关键词: 高强钢, 马氏体, 回火温度, 碳化物

Abstract: Microstructure and mechanical properties changes of the tested steel of low carbon and micro-alloyed with Nb, Ti, B, Cr, Mo, Ni tempered at different temperatures were systematically studied by means of scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results show that the decomposition of martensite occurs after tempering at 220 ℃, the lath bundles of martensite become coarser, the laths in the bundles merge gradually, the retained austenite decomposes gradually, the dislocation density decreases greatly, and the internal stress caused by quenching is released. The tested steel has the best comprehensive mechanical properties. After tempering at 300 ℃, a large number of carbides gather and grow in austenite grain boundaries or between tempered martensite laths, which reduces the binding force between grain boundaries and laths, resulting in tempering embrittlement.

Key words: high strength steel, martensite, tempering temperature, carbide