U.S. patent application number 12/374482 was filed with the patent office on 2009-12-31 for austenitic stainless cast steel part, method for production and use thereof.
This patent application is currently assigned to ACTECH GMBH. Invention is credited to Heiner Gutte, Matthias Radtke, Piotr Scheller, Andreas Weiss.
Application Number | 20090324441 12/374482 |
Document ID | / |
Family ID | 38562226 |
Filed Date | 2009-12-31 |
United States Patent
Application |
20090324441 |
Kind Code |
A1 |
Weiss; Andreas ; et
al. |
December 31, 2009 |
AUSTENITIC STAINLESS CAST STEEL PART, METHOD FOR PRODUCTION AND USE
THEREOF
Abstract
A rustproof austenitic cast steel part having tensile strength
greater than 550 MPA and elongation at break over 30%, is
characterised in that the cast steel having an aluminium content of
0 to 4% and a silicon content of 1 to 4% is within an alloying
range that is determined by the coordinates of four points
(Cr.sub.equiv.=14; Ni.sub.equiv.=8), (Cr.sub.equiv.=14;
Ni.sub.equiv.=14), (Cr.sub.equiv.=22; Ni.sub.equiv.=8) and
(Cr.sub.equiv.=22 Ni.sub.equiv.=16), wherein the chromium and
nickel equivalents are calculated from the chemical composition of
a cast steel using the relations (1) and (2): Cr equiv . = % Cr + %
Mo + 1.5 % Si + 0.5 % W + 0.9 % Nb + 4 % A 1 + 4 % Ti + 1.5 % V + 0
.9 % Ta ( 1 ) Ni equiv . = % Ni + 30 % C + 18 % N + 0.5 % Mn + 0.3
% Co + 0.2 % Cu - 0.2 % A 1 ( 2 ) ##EQU00001## wherein the figures
must be quoted in mass percent and the remainder substantially
comprises iron and other elements usually present in cast steel (O,
P, S). Said cast steel exhibits a TRIP effect and serves as a
material for plant and refrigeration engineering, particularly for
facilities and components for obtaining gases and for liquefying
and fractioning of gases, and as a material in the construction of
special vehicles and airplanes for the transport of liquid gases
and for components exposed to low temperatures, in addition to
crash stressed castings.
Inventors: |
Weiss; Andreas; (Freiberg,
DE) ; Gutte; Heiner; (Freiberg, DE) ; Radtke;
Matthias; (Leipzig, DE) ; Scheller; Piotr;
(Radebeul, DE) |
Correspondence
Address: |
PAI PATENT & TRADEMARK LAW FIRM
1001 FOURTH AVENUE, SUITE 3200
SEATTLE
WA
98154
US
|
Assignee: |
ACTECH GMBH
Freiberg
DE
|
Family ID: |
38562226 |
Appl. No.: |
12/374482 |
Filed: |
July 19, 2007 |
PCT Filed: |
July 19, 2007 |
PCT NO: |
PCT/EP07/57473 |
371 Date: |
March 20, 2009 |
Current U.S.
Class: |
420/44 ; 164/47;
420/34; 420/56; 420/65 |
Current CPC
Class: |
C22C 38/58 20130101;
C21D 8/005 20130101; C22C 38/18 20130101 |
Class at
Publication: |
420/44 ; 420/34;
420/56; 420/65; 164/47 |
International
Class: |
C22C 38/58 20060101
C22C038/58; C22C 38/38 20060101 C22C038/38; C22C 38/18 20060101
C22C038/18; B22D 23/00 20060101 B22D023/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 20, 2006 |
DE |
10 2006 033 973.8 |
Claims
1. An austenitic stainless cast steel part having an aluminium
content of greater than 0% and equal or smaller than 4% and a
silicon content of 0 to 4%, and tensile strength greater than 550
MPa and elongation at break greater than 30% produced in an
alloying range determined by the coordinates of four points
(Cr.sub.equiv.=14; Ni.sub.equiv.=8), (Cr.sub.equiv.=14;
Ni.sub.equiv.=14), (Cr.sub.equiv.=22; Ni.sub.equiv.=8) and
(Cr.sub.equiv.=22 Ni.sub.equiv.=16), wherein the chromium and
nickel equivalent are calculated via relation (1) and (2) Cr equiv
. = % Cr + % Mo + 1.5 % Si + 0.5 % W + 0.9 % Nb + 4 % A 1 + 4 % Ti
+ 1.5 % V + 0 .9 % Ta ( 1 ) Ni equiv . = % Ni + 30 % C + 18 % N +
0.5 % Mn + 0.3 % Co + 0.2 % Cu - 0.2 % A 1 ( 2 ) ##EQU00003## from
the chemical composition of the cast steel part, where the figures
must be quoted in mass percent and the rest essentially consists of
iron and other inevitable elements of cast steel part and that this
cast steel part exhibits a TRIP effect under load.
