钢在淬火时,由于化学成分、零件大小和冷却条件等因素的影响,往往不能获得全部马氏体组织。对于低、中碳低合金钢,因淬透性较小,淬火后很容易获得马氏体与贝氏体的混合组织。另外,低、中碳低合金钢在焊接时,由于热影响区的冷却速度不一致,也可能获得部分的马氏体与贝氏体的混合组织.因此,研究这类混合组织的显微特征与力学性能之间的关系,具有一定的实际意义。关于马氏体和贝氏体混合组织的力学性能与显微组织之间的关系,自Edwards报道了中碳3％Ni·Cr·Mo钢的显微组织为 Steel quenching, due to chemical composition, parts size and cooling conditions and other factors, often can not get all the martensite. For low and medium carbon low alloy steel, due to the smaller hardenability, it is easy to obtain the mixed structure of martensite and bainite after quenching. In addition, when low and medium carbon low alloy steels are welded, part of the mixed microstructure of martensite and bainite may be obtained due to inconsistent cooling rates in the heat-affected zone. Therefore, The relationship between mechanical properties, has a certain practical significance. Regarding the relationship between the mechanical properties of the mixed martensite and bainite microstructure, Edwards reported that the microstructure of the medium carbon 3% Ni · Cr · Mo steel is