U.S. patent application number 11/815087 was filed with the patent office on 2009-07-02 for austenitic steel having high strength and formability, method of producing said steel and use thereof.
This patent application is currently assigned to Corus Staal BV. Invention is credited to Calum McEwan.
Application Number | 20090165897 11/815087 |
Document ID | / |
Family ID | 36406514 |
Filed Date | 2009-07-02 |
United States Patent
Application |
20090165897 |
Kind Code |
A1 |
McEwan; Calum |
July 2, 2009 |
AUSTENITIC STEEL HAVING HIGH STRENGTH AND FORMABILITY, METHOD OF
PRODUCING SAID STEEL AND USE THEREOF
Abstract
Substantially austenitic steel having high strength and good
formability for cold rolling including (in weight percent): 0.05 to
1.0% C; 11.0 to 14.9% Mn; 1.0 to 5.0% Al; O to 2.5% Ni the
remainder being iron and unavoidable impurities, wherein the
microstructure includes at least 75% in volume of austenite, and
wherein (Ni+Mn) is from 11.0 to 15.9%.
Inventors: |
McEwan; Calum; (Haarlem,
NL) |
Correspondence
Address: |
Dickinson Wright PLLC;James E. Ledbetter, Esq.
International Square, 1875 Eye Street, NW., Suite 1200
WASHINGTON
DC
20006
US
|
Assignee: |
Corus Staal BV
Ijmuiden
NL
|
Family ID: |
36406514 |
Appl. No.: |
11/815087 |
Filed: |
February 1, 2006 |
PCT Filed: |
February 1, 2006 |
PCT NO: |
PCT/EP2006/001034 |
371 Date: |
May 20, 2008 |
Current U.S.
Class: |
148/329 ;
164/462; 164/463; 164/476; 164/76.1 |
Current CPC
Class: |
C22C 38/06 20130101;
C22C 38/04 20130101; C21D 8/0236 20130101; C21D 2211/001 20130101;
C21D 8/0205 20130101 |
Class at
Publication: |
148/329 ;
164/476; 164/462; 164/76.1; 164/463 |
International
Class: |
C22C 38/04 20060101
C22C038/04; B22D 11/00 20060101 B22D011/00; B22C 9/00 20060101
B22C009/00 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 2, 2005 |
EP |
05075258.3 |
Aug 25, 2005 |
EP |
05076960.3 |
Claims
1. Substantially austenitic steel strip having high strength and
good formability for cold rolling comprising (in weight percent):
0.05 to 0.78% C 11.0 to 14.9% Mn 1.0 to 5.0% Al 0 to 2.5% Ni the
remainder being iron and unavoidable impurities, wherein the
microstructure comprises at least 80% in volume of austenite, and
wherein (Ni+Mn) is from 11.0 to 15.9%.
2. Steel according to claim 1, wherein the microstructure comprises
at least 85%.
3. Steel according to claim 1, wherein the carbon content is
between 0.30 and 0.75%.
4. Steel according to claim 1, wherein the nickel content is at
most 0.05%.
5. Steel according to claim 1, wherein the aluminium content is at
most 4.0%.
6. Steel according to claim 1, wherein the manganese content is at
least 11.5%.
7. Steel according to claim 1, wherein the manganese content is at
most 14.7%.
8. Steel according to claim 1, provided in the form of a hot rolled
steel having a thickness between 0.5 and 20 mm.
9. Steel according to claim 1, wherein the steel is provided in the
form of a cold-rolled strip, or in the form of a cold-rolled and
continuously annealed or batch-annealed strip, optionally coated
with a coating system comprising one or more metallic and/or
organic layer or layers.
10. Cold rolled steel according to claim 9, wherein the
microstructure after rolling and annealing comprises at least 80%
in volume of austenite.
