U.S. patent application number 13/255548 was filed with the patent office on 2012-05-17 for method for producing a hot rolled strip and hot rolled strip produced from triplex lightweight steel.
This patent application is currently assigned to SALZGITTER FLACHSTAHL GMBH. Invention is credited to Hellfried Eichholz, Zacharias Georgeou, Joachim Konrad, Markus Schaperkotter, Karl-Heinz Spitzer, Bianca Springub.
Application Number | 20120121452 13/255548 |
Document ID | / |
Family ID | 41050967 |
Filed Date | 2012-05-17 |
United States Patent
Application |
20120121452 |
Kind Code |
A1 |
Spitzer; Karl-Heinz ; et
al. |
May 17, 2012 |
METHOD FOR PRODUCING A HOT ROLLED STRIP AND HOT ROLLED STRIP
PRODUCED FROM TRIPLEX LIGHTWEIGHT STEEL
Abstract
The invention relates to a method for producing a hot strip from
a triplex lightweight steel, wherein a melt is cast into a roughed
strip and the latter is subsequently rolled into a hot strip. For
this purpose, it is provided that the melt is cast in a horizontal
strip casting facility under conditions of a calm flow and free of
bending into a roughed strip in the range between 6 and 20 mm and
is subsequently rolled into hot strip having a degree of
deformation of at least 50%.
Inventors: |
Spitzer; Karl-Heinz;
(Clausthal, DE) ; Springub; Bianca; (Hannover,
DE) ; Konrad; Joachim; (Dusseldorf, DE) ;
Eichholz; Hellfried; (Ilsede, DE) ; Schaperkotter;
Markus; (Braunschweig, DE) ; Georgeou; Zacharias;
(Wolfsburg, DE) |
Assignee: |
SALZGITTER FLACHSTAHL GMBH
Salzgitter
DE
|
Family ID: |
41050967 |
Appl. No.: |
13/255548 |
Filed: |
March 11, 2009 |
PCT Filed: |
March 11, 2009 |
PCT NO: |
PCT/DE2009/000329 |
371 Date: |
November 10, 2011 |
Current U.S.
Class: |
420/72 ; 164/463;
164/76.1; 420/8 |
Current CPC
Class: |
B21B 1/463 20130101;
B22D 11/0631 20130101 |
Class at
Publication: |
420/72 ;
164/76.1; 164/463; 420/8 |
International
Class: |
C22C 38/04 20060101
C22C038/04; B22D 11/00 20060101 B22D011/00; C22C 38/00 20060101
C22C038/00; B22D 25/02 20060101 B22D025/02 |
Claims
1.-15. (canceled)
16. A method for producing a hot strip from a triplex lightweight
steel, comprising the steps of: casting a melt in a horizontal
strip casting facility under conditions of a calm flow and free of
bending to form a roughed strip having a thickness in a range
between 6 and 20 mm; and rolling the roughed strip into a hot strip
with a degree of deformation of at least 50%.
17. The method of claim 16, further comprising feeding the melt
into the horizontal strip casting facility at a speed which equals
a speed of a revolving conveyor belt of the horizontal strip
casting facility.
18. The method of claim 17, further comprising subjecting all
surface elements of a strand shell, forming at the start of
solidification, of a strip extending across a width of the conveyor
belt to approximately same cooldown conditions.
19. The method of claim 17, wherein the melt on the conveyor belt
has substantially solidified at an end of the conveyor belt.
20. The method of claim 16, further comprising passing the roughed
strip through a homogenizing zone after complete solidification and
before starting a further treatment.
21. The method of claim 20, wherein the further treatment involves
cutting the roughed strip into panels.
22. The method of claim 21, further comprising heating the panels
to a rolling temperature, and subsequently subjecting the panels to
a rolling process.
23. The method of claim 20, wherein the further treatment involves
a coiling of the roughed strip.
24. The method of claim 23, further comprising unwinding the
roughed strip, heating the roughed strip to a rolling temperature,
and subsequently subjecting the panels to a rolling process.
25. The method of claim 24, further comprising reheating the
roughed strip before being the unwinding step.
26. The method of claim 16, further comprising subjecting the
roughed strip in line to the rolling step, and further comprising
coiling up the roughed strip.
27. The method of claim 16, wherein the degree of deformation is
>70% during hot rolling.
28. The method of claim 17, further comprising applying a negative
pressure in an area of the conveyor belt.
29. The method of claim 17, further comprising supporting an
underside of the conveyor belt by a plurality of rollers in
side-by-side relationship.
30. Hot strip from a triplex lightweight steel, having a mean grain
size of>6 ASTM.
31. The hot strip of claim 30, wherein the triplex lightweight
steel has a chemical composition in weight-% of <0.6 C; >18
Mn; >8 Al; <0.25 Si, remainder iron including unavoidable
steel-incidental elements.
32. The hot strip of claim 31, wherein the triplex lightweight
steel has optionally one or more precipitation-forming elements of
type B, Ta, Zr, Nb, V, Ti, Mo and W collectively at a maximum of 2
weight-%.
Description
[0001] The invention relates to a method for producing a hot strip
from a triplex lightweight steel, wherein a melt is cast into a
roughed product and the latter is then rolled into a hot strip.
[0002] Triplex lightweight steels cannot be produced by using the
common continuous casting route, i.e. continuous casting of the
melt into a slab or thin slab which is rolled either in-line or
separately into a hot strip, with the required properties.
[0003] The reasons for that reside in the fact that the slab or
thin slab, produced by continuous casting, has macro segregations
and forms shrink marks. Moreover, the roughed product has a very
coarse grain and casting with casting powder poses problems because
of the high aluminum content of the ferritic steel.