2. The cast steel part in accordance with claim 1, characterised by
the fact that the manganese content is 0 to 25%; the chromium
content is 12 to 20%; the nickel content is 0 to 12%; the niobium
content is 0 to 1.2%; the tantalum content is 0 to 0.2%; the carbon
content is 0.01 to 0.15%; the nitrogen content is 0.005 to 0.5%;
the copper content is 0 to 4%; the cobalt content is 0 to 1%; the
molybdenum content is 0 to 4%; the tungsten content is 0 to 3%; the
titanium content is 0 to 1%; and the vanadium content is 0 to
0.15%.
3. The cast steel part in accordance with claim 2, characterised by
the fact that the manganese content is 5 to 12%; the nickel content
is 2 to 8%; the copper content is 0 to 2%; the cobalt content is 0
to 0.5%; the molybdenum content is 0 to 2.5%; and/or the vanadium
content is 0 to 0.5%.
4. The cast steel part in accordance with claim 3, characterised by
the fact that the chromium content is 16.5%; the nickel content is
6.5%; the silicon content is 1.1%; the manganese content is 7%; the
aluminium content is 0.05%; the nitrogen content is 0.1%; and the
carbon content is 0.04%.
5. A method for producing a cast steel part comprising the
following steps: Provision of an alloy comprising an aluminium
content of 0 to 4% and a silicon content of 0 to 4%, with the alloy
produced in an alloying range determined by the coordinates of four
points (Cr.sub.equiv.=14; Ni.sub.equiv.=8), (Cr.sub.equiv.=14;
Ni.sub.equiv.=14), (Cr.sub.equiv.=22; Ni.sub.equiv.=8) and
(Cr.sub.equiv.=22; Ni.sub.equiv.=16), with the chromium and nickel
equivalent being calculated via relation (1) and (2) Cr equiv . = %
Cr + % Mo + 1.5 % Si + 0.5 % W + 0.9 % Nb + 4 % A 1 + 4 % Ti + 1.5
% V + 0 .9 % Ta ( 1 ) Ni equiv . = % Ni + 30 % C + 18 % N + 0.5 %
Mn + 0.3 % Co + 0.2 % Cu - 0.2 % A 1 ( 2 ) ##EQU00004## from the
chemical composition of the cast steel part, wherein the figures
must be quoted in mass percent and the rest essentially consists of
iron and other inevitable elements of cast steel; and the casting
steel part is cast in a casting mould.
6. The method in accordance with claim 5, characterised by the fact
that the cast steel part undergoes a heat treatment process in a
further step.
7. The method in accordance with claim 5, characterised by the fact
that the alloy has a manganese content of 0 to 25%; a chromium
content of 12 to 20%; a nickel content of 0 to 12%; a niobium
content of 0 to 1.2%; a tantalum content of 0 to 0.2%; a carbon
content is 0.01 to 0.15%; a nitrogen content of 0.005 to 0.5%; a
copper content of 0 to 4%; a cobalt content of 0 to 1%; a
molybdenum content of 0 to 4%; a tungsten content of 0 to 3%; a
titanium content of 0 to 1%; and a vanadium content of 0 to
0.15%.
8. The method in accordance with claim 7, characterised by the fact
that the alloy has a manganese content of 5 to 12%; a nickel
content of 2 to 8%; a copper content of 0 to 2%; a cobalt content
of 0 to 0.5%; a molybdenum content of 0 to 2.5%; and/or a tungsten
content of 0 to 0.5%.
