Patent ID: 9657380
Date: 2017-05-23
CPC Classifications: B32B,C21D,C22C

Claim:
1. A high strength hot-rolled steel sheet having excellent ductility, stretch flangeability, and uniformity of material, the steel sheet having a steel composition comprising: in percent by mass, 0.020% to 0.065% of C; 0.1% or less of Si; 0.40% to less than 0.80% of Mn; 0.030% or less of P; 0.005% or less of S; 0.104% to 0.20% of Ti; 0.005% to 0.1% of Al; 0.005% or less of N; and the balance being Fe and incidental impurities, in which Ti* specified by expression (1) below satisfies expressions (2) and (3) below, and the steel sheet has a steel microstructure including, in terms of area fraction, 95% or more of a ferrite phase and the balance being at least one of a pearlite phase, a bainite phase, and a martensite phase; the average ferrite grain size is 10 μm or less; the average grain size of Ti carbides precipitated in steel is 10 nm or less; and Ti in an amount of 80% or more of Ti* is precipitated as Ti carbides: where Ti, N, and C represent contents of corresponding elements (percent by mass).