U.S. patent application number 13/255269 was filed with the patent office on 2012-01-05 for corrosion-resistant austenitic steel.
This patent application is currently assigned to MAX-PLANCK-INSTITUT FUER EISENFORSCHUNG GMBH. Invention is credited to Lais Mujica Roncery, Sebastian Weber.
Application Number | 20120000580 13/255269 |
Document ID | / |
Family ID | 42313803 |
Filed Date | 2012-01-05 |
United States Patent
Application |
20120000580 |
Kind Code |
A1 |
Weber; Sebastian ; et
al. |
January 5, 2012 |
Corrosion-Resistant Austenitic Steel
Abstract
A corrosion-resistant austenitic steel is claimed which, in each
case relative to 100 mass percent, contains 20 to 32% manganese, 10
to 15% chromium, a total of 0.5 to 1.3% carbon and nitrogen,
wherein the ratio of carbon to nitrogen is 0.5 to 1.5, the
remainder being iron and melt-related impurities. The claimed steel
can be produced and processed at normal pressure and has TWIP
properties. It is in particular suited for producing structural
components in constructs, such as in the automotive industry.
Inventors: |
Weber; Sebastian; (Essen,
DE) ; Roncery; Lais Mujica; (Kamen, DE) |
Assignee: |
MAX-PLANCK-INSTITUT FUER
EISENFORSCHUNG GMBH
Duesseldorf
DE
|
Family ID: |
42313803 |
Appl. No.: |
13/255269 |
Filed: |
March 3, 2010 |
PCT Filed: |
March 3, 2010 |
PCT NO: |
PCT/DE2010/000232 |
371 Date: |
September 8, 2011 |
Current U.S.
Class: |
148/610 ;
148/327; 148/609; 148/611 |
Current CPC
Class: |
C22C 38/26 20130101;
C21D 2211/001 20130101; C21D 8/02 20130101; C22C 38/18 20130101;
C22C 38/38 20130101; C22C 38/04 20130101; C22C 38/001 20130101 |
Class at
Publication: |
148/610 ;
148/327; 148/611; 148/609 |
International
Class: |
C21D 8/00 20060101
C21D008/00; C22C 38/38 20060101 C22C038/38; C21D 6/00 20060101
C21D006/00; C22C 38/22 20060101 C22C038/22; C22C 38/26 20060101
C22C038/26 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 10, 2009 |
DE |
10 2009 003 598.2 |
Claims
1-15. (canceled)
16. A corrosion-resistant austenitic steel comprising, in addition
to iron, in percent by weight based on 100 percent by weight of the
steel: 20 to 32% of manganese, 10 to 15% of chromium, a total of
0.5 to 1.3% carbon and nitrogen, wherein the ratio of carbon to
nitrogen is 0.5 to 1.5, and melt-related impurities.
17. The corrosion-resistant austenitic steel according to claim 16,
further comprising alloying components selected from the group
consisting of Mo, Si, Nb, Hf, V, Zr, Ti, Nd, and Co.
18. The corrosion-resistant austenitic steel according to claim 17,
wherein Mo is contained in a quantity of 1.0 percent by weight to
2.0 percent by weight.
19. The corrosion-resistant austenitic steel according to claim 17,
wherein Si is contained in a quantity of 0.1 percent by weight to
2.0 percent by weight.
20. The corrosion-resistant austenitic steel according to claim 17,
wherein Nb is contained in a quantity of 0.02 percent by weight to
0.1 percent by weight.
21. The corrosion-resistant austenitic steel according to claim 17,
wherein Hf, V, Zr, Ti, and Nd each are contained in a quantity of
up to 0.5 percent by weight.
22. The corrosion-resistant austenitic steel according to claim 16,
wherein manganese is contained in a quantity of 22 percent by
weight to 30 percent by weight.
23. The corrosion-resistant austenitic steel according to claim 16,
wherein chromium is contained in a quantity of 11.0 percent by
weight to 13.0 percent by weight.
