Patent ID: 9708680
Date: 2017-07-18
CPC Classifications: C21D,C22C,E04C

Claim:
1. A hot rolled steel sheet for a square column for building structural members, the hot rolled steel sheet having a composition of, in terms of % by mass, C: 0.07 to 0.17%, Mn: 0.3 to 1.5%, P: 0.03% or less, S: 0.015% or less, Al: 0.01 to 0.06%, N: 0.006% or less, and the balance being Fe and unavoidable impurities, and having a microstructure that includes a primary phase constituted of ferrite and a second phase constituted of pearlite or pearlite and bainite, wherein a second phase frequency defined by equation (1) below is 0.20 to 0.42 and a mean crystal grain diameter of the primary phase and the second phase together is 7 to 15 μm