9. A cast steel part, produced by a method in accordance with claim
5, characterised by the fact that the cast steel part has a tensile
strength greater than 550 MPa and an elongation at break greater
than 30%.
10. A cast steel part, produced by a method in accordance with
claim 5, characterised by the fact that the cast steel part
exhibits a TRIP effect under load.
11. A method for using a cast steel part in a technical
application, comprising the steps: Performance of the steps of one
of the methods in accordance with claim 5 for the manufacture of
the cast steel part; and use of the cast steel part in the
technical application, wherein use after casting proceeds without
the performance of a chipless cutting process.
12. Use of the cast steel part in accordance with claim 1 as
material for plant and refrigeration engineering.
13. Use of the cast steel part in accordance with claim 1 as
material for plant and components for producing gases and for
liquefying and fractionating gases.
14. Use of the cast steel part in accordance with claim 1 as
material for applications in automotive and aircraft
construction.
15. Use of the cast steel part in accordance with claim 1 as
material for crash-stressed parts, such as crash boxes in motor
vehicles.
16. Use of the cast steel part in accordance with claim 1 as
material for transporting liquid gases and as a component that is
exposed to low temperatures.
17. Use of the cast steel part in accordance with claim 1 as
casting steel foam for foamed parts.
18. Component for automotive or aircraft construction, especially,
crash box, A, B or C-pillar of a motor vehicle, which is formed as
a cast steel part in accordance with claim 1.
19. The method in accordance with claim 6, characterised by the
fact that the alloy has a manganese content of 0 to 25%; a chromium
content of 12 to 20%; a nickel content of 0 to 12%; a niobium
content of 0 to 1.2%; a tantalum content of 0 to 0.2%; a carbon
content is 0.01 to 0.15%; a nitrogen content of 0.005 to 0.5%; a
copper content of 0 to 4%; a cobalt content of 0 to 1%; a
molybdenum content of 0 to 4%; a tungsten content of 0 to 3%; a
titanium content of 0 to 1%; and a vanadium content of 0 to
0.15%.
20. The method in accordance with claim 19, characterised by the
fact that the alloy has a manganese content of 5 to 12%; a nickel
content of 2 to 8%; a copper content of 0 to 2%; a cobalt content
of 0 to 0.5%; a molybdenum content of 0 to 2.5%; and/or a tungsten
content of 0 to 0.5%.
21. A cast steel part, produced by a method in accordance with
claim 7, characterised by the fact that the cast steel part has a
tensile strength greater than 550 MPa and an elongation at break
greater than 30%.
22. A cast steel part, produced by a method in accordance with
claim 19, characterised by the fact that the cast steel part has a
tensile strength greater than 550 MPa and an elongation at break
greater than 30%.
23. A cast steel part, produced by a method in accordance with
claim 8, characterised by the fact that the cast steel part has a
tensile strength greater than 550 MPa and an elongation at break
greater than 30%.
24. A cast steel part, produced by a method in accordance with
claim 20, characterised by the fact that the cast steel part has a
tensile strength greater than 550 MPa and an elongation at break
greater than 30%.
25. A cast steel part, produced by a method in accordance with
claim 7, characterised by the fact that the cast steel part
exhibits a TRIP effect under load.
26. A cast steel part, produced by a method in accordance with
claim 19, characterised by the fact that the cast steel part
exhibits a TRIP effect under load.
27. A cast steel part, produced by a method in accordance with
claim 8, characterised by the fact that the cast steel part
exhibits a TRIP effect under load.
28. A cast steel part, produced by a method in accordance with
claim 20, characterised by the fact that the cast steel part
exhibits a TRIP effect under load.
29. Use of the cast steel part in accordance with claim 2 as
material for plant and refrigeration engineering.
30. Use of the cast steel part in accordance with claim 2 as
material for plant and components for producing gases and for
liquefying and fractionating gases.
31. Use of the cast steel part in accordance with claim 2 as
material for applications in automotive and aircraft
construction.
32. Use of the cast steel part in accordance with claim 2 as
material for crash-stressed parts, such as crash boxes in motor
vehicles.
