前言 近年来对中碳低合金结构钢的研究表明,经等温处理后获得的M(马氏体)+B下(下贝氏体)复相组织是一种强韧性比较好的组织。这种复相组织与淬火回火单相马氏体组织比较,可在不降低甚至略有升高强度的同时提高韧性值。但这种组织用于环境工作时必须考虑应力腐蚀问题,如高强度螺栓,弹簧等构件,这类构件强度级别较 Preface In recent years, research on medium-carbon low-alloy structural steels shows that the complex phase of M (martensite) + B (lower bainite) obtained after isothermal treatment is a kind of tissue with good toughness. Compared with quenched and tempered single-phase martensite, the complex phase structure can improve the toughness value without reducing or even slightly increasing the strength. However, such organizations must consider the issue of stress corrosion when used in environmental work, such as high-strength bolts, springs and other components, such components strength level than