将一种直径为100 mm的高强度低合金贝氏体圆钢，于980℃奥氏体化1 h水淬，切割成试片，然后进行620℃×0．5 h回火处理。采用透射电子显微镜（TEM）和三维原子探针分析技术（3DAP）详细研究了钢的淬火态组织和碳化物析出相。结果，钢的淬火态组织为上、下贝氏体和马氏体，回火后，主要析出相是三种合金碳化物：（1）θ-M3 C型渗碳体，其大小为50 nm以下，主要分布在板条铁素体晶界；（2）铁素体板条内析出的针形ε-M2 C型碳化物，宽度小于20 nm，长度小于200 nm，分布较均匀；（3）铁素体板条内析出的约2 nm大小的高密度MC型碳化物。此外，论述了三种析出相对材料性能可能的影响。%A bar steel 100 mm in diameter,made of high-strength low-alloy bainitic steel,was austenitized at 980 ℃ for 1 h and quenched in water,cut into test pieces,and then tempered at 620 ℃for 30 min.As-quenched microstructure and various precipitated carbides in the steel were investigated in detail by using TEM and three-dimensional atom probe (3 DAP).The results indicate that as-quenched microstructure of the steel consists of upper beinite,lower beinite and martensite;and that there are three categories of alloy carbide were observed in the steel tempered:(1 )θ-M3 C cementite as size as less than 50 nm,essentially lies in lath ferrite boundaries;(2)acicularε-M2 C carbide,which precipitates in lath ferrite of the steel,is as size as less than 20 nm wide by less than 200 nm long,and exhibits uniform distribution;(3 )highly dense MC carbide as size as about 2 nm.Beyond this, the possible effect of the three types of precipitates on mechanical properties of the steel was discussed.
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