Patent ID: 9200357
Filing Date: 2015-12-01
Classification: C21D,C22C,C23C

Abstract:
1. A steel, consisting essentially of, by mass percent based on a total mass of the steel: C: 0.05-0.8%; Si: 0.03-2%; Mn: 0.2-1.8%; Al: 0.1-0.5%; B: 0.0005-0.008%; N: 0.002-0.007%; P: 0.03% or less, excluding 0%; S: 0.03% or less, excluding 0%; and O: 0.002% or less, excluding 0%; with the remainder iron and unavoidable impurities, wherein a mass ratio of BN to AlN (BN/AlN), precipitated in the steel, is in a range from 0.020-0.2, and wherein a number ratio of BN precipitated on an old austenitic grain boundary to BN precipitated inside an old austenitic grain, (grain boundary BN/intra-grain BN), out of BN precipitated in the steel is 0.50 or less.