Thyssenkrupp Steel Europe Ag

Thyssen Krupp Ag

Elena Schaffnit

Andreas Kern

Hans-Joachim Tschersich

Gabriel Kolek

Wolfgang Gervers

Alexander Gaganov

Christian Mertin

Tim Stötzel

Achim Peuster

Prof Dr-Ing Andreas Kern

Swen Prochotta

A hot rolled flat steel product including (in % by weight) of C: 0.05-0.08%, Si: 0.015-0.500%, Mn: 1.60-2.00%, P: up to 0.025%, S: up to 0.010%, Al: 0.020-0.050%, N: up to 0.006%, Cr: up to 0.40%, Nb: 0.060-0.070%, B: 0.0005-0.0025%, Ti: 0.090-0.130%, unavoidable impurities including up to 0.12% Cu, up to 0.100% Ni, up to 0.010% V, up to 0.004% Mo, and up to 0.004% Sb, and the remainder being iron. The hot rolled flat steel product has a yield strength of 700-850 MPa, a fracture elongation of at least 12%, and a microstructure of at least 70% by volume bainitic microstructure.

High-strength flat steel product

The disclosed flat steel products have optimal mechanical properties such as high strength and good toughness, but are also well-suited for welding and other manufacturing processes. The steel products may have a ferrite-free microstructure with at least 95% by volume martensite and bainite, with a martensite content of at least 5% by volume, and no more than 5% by volume residual austenite and unavoidable microstructure constituents from the production process. In addition to iron and unavoidable impurities, a composition of the flat steel products may include in percent 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, and up to 0.006% N. Impurities can 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.

High-strength flat steel product having a bainitic-martensitic microstructure and method for producing such a flat steel product

Methods for producing flat steel product with a yield strength of at least 700 MPa and an at least 70% by volume bainitic microstructure may comprise several steps. For example, one method may involve smelting a steel melt including in percent by weight 0.05-0.08% C, 0.015-0.500% Si, 1.60-2.00% Mn, 0.025% P, up to 0.010% S, 0.020-0.050% Al, up to 0.006% N, 0.40% Cr, 0.060-0.070% Nb, 0.0005-0.0025% B, 0.090-0.130% Ti, unavoidable impurities, and Fe. The may further involve casting the melt to give a slab, reheating the slab, rough-rolling the slab, hot finish-rolling the rough-rolled slab, cooling the hot-finish-rolled flat steel product within ten seconds of hot finish-rolling, and coiling the hot-finish-rolled flat steel product.

Method for producing a high-strength flat steel product

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Düsseldorf, Germany

Elena Schaffnit