A hot-rolled steel strip product and method for its production

Abstract

Described is a hot-rolled steel strip product having a tensile strength (R m ) above 1400 MPa and a microstructure that includes at least 90% by volume of martensite. The steel has a composition includes, in percent by weight (wt.-%): C 0.20-0.26 Si 0.05-0.5, Mn 0.2-0.8, Cr 0.2-0.6, Ni 0.2-0.5, Al 0.015-0.065, Ti 0.005-0.02, B 0.001-0.005, optionally Mo<0.10, optionally Nb<0.01, optionally V<0.04, balance Fe and unavoidable impurities.

1 . A hot-rolled steel strip product with a tensile strength (R m ) above 1400 MPa and having a microstructure comprising at least 90% by volume of martensite, the steel having a composition comprising, in percent by weight (wt.-%):
 C 0.20-0.26   Si 0.05-0.5,   Mn 0.2-0.8,   Cr 0.2-0.6,   Ni 0.2-0.5,   Al 0.015-0.065,   Ti 0.005-0.02,   B 0.001-0.005,   optionally Mo<0.10,   optionally Nb<0.01,   optionally V<0.04,   balance Fe and unavoidable impurities;   wherein the unavoidable impurities P, S and N are limited to:   P≤0.02,   S≤0.005, and   N≤0.0055.   
     
     
         2 . The hot-rolled steel strip product according to  claim 1 , having a microstructure comprising at least 95% by volume of martensite. 
     
     
         3 . The hot-rolled steel strip product according to  claim 1 , having a thickness of from 1.5 mm to 6 mm. 
     
     
         4 . The hot-rolled steel strip product according to  claim 1 , comprising 0.20-0.25 wt.-% C. 
     
     
         5 . The hot-rolled steel strip product according to  claim 1 , comprising 0.10-0.45 wt.-% Si. 
     
     
         6 . The hot-rolled steel strip product according to  claim 1 , comprising 0.3-0.8 wt.-% Mn. 
     
     
         7 . The hot-rolled steel strip product according to  claim 1 , comprising 0.2-0.5 wt.-% Cr. 
     
     
         8 . The hot-rolled steel strip product according to  claim 1 , comprising 0.2-0.4 wt.-% Ni. 
     
     
         9 . The hot-rolled steel strip product according to  claim 1 , comprising 0.006-0.015 wt.-% Ti. 
     
     
         10 . The hot-rolled steel strip product according to  claim 1 , comprising 0.001-0.004 wt.-% B. 
     
     
         11 . The hot-rolled steel strip product according to  claim 1 , wherein the unavoidable impurities comprise Cu, wherein Cu is limited to Cu≤0.10 wt.-%. 
     
     
         12 . The hot-rolled steel strip product according to  claim 1 , wherein the martensite is tempered. 
     
     
         13 . The hot-rolled steel strip product according to  claim 1 , having a tensile strength (R m ) of at least 1475 MPa, a yield strength (R p0.2 ) of at least 1100 MPa, and an elongation (A 50 ) of at least 4%. 
     
     
         14 . The hot-rolled steel strip product according to  claim 1 , having a time to fracture of at least 130 minutes when subjected to a constant load test, as described in the detailed description, at a load of 80% of the tensile strength of the hot-rolled steel strip product. 
     
     
         15 . A method for producing the hot-rolled steel strip product according to  claim 1 , the method comprising:
 providing a steel slab having the composition;   heating the steel slab to an austenitizing temperature of 1150-1300° C.;   hot-rolling the steel slab to a desired thickness from a temperature in the range of Ar3 to 1280° C. to a desired final thickness of the steel product, wherein the finish rolling temperature is in the range of 800-960° C.;   quenching the hot-rolled strip to a coiling temperature of 250° C. or less with an average cooling rate of at least 30° C./s;   optionally galvanizing the hot-rolled strip;   optionally temper annealing the hot-rolled strip at a temperature of 100-250° C.   
     
     
         16 . An automotive component produced from the hot-rolled steel strip product according to  claim 1 . 
     
     
         17 . The method according to  claim 15 , wherein hot-rolled steel strip product having a microstructure comprising at least 95% by volume of martensite. 
     
     
         18 . The method according to  claim 15 , comprising hot-rolling the steel slab to a thickness of from 1.5 mm to 6 mm. 
     
     
         19 . The method according to  claim 15 , wherein a hot-rolled steel strip comprising 0.20-0.25 wt.-% C is produced.