热处理工艺对17CrNiMo6齿轮钢带状组织的影响

Heat Treatment on Banded Structure of 17CrNiMo6 Gear Steel

17CrNiMo6大伞齿轮锻件经“880℃×4 h,空冷”正火+“680℃×5 h,空冷”回火预备热处理和“840℃×2 h,油冷”淬火+“200℃×2 h,空冷”回火最终热处理后,其切向、横向均存在5级带状组织,造成大伞齿轮锻件产品各向异性,使其横向的屈服强度、抗拉强度及塑韧性均低于要求值。分析了带状组织产生的原因,提出优化锻造加热和正火工艺。锻造加热过程中在950℃保温2 h进行高温扩散,正火温度升高至900℃保温6 h,同时在正火升温和降温至650℃均保温2 h,保证成分均匀,组织转变充分。最终带状组织消除,17CrNiMo6大伞齿轮锻件产品的力学性能尤其是塑韧性得到大幅提升。

17CrNiMo6 large bevel gear forgings were 5 grade band structure in tangential direction and transverse direction after the preliminary heat treatment of"880 C×4 h,air cooling"normalizing+"680℃×5 h,air cooling"tempering and the final heat treatment of"840℃×2 h,oil cooling"quenching+"200℃×2 h,air cooling"tempering,causing the large bevel gear forgings appeared anisotropy,sothat the transverse yield strength,tensile strength and plastic toughness lower than the required value.The forging heating and normal heat treatment processes were optimized after analyzing the causes for the formation of banded structure.During the forging heating process,the high temperature diffusion was carried out at 950℃ for 2 h,and the normalizing temperature was increased to 900℃ for 6 h.At the same time,during the normalizing heating and cooling process,the temperature was kept at 650℃ for 2 h to ensure uniform composition and adequate structural transformation.The results showed that the banded structure was eliminated,and the mechanical properties,especially the plastic toughness,of 17CrNiMo6 large bevel gear forgings were greatly improved.