Patent ID: 11970753
Assignee: VOESTALPINE STAHL GMBH
Field: Materials, metallurgy (Chemistry)
Classification: CPC C | IPC C

Claim 14:
15. A method for producing a hot-rolled steel, comprising the steps of:
providing a steel alloy including the following elements in the following amounts, expressed as percent by mass:, C=0.09 to 0.20,, Si=0.10 to 0.50,, P=max. 0.0150,, S=max. 0.0050,, Al=0.015 to 0.055,, Ni=max. 0.5,, Mo=max. 0.3,, V=max. 0.12,, Nb=max. 0.035,, N=max. 0.0100,, Ti=0.015 to 0.030,, B=0.008 to 0.040,, Cr=0.2 to 1.0,, Mn=1.0 to 3.0, and, optional: Ca=0.0010 to 0.0040, and, remainder iron and inevitable impurities;
casting the steel alloy to form a cast steel alloy;
heating the cast steel alloy;
hot rolling the cast steel alloy to form a hot rolled steel alloy strip;
hardening the hot rolled steel alloy strip immediately after hot rolling by quenching at a cooling rate of at least 10 K/sec.;
mechanically straightening the hot rolled steel alloy strip without elongating it to produce mobile dislocations in the hot rolled steel alloy strip, such that a volume fraction of the hot rolled steel alloy strip that exceeds a yield point in the straightening process is not less than 70%; and
annealing the mechanically straightened hot rolled steel alloy strip at a temperature of about 100° C. to about 200° C.;
wherein the B, Mn and Cr delay diffusive transformation of the steel alloy from an austenite structure to achieve a martensite structure during the hardening after the hot rolling of the steel alloy strip;
the martensite structure forms from the austenite structure during the hardening of the hot rolled steel alloy strip; and
the Cr improves the hardenability of the steel alloy during the step of hardening the hot rolled steel alloy strip.