SCM435冷镦钢线材球化退火工艺探讨

介绍SCM435冷镦钢线材对原材料的成分要求及其球化退火的重要性,通过2种球化退火工艺试验,探讨SCM435线材球化退火机制,并利用渗碳体球化率、金相组织、硬度指标说明球化退火的最佳工艺。试验得知随着保温温度的升高,SCM435线材的渗碳体球化率、均匀度显著提高,且球状渗碳体颗粒更细小;在保温温度一定的情况下,随着保温时间的延长,球化效果更好,但保温时间过长,渗碳体颗粒会按照Ostwald熟化机制长大,反而不利于冷镦变形。SCM435线材球化退火热处理最佳工艺为随炉加热到780℃→保温2～2.5h→随炉冷却到680℃→保温2.5～3h→随炉冷却到580℃→空冷。

Discussion on spheroidizing annealing technology of SCM435 cold heading steel wire rod

To introduce the requirements of SCM435 cold heading steel wire rod and importance of spheroidizing annealing. Through two spheroidizing annealing technology experiments, the mechanism of SCM435 steel spheroidizing annealing was discussed. And the optimum technology of spheroidizing annealing was illustrated by using cementite spheroidizing level, metallographic structure, hardness index. Experiment shows that with the rising of holding temperature, eementite spheroidizing level, uniformity are increased remarkably, and sphericity cementite grain is more fine. At constant holding temperature, spheroidizing effect is better with the holding time prolongation. But when the holding time is overlong, cementite grain will grow up according to the Ostwald ripening mechanism, on the contrary, it is unfavorable for cold heading deformation. The optimum technology of SCM435 steel spheroidizing annealing heat treatment is as follows ： heat up to 780 ℃ with the furnace, holding time 2 - 2.5 h, furnace cooling to 680 ℃, holding time 2.5 - 3 h, furnace cooling to 580 ℃, then air cooling.