AUSTENITIC STAINLESS STEEL HAVING SUPERIOR TOUGHNESS AFTER AGING IN ENVIRONMENT AT HIGH TEMPERATURE AND SUPERIOR RESISTANCE TO INTERGRANULAR CORROSION AT HIGH TEMPERATURE

摘要

PURPOSE:To improve the toughness of an austenitic stainless steel in an environment contg. Cl and SO4 ions at high temp. and the resistance to intergranular corrosion at high temp. by regulating the amounts of N, Si, Cr and C in the steel to a specified value each so as to stabilize the austenite structure in spite of the low Ni content. CONSTITUTION:A heat resistant austenitic steel having a composition contg., by weight, 0.03% C, 0.60% Si, 5.0% Mn, 0.04% P, 0.03% S, 23-30% Cr, 5-18% Ni and 0.25-0.45% N or further contg. one or more among 0.1-3.0% Mo, 0.05-2.0% Nb, 0.02-0.5% Ti, 0.2-5% Cu, 0.01% B, 0.05% Ce and 0.01% Ca and satisfying a formula Ni%+0.5XMn%30X(C%+N %)=20% is used as a tube material for the super-heater of a soda recovery boiler used in a paper mill. The steel tube material has superior toughness after aging and superior resistance to intergranular corrosion at high temp.