Thyssenkrupp Steel Europe Ag

Sigrun Ebest

Roland Sebald

Dorothea Mattissen

Ekatherina Bocharova

Stefan Follner

The invention relates to a cold-rolled flat steel product which, despite high strength values, has a high level of deformability characterized by a high elongation at break and a good hole expansion ratio &#x3bb;. For this purpose the flat steel product is produced from a steel that is composed of (in % by weight) C: 0.12-0.19%, Mn: 1.5-2.5%, Si: &#x3e;0.60-1.0%, Al: &#x2264;0.1%, Cr: 0.2-0.6%, Ti: 0.05-0.15% with the remainder being iron and unavoidable impurities caused by the production process, and which comprises a perlite- and bainite-free structure having 4-20% by vol. martensite, 2-15% by vol. residual austenite, remainder ferrite, an elongation at break A80 of at least 15%, a tensile strength Rm of at least 880 MPa, a yield strength ReL of at least 550 MPa and a hole expansion ratio &#x3bb;of more than 6%. The invention also relates to a method which easily enables production of a flat steel product according to the invention.

Cold-rolled flat steel product and method for its production

The invention relates to a steel and to a flat steel product produced therefrom that have optimized mechanical properties and at the same time can be produced at low cost, without having to rely for this on expensive alloying elements that are subject to great fluctuations with regard to their procurement costs. The steel and the flat steel product have for this purpose the following composition according to the invention (in % by weight): C: 0.11-0.16%; Si: 0.1-0.3%; Mn: 1.4-1.9%; Al: 0.02-0.1%; Cr: 0.45-0.85%; Ti: 0.025-0.06%; B: 0.0008-0.002%, the remainder Fe and impurities that are unavoidable for production-related reasons, which include contents of phosphorus, sulfur, nitrogen or molybdenum as long as the following respectively apply for their contents: P: &#x2264;0.02%, S: &#x2264;0.003%, N: &#x2264;0.008%, Mo: &#x2264;0.1%. Similarly, the invention relates to a method for producing a flat steel product that consists of a steel according to the invention.

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Oberhausen, Germany

Sigrun Ebest