SWRCH35K冷镦钢的球化退火工艺

Spheroidizing process of SWRCH35K cold heading steel

为改善SWRCH35K钢的球化组织质量以提高其冷镦性能,并实现热轧后在线退火调控,通过热力学模拟得出SWRCH35K钢的相变点,采用等温球化退火、高温回火和高温回火+等温球化退火分别对热轧材进行热处理。结果表明:等温球化退火后形成的粒状珠光体组织中存在部分长片状碳化物,同时加热温度在两相区的高温段由于先共析铁素体的再析出导致碳化物分布不均匀,并在790℃有片状珠光体生成;高温回火可以使片状珠光体中的碳化物转变成粒状,但粒状碳化物存在分布不均匀的现象;高温回火+等温球化退火得到的粒状珠光体组织良好,碳化物分布均匀且未发现明显的长片状碳化物,其最佳的热处理制度为685℃×1.5 h空冷+740℃×0.5 h炉冷至685℃×3 h空冷。

In order to improve the spheroidized structure and cold heading quality of SWRCH35K steel,and to realize on-line annealing control after hot rolling,the phase transformation point of the SWRCH35K cold heading steel was obtained by thermodynamic simulation,and the hot rolled steel was heat treated by isothermal spheroidizing,high temperature tempering and high temperature tempering+isothermal spheroidizing.The results show that there are some long lamellar carbides in the granular pearlite formed after isothermal spheroidizing,and the uneven distribution of carbides is due to the re-precipitation of proeutectoid ferrite heated at the high temperature of the two-phase region,and lamellar pearlite is formed at 790℃;the carbides in the lamellar pearlite can become granular form by high temperature tempering,but the distribution of granular carbides is not uniform.The granular pearlite obtained by high temperature tempering and isothermal spheroidizing has good microstructure,uniform distribution of carbides and no obvious long lamellar carbides,so its best heat treatment system is 685℃×1.5 h,air cooling+740℃×0.5 h,furnace cooling to 685℃×3 h,then air cooling.