33. Use of the cast steel part in accordance with claim 2 as
material for transporting liquid gases and as a component that is
exposed to low temperatures.
34. Use of the cast steel part in accordance with claim 2 as
casting steel foam for foamed parts.
35. Component for automotive or aircraft construction, especially,
crash box, A, B or C-pillar of a motor vehicle, which is formed as
a cast steel part in accordance with claim 2.
36. Use of the cast steel part in accordance with claim 3 as
material for plant and refrigeration engineering.
37. Use of the cast steel part in accordance with claim 3 as
material for plant and components for producing gases and for
liquefying and fractionating gases.
38. Use of the cast steel part in accordance with claim 3 as
material for applications in automotive and aircraft
construction.
39. Use of the cast steel part in accordance with claim 3 as
material for crash-stressed parts, such as crash boxes in motor
vehicles.
40. Use of the cast steel part in accordance with claim 3 as
material for transporting liquid gases and as a component that is
exposed to low temperatures.
41. Use of the cast steel part in accordance with claim 3 as
casting steel foam for foamed parts.
42. Component for automotive or aircraft construction, especially,
crash box, A, B or C-pillar of a motor vehicle, which is formed as
a cast steel part in accordance with claim 3.
43. Use of the cast steel part in accordance with claim 4 as
material for plant and refrigeration engineering.
44. Use of the cast steel part in accordance with claim 4 as
material for plant and components for producing gases and for
liquefying and fractionating gases.
45. Use of the cast steel part in accordance with claim 4 as
material for applications in automotive and aircraft
construction.
46. Use of the cast steel part in accordance with claim 4 as
material for crash-stressed parts, such as crash boxes in motor
vehicles.
47. Use of the cast steel part in accordance with claim 4 as
material for transporting liquid gases and as a component that is
exposed to low temperatures.
48. Use of the cast steel part in accordance with claim 4 as
casting steel foam for foamed parts.
49. Component for automotive or aircraft construction, especially,
crash box, A, B or C-pillar of a motor vehicle, which is formed as
a cast steel part in accordance with claim 4.
50. Use of the cast steel part in accordance with claim 9 as
material for plant and refrigeration engineering.
51. Use of the cast steel part in accordance with claim 9 as
material for plant and components for producing gases and for
liquefying and fractionating gases.
52. Use of the cast steel part in accordance with claim 9 as
material for applications in automotive and aircraft
construction.
53. Use of the cast steel part in accordance with claim 9 as
material for crash-stressed parts, such as crash boxes in motor
vehicles.
54. Use of the cast steel part in accordance with claim 9 as
material for transporting liquid gases and as a component that is
exposed to low temperatures.
55. Use of the cast steel part in accordance with claim 9 as
casting steel foam for foamed parts.
56. Component for automotive or aircraft construction, especially,
crash box, A, B or C-pillar of a motor vehicle, which is formed as
a cast steel part in accordance with claim 9.
57. Use of the cast steel part in accordance with claim 10 as
material for plant and refrigeration engineering.
58. Use of the cast steel part in accordance with claim 10 as
material for plant and components for producing gases and for
liquefying and fractionating gases.
59. Use of the cast steel part in accordance with claim 10 as
material for applications in automotive and aircraft
construction.
60. Use of the cast steel part in accordance with claim 10 as
material for crash-stressed parts, such as crash boxes in motor
vehicles.
61. Use of the cast steel part in accordance with claim 10 as
material for transporting liquid gases and as a component that is
exposed to low temperatures.
62. Use of the cast steel part in accordance with claim 10 as
casting steel foam for foamed parts.
63. Component for automotive or aircraft construction, especially,
crash box, A, B or C-pillar of a motor vehicle, which is formed as
a cast steel part in accordance with claim 10.
Description
[0001] The innovation relates to an austenitic stainless cast steel
part, and a method for the production and use thereof.
PRIOR ART
[0002] After solution annealing, commercial austenitic stainless
cast steel alloys have a tensile strength of 440 to 640 MPa and
elongation at break of more than 20% in the cast [1, 2].
[0003] Austenitic stainless cast steel alloys are not alloyed with
aluminium, and usually contain silicon levels of about 1%.