11. Method of producing austenitic steel strip, having an austenite
content according to claim 1, comprising the steps of: providing
molten steel having a composition comprising (in weight percent):
0.05 to 0.78% C 11.0 to 14.9% Mn 1.0 to 5.0% Al 0 to 2.5% Ni the
remainder being iron and unavoidable impurities wherein the
microstructure comprises at least 80% in volume of austenite, and
wherein (Ni+Mn) is from 11.0 to 15.9%; casting said steel into an
ingot, or a continuously cast slab, or a continuously cast thin
slab or a strip-cast strip; providing a hot-rolled strip by hot
rolling the ingot, the continuously cast slab, the continuously
cast thin slab or the strip-cast strip to the desired hot rolled
thickness.
12. Method according to claim 11, wherein the hot-rolled strip is
cold-rolled to the desired final thickness.
13. Method according to claim 12, wherein the cold-rolled strip is
annealed after cold rolling to the desired final thickness in a
continuous or batch annealing process.
14. Method according to claim 11, wherein the strip-cast strip is
obtained after strip casting using a twin-roll casting,
belt-casting or drum-casting device.
15. Strip or sheet produced from a steel comprising (in weight
percent): 0.05 to 0.78% C 11.0 to 14.9% Mn 1.0 to 5.0% Al 0 to 2.5%
Ni the remainder being iron and unavoidable impurities wherein the
microstructure comprises at least 80% in volume of austenite, and
wherein (Ni+Mn) is from 11.0 to 15.9%, by a method according to
claim 11.
16. A method comprising producing automotive inner or outer parts
or wheels from a steel according to claim 1.
17. A method comprising hydroforming a steel according to claim
1.
18. Steel according to claim 1, wherein the microstructure
comprises at least 90% in volume of austenite.
19. Steel according to claim 1, wherein the microstructure
comprises at least 95% in volume of austenite.
20. Steel according to claim 1, wherein the manganese content is at
least 12.0%.
21. Steel according to claim 1, provided in the form of a hot
rolled steel having a thickness between 0.7 and 10 mm
22. Steel according to claim 1, provided in the form of a hot
rolled steel strip having a strip thickness is at most 8 mm.
23. Steel according to claim 1, provided in the form of a hot
rolled steel strip having a strip thickness between 0.8 and 5
mm.
24. Cold rolled steel according to claim 9, wherein the
microstructure after rolling and annealing comprises at least 85%
in volume of austenite.
25. Cold rolled steel according to claim 9, wherein the
microstructure after rolling and annealing comprises at least 90%
in volume of austenite.
26. Cold rolled steel according to claim 9, wherein the
microstructure after rolling and annealing comprises at least 95%
in volume of austenite.
27. Method according to claim 11, wherein the hot-rolled strip is
cold-rolled to the desired final thickness, wherein the
cold-rolling reduction is between 10 to 90%
28. Method according to claim 11, wherein the hot-rolled strip is
cold-rolled to the desired final thickness, wherein the
cold-rolling reduction is between 30 and 85.
29. Method according to claim 11, wherein the hot-rolled strip is
cold-rolled to the desired final thickness, wherein the
cold-rolling reduction is between 45 and 80%.
30. The strip or sheet of claim 15, wherein the steel is
galvanized.
31. A method comprising producing automotive inner or outer parts
or wheels from a steel strip or sheet of claim 15.
32. A method comprising hydroforming a strip or sheet according to
claim 15.
Description
[0001] The invention relates to a substantially austenitic steel
having high strength and good formability for cold rolling. The
invention also relates to a method of producing said steel and the
use thereof.
[0002] Austenitic steels having a high strength, such as Hadfield
steels, comprising manganese (11 to 14%) and carbon (1.1 to 1.4%)
as its main alloying elements, have been known for a long time. The
original Hadfield steel, containing about 1.2% C and 12% Mn, was
invented by Sir Robert Hadfield in 1882. This steel combines high
toughness and a reasonable ductility with high work-hardening
capacity and, usually, good resistance to wear. However, Hadfield
steels do not have good formability due to large amounts of brittle
carbides. Due to the high work-hardening rate, the steels are
difficult to machine. GB 297420 discloses a cast Hadfield-type
steel with additions of aluminium to improve the machinability. The
addition of aluminium results in the formation of particles which
improve the machinability, particularly machinability by material
detaching tools.
