EFFECT OF B-CONTENTS ON TOUGHENING BY THE SOLUTION TREATMENT UNDER UNRECRYSTALLIZED AUSTENITE IN 18-PERCENT-NI MARAGING-STEEL

Effects of B contents on strengthening and toughening by the solution treatment under unrecrystallized austenite were examined in 2.1GPa gra de 18%Ni maraging steels. Because addition of B retarded the recovery process, and further to the suppression of recrystallization, when B w as added in 18%Ni maraging steels, recrystallization temperature of th e reverse-transformed gamma 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 sid e at 1123K. This decrease of toughness is a phenomenon called thermal embrittlement. The thermal embrittlement was caused by the precipitati on and growth of borides at the prior austenite grain boundaries. The optimum amounts of B addition is about 0.0010mass% for strengthening a nd toughening due to the solution treatment under unrecrystallized aus tenite as well as avoiding the thermal embrittlement.