24. The corrosion-resistant austenitic steel according to claim 16,
wherein carbon and nitrogen are contained in total in a quantity of
0.5 percent by weight to 0.8 percent by weight and wherein the
ratio of carbon to nitrogen is between 0.5 and 0.8.
25. The corrosion-resistant austenitic steel according to claim 16
having TWIP properties.
26. The corrosion-resistant austenitic steel according to claim 16
having a tensile strength of >900 MPa.
27. The corrosion-resistant austenitic steel according to claim 16
having a tensile elastic limit of >400 MPa and an elongation at
fracture of >90%.
28. A method for producing a corrosion-resistant austenitic steel,
the method comprising the steps of: melting alloying metals at
normal pressure, annealing the alloying metals in a temperature
range between 1,000.degree. C. and 1,250.degree. C. for a duration
of 1 to 72 hours, and quenching the alloying metals.
29. The method according to claim 13, further comprising,
subsequent to quenching, a deformation step employing hot
deforming; cold deforming; or hot deforming and cold deforming.
30. A method for producing structural components, the method
comprising the step of providing a corrosion-resistant austenitic
steel according to claim 16.
Description
[0001] The present invention concerns a corrosion-resistant
austenitic steel, a method for its production, and the use of said
steel.
[0002] The strength of austenitic steels is increased in particular
by the interstitially dissolved atoms of the elements carbon and
nitrogen. In order to dissolve the volatile element nitrogen in the
melt, in general chromium and manganese are added to the alloy.
While chromium enhances solely the ferrite formation, with
manganese, by so-called solution annealing, an austenitic structure
can be obtained that is stabilized by quenching to room
temperature.
[0003] An austenitic steel grade is the so-called TWIP steel
(twinning induced plasticity, in German "Zwillingsbildung
induzierte Platistizat") that exhibits an intensive twinning when
undergoing plastic deformation. This process generally occurs
already at minimal load and hardens the steel wherein the
elongation at fracture is above 60%. As a result of these
properties, the steel is suitable excellently for producing sheet
metal in the automotive industry, in particular for
accident-relevant parts of the car body. The TWIP steel has in
general a carbon contents of approximately 0.02 to 0.5% by weight;
as alloying elements manganese in quantities of 20 to 30% by weight
as well as, in certain TWIP steels, aluminum and silicon, each with
up to 3% by weight, are used.
[0004] EP 0 889 144 discloses a so-called TWIP steel, a lightweight
construction steel, that has a tensile strength of up to 1,100 MPa
and contains 1 to 6% by weight Si, 1 to 8% by weight of Al, wherein
the total contents of Al and Si is not greater than 12% by weight,
as well as 10 to 30% by weight of Mn. The disclosed steels are
distinguished by higher yield stress of 400 MPa as well as uniform
strain values up to 70% and elongation at fracture up to 90%. A
disadvantage of the steel disclosed in this document is the minimal
corrosion resistance.
[0005] In DE 101 a high-strength, stainless austenitic steel is
characterized in that it is melted under normal atmospheric
pressure of approximately 1 bar and, in addition to iron, contains
12 to 15% by weight of chromium, 17 to 21% by weight of manganese,
<0.7% by weight of silicon, 0.4 to 0.7% by weight of carbon and
nitrogen in sum, and <1.0% by weight of further
production-related elements in sum, wherein the ratio of carbon
content and nitrogen content is between 0.6 and 1.0. The disclosed
steel exhibits no TWIP effect and may form martensite at strong
deformation, which is expressed inter alia in a minimal nominal
strain.