Aluminium and high levels of silicon impair the purity of the cast
steel part if contact between the molten steel and oxygen is not
suppressed during the metallurgical production process. For this
reason, the aluminium and silicon content in austenitic stainless
cast steel alloys is minimised or restricted.
[0004] Typical commercial austenitic stainless cast steel parts
usually have .delta.-ferrite levels of 5 to 10%. The
.delta.-ferrite level fractions lead to an increase in yield
strength at 0.2% offset and in tensile strength and a decrease in
elongation at break compared with the purely austenitic
microstructure state. To form austenitic-ferritic microstructure
states, a balanced nickel and chromium equivalent is adjusted via
the chemical composition of the cast steel. The low 6-ferrite
content changes the solidification structure. Undesirable liquation
products, which accumulate at the grain boundaries, are reduced, a
fact which positively affects the susceptibility to hot
cracking.
[0005] In general, the chromium content of austenitic stainless
cast steel is around 19%. Moreover, it is often alloyed with 2 to
3% molybdenum. The chromium and molybdenum content creates a
passivating protective layer that increases the resistance to
corrosion, especially by halides. It also supports ferrite
formation. The nickel content of rustproof austenitic cast steel is
about 10% and the carbon content is about 0.03% [1-3, 6]. Through
changes to the chemical composition, it is possible to produce cast
steel alloys that have special properties. Thus, patent application
[7] discloses a stainless cast steel that has a high corrosion
fatigue strength and high pitting corrosion resistance.
[0006] Unlike the case for austenitic steels, the TRIP effect
(transformation induced plasticity) has yet to be studied in
austenitic cast steel alloys. Nor have technical applications
materialized that exploit the TRIP effect in austenitic cast steel.
The reason for this is apparently the fact that austenitic cast
steel parts are not cold formed and the manufactured parts are used
in the cast state. Thus, it is not technically possible to use the
TRIP effect in cast alloy parts, as opposed to wrought alloy parts,
to improve cold formability. As yet, there are no references in the
literature to the occurrence of a TRIP effect in austenitic cast
steel alloy parts. This is due primarily to the fact that the TRIP
effect in the form of a plastic yield contribution has not yet been
quantified.
[0007] So far, lightweight austenitic steels that have a TRIP
effect at room temperature and can be alloyed inter alia with
aluminium and silicon are used in wrought alloys in various
branches of industry.
[0008] These are both austenitic stainless and non-passivating
steels, such as the high-manganese, austenitic lightweight
construction steels. Thanks to the TRIP effect, these steels are
notable for their high cold formability [4, 5].
[0009] High-manganese austenitic steels usually have a chromium
content of less than 12%, which is why they are non-rusting. In
these steels, iron oxide layers are formed on the surface and the
material rusts. If aluminium and silicon oxides are occluded in
these rust layers, the corrosion resistance grows. Patent DE 199 00
199 describes such a high-strength lightweight construction steel
that contains manganese. The concentrations of the alloying
elements aluminium, silicon, nickel, manganese and nitrogen are
similar to the concentrations of the inventive cast steel. Unlike
the inventive steel, this steel has a chromium content of less than
10% and is therefore not a stainless steel. Moreover, this steel is
not used in the cast state, but rather is worked to produce vehicle
bodies and semifinished prestressed concrete goods.
[0010] Warm- or cold-rolled semifinished goods serve as starting
material for cold-formed parts. The TRIP effect in austenitic
alloys is regulated via the chemical composition of the austenite
and the forming conditions [5].
[0011] The disadvantage of the prior art remains the
non-exploitation of the TRIP effect, which is known from austenitic
wrought alloys, to improve the properties of cast steel.
LITERATURE CITED
[0012] [1] DIN EN 10213 [0013] [2] DIN EN 10283 [0014] [3]
Konstruieren und Giessen 29 (2004)1, p. 27-55 [0015] [4] Bander,
Bleche Rohre 5/2006, p. 30-31 [0016] [5] ATZ 1/2005, volume 107, p.
