Abstract
Effects of B contents on strengthening and toughening by the solution treatment under unrecrystallized austenite were examined in 2.1GPa grade 18%Ni maraging steels. Because addition of B retarded the recovery process, and further to the suppression of recrystallization, when B was added in 18%Ni maraging steels, recrystallization temperature of the reverse-transformed γ increased with B contents. In addition of B more than 0.0020mass%, however, toughness decreased on the solution treatment under unrecrystallized austenite of a higher temperature side at 1123K. This decrease of toughness is a phenomenon called thermal embrittlement. The thermal embrittlement was caused by the precipitation and growth of borides at the prior austenite grain boundaries. The optimum amounts of B addition is about 0.0010mass% for strengthening and toughening due to the solution treatment under unrecrystallized austenite as well as avoiding the thermal embrittlement.
