PREPARATION OF NI-CONTAINING LOW TEMPERATURE STEEL EXCELLENT IN CRACK LEADING END OPENING DISPLACEMENT AMOUNT

摘要

PURPOSE:To certainly prepare the titled steel having good tensile strength and good characteristics even in steel plate strain, by a method wherein an Ni-containing steel piece in which P and S contents are prescribed is rolled under a specific condition and thereafter, accerelated cooling and tempering treatment are applied to the rolled steel piece. CONSTITUTION:An Ni-containing low temp. steel piece containing, on the basis of wt%, 7.5-10% Ni, 0.010% or less P and 0.005% or less S is heated to 1,200 deg.C or less and rolling is applied to the heated steel piece under such a condition that a cumalative draft at 950 deg.C or less is regulated to 30% or more and a finish temp. is set to 850 deg.C or less. After rolling, the rolled steel piece is cooled to a temp. 50-150 deg.C lower than the finish temp. in air and cooled to 350 deg.C or less at a cooling speed of 2.0 deg./sec or more. Subsequently, tempering processing is applied to the cooled steel piece at a temp. of AC1 or less. By this method, Ni-containing low temp. steel excellent in a crack leading end opening displacement amount is prepared.