68-72 [0017] [6] SEW 410 [0018] [7] Patent DE 33 06 104 A1 [0019]
[8] High Nitrogen Steels, Springer-Verlag Berlin Heidelberg
1999
[0020] It is an object of the invention cited in the main claims to
produce austenitic stainless cast steel parts having a tensile
strength greater than 550 MPa and an elongation at break of more
than 30% and of using it in technical applications.
[0021] This object is achieved in the invention in such a way that
an austenitic stainless cast steel part (steel casting or steel
casting part) having an aluminium content greater than 0 and equal
or less than 4% and a silicon content of 0 to 4%, especially 1 to
4%, and tensile strength greater than 550 MPa and elongation at
break exceeding 30% is produced in an alloying range, which is
determined by the coordinates of four points (Cr.sub.equiv.=14;
Ni.sub.equiv.=8), (Cr.sub.equiv.=14; Ni.sub.equiv.=14),
(Cr.sub.equiv.=22; Ni.sub.equiv.=8) and (Cr.sub.equiv.=22
Ni.sub.equiv.=16), wherein the chromium and nickel equivalents are
calculated from the chemical composition of the cast steel via the
relations (1) and (2)
Cr.sub.equiv.=% Cr+% Mo+1.5% Si+0.5% W+0.9% Nb+4% Al+4% Ti+1.5%
V+0.9% Ta (1)
Ni.sub.equiv.=% Ni+30% C+18% N+0.5% Mn+0.3% Co+0.2% Cu-0.2% Al
(2)
where the figures must be quoted in mass percent and the rest
essentially consists of iron and other inevitable elements of cast
steel, for example, O, P, S, and that this cast steel exhibits a
TRIP effect under load.
[0022] Surprisingly, it was found that, in those inventive
austenitic cast steel alloy parts which contain aluminium and are
alloyed with silicon, deformation-induced martensite formation is
triggered at room temperature and low temperatures in the tensile
test. This martensite formation causes the TRIP effect. As a result
of the TRIP effect, the tensile strength and the elongation at
break are increased and necking is improved.
[0023] The advantages of the inventive austenitic cast steel alloy
parts are to be found in the increase in tensile strength and
elongation at break. That means that the TRIP effect renders the
cast steel part stronger and tougher simultaneously. It can
therefore accommodate greater forces and deform more extensively,
without breaking. As a result, the application range of the
inventive TRIP cast steel alloy parts is expanded. Above all, the
resultant lightweight construction leads to savings on costs for
energy and material. The inventive cast steel yields tensile
strength greater than 550 MPa and elongation at break of more than
30%. Consequently, the cast steel can be used to make cast parts
with a kind of crash reserve. This means that the steel is cast and
integrated into an application, without exposure to a tensile load.
If, however, a crash or a heavy load occurs, the part, thanks to
the potential to exhibit the TRIP effect, can accommodate/absorb
high tensile strength and elongation at break.
[0024] In the case of austenitic cast steel alloy parts, the TRIP
effect can be influenced via the chemical composition of the
austenite. Moreover, it requires that the austenite- and
ferrite-stabilising elements be coordinated. The microstructure of
austenitic cast steel and the microstructure of formed austenitic
wrought alloys of the same chemical composition differ, however.
For one thing, the microstructure of austenitic cast steel parts
contains solidification-induced liquation, the vast bulk of which
is retained during technical cooling. For another, dendritic
solidification influences the defect structure of the austenite.
When austenite and ferrite are simultaneously present in a
stainless cast steel, internal stresses are formed during cooling.
Moreover, in the high-temperature range, separation of the alloying
elements occurs. When this happens, the austenite-stabilising
elements accumulate chiefly in the austenite. At the same time, the
austenite becomes depleted in ferrite-stabilising elements. The
influence of these factors on the TRIP effect in cast steel alloy
parts is not yet known.
[0025] In order for deformation-induced martensite and thus a TRIP
effect to form, the microstructure of the inventive cast material
must consist of metastable austenite. Consequently, austenite has a
corresponding tendency to form deformation-induced martensite at
room temperature and at low temperatures. For the purpose of
producing such austenite, a corresponding chromium and nickel
equivalent is adjusted in the austenitic cast steel. In other
words, the chemical composition of the steels must be coordinated
with regard to the ferrite-stabilising and austenite-stabilising
elements, as specified in the patent claim. The chromium and nickel
equivalent to be adjusted for producing an austenitic cast steel
part which has a TRIP effect differs from the chromium and nickel
equivalent for austenitic wrought alloys which have a TRIP
effect.
