Abstract
The effect of solution treatment temperature on the tensile properties of aged 210 kg/mm2 and 245 kg/mm2 grade 18% Ni maraging steels has been investigated.
To obtain fine austenite grains, solution treatment is carried out after cold rolling. Temperatures of solution treatment are 750°, 775°, 820°, and 850°C. Time of solution treatment is 1 hr. The strength of the maraging steels is increased as the solution treatment temperature is lowered. An improvement of notch toughness is observed after aging the fine grained maraging steels. However, the notch trough ness of the 210 kg/mm2 grade maraging steel tends to decrease remarkably with the solution treatment at 775°or 750°C. A decrease in the notch toughness of the 245 kg/mm2 grade maraging steel is also observed in the solution treatment at 750°C. Because no undissolved precipitate remains even in the solution at 750°C for 1 hr, it is considered that the rapid decrease in notch toughness is related to the micro-segregation of solute atoms.
The temperature range of the γ-to-αM transformation is lowered when the solution temperature is decreased. The lowering of the transformation temperature is considered to be caused by the micro-segregation of solute atoms and the strength increase in fine-grained austenite.
