Thyssen Krupp Ag

Evonik Operations Gmbh

Thyssenkrupp Steel Europe Ag

Manuela Irnich

Rainer Fechte-Heinen

Richard Georg Thiessen

Miriam Lange

Jens Horstmann

Bernd Linke

Jan-Hendrik Rudolph

The present invention relates to a flat steel product which has good deep-drawing ability, low edge-crack sensitivity and good bending behaviour. To this end, the flat steel product contains a steel which consists of (in wt %) 0.1-0.5% C, 1.0-3.0% Mn, 0.9-1.5% Si, up to 1.5% Al, up to 0.008% N, up to 0.020% P, up to 0.005% S, 0.01-1% Cr and optionally one or more of the following elements: up to 0.2% Mo, up to 0.01% B, up to 0.5% Cu, up to 0.5% Ni and optionally a total of 0.005-0.2% microalloying elements, the remainder being iron and unavoidable impurities, wherein 75&#x3c;(Mn2+55*Cr)/Cr&#x3c;3000 where Mn is the Mn content of the steel in wt % and Cr is the Cr content of the steel in wt %. The steel has a structure which consists of at least 80 area % martensite, of which at least 75 area % is tempered martensite and at most 25 area % is non-tempered martensite, at least 5 volume % residual austenite, 0.5 to 10 area % ferrite and at most 5 area % bainite, wherein in the region of the phase boundary between tempered martensite and residual austenite there is a low-Mn ferrite seam which has a width of at least 4 nm and at most 12 nm and the Mn content of which is at most 50% of the average Mn content of the flat steel product. The flat steel product contains carbides with a length of less than or equal to 250 nm. The invention also relates to a method for producing a flat steel product according to the invention, in which method the structural characteristics of the flat steel product according to the invention are set by suitable heat treatment.

Flat steel product and method for producing same

A hot-rolled flat steel product including (in wt %) C: 0.1-0.3%, Mn: 1.5-3.0%, Si: 0.5-1.8%, Al: &#x2264;1.5%, P: &#x2264;0.1%, S: &#x2264;0.03%, N: &#x2264;0.008%, optionally one or more of Cr: 0.1-0.3%, Mo: 0.05-0.25%, Ni: 0.05-2.0%, Nb: 0.01-0.06%, Ti: 0.02-0.07%, V: 0.1-0.3%, and B: 0.0008-0.0020%, the balance being iron and unavoidable impurities. This flat steel product possesses a tensile strength of 800-1500 MPa, a yield strength of &#x3e;700 MPa, an elongation at break of 7-25%, and a hole expansion of more than 20%. The structure is at least 85 area % martensite, of which at least half is tempered martensite, with the remainder being &#x2264;15 vol % residual austenite, &#x2264;15 area % bainite, &#x2264;15 area % polygonal ferrite, &#x2264;5 area % cementite and/or &#x2264;5 area % nonpolygonal ferrite, and has a kernel average misorientation of at least 1.50&#xb0;. Also, a method for producing the flat steel product, wherein the microstructure of the flat steel product is set by the heat treatment.

Hot-rolled flat steel product and method for the production thereof

Growing community of inventors

Rheinberg, Germany

Manuela Irnich