[0026] Nickel and/or manganese are added to cast austenitic steel
in order that austenite may be formed at high temperatures.
Manganese serves in this regard as an inexpensive substitute for
nickel. This is usually accompanied by a deterioration in corrosion
resistance. Adding nitrogen can compensate this negative effect in
certain circumstances. The nitrogen improves the strength and
corrosion properties [8] and simultaneously effects austenite
stabilisation. The chromium content of the inventive cast steel
ranges from 12 to 20%, but is never less than 10%. Steel with a
chromium content higher than 12% acts as guarantor for passivation
of the material. In addition, chromium is added to stabilise
ferrite. It simultaneously influences the austenite stability as
well because it hampers martensite formation as the chromium
content rises. To obtain a TRIP effect at room temperature in the
inventive materials, the contents of the elements for stabilising
austenite and ferrite have to be coordinated with each other. In
the inventive cast steel, the elements aluminium and silicon are
used first to adjust the necessary chromium or nickel equivalent.
The influence which the aluminium and silicon dissolved in the
austenite exert on the corresponding equivalents is thereby
described with the aid of effective factors. Moreover, via
different levels of aluminium and silicon, the TRIP effect can be
adjusted selectively via the solution or segregation state of
nitrides, such as AlN. Moreover, as a result of the segregation
state, both grain refinement and consolidation of the austenite are
achieved. The profile of a cast steel part as regards its strength
and toughness properties are additionally improved by highly
disperse AlN segregations in the fine-grained austenite. The ready
availability of the elements silicon and aluminium means that more
costly steel alloying elements in steel, such as nickel and
chromium, can be replaced.
[0027] Preferably, the inventive austenitic stainless cast steel
part has a manganese content of 0 to 25%, a chromium content of 12
to 20%, but never less than 10%, a nickel content of 0 to 12%, a
niobium content of 0 to 1.2%, a tantalum content of 0 to 1.2%, a
carbon content of 0.01 to 0.15%, a nitrogen content of 0.005 to
0.5%, a copper content of 0 to 4%, a cobalt content of 0 to 1%, a
molybdenum content of 0 to 4%, a tungsten content of 0 to 3%, a
titanium content of 0 to 1% and a vanadium content of 0 to 0.15%.
Due to the TRIP effect, which is triggered by tensile loading in
the inventive cast steel part at room temperature and low
temperatures, the mechanical properties improve. Thus, the tensile
strength increases to more than 550 MPa and the elongation at break
to more than 30%. At room temperature and low temperatures, cast
steel material is particularly tough despite the increased strength
values. Moreover, the inventive cast steel part has a high energy
absorption capacity at room temperature and low temperatures. The
energy absorption capacity for these alloy parts is approximately
between 0.30 and 0.40 J/mm.sup.3 at room temperature. This means
that in the event of a sudden stress, such as a crash, the cast
steel part consolidates and simultaneously deforms, without
breaking. Therefore, the cast steel part is particularly suitable
for crash-stressed parts used in automotive construction.
[0028] Preferably, in the inventive cast steel part, the manganese
content is 0 to 25%, the chromium content is 12 to 20%, the nickel
content is 0 to 12%, the niobium content is 0 to 1.2%, the tantalum
content is 0 to 0.2%, the carbon content is 0.01 to 0.15%, the
nitrogen content is 0.005 to 0.5%, the copper content is 0 to 4%,
the cobalt content is 0 to 1%, the molybdenum content is 0 to 4%,
the tungsten content is 0 to 3%, the titanium content is 0 to 1%,
and the vanadium content is 0 to 0.15%.
[0029] Preferably, the inventive austenitic stainless cast steel
part has a chromium content of 16.5%, a nickel content of 6.5%, a
silicon content of 1.1%, a manganese content of 7% and an aluminium
content of 0.05%. The carbon content is 0.04% and the nitrogen
content is 0.1%.