[0003] A disadvantage of these types of steel is that they are
difficult to cold roll. The high work-hardening rate and the
presence of brittle carbides makes the steel work harden very
quickly. U.S. Pat. No. 2,448,753 attempted to solve this problem by
repeatedly heating, quenching, pickling and cold-rolling the hot
rolled material until the desired cold rolled thickness is reached.
However, this is a very costly process.
[0004] U.S. Pat. No. 5,431,753 discloses a process for
manufacturing a cold rolled steel having a manganese content of
between 15 and 35%, up to 1.5% in carbon and between 0.1 and 3.0%
of Aluminium. A lower manganese content is disclosed to be
undesirable.
[0005] It is an object of the invention to provide a substantially
austenitic steel having high strength and good formability which
can be cold rolled to its final thickness without an intermediate
annealing step.
[0006] It is also an object of the invention to provide a
substantially austenitic steel having improved strength and
formability.
[0007] It is also an object of the invention to provide a
substantially austenitic steel having high strength and formability
which can be produced in an economical way.
[0008] At least one of these objects can be reached by a steel for
cold rolling comprising (in weight percent)
[0009] 0.05 to 1.0% C
[0010] 11.0 to 14.9% Mn
[0011] 1.0 to 5.0% Al
[0012] 0 to 2.5% Ni
[0013] the remainder being iron and unavoidable impurities, wherein
the microstructure comprises at least 75% in volume of austenite,
and wherein (Ni+Mn) is from 11.0 to 15.9%.
[0014] The carbon content of the steel according to the invention
is much lower than the Hadfield steels, which is known to be about
1.2%. The contribution of the alloying elements is believed to be
as follows hereinafter. Carbon inhibits the formation of
.epsilon.-martensite by increasing the Stacking Fault Energy (SFE).
Stacking faults are precursors to .epsilon.-martensite, so
increasing the SFE decreases the tendency to form
.epsilon.-martensite. The lower carbon content results in a lower
tendency to form embrittling phases and/or precipitates during
cooling after rolling, and the lower carbon content in comparison
to Hadfield steels is also beneficial for the weldability of the
steel. In addition carbon improves the stability of the austenite
since carbon is an austenite stabilising element.
[0015] The main deformation mechanisms in the austenitic steel
according to the invention are strain induced twinning and
transformation induced plasticity.
[0016] Manganese improves the strength of the steel by
substitutional hardening and it is an austenite stabilising
element. Lowering the manganese content results in a reduction of
the SFE of the alloy and hence in a promotion of strain induced
twinning. The manganese range according to the invention provides a
stable or meta-stable austenite at room temperature.
[0017] Aluminium reduces the activity of carbon in austenite in
steels according to the invention. The reduction in carbon activity
increases the solubility of carbon in austenite, thereby decreasing
the driving force for precipitation of carbides, particularly of
(FeMn)-carbides, by reducing the carbon super-saturation. Aluminium
also reduces the diffusivity of carbon in austenite and thereby
reduces the susceptibility to dynamic strain ageing during
deformation processes such as cold rolling. The lower diffusivity
also leads to a slower formation of carbides, and thus prevents or
at least hinders the formation of coarse precipitates. Since higher
aluminium contents also lead to a higher SFE, the tendency for
strain induced twinning is lowered at increasing Aluminium levels.
Consequently, a decrease in carbon content can be compensated by an
increase in aluminium content with regard to the suppression of the
formation of .epsilon.-martensite and the prevention or hindering
of the formation of brittle carbides, particularly (FeMn)-carbides.
These carbides are believed to contribute to poor workability of
the steels according to the invention and their formation has thus
to be avoided. So the combination of a reduced carbon activity and
a reduced carbon diffusivity lead to a reduced or no formation of
brittle carbides, particularly (FeMn)-carbides, and therefore to an
improved formability and also an improved cold rollability. It was
found that below 1% aluminium the suppression of
.epsilon.-martensite was insufficient, and at levels exceeding 5%
aluminium, the SFE becomes too high, thereby adversely affecting
the twinning deformation mechanism.
