关键词: 马氏体时效不锈钢, 锻态粗晶, 粗晶遗传, 再结晶, 重复加热/冷却

Abstract: In order to solve the problem of coarse grains remained in hot forging rings of a Cr-Ni-Mo-Ti maraging stainless steel, the temperature range of inheriting of forged coarse grains was investigated, and the recrystallization temperature for grain size refinement was determined. Moreover, the effect of repeated solution treatment on the grain size refinement and mechanical properties was determined. The results show that the forged coarse grains are inherited in a wide temperature range above Af of the steel. After solution treatment near 950 ℃, the austenite grains with completely closed grain boundaries and obvious refinement are formed, indicating that the recrystallization temperature T_re is approximately equal to 950 ℃, moreover, further increasing the solution temperature leads to grain growth. Repeated heating and cooling slightly below 950 ℃ lead to large grain boundary migration and forming the fine grain with open boundries. The repeated heating and cooling at 950 ℃ can still fine the grains, while the effect is weakened with the further increase of temprature, untill the effect vanish at 1050 ℃. The grain refinement by repeated heating and cooling at 875 ℃ significantly improves the impact properties, but the tensile strength and yield strength decrease, showing that the strength decreases with the grain refinement. The strength and toughness when heating and cooling once at 925, 975 ℃ (near T_re) are close to those of repeated heating and cooling for 3 cycles at 875 ℃, while the grains are slightly refined with the increase of repeated heating and cooling times, and there is no significant change in mechanical properties.

Key words: maraging stainless steel, forged coarse grains, coarse grain inheritance, recrystallization, repeated heating and cooling