[0030] The inventive method for producing a cast steel part (steel
casting or steel casting part) comprises the following steps:
Provision of an alloy comprising an aluminium content of 0 to 4%
and a silicon content of 0 to 4%, with the alloy produced in an
alloying range determined by the coordinates of four points
(Cr.sub.equiv.=14; Ni.sub.equiv.=8), (Cr.sub.equiv.=14;
Ni.sub.equiv.=14), (Cr.sub.equiv.=22; Ni.sub.equiv.=8) and
(Cr.sub.equiv.=22 Ni.sub.equiv.=16), with the chromium and nickel
equivalent being calculated via relation (1) and (2)
Cr equiv . = % Cr + % Mo + 1.5 % Si + 0.5 % W + 0.9 % Nb + 4 % A 1
+ 4 % Ti + 1.5 % V + 0 .9 % Ta ( 1 ) Ni equiv . = % Ni + 30 % C +
18 % N + 0.5 % Mn + 0.3 % Co + 0.2 % Cu - 0.2 % A 1 ( 2 )
##EQU00002##
from the chemical composition of the cast steel, wherein the
figures must be quoted in mass percent and the rest essentially
consists of iron and other inevitable elements of cast steel; and
the casting steel part is cast in a casting mould.
[0031] Preferably, the cast steel part can undergo heat treatment
in a further step.
[0032] The alloy used in the method has, especially, a manganese
content of 0 to 25%, a chromium content of 12 to 20%, a nickel
content of 0 to 12%, a niobium content of 0 to 1.2%, a tantalum
content of 0 to 0.2%, a carbon content of 0.01 to 0.15%, a nitrogen
content of 0.005 to 0.5%, a copper content of 0 to 4%, a cobalt
content of 0 to 1%, a molybdenum content of to 4%, a tungsten
content of 0 to 3%, a titanium content of 0 to 1%, and a vanadium
content of 0 to 0.15%.
[0033] Especially, the alloy employed in the method has a manganese
content of 5 to 12%, a nickel content of 2 to 8%, a copper content
of 0 to 2%, a cobalt content of 0 to 0.5%, a molybdenum content of
0 to 2.5%, and/or a tungsten content of 0 to 0.5%.
[0034] The object is also achieved by a cast steel part (steel
casting or steel casting part), produced by a method as previously
described, characterised in that the cast steel part has a tensile
strength greater than 550 MPa and an elongation at break of more
than 30%.
[0035] Especially, the cast steel part exhibits a TRIP effect under
load.
[0036] An inventive method for using a cast steel part in a
technical application comprises the steps: performing the steps of
one of the methods described above for the production of the cast
steel part; and use of the cast steel part in a technical
application, wherein use after casting proceeds without the
performance of a chipless forming process. In the context of this
invention, chipless or non-cutting forming processes are all
forming processes which, due to mechanical action, would trigger
the TRIP process in the cast steel part. These forming processes,
such as rolling, forging, pressing, etc. are not performed, with
result that the cast steel part, after being integrated in the
application, still has the potential to exhibit the TRIP effect and
thus, in the event of a stress situation, has a reserve with regard
to tensile strength and elongation at break. It should, however, be
possible to perform cutting processes on the cast steel part which
do not trigger the TRIP effect, without departing from the
framework of the invention.
[0037] Especially, the cast steel part is used as casting material
for plant and refrigeration technology, for equipment and
components for the production of gases and for liquefying and
fractionating gases, for use in automotive and aircraft
construction, for crash-stressed parts, such as crash boxes in
motor vehicles, for components for transporting liquid gases and as
a component which is exposed to low temperatures, and/or as casting
steel foam.
[0038] An inventive component for automotive or aircraft
construction, especially, crash box, A, B or C pillar of a motor
vehicle, is formed as a cast steel part as described above.
[0039] The austenitic cast steel part has an austenitic
microstructure at room temperature with a 5% .delta.-ferrite
content. On account of the TRIP effect triggered in the tensile
test, tensile strength greater than 550 MPa and elongation at break
greater than 30% are obtained. At temperatures below room
temperature, the cast steel material is tough despite increased
strength values. The inventive cast steel has an energy absorption
capacity at room temperature of approximately 0.37 J/mm.sup.3.
* * * * *