Patent ID: 9194017
Filing Date: 2015-11-24
Classification: C21D,C22C

Abstract:
1. A hot-rolled steel sheet having a tensile strength of 500 MPa or less and, the steel sheet having a chemical composition comprising, by mass %, C: 0.18% or more and 0.29% or less, Mn: 0.88% or less, S: 0.03% or less, N: 0.0050% or less, Ti: 0.002% or more and 0.05% or less, B: 0.0005% or more and 0.0050% or less, and Si: 0.4% or less, P: 0.1% or less, sol.Al: 0.1% or less, the balance being Fe and inevitable impurities and a microstructure wherein a fraction of ferrite and pearlite with respect to the whole microstructure is 95% or more in terms of a sum of volume fractions of both ferrite and pearlite, wherein mean grain diameter of the ferrite is 7.0 μm or more and 15.0 μm or less, and wherein a volume fraction of the ferrite with respect to the whole microstructure is 50% or more.