Patent ID: 7731808
Filing Date: 2010-06-08
Classification: B32B,C21D,C22C,C23C

Abstract:
1. A hot-rolled steel sheet of carbon steel or low-alloy steel comprising C: 0.01 to 0.25% by mass, the main phase of which is ferrite, and is characterized in that the average ferrite crystal grain diameter D (μm) at the depth of ¼ of the sheet thickness from the steel sheet surface satisfies the relations respectively defined by the formulas (1) and (2) given below and the increase rate X (μm/min) in average ferrite crystal grain diameter at 700° C. at the depth of ¼ of the sheet thickness from the steel sheet surface and said average crystal grain diameter D (μm) satisfy the relation defined by the formula (3) given below: wherein C and Mn represent the contents (in % by mass) of the respective elements in the steel.