Patent ID: 6090226
Filing Date: 2000-07-18
Classification: C21D,C22C

Abstract:
A steel plate excellent in brittle crack propagation arrest properties and low temperature toughness comprising, based on weight, 0.04 to 0.30% of C, up to 0.5% of Si, up to 2.0% of Mn, up to 0.1% of Al, 0.001 to 0.10% of Ti, 0.001 to 0.01% of N and the balance Fe and unavoidable impurities,the average grain size d of the structure in the front surface layer region and the back surface layer region each having a thickness corresponding from 2 to 33% of the plate thickness being up to 3 .mu.m, andthe Vickers hardness of the structure satisfying the following expression (1):Hv.ltoreq.200[Ceq %]+20+(9[Ceq %]+3.7)/.sqroot.(d) (1)wherein [Ceq %]=C %+Si %/24+Mn %/6 (wherein C %, Si % and Mn % are percent by weight of C, Si and Mn, respectively).