[0004] Triplex lightweight are known, for example, from DE 10 2005
057 599 A1 and DE 102 31 125 A1. They are characterized by a
3-phase microstructure .alpha.(.gamma.) .kappa. and in view of the
high proportion on alloying components with a specific weight below
the specific weight of iron by a respectively low weight.
[0005] Moreover, this steel is able to achieve a beneficial
combination of high strength paired with high elongation in the
structure, when treated accordingly.
[0006] Triplex lightweight steels are therefore especially suitable
for the automobile industry which demands such combinations for
certain body parts in order to be able to show proof of deformation
reserves in the event of an accident.
[0007] DE 100 60 948 C2 discloses a production of hot strips from
steel having a high manganese content with 12 to 30 weight-% of
manganese and up to 3.5 weight-% of each of aluminum and silicon in
such a way that the steel melt is cast in a double-roller casting
machine to form a roughed strip close to the final dimensions with
a thickness of up to 6 mm, and subsequently the roughed strip is
hot rolled continuously preferably in a single pass.
[0008] The stated upper limit for the thickness with 6 mm cannot be
achieved with existing facilities. The maximum thickness that can
actually be adjusted is typically 4 mm, in exceptional cases
maximal 5 mm.
[0009] This known method has the advantage that macro segregations
are reduced, shrink marks are suppressed, and the problem
associated with casting powder is not relevant.
[0010] It is, however, disadvantageous that the small starting
thickness of the roughed strip permits only a small hot deformation
degree during rolling, when a thickness of 2-3 mm of the hot strip
is desired. This thickness range, for example, is however of
interest for the use of the hot strip as lightweight component in
the area of the chassis, e.g., as transverse control arm or
longitudinal control arm, on the one hand. On the other hand, a
cold strip with a thickness of, for example, 1.0-1.8 mm can be
produced from a hot strip of a thickness of 2-3 mm at a degree of
deformation of 40-50% and can be used, e.g., for B pillars or side
rails at the front or back. A small hot deformation degree means,
however, coarse grain which adversely affects ductility and thus
the formability.
[0011] It is therefore an object of the invention to provide a
method for producing a hot strip from a triplex lightweight steel
which method is able to realize a fine grain in the hot strip of
2-3 mm thickness while maintaining the benefits of the
double-roller casting machine.
[0012] This object is attained by a method in which the melt is
cast in a horizontal strip casting facility under conditions of a
cairn flow and free of bending into a roughed strip in the range
between 6 and 20 mm, and subsequently rolled into a hot strip with
a degree of deformation of at least 50%.
[0013] The proposed method has the advantage that the benefits of
the known double-roller casting machine, like reduction of macro
segregations, suppression of shrink marks, and prevention of the
problem associated with casting powder, are retained, even when the
ferritic steel has high Al contents, when using a horizontal strip
casting facility, and furthermore the thickness of the roughed
strip is significantly above the thickness of a roughed strip
produced by means of a double-roller casting machine.
[0014] This affords the possibility to attain sufficiently high
degrees of deformation in terms of adjusting a fine grain in the
microstructure of the hot strip; this is true in particular when
the hot strip has a thickness in the range of 2-3 mm. Triplex
lightweight steels do no show a complete .gamma.-.alpha.
transformation so that there is a tendency to form coarse grain
which can be reversed through a sufficient degree of deformation
during hot rolling.
[0015] A further advantage involves a very rapid cooldown and
solidification of the deposited melt in a strip casting facility.
The triplex lightweight steel exhibits its positive properties also
from the nano-sized dispersed "kappa" carbides in the austenite
matrix. The rapid cooldown of the melt promotes the fine
distribution and a slight growth of the carbides. Therefore, the
advantages of the proposed casting process are maintained even
after hot rolling and annealing as a result of the beneficial
carbide distribution.
[0016] In terms of the process, it is proposed to achieve the
calmness of flow by using a co-moving electromagnetic brake which
ensures that in the ideal case the speed of the melt feed equals
the speed of the revolving conveyor belt.
[0017] The bending considered disadvantageous during solidification
is prevented by supporting the underside of the casting belt
receiving the melt upon a multiplicity of rollers placed
side-by-side. The support is reinforced by generating in the region
of the casting belt a negative pressure to press the casting belt
firmly against the rollers.
[0018] In order to maintain these conditions during the critical
phase of solidification, the length of the conveyor belt is
selected in such a way that the roughed strip is substantially
solidified at the end of the conveyor belt before the latter is
deflected.
[0019] The end of the conveyor belt is followed by a homogenization
zone which is utilized for a temperature equalization and possible
stress relief.
[0020] Rolling of roughed strip into hot strip may be realized
either in-line or separately off-line. Before off-line rolling, the
roughed strip after production and before cooldown can either be
coiled directly in hot state or cut into panels. The strip or panel
material is then reheated after possible cooldown and unwound for
off-line rolling or reheated as panel and rolled.
[0021] Beneficial technical values are attained when the degree of
deformation is>70% and a mean grain size of>6 ASTM can be
adjusted.
[0022] A preferred grade for the triplex lightweight steel includes
high Mn contents of>18 weight-%, with high Al contents of>8
weight-%, with C contents of>0.6 weight-%, and small Si contents
with<0.25 weight-%.
[0023] Optionally one or more precipitation-forming elements of
type B, Ta, Zr, Nb, V, Ti, Mo and W may be added collectively at a
maximum of 2 weight-%.
* * * * *