HEAT TREATMENT OF FERRITIC HEAT RESISTING STEEL HAVING EXCELLENT TOUGHNESS AND CREEP STRENGTH

摘要

PURPOSE:To improve the creep rupture strength at a high temp. by subjecting a ferritic heat resisting steel having a specific compsn. to hot working, then holding the steel in a martensite region and subjecting this steel to controlled cooling and tempering after heating up and holding the steel to and in an austenitization region. CONSTITUTION:The ferritic heat resisting steel consisting, by weight %, 0.01 to 0.30% C, 0.01 to 0.80% Si, 0.10 to 1.50% Mn, 8.00 to 13.00% Cr, 0.20 to 3.00% W, 0.005 to 1.00% Mo, 0.05 to 0.50% V, 0.02 to 0.12% Nb, 0.0003 to 0.008% B, 0.01 to 0.10% N, 0.0005 to 0.050% Al, = 0.050% P, = 0.010% S, = 0.015% O, and the balance Fe and unavoidable impurities is hot worked. This steel is subjected to the 1st stage of the holding at 500 to 600 deg.C of the martensite region and is then subjected to the 2nd stage of the holding at 1000 to 1150 deg.C by heating up the steel. The steel is thereafter cooled at = 0.5 deg.C/min cooling rate and is further tempered at 700 to 820 deg.C. The finer crystal grain sizes are obtd. and the toughness is improved in this way.