[0018] Since aluminium is also a ferrite stabilising element, the
influence on the austenite stability of the aluminium additions has
to be compensated for by manganese and other austenite stabilising
elements. Manganese can, at least partly, be replaced by elements
which also promote austenite stability such as nickel. It is
believed that Nickel has a beneficial effect on the elongation
values and impact strength.
[0019] Since the amount of alloying additions is kept as low as
possible whilst maintaining favourable cold rolling and mechanical
properties, the austenite is meta-stable and the microstructure of
the steel may not be fully austenitic. The microstructure in the
steel according to the present invention as a function of
composition may comprise a mixture of ferrite and austenite with
components of martensite.
[0020] Upon deforming the steel according to the invention, a
beneficial combination of the deformation mechanisms of plasticity
induced by twinning and plasticity induced by transformation under
the influence of deformation provides excellent formability,
whereas the lower strain hardening and work hardening rate as
compared to conventional Hadfield steel in combination with a lower
susceptibility to dynamic strain ageing as a result of the
aluminium addition and the absence of coarse and/or brittle
carbides results in good cold-rolling and forming properties. It
has been found that the favourable cold rolling and mechanical
properties are already obtained when the microstructure comprises
at least 75% in volume of austenite. The steel according to the
invention also has a good galvanisability as a result of the
absence of silicon as an alloying element, i.e. in the sense of a
deliberate addition of silicon for alloying purposes. In addition,
there is no risk of low melting silicon oxide, thereby preventing
the occurrence of sticking silicon oxides on the surface of the hot
rolled strip. It should be noted that the steel not only has
excellent cold-rollability, but that similar excellent properties
in terms of strength and formability are obtained in its pre-cold
rolling state, i.e. for instance in its as-hot-rolled state, but
also in the recrystallised state after cold-rolling and
annealing.
[0021] In an embodiment of the invention (Ni+Mn) is at most 14.9%.
This embodiment allows the steel to be produced in a more
economical way, because the amount of expensive alloying elements
is reduced.
[0022] In an embodiment of the invention the microstructure, in
particular after cold-rolling and annealing, comprises at least
80%, preferably at least 85%, more preferably at least 90% and even
more preferably at least 95% in volume of austenite. The inventor
found that a further improvement of the cold rolling and mechanical
properties could be obtained if the steel was chosen such that the
austenite content in the microstructure comprises at least 80%,
preferably at least 85%, more preferably at least 90% and even more
preferably at least 95% in volume of austenite. Due to the
meta-stability of the austenite, and the occurrence of
transformation induced plasticity, the amount of austenite tends to
decrease during subsequent processing steps. In order to ensure
good formability and high strength, even during a later or its last
processing step, it is desirable to have an austenite content which
is as high as possible at any stage of the processing, but in
particular after cold-rolling and annealing.
[0023] It was found that the amount of austenite is favourably
influenced by selecting the carbon content to be at least 0.10% or
at least 0.15%, but preferably to be at least 0.30% and more
preferably at least 0.50%.
[0024] In an embodiment of the invention, the carbon content of the
steel is at most 0.78%, preferably at most 0.75%, more preferably
at most 0.70%. It was found that the weldability of the steel is
improved by limiting the carbon content. It was found that a steel
having a carbon content of at most 0.78%, preferably at most 0.75%,
more preferably at most 0.70% or even more preferably of at most
0.65% provides a good balance between the mechanical properties and
the risk of martensite formation. In an embodiment of the
invention, the carbon content is between 0.15 and 0.75%, preferably
between 0.30 and 0.75%. From an economic point of view, the
properties point of view, and a process control point of view, this
range provides stable conditions.
