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US 2026/0242908 A1Published application
A high strength steel strip or sheet, and a method for producing the same
Assigneevoestalpine Stahl GmbH
InventorsDaniel KRIZAN, Johannes REHRL, Christoph KICKINGER
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Abstract
A high strength steel strip or sheet includes, in wt. %: 0.18-0.3 C, 0.7-2.0 Si, 2.3-4.5 Mn, 0.03-1.7 Al, 0.6-2.0 Si+Al. The strip or sheet has a tensile strength (Rm) of 1100-1350 MPa and a microstructure including 15-30 vol % retained austenite. The retained austenite fulfils a mechanical stability (kp) of 5-35, a carbon content xcγ of the retained austenite of 0.8-1.2, and RA*kp/xcγ≥200. A method includes a double annealing cycle for producing the strip or sheet.
Claims8
A high strength steel strip or sheet having:
- a) a composition consisting of the following elements in wt. %:
- C
- 0.18-0.3
- Si
- [[0.5]] 0.7-2.0
- Mn
- 2.3-4.5
- Al
- 0.03-1.7
- Si + Al
- 0.6-2.0
- Optionally Ti
- ≤0.1
- Nb
- ≤0.1
- V
- ≤0.1
- Cr
- ≤0.5
- B
- ≤0.005
- Mo
- ≤0.2
- balance Fe apart from impurities;
- b) a tensile strength (Rm) 1100-1350 MPa
- wherein the tensile strength Rm is derived in accordance with the Industrial Standard DIN EN ISO 6892-1, wherein the samples with a gauge length of 80 mm are taken in the longitudinal direction of the strip;
- c) a microstructure comprising of in vol. %:
- retained austenite 15-30
- wherein the amount of retained austenite is measured by means of the saturation magnetization method described in detail in Proc. Int. Conf. on TRIP-aided high strength ferrous alloys (2002), Ghent, Belgium, p. 61-64;
- d) wherein the retained austenite fulfil:
- a mechanical stability (kp)
- 5-35,
- kp as defined by Ludwigson and Berger in J. Iron Steel Inst. 1969, vol. 207, 10 pp. 63, where p=1:
- V
- γ
-
- 0
- -
- V
- γ
- V
- γ
- =
- k
- p
- ×
- ε
- p
- V
- γ
-
- 0
-
- …
-
- initial
-
- retained
-
- austenite
-
- content
- V
- γ
-
- …
-
- retained
-
- austenite
-
- content
-
- after
-
- deformation
- ε
-
- …
-
- true
-
- strain
- ;
- a carbon content of the retained austenite (in wt. %):
- xcγ0.8-1.2
- wherein xcγ is determined by the formula:
- aγ=3.556+0.0453xcγ+0.00095xMn+0.0056xA1
- where xMn, and xA1 are the content of manganese, and aluminium in austenite (in wt. %), and wherein the contents for xMn and xA1 are assumed to be equal the nominal content, and the lattice parameter aγ is obtained from the γ reflections in X-ray diffraction (XRD) measurements using the following equation described in N. H. van Dijk, A. M. Butt, L. Zhao, J. Sietsma, S. E. Offerman, J. P. Wright, and S. van der Zwaag, Thermal stability of retained austenite in TRIP steels studied by synchrotron X-ray diffraction during cooling, Acta Materialia 53 (2005) 5439-5447;
- and
- RA
- *
- k
- p
- /
- x
- c
-
- γ
- ≥
- 20
-
- 0
- .
101 more elements
Dependencies are inferred from the claim text.