[0006] WO 2006/025412 discloses a corrosion-resistant TWIP steel
that contains Fe, Al, Si, Mn, Cr, and Ni as main elements. The
obtained steel shows uniform strain values above 50% and a tensile
strength between 600 and 800 MPa. The mechanical properties are
comparable to those of the steel disclosed in EP 0 889 144 on the
basis of Fe, Al, Si, and Mn but the addition of nickel increases
the production costs and the lack of interstitial atoms leads to a
minimal strength. A further austenitic steel that contains C and N
as alloying elements is disclosed in WO 2006/027091 wherein the
steel described therein contains, in addition to the alloying
metals chromium and manganese, each in quantities of 16 to 21% by
weight, also 0.5 to 2.0% by weight of molybdenum as well as a total
of 0.8 to 1.1% by weight of carbon and nitrogen with a
carbon/nitrogen ratio of 0.5 to 1.1. The disclosed steel exhibits
mechanical strength, ductility, wear and corrosion resistance and
no ferromagnetism. A disadvantage is however that, upon
solidification during the production of these alloys, a primary
ferrite formation occurs that may cause escape of nitrogen during
melting and/or welding.
[0007] The present invention was based on the object to provide a
corrosion-resistant weldable austenitic steel that has a high
tensile elastic limit and also a high tensile strength as well as
an elongation at fracture of above 90% and that is, at the same
time, corrosion-resistant.
[0008] Object of the present invention is a corrosion-resistant
austenitic steel containing, in addition to iron, based on 100
percent by weight,
[0009] 20 to 32% of manganese
[0010] 10% to 15% of chromium, a total of 0.5 to 1.3% of carbon and
nitrogen, wherein the ratio of carbon to nitrogen is 0.5 to
1.5,
as well as melt-related impurities.
[0011] The austenitic steel according to the invention exhibits the
TWIP properties (TWIP=twinning induced plasticity) as well as good
corrosion resistance. A significant property of this TWIP steel is
to obtain a plasticity by formation of twinned grain boundaries
with excellent corrosion resistance; this means a steel that upon
deformation forms numerous twinned grain boundaries in its
microstructure, thereby hardens greatly and uniformly, exhibits
high nominal strain values in a tensile test, as well as remains
completely austenitic without formation of martensite.
[0012] The steel according to the invention exhibits a stabilized
austenitic structure that is formed by combination of the main
alloying elements Fe, Mn, and Cr as well as the interstitial
elements C and N. The steel according to the invention shows in
tensile test an elongation at fracture of above 90%, a tensile
elastic limit of above 400 MPa, and a tensile strength of above 900
MPa. Because of the combination of high elongation at fracture and
tensile elastic limit, the steel according to the present invention
is extremely ductile. Moreover, the alloys according to the present
invention exhibit no .alpha. martensite or .epsilon. martensite
formation detectable by x-ray diffraction after a targeted
deformation.
[0013] It was found that the alloy according to the invention with
the above described proportions of Cr, Mn, C, and N enables a
primary austenitic solidification so that a melt is obtained from
which nitrogen will not escape during solidification and/or
welding. The alloy can thus be produced and also processed under
normal pressure. The alloy according to the invention exhibits a
stable austenitic structure that prevents formation of ferrite. The
alloying metal Cr and the contained N effect a higher corrosion
resistance in comparison to TWIP steels of the prior art.
[0014] The individual quantity ratios of the alloying elements Cr
and Mn as well as the additives N and C are adjusted in such a
ratio that the quantity of Cr not only improves the solubility of N
in the melt but also advantageously effects the corrosion
resistance of the alloy without ferrite being formed primarily upon
solidification of the melt. The formation of ferrite is
disadvantageous because it provides a reduced solubility for
nitrogen and thus causes pore formation. Moreover, in the alloy
according to the invention the formation of precipitations, for
example, carbides and nitrides, was shifted to lower temperatures.
This enables a slower cooling from the austenitization temperature
as well as an unproblematic manufacture of larger component
cross-sections.
[0015] Also, the weldability of the alloy according to the
invention is affected positively by avoiding nitrogen gas escape
during solidification after fusion welding as well as by avoiding
the formation of precipitations during the subsequent cooling of
the solid material of the weld seam and of the heat-affected zone
to room temperature. This is important primarily for technological
reasons because the material cools relatively slowly after welding
and formation of precipitations at the weld seam and in the
heat-affected zone is undesirable.