[0025] In an embodiment of the invention the nickel content is at
most 1.25%. It is believed that nickel has a beneficial effect on
the elongation values and impact strength. It has been found that
at Nickel additions exceeding 2.5% the effect saturates. Since
Nickel is also an expensive alloying element, the amount of Nickel
is to be kept as low as possible if the demands to elongation
values and/or impact strength are somewhat relaxed. In an
embodiment of the invention the Nickel content is at most 0.10%,
preferably at most 0.05%.
[0026] In an embodiment of the invention the aluminium content is
at most 4.0%. This embodiment limits the increase in stacking-fault
energy by the addition of Aluminium, whilst still maintaining
favourable properties.
[0027] In an embodiment of the invention the manganese content is
at least 11.5%, preferably at least 12.0%. This embodiment allows a
more stable austenite to be formed.
[0028] In an embodiment of the invention the manganese content is
at most 14.7%. This embodiment allows a further reduction in costs
of the steel according to the invention.
[0029] In an embodiment, the steel according to the invention is
provided in the form of a continuously cast slab with a typical
thickness of between 100 and 350 mm, or in the form of a
continuously cast thin slab with a typical thickness of between 50
and 100 mm. Preferably, the steel according to the invention is
provided in the form of a continuously cast and/or hot rolled
strip, preferably with a typical thickness between 0.5 and 20 mm,
more preferably between 0.7 and 10 mm. Even more preferably the
strip thickness is at most 8 mm or even at most 6 mm.
[0030] In an embodiment, the steel according to the invention is
provided in the form of a hot rolled steel having a thickness
between 0.5 and 20 mm, preferably between 0.7 and 10 mm, more
preferably the strip thickness is at most 8 mm, or even more
preferably between 0.8 and 5 mm.
[0031] It was found that this type of hot-rolled steel has
excellent tensile strength and formability which renders it
particularly useful for applications where these properties are
called for, for instance in automotive and other transport
applications.
[0032] In an embodiment the steel according to the invention is
provided in the form of a cold-rolled strip, or in the form of a
cold-rolled and annealed (continuously or batch-annealed) strip
which may be coated with a coating system comprising one or more
metallic and/or organic layer or layers. The metallic coating may
be provided in a hot-dip line, an electro-coating line, but also in
a CVD or PVD process, or even by cladding.
[0033] Preferably, the microstructure of the cold rolled steel
microstructure after rolling and annealing, and the optional
coating, comprises at least 80%, preferably at least 85%, more
preferably at least 90%, and even more preferably at least 95% in
volume of austenite. It was found that the cold rolled steel after
rolling and annealing has optimal formability when the
microstructure of the cold rolled steel microstructure after
rolling and annealing, and the optional coating, comprises only or
substantially only austenite.
[0034] According to a second aspect of the invention, there is
provided a method of producing a substantially austenitic steel
strip, having an austenite content as described above, comprising
the steps of: [0035] providing molten steel having a composition as
described above; [0036] casting said steel into an ingot, or a
continuously cast slab, or a continuously cast thin slab or a
strip-cast strip; [0037] providing a hot-rolled strip by hot
rolling the ingot, the continuously cast slab, the continuously
cast thin slab or the strip-cast strip to the desired hot rolled
thickness
[0038] In view of the composition of the steel according to the
invention, the molten steel will most likely be provided by an
EAF-process. The molten steel is then subsequently cast in a mould
so as to obtain a solidified steel in a form suitable for hot
rolling. This form may be an ingot which after slabbing and
reheating is suitable for hot rolling. It may also be a
continuously cast thick or thin slab having a typical thickness of
between 50 and 300 mm. Also, the form suitable for hot rolling may
be a continuously cast strip, such as obtained after strip casting
using some form of strip-casting device, such as twin-roll casting,
belt-casting or drum casting. In order to convert the cast
microstructure into a wrought microstructure, hot deformation such
as rolling of the solidified steel is required. This can be done in
a conventional rolling mill comprising a single conventional
rolling stand or a plurality of rolling stands, in the latter case
usually in a tandem set-up. In case the deformation of the cast
steel has to be obtained using a low amount of thickness reduction,
such as after strip casting, the method as disclosed in EP 1 449
596 A1 may be used to generate a substantial amount of deformation
in a steel strip without reducing the thickness of the strip to the
same extent. This method comprises a rolling process wherein the
steel product is passed between a set of rotating rolls of a
rolling mill stand in order to roll the steel product,
characterised in that the rolls of the rolling mill stand have
different peripheral velocities such that one roll is a faster
moving roll and the other roll is a slower moving roll, in that the
peripheral velocity of the faster moving roll is at least 5% higher
and at most 100% higher than that of the slower moving roll, in
that the thickness of the steel product is reduced by at most 15%
per pass, and in that the rolling takes place at a maximum
temperature of 1350.degree. C.
