Patent ID: 9540719
Date: 2017-01-10
CPC Classifications: B65G,C21D,C22C,C23C,F27B,F27D

Claim:
1. A hot-rolled steel sheet with an elastic limit greater than 690 MPa and less than or equal to 840 MPa, with a strength between 780 MPa and 950 MPa, an elongation at failure greater than 10% and a hole expansion ratio (Ac) greater than or equal to 50%, the chemical composition of which contains, whereby the contents are expressed in percent by weight: 0.040%≦C≦0.065%, 1.4%≦Mn≦1.9%, 0.1%≦Si≦0.55%, 0.095%≦Ti≦0.145%, 0.025%≦Nb≦0.045%, 0.005%≦Al≦0.1%, 0.002%≦N≦0.007%, S≦0.004%, and P<0.020, the remainder consisting of iron and unavoidable impurities resulting from processing, the microstructure of which contains cementite in an area percentage of less than 1.5%, granular bainite, ferrite, and carbonitrides of titanium and niobium, whereby the density of titanium nitrides of average size greater than 6 μm is less than or equal to 3/mm a ratio between the grain size D