The experimental results show that sharp increment of toughness mainly results from fine grain size and a few unsoluble needle ferrites in the microstructure of steel after intercritical heat treatment(IHT).

• 试验结果表明,冲击韧性的显著提高,主要是由于亚温淬火钢具有细小的晶粒尺寸,其次是显微组织中存在着少量未溶针状铁素体。