SCM435冷镦钢的球化退火工艺

Spheroidizing Processes of SCM435 Cold-heading Steel

为获得球状珠光体以改善冷镦性能,对SCM435冷镦钢进行了亚温退火和亚温退火加两相区温度退火,前者为700℃保温4 h炉冷至580℃空冷,后者为700℃保温3.5 h,再升温至745℃保温0.5 h炉冷至580℃空冷。检测了退火后钢的显微组织、力学性能和冷镦性能。结果表明:经两种工艺球化退火后,SCM435钢的显微组织均为铁素体和球状珠光体,与热轧态相比断后伸长率和断面收缩率均提高、抗拉强度降低;经两种工艺球化退火的SCM435钢均能进行大变形率冷镦而不开裂。

In order to obtain spheroidal pearlite to improve cold-heading ability,SCM435 cold-heading steel was subjected to subcritical annealing,and to subcritical annealing plus annealing at two-phase region temperature.The former consisted of holding at 700℃for 4 h then furnace cooling to 580℃and air cooling,and the latter consisted of holding at 700℃for 3.5 h,again heating to 745℃and holding for 0.5 h,furnace cooling to 580℃followed by air cooling.The steel was tested for microstructure,mechanical properties and cold-heading ability.The results showed that(a)after being spheroidized by two processes,SCM435 steel exhibited microstructure consisting of ferrite and spheroidal pearlite,and increased in both elongation and area reduction,and decreased in tensile strength,compared with those of the steel in hot-rolled condition;and(b)SCM435 steel spheroidized by two processes was likely to be cold-upset to large deformation rate without cracking.