Hot rolled steel sheet and method for manufacturing the same

摘要

A semi-manufactured steel material has a chemical composition including, by mass %, C: 0.055% to 0.15%, Si: not more than 0.2%, Mn: not more than 1.3%, P: not more than 0.03%, S: not more than 0.007%, Al: not more than 0.1%, N: not more than 0.01%, and Ti: 0.14% to 0.30%, the balance comprising Fe and inevitable impurities. In the composition, 1.0≦([C]/12)/([Ti*]/48) is satisfied ([C], [S], [N] and [Ti]: contents (mass %) of the respective elements, and [Ti*]=[Ti]−3.4×[N]−1.5×[S]), and the contents of niobium and boron as impurities are limited to Nb: less than 0.03% and B: less than 0.0005%.

主权项

1. A method of manufacturing a hot rolled steel sheet comprising subjecting a semi-manufactured steel material to heating, hot rolling including rough rolling and finish rolling, cooling after the completion of finish rolling, and coiling, thereby producing a hot rolled steel sheet, wherein
the semi-manufactured steel material has a chemical composition including, by mass%, C: 0.055% to 0.15%, Si: not more than 0.2%, Mn: not more than 1.3%, P: not more than 0.03%, S: not more than 0.007%, Al; not more than 0.1%, N: not more than 0.01%, and Ti: 0.14% to 0.30%, the contents of carbon, sulfur, nitrogen and titanium satisfying the inequality (1) below, the contents of niobium and boron as impurities being Nb: less than 0.03% and B: less than 0.0005%, the balance comprising Fe and inevitable impurities, the heating is performed at a heating temperature T (° C.) of not less than 1150°C., the heating temperature satisfying the inequality (2) below, the semi-manufactured steel material being held at the temperature range of not less than 1150°C. for 15 minutes or more, the hot rolling is performed with a total reduction ratio in a temperature range of 980°C. or below of not more than 40%, the finish rolling is performed at a finish rolling temperature of not less than 880°C., the cooling is started within 3 seconds after the completion of finish rolling and is performed at an average cooling rate of 40°C/sec, to 200°C/sec., and the coiling is performed at a coiling temperature of 500°C. to 680°C., wherein:
1.0≦([C]/12)/([Ti*]/48)  (1)[Ti*]<10{−7000/(T+273)+2.75}/[C]  (2)[Ti*]=[Ti]−3.4×[N]−1.5 ×[S]T: heating temperature (° C.) for the semi-manufactured steel material ([C], [S], [N] and [Ti]: contents (mass %) of the respective elements).