18CrNiMo7-6渗碳钢等温正火新工艺探讨

18CrNiMo7-6渗碳钢采用常规等温正火处理,极易产生粒状贝氏体组织,很难有效改善二次带状。对18CrNiMo7-6渗碳钢等温正火新工艺的组织和性能进行了研究,具体工艺为40 mm的试棒保温结束后,直接浸入正火液冷却至700～750 ℃出液,迅速转移到等温炉650 ℃等温5～7 h。结果表明,采用等温正火新工艺,获得了铁素体+片状珠光体的平衡态组织,消除了粒状贝氏体,晶粒大小均匀,无明显混晶,有利于降低热处理畸变;硬度达到170～185 HBW,有利于后续机加工。

Discussion on a new isothermal normalizing process of 18CrNiMo7-6 carburizing steel

18CrNiMo7-6 carburizing steel is treated with conventional isothermal normalizing,which is prone to produce granular bainite microstructure and difficult to change the secondary strip effectively.Microstructure and performance of the 18CrNiMo7-6 carburizing steel and isothermal normalizing new process were studied.The specific process consisted of,after austenitizing and holding,for the φ40 mm specimen,directly immersed in the normalizing liquid and cooled to 700-750℃.The specimen was then quickly transferred to the isothermal furnace,at 650℃ for 5-7 h.The results show that the equilibrium microstructure of ferrite and lamellar pearlite is obtained by using the new isothermal normalizing process,the granular bainite is eliminated,the grain size is uniform,and there is no obvious crystal mixing,which is beneficial to reduce the heat treatment distortion.The hardness can be guaranteed at 170-185 HBW,which is conducive to machining.