphide. Manganese therefore should
exist in an amount of at least 0.1%, preferably in an amount of at
least 0.2%. Manganese also promotes the hardenability, which is
favourable, but must not exist in amounts above 2.0% in order to
avoid embrittlement problems. Preferably, the steel does not
contain more than max 1.0% Mn. A nominal content of manganese is
0.5%.
[0014] Chromium shall exist in an amount of at least 12%,
preferably in an amount of at least 13% in order to afford the
steel a desirable corrosion resistance. Furhter chromium is an
important carbide former and forms M.sub.7C.sub.3-carbides together
with carbon, which carbides in combination with the MC-carbides
contribute to a desired wear resistance. Chromium also strongly
promotes the hardenability. The term hardenability means the
capacity of achieving a high hardness more or less deep in the
article that shall be hardened. The hardenability shall be
sufficient for the article to be through hardened even if the
article has comparatively large dimensions, without employing very
rapid cooling in oil or water at the hardening operation, which
might cause dimension changes. The hardness in the steel shall be
at least 55 HSC, suitably 58-64 HRC, after tempering. Chromium,
however, is a strong ferrite former. In order to avoid ferrite
after hardening from 1020-1150.degree. C., the chromium content
must not exceed 16%, preferably max 15.5%. A suitable chromium
content is 13.2-14.5%, nominally 14.0%.
[0015] Vanadium shall exist in the steel in an amount of 5.0-8.0%
in order, together with carbon and possibly nitrogen, to form said
MC-carbides or carbonitrides in the martensitic matrix of the steel
in the hardened and. tempered condition. Preferably, the steel
contains at least 6.1% and max 7.5% V. A suitable vanadium content
is 6.3-7.3%, nominally 6.8% V.
[0016] In principle, vanadium may be replaced by niobium for the
formation of MC-carbides, but for this twice as much niobium is
required as compared with vanadium, which is a drawback. Further,
niobium has the effect that the carbides will get a more edgy shape
and be larger than pure vanadium carbides, which may initiate
ruptures or chippings and therefore reduce the toughness of the
material. This may be particularly serious in the steel of the
invention, the composition of which has been optimised for the
purpose of achieving an excellent wear resistance in combination
with a high hardness and tempering resistance, as far as the
mechanical features of the material are concerned. The steel
therefore must not contain more than max 0.1% niobium, preferably
max 0.04% niobium. According to the most preferred embodiment,
niobium is tolerated only as an unavoidable impurity in the form of
a residual element from the raw materials which are used in
connection with the manufacturing of the steel.
[0017] Molybdenum shall exist in an amount of at least 2.1%,
preferably at least 2.3%, in order to afford the steel a desired
hardenability in combination with chromium and the limited amount
of manganese. Molybdenum also contributes to the corrosion
resistance of the steel but is a strong ferrite former. The steel
therefore must not contain more than 3.5% Mo, preferably max 3.0,
suitably max 2.5%.
[0018] In principle, molybdenum may completely or partly be
replaced by tungsten, but for this twice as much tungsten is
required as compared with molybdenum, which is a drawback. Also the
use of any scrap will become more difficult. Therefore tungsten
should not exist in an amount of more than max 1.0%, preferably max
0.5%. Most conveniently, the steel should not contain any
intentionally added tungsten, which according to the most preferred
embodiment of the invention is tolerated only as an unavoidable
impurity in the form of a residual element from the raw materials
which are used in connection with the manufacturing of the
steel.
[0019] Besides the mentioned alloy elements the steel does not
need, and should not, contain any more alloy elements in
significant amounts. Some elements are definitely undesired,
because they may have an undesired influence on the features of the
steel.
[0020] This is true, e.g. as far as phosphorus is concerned, which
should be kept at as low level as possible, preferably at max
0.03%, in order not to have an unfavourable effect on the toughness
the steel. Also sulphur in most respects is an undesired element,
but its negative effect on, in the first place, the toughness,
essentially can be neutralised by means of manganese, which forms
essentially harmless manganese sulphides, wherefore sulphur may be
tolerated in a maximal amount of 0.2% in order to improve the
machineability of the steel. Preferably, the steel, however,
normally does not contain more than max 0.1%, preferably max 0.05%
sulphur.
[0021] Further features and aspects of the invention will be
apparent from the following description of performed experiments
and from the appending patent claims.
BRIEF DESCRIPTION OF DRAWINGS
[0022] In the following description of performed experiments,
reference will be made to. the accompanying drawings, in which
[0023] FIG. 1 is a photography which shows the micro-structure of a
portion of an article according to the invention,
[0024] FIG. 2 shows tempering curves for a number of examined steel
alloys,
[0025] FIG. 3 shows a section of the curves of FIG. 2 at a larger
scale,
[0026] FIG. 4 in the form of a chart illustrates the hardenability
of a steel according to the invention and of two reference
materials with data from CCT-diagrams,
[0027] FIG. 5 shows the abrasive wear resistance of a steel
according to the invention and of two reference materials, and
[0028] FIG. 6 illustrates the corrosion resistance of the examined
materials in the form of the corrosion current, I.sub.cr, from the
polarisation curves of the materials.
