Toughening of 18% Ni maraging steel by the combined addition of Nb and B

摘要

Effects of Nb content and solution treatment temperature on the tensile strength and fracture toughness were examined in 18% Ni marii iii steel containing 0.0012～0.0013% B. When Nb was added as a boride former element, the recovery process. ofreverse-transformed austenite was retarded. This retardation of recovery led to the suppression of recrystallization and further to the rising in recrystallization temperature of reverse-transformed austenite. The recrystallization temperature was raisedwith increasing the Nb contents. When the addition of Nb was more than 0.16 mass%, however, the fracture toughness was reduced markedly. This decrease of fracture toughness was ascribed to the thermal embrittlement which was caused by growth of NbB{sub}2type borides. In conlusion, when Nb was added by an amount of 0.005 to 0..07mass%, both strengthening and toughening can be realized without any thermal embrittlement, by means of the solution treatment in wide temperature range where the steels are in astate of unrecrystallized austenite.