论文部分内容阅读
本文研究了高温淬火0.5%C-CrMnMo钢高温回大状态的组织和强韧性。在高温回大状态下,这种钢可以通过适当提高淬火温度增加淬火组织中板条马氏体数量的方法,显著改善钢的断裂韧度K_(IC),并获得以塑性断裂为主的断裂特点。但是淬火温度过高,在板条马氏体边界会形成明显数量的残留奥氏体薄膜。这种残留奥氏体在500℃回火时,将促进渗碳体沿马氏体边界的连续分布,大大损害钢的断裂韧度,并使钢在断裂时表现出一定的晶间断裂倾向。延长500℃的回火时间,可以通过碳化物的球化和消除片状马氏体内的孪晶亚结构进一步改善钢的K_(Ic),提高断裂过程中塑性断裂的比例。同时,本文讨论了碳化物尺寸变化对裂纹扩展方式的影响。试验分析表明,由于淬火温度改变而造成的K_(Ic)变化,可用Hahn-Rosenfield关系很好地表示出来。
In this paper, the microstructure and toughness of high temperature quenched 0.5% C-CrMnMo steel were investigated. In the condition of high temperature back to big, this kind of steel can improve the fracture toughness K IC of the steel by increasing the quenching temperature by increasing the number of lath martensite in the quenched structure, and get the fracture mainly of plastic fracture Features. However, the quenching temperature is too high, the lath martensite boundary will form a significant number of residual austenite film. When the residual austenite is tempered at 500 ℃, it will promote the continuous distribution of cementite along the martensite boundary, greatly impair the fracture toughness of the steel and make the steel show a tendency of intergranular fracture at the time of fracture. By lengthening the tempering time at 500 ℃, the K_ (Ic) of the steel can be further improved by the spheroidization of carbides and the elimination of the twin sub-structure in the sheet martensite, and the proportion of plastic fracture in the fracture process can be increased. In the meantime, this paper discusses the effect of carbide size change on crack propagation. Experimental analysis shows that the change of K_ (Ic) due to the quenching temperature can be well represented by the Hahn-Rosenfield relationship.