中文摘要：

将一种直径为100mm的高强度低合金贝氏体圆钢，于980（℃奥氏体化1h水淬，切割成试片，然后进行620℃×0．5h回火处理。采用透射电子显微镜（TEM）和三维原予探针分析技术（3DAP）详细研究了铜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-M3C型渗碳体，其大小为50nm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-M2C型碳化物，宽度小于20nm，长度小于200m，分布较均匀；（3）铁素体板条内析出的约2nm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。

英文摘要：

A bar steel 100 mm in diameter, made of high-strength low-alloy bainitie steel, was austenitized at 980 ℃ for 1 h and quenched in water, cut into test pieces, and then tempered at 620 ℃ for 30 rain. As-quenched mierostrueture and various precipitated carbides in the steel were investigated in detail by using TEM and threedimensional atom probe （3DAP）. 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 eementite as size as less than 50 nm, essentially lies in lath ferrite boundaries ; （2） aeicular ε-M2C 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 era-bide 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.