Abstract: Effect of pre-treatment temperature on strength of Cr-Ni-Co-Mo maraging stainless steel was investigated, including the effect on heritability of the original forged coarse grains and spontaneous recrystallization, as well as the effect of pre-treatment temperature on the amount of retained and reversed austenite and the mechanical properties after the final heat treatments. The results show that, the pre-treatment below 900 ℃ inherits the forging coarse grains, that is, the austenite with high defect density is formed by the α′→γ shear mechanism. The pre-treatment temperature rises, the amount of retained austenite after solid solution at 750 ℃, cryogenic treatment at －73 ℃, and the amount of retained and reversed austenite after aging at 500 ℃ decrease, so the final tensile and yield strength increase. The pre-treatment above 800 ℃ does not influence much on retained and reversed austenite amount after final heat treatment, and the tensile and yield strengths tend to stabilize. The spontaneous recrystallization of the inherited forged coarse grains via pre-treatment above 900 ℃ refines the grains and reduces the density of defects in the formed austenite, and finally reduces the density of defects accumulated in the austenite after solution treatment at 750 ℃, so the final aging strengthening effect is reduced, resulting in that the grain refinement is not enough to improve the final strength.

Key words: maraging stainless steel, pre-treatment temperature, strength, retained austenite, reversed austenite