[0039] In an embodiment of the invention the hot-rolled strip is
cold-rolled to the desired final thickness, preferably wherein the
cold-rolling reduction is between 10 to 90%, more preferably
between 30 and 85, even more preferably between 45 and 80%.
[0040] In an embodiment of the invention, the cold-rolled strip is
annealed after cold rolling to the desired final thickness in a
continuous or batch annealing process. This annealing treatment
results in a substantially recrystallised product.
[0041] In an embodiment of the invention, the cold-rolled strip is
galvanized. The absence of silicon as an alloying element, i.e. in
the sense of a deliberate addition of silicon for alloying
purposes, is beneficial for the galvanisability of the austenitic
steel. The adherence of the zinc layer to the substrate is thereby
greatly improved.
[0042] The steel according to the invention may be annealed at
annealing temperatures between 550 to 1100.degree. C., preferably
between 650 to 1100.degree. C. either in a batch annealing process,
in which case the maximum annealing temperature is preferably
between 550 and 800.degree. C., preferably between 650 and
800.degree. C., more preferably at least at 700 and/or below
780.degree. C., or in a continuous annealing process, in which case
the maximum annealing temperature is at least 600.degree. C.,
preferably wherein the maximum annealing temperature is between 700
and 1100.degree. C., more preferably below 900.degree. C. After the
cold rolling step and/or the annealing step the strip may be
subjected to a temper rolling process.
[0043] According to a third aspect an austenitic steel strip or
sheet is provided as described above, produced according to a
process as described above. These steels provide excellent strength
and good formability in any process stage.
[0044] The resulting steel strips may be processed to blanks for
further processing such as a stamping operation or a pressing
operation in a known way.
[0045] The steel may be used to produce parts for automotive
applications, both in the load bearing parts, such as chassis parts
or wheels, but also in the outer parts, such as body parts. The
steel is also suitable for the production of tubes and pipes,
particularly for low temperature application. Due to its large
forming potential, the steel is very well suited for shaping by
hydroforming or similar processes. Its high work hardening
potential and work hardening rate makes the steel suitable for
producing products wherein the steel is subjected to impact
loads.
[0046] The invention will now be explained in more detail below
with reference to the following non limitative examples and steels,
of which the composition is given in Table 1 (a hyphen indicating
that the element is present only as an unavoidable impurity and/or,
in the case of aluminium, for killing the steel).
TABLE-US-00001 TABLE 1 Steels according to the invention (in wt.
%). Material C Mn Al Ni Hadfield 1.2 12 -- -- 1 0.63 13.2 2.6 -- 2
0.63 14.5 2.6 -- 3 0.55 14.5 3.5 -- 4 0.30 13.9 4.5 -- 5 0.90 14.5
1.5 -- 6 0.63 12 2.6 2.5 7 0.15 14.2 4.5 -- 8 0.05 14.5 4.5 -- 9
0.66 14.1 2.2 -- 10 0.52 14.9 3.2 -- 11 0.59 11.9 2.4 2.6 12 0.95
14.5 2.5 --
[0047] Rolled ingots of 30 mm thickness were reheated to a
temperature of 1220.degree. C. (except for steel 12 where a
reheating temperature of 1070.degree. C. was used in view of the
ductility of the steel) and subsequently hot-rolled to a gauge of 3
mm using a 7-pass rolling schedule. A finishing temperature of
900.degree. C. was used. The coiling temperatures ranged from
600.degree. C. to 680.degree. C. Details of the finishing schedule
are summarized in table 2 below.
