Simultaneous Improvement of Toughness and Fatigue Life in a Typical Ultrahigh Strength Steel by a New Deep Cryogenic Treatment Process

As a supplemental process of heat treatment, deep cryogenic treatment (DCT) is believed to have favorable effects on the mechanical properties steels. In this study, three different sequences DCT and tempering, including QCTT (Q: quenching, C: DCT, T: tempering), QTC, QTCT, were investigated discover an effective method improve impact toughness fatigue life typical ultrahigh strength steel simultaneously. Compared with traditional process, toughness, fracture elongation, improved by 10%, 17.8%, 13.7%, respectively, after QTC process. The microstructures characterized scanning electron microscope (SEM), backscatter diffraction (EBSD), transmission microscopy (TEM), probe micro-analysis (EPMA). results indicate that formation cracks was restricted due decrease carbides disappear twinned martensite, both which would serve as sources cracks. Besides, propagation hindered because blocky retained austenite increase filmy austenite. result, elongation are This work provides new simultaneously