Hot rolled steel product and method for producing same

Claim 1

A hot-rolled steel strip having a composition consisting essentially of, in wt.%: carbon--0.04-0.08 manganese--1.1-1.6 columbium--from about 0.03 to less than about 0.08 vanadium--0.08-0.1 nitrogen--0.013-0.020 silicon--less than 0.05 sulfur--less than 0.02 phosphorus--less than 0.02 aluminum--0.02-0.10 iron--essentially the balance said steel strip having a microstructure consisting essentially of a ferrite matrix as a major portion and scattered pearlite as a minor portion; said composition including a sulfur controlling agent; said microstructure having a ferrite grain size at least as fine as ASTM 12; said steel strip having a yield strength of at least 80 ksi (545 MPa), and an elongation of at least 20% in 2 inches (5 cm).

Claim 7

A method for producing a hot rolled steel strip having a microstructure consisting essentially of a ferrite matrix as a major portion and scattered pearlite as a minor portion, a ferrite grain size at least as fine as ASTM 12, a yield strength of at least 80 ksi (550 MPa) and an elongation of at least 20% in 2 inches (5 cm), said method comprising the steps of: providing a steel slab having a composition consisting essentially of, in wt.%: carbon--0.04-0.08 manganese--1.1-1.6 columbium--from about 0.03 to less than about 0.08 vanadium--0.08-0.1 nitrogen--0.013-0.020 silicon--less than 0.05 sulfur--less than 0.02 phosphorus--less than 0.02 aluminum--0.02-0.10 iron--essentially the balance said composition including a sulfur controlling agent; heating said slab to a mean slab temperature in the range of about 1204° to 1316° C. (2200° to 2400° F.); hot rolling said slab to produce an intermediate strip having a thickness substantially less than said slab but substantially greater than the desired final thickness of said strip, said intermediate strip having a strip temperature, at the end of said hot rolling step, greater than about 1049° C. (1920° F.); cropping the ends from said intermediate strip; subjecting said intermediate strip to finish hot rolling to reduce said strip to said desired final thickness; said intermediate strip having a strip temperature no less than about 982° C. (1800° F.) at the beginning of said finish hot rolling, and said strip having a strip temperature no less than about 899° C. (1650° F.) at the end of the finish hot rolling; cooling said strip after said finish hot rolling to a strip temperature below about 621° C. (1150° F.); and collecting said strip at a strip temperature below about 621° C. (1150° F.).

Claim 8

A method for producing a hot rolled steel strip having a microstructure consisting essentially of a ferrite matrix as a major portion and scattered pearlite as a minor portion, a ferrite grain size at least as fine as ASTM 12, a yield strength of at least 80 ksi (550 MPa) and an elongation of at least 20% in 2 inches (5 cm), said method comprising the steps of: providing a steel slab having a composition consisting essentially of, in wt.%: carbon--0.04-0.08 manganese--1.1-1.6 columbium--from about 0.03 to less than about 0.08 vanadium--0.08-0.1 nitrogen--0.013-0.020 silicon--less than 0.05 sulfur--less than 0.02 phosphorus--less than 0.02 aluminum--0.02-0.10 iron--essentially the balance said composition including a sulfur controlling agent; heating said slab to a mean slab temperature in the range of about 1204° to 1316° C. (2200° to 2400° F.); hot rolling said slab to produce an intermediate strip having a thickness substantially less than said slab but substantially greater than the desired final thickness of said strip, said intermediate strip having a strip temperature, at the end of said hot rolling step, greater than about 1049° C. (1920° F.); cropping the ends from said intermediate strip; subjecting said intermediate strip to finish hot rolling to reduce said strip to said desired final thickness; said intermediate strip having a strip temperature no less than about 982° C. (1800° F.) at the beginning of said finish hot rolling, and said strip having a strip temperature no less than about 899° C. (1650° F.) at the end of the finish hot rolling; cooling said strip after said finish hot rolling to a strip temperature below about 621° C. (1150° F.); and collecting said strip at a strip temperature below about 621° C. (1150° F.).