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1. (WO2015117934) HIGH-STRENGTH FLAT STEEL PRODUCT HAVING A BAINITIC-MARTENSITIC MICROSTRUCTURE AND METHOD FOR PRODUCING SUCH A FLAT STEEL PRODUCT

Pub. No.:    WO/2015/117934    International Application No.:    PCT/EP2015/052135
Publication Date: Fri Aug 14 01:59:59 CEST 2015 International Filing Date: Wed Feb 04 00:59:59 CET 2015
IPC: C21D 9/46
C22C 38/00
C22C 38/02
C22C 38/04
C22C 38/06
C22C 38/12
C22C 38/18
C22C 38/22
C22C 38/32
C22C 38/20
C22C 38/24
C22C 38/40
Applicants: THYSSENKRUPP STEEL EUROPE AG
Inventors: KERN, Andreas
SCHAFFNIT, Elena
TSCHERSICH, Hans-Joachim
Title: HIGH-STRENGTH FLAT STEEL PRODUCT HAVING A BAINITIC-MARTENSITIC MICROSTRUCTURE AND METHOD FOR PRODUCING SUCH A FLAT STEEL PRODUCT
Abstract:
A flat steel product according to the invention, which not only has optimum mechanical properties, such as a high strength combined with good toughness, but also has good suitability for welding, has, in the hot-rolled state, a ferrite-free microstructure consisting to an extent of ≥ 95% by volume of martensite and bainite, with a martensite proportion of ≥ 5% by volume and in total ≤ 5% by volume residual austenite and also production-related unavoidable microstructure constituents. In addition to Fe and unavoidable impurities, the flat steel product according to the invention additionally comprises (in % by weight) 0.08 - 0.10% C, 0.015 - 0.50% Si, 1.20 - 2.00% Mn, 0.020 - 0.040% Al, 0.30 - 1.00% Cr, 0.20 - 0.30% Mo, 0.020 - 0.030% Nb, 0.0015 - 0.0025% B, up to 0.025% P, up to 0.010% S, up to 0.006% N, in particular 0.001 - 0.006% N. The impurities include up to 0.12% Cu, up to 0.090% Ni, up to 0.0030% Ti, up to 0.009% V, up to 0.0090% Co, up to 0.004% Sb and up to 0.0009% W. The invention additionally provides a method which makes it possible to produce a flat steel product according to the invention reliably and with reduced complexity.