一种高强度低合金贝氏体钢高温回火析出的极细MC相

Ultra-Fine MC-Type Precipitates Formed During High Tempering in a High-Strength Low-Alloy Bainitic Steel

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(3:DAP)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-M_3C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-M_2C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 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.