[0016] The quantity of Mn improves the ductility (plasticity,
shape-changing capability). The further components C and N improve
the mechanical properties and the corrosion resistance without
nitrides and carbides being formed. The inventive ratio of C and N
enables a completely austenitic solidification without gases
escaping during melting or carbides or nitrides being formed during
accelerated cooling. The solubility for the desired quantity of
nitrogen in the melt is preferably realized at 1,500.degree. C. and
a pressure of 1 bar.
[0017] In a preferred embodiment the alloying metals are present in
a quantity of 22.0 to 30.0% by weight of Mn and in a quantity of
11.0 to 13% by weight of chromium, in particular 12.0 to 13% by
weight. A total content of carbon and nitrogen between 0.5 to 0.8%
by weight at a ratio of carbon to nitrogen of 0.5 to 0.8 has been
found to be particularly beneficial. The alloys of this embodiment
exhibit advantageous material properties so that they are suitable
for use in lightweight construction.
[0018] In a further embodiment, the alloy according to the
invention contains secondary alloying metals with which the
mechanical properties can be further adjusted. The secondary
alloying elements are preferably selected from Mo, Si, Nb, Hf, V,
Zr, Ti, and Nd. Of these alloying metals, Mo is preferably
contained in a quantity of 1.0 to 2.0% by weight, Si in a quantity
of 0.1 to 2% by weight. The metals Nb, Hf, V, Zr, Ti, and Nd may be
contained in smaller quantities and are also referred to as
microalloying elements. Of the microalloying elements, Nb can be
present in a quantity of 0.02 to 0.1% by weight, the metals Hf, V,
Zr, Ti, and Nd each, independent of each other, in quantities of 0
to 0.5% by weight.
[0019] A further object of the present invention is a method for
producing a corrosion-resistant austenitic steel with TWIP
properties in which the individual alloying metals are melted under
normal pressure and diffusion annealing is carried out in a
temperature range between 1,000 and 1,250.degree. C. for a duration
of 1 to 72 hours with subsequent quenching and hot/cold
deformation.
[0020] The melting process can be performed at a pressure of
800-1,000 mbar in pure nitrogen or in a furnace at environmental
pressure which corresponds to a partial pressure of nitrogen of
approximately 800 mbar.
[0021] A further object of the present invention concerns the use
of the austenitic steel according to the invention for producing
structural components in structures, in particular in the
automotive industry.
EXAMPLES
[0022] In the following Table 1 examples of alloys according to the
invention are represented.
TABLE-US-00001 TABLE 1 contents in % by weight Fe Mn Cr C N Nb Mo C
+ N C/N grade 1 bal. 30.0 12.0 0.3 0.4 0 0 0.56 0.75 30Mn12CrCN 2
bal. 25.0 12.0 0.3 0.4 0 0 0.7 0.75 25Mn12CrCN 3 bal. 20.0 12.0
0.24 0.32 0 0 0.7 0.75 20Mn12CrCN 4 bal. 25.0 12.0 0.3 0.4 0.05 0
0.7 0.75 -- 5 bal. 25.0 12.0 0.3 0.4 0.05 0.5 0.7 0.75 -- 6 bal.
25.0 12.0 0.3 0.4 0.05 1.0 0.7 0.75 -- 7 bal. 25.0 12.0 0.3 0.4
0.05 1.5 0.7 0.75 --
[0023] The mechanical properties are listed in Table 2.
TABLE-US-00002 0.2% yield tensile strength in strength in
elongation at Vickers hardness example MPa MPa fracture in % in
HV10 30Mn12CrCN 449.76 906.92 108.5 234.2 25Mn12CrCN 445.38 889.96
93.8 230.3 20Mn12CrCN 434.00 825.08 93.1 200.6
[0024] In the subsequent diagrams the stress-strain curves under
load at room temperature (diagram 1), impact strength (diagram 2),
and a computed phase diagram in which the primary austenite
formation can be seen (diagram 3) are illustrated graphically.
* * * * *