DESCRIPTION OF PERFORMED TESTS
Materials
[0029] The chemical compositions of the materials which are
included in the test series are stated in Table 1. Steels No. 1 and
2 are reference materials. Both are powder metallurgy manufactured.
Steel No. 1 is a commercial steel of type ELMAX.TM., which has been
mentioned in the description of the background of the invention,
and steel No. 2 is another commercially available steel. Steels No.
3A and No. 4A refer to aimed compositions, while steel No. 3 and
No. 4 are analysed compositions of two steels, the contents of
vanadium of which lie in the lower and the upper section,
respectively, of the widest aspects of the chemical composition of
the steel of which the article according to the invention is made.
The steels 3 and 4 have been manufactured by the so called spray
forming technique, which also is referred to as the OSPRAY-method,
according to which an ingot, which rotates about its longitudinal
axis, successively is established from a molten material which in
the form of drops which are sprayed against the growing end of the
ingot that is produced continuously, the drops being caused to
solidify comparatively rapidly once they have hit the substrate,
however not as fast as when powder is produced and not as slow as
in connection with conventional manufacturing of ingots or in
connection with continuous casting. More specifically, the drops
are caused to solidify so rapidly that formed MC- and M7C3-carbides
will grow to the desired size according to the invention. The
spray-formed ingots of steel No. 3 and of steel No. 4 hade a mass
of about 2.9 and about 2.2 tons, respectively. The diameter of the
ingots was about 500 mm. The spray-formed ingots of steel No. 3 and
steel No. 4 were heated to a forging temperature of 1100.degree. C.
and were forged to the shape of blanks for further
examinations.
1TABLE 1 Chemical composition, weight-% Steel, No. C Si Mn S Cr Mo
V Nb N Balance 1 1.71 0.84 0.30 0.019 17.9 1.08 3.01 0.015 0.104 Fe
and unavoidable impurities 2 2.41 0.29 0.43 0.019 13.1 1.12 7.91
0.003 0.083 -"- 3A* 1.85 0.50 0.40 .ltoreq.0.020 14.0 2.30 6.00 --
.ltoreq.0.10 -"- 3 1.93 0.61 0.39 0.019 13.7 2.32 5.64 0.02 0.10
-"- 4A* 2.35 0.50 0.40 .ltoreq.0.020 14.4 2.30 8.20 -- .ltoreq.0.10
-"- 4 -"- *Aimed compositions
[0030] In the studies which shall be explained in the following,
steels No. 1, 2 and 3 were tested with reference to
[0031] micro-structure
[0032] hardness versus austenitising and tempering temperature
[0033] hardenability
[0034] ductility
[0035] abrasive wear resistance
[0036] corrosion resistance
Micro-Structure
[0037] The micro-structure of steels No. 1 and 2 is typical for
powder metallurgy manufactured steels, which implies that all
carbides are very small, max about 3 .mu.m, and evenly distributed
in the matrix of the steel independent of its heat treatment. The
micro-structure in the hardened, T.sub.A=1120.degree. C./30 min.
and tempered, 525.degree. C./2.times.2 h, condition, of steel No. 3
is apparent from FIG. 1, which shows a portion in the centre of an
examined bar having the cross section 350.times.63.5 mm. In the
matrix of the steel, which consists of tempered martensite, there
are primary carbides of MC-type having a typically rounded shape
and a size of from about 1 .mu.m up to max about 10 .mu.m, and
chromium carbides, M.sub.7C.sub.3, having a substantially more
extended shape. The size of the chromium carbides was max about
15.times.50 .mu.m in the centre of the bar. In the surface of the
bar, which also was examined but which is not shown in any picture,
the MC-carbides as well as the chromium carbides were somewhat
smaller; up to about 6 .mu.m and up to about 8.times.30 .mu.m,
respectively. A macro-etched cross section of the rod also
evidenced that the structure is very even over the whole cross
section.
[0038] The carbide content was examined by the point calculation
method in a scanning electron microscope. The measured total
content of carbides in steel No. 3 was 20.4%, of which 15.4% were
rich in chromium (M7C3) and 5% were rich in vanadium (MC). As far
as steel No. 2 is concerned, the measured total content of carbides
was 23.9 vol-%, of which 13.1% were rich in chromium (7C3) and
10.8% were rich in vanadium (MC). The measured total content of
carbides in steel No. 1 was 14%, of which 13% were rich in chromium
(M7C3) and 1% was rich in vanadium (MC). All carbide contents refer
to vol-%. The heat treatment condition was T.sub.A=1120.degree.