TABLE-US-00002 TABLE 2 Summary of Hot Rolling Reheating Finishing
Coiling Temperature Rolling Schedule Temperature Temperature
1220.degree. C. 30 > 22 > 15 > 10 > 7 > 900.degree.
C. 680-600.degree. C. 5 > 3.8 > 3 (mm)
[0048] Quenching after coiling to avoid carbide embrittlement
proved to be not necessary due to the carefully chosen chemical
composition, particularly the low C-level or the Al-addition.
[0049] Cold rolling of the 3 mm hot-rolled samples was undertaken
without difficulty to provide cold-rolled samples of 1.5, 1.3 mm or
1 mm gauge respectively. Annealing of small samples at various
conditions and subsequently determining the extent of
recrystallisation using hardness testing was undertaken to
determine the batch annealing conditions. This revealed that a
minimum temperature of 700.degree. C. with a soak time of 4 hours
was adequate to achieve substantially complete recrystallisation.
In order to provide a reasonable safety margin, a minimum annealing
temperature of 715.degree. C. for 4 hours or 730.degree. C. for 4
hours is preferable for batch-type annealing to provide complete
recrystallisation. It should be noted that the annealing time and
annealing temperature for batch annealing are exchangeable to a
certain degree, reference is made to EP 0 876 514.
[0050] Samples were removed from all plates and these were batch
annealed (see table 4).
[0051] The tensile properties in the rolling direction for steel 1
and steels 9-12 are shown in tables 3 and 4. Different levels of
cold reduction appear to have little effect on the driving force
for recrystallisation. Fluctuations in coiling temperature between
600.degree. C. and 680.degree. also appear to have little effect.
The tensile tests were performed on a standard tensile specimen and
a gauge length of 80 mm was used, except for steel 12, where a
gauge length of 50 mm was used. The tensile tests were performed
according to EN 10002-1 in the longitudinal direction.
TABLE-US-00003 TABLE 3 Tensile Results of Hot Rolled Samples
Mechanical Properties - Hot Rolled Coiling A80 Gauge Temperature Rp
Rm (* = A50) (mm) (.degree. C.) (N/mm.sup.2) (N/mm.sup.2) % n
(10-20) r (20) 1 3 600 414 793 58 0.38 0.81 1 3 680 448 787 52 0.34
0.76 9 3 630 425 784 49 0.32 0.85 10 3 670 496 797 41 0.37 1.02 11
3 620 413 866 31 n.d. 0.98 12 3 620 581 861 8 (*) n.d. 1.81
TABLE-US-00004 TABLE 4 Tensile Results of Cold Rolled Samples
Mechanical Properties - Cold Rolled and Annealed Steel Coiling Cold
Annealing A80 Gauge Temperature Reduction Time/Temp Reh Rm (* =
A50) (mm) (.degree. C.) (%) (.degree. C. & hours) (N/mm.sup.2)
(N/mm.sup.2) % n (10-20) r (20) 1 1.3 625 56 730/4 443 814 47 0.38
0.81 1 1.3 660 56 730/4 438 830 48 0.39 0.81 1 1 660 66 730/4 453
831 45 0.38 0.81 1 1 660 66 760/8 420 760 29 0.38 0.79 9 1.3 630 56
715/4 510 930 51 (*) 0.39 1.10 10 1.3 610 56 715/4 520 851 44 (*)
0.36 1.27 11 1.3 640 56 715/4 441 855 42 (*) 0.39 0.90 12 1.5 620
52 715/4 438 874 28 (*) 0.27 1.14
[0052] It is of course to be understood that the present invention
is not limited to the described embodiments and examples described
above, but encompasses any and all embodiments within the scope of
the description and the following claims.
* * * * *