C./30 min.+250.degree. C./2.times.2 h for steel No. 2 and steel No.
3 and T.sub.A=105C./30 min.+250.degree. C./2.times.2 h for steel
No. 1.
Hardness after Heat Treatment
[0039] In the soft annealed condition, the steel according to the
invention has a hardness (Brinell-hardness) of 200-300 HB,
typically about 250 HB. The influence of the tempering temperature
on the hardness after austenitising between 1080 and 1150.degree.
C. is shown in FIG. 2. Steel No. 3 exhibits a stronger secondary
hardening than the two reference steels 1 and 2 after austenitising
at 1120 and 1150.degree. C. and reaches a hardness of 63 HRC after
tempering at 5252.times.2 h. A section of the region which
comprises the hump on the tempering curves is shown at a larger
scale in FIG. 3. Steel No. 2 had the same hardness as steel No. 1
after austenitising at 1120.degree. C., but a substantially lower
tempering resistance than both steel No. 1 and No. 3.
Hardenability
[0040] The hardness versus the required time for cooling from 800
to 500.degree. C. is shown graphically in FIG. 4. It is apparent
from this chart that the hardenability of steel No. 3 is
significantly better than that of steel No. 1 and much better than
that of steel No. 2.
Toughness
[0041] The impact energy was examined, un-notched test specimens
being used after hardening from T.sub.A=1120.degree. C./30 min for
steels Nos. 2 and 3, and from T.sub.A=1100.degree. C./30 min.
respectively, for steel No. 1 after varying tempering temperatures
between 200 and 550.degree. C. The dimension of the bar of the
examined steel, however, varied, wherefore the results are not
fully comparable. However, it could be settled that the impact
energy of all examined steels exceeded 10 J for all longitudinal
samples, which satisfies the criteria as far as approvable impact
toughness is concerned for the intended field of application of the
article according to the invention.
Abrasive Wear
[0042] The wear resistance was examined in the form of a pin-to-pin
test using SiO.sub.2 as an abrasive agent. As far as the dimensions
and hardening temperatures of the examined samples are concerned
the following applies. Steel No. 1: .O slashed. 38
mm/T.sub.A=1100.degree./30 min; steel No. 2: .O slashed. 37
mm/T.sub.A=1120.degree. C./30 min; steel No. 3: 350.times.63.5
mm/T.sub.A=1120.degree. C./30 min. The results are apparent from
the bar chart in FIG. 5. This chart. illustrates that steel No. 3
for all tempering temperatures exhibited the by far best wear
resistance.
Corrosion Resistance
[0043] The corrosion resistance was measured via potential curves
in 0.05 pH.sub.2SO.sub.4, pH=1.2. I.sub.cr at the active peak
defines the relative corrosion resistance, which means that the
corrosion current should be as low as possible. In the bar chart in
FIG. 6, the different materials are compared as a function of the
heat treatment condition. Steel No. 3 had the best corrosion
resistance after tempering up to at least 400.degree. C. After
tempering at 525.degree. C., the corrosion resistance was reduced
for all examined materials; steel No. 3 slightly more than steel
No. 2 and considerably more than steel No. 1. It should, however,
be observed, as far as this comparison is concerned, that steel No.
3 after tempering had an essentially higher hardness than the
comparative materials.
Discussion
[0044] The described tests show that of steels according to the
invention there can be manufactured articles having a very high
wear resistance, which can be attributed to a combination of the
hardness of the steel and its content of carbides in a sufficient
amount and of sufficient size. Another important factor is the
hardenability of the steel, which is very good and better than
comparable steels. Hardnesses of between 59 to 62 HRC in
combination with an excellent corrosion resistance were measured
after tempering at 200 and 400.degree. C. and hardness of between
61 to 63 HRC after tempering at 500.degree. C. By tempering at
about 525.degree. C. there can be achieved a hardness peak of
between 61 to 64 HRC. In the latter case some corrosion resistance
is lost, but the high hardness can be utilised for certain
applications where high requirements on the corrosion resistance do
not exist. The invention thus provides a pronounced flexibility
with reference to the adaptility of the usefulness of the steel for
various applications by choice of a suitable heat treatment.
Another important factor for the usability of the steel is its
manufacturing, which is based on the spray forming technique, which
is essentially more economical than powder metallurgy
manufacturing.
[0045] It should also be realised that the article according to the
invention may have any conceivable shape, including spray formed
ingots, blanks in the form of, e.g., plates, bars, blocks, or the
like, which normally are delivered by the steel manufacturer in the
soft annealed condition with a hardness of 200-300 HB, typically
about 250 HB to the customers for machining to final product shape,
as well as the final product which has been hardened and tempered
to intended hardness for the application in question.
* * * * *