两相区正火和回火对微合金化钢力学性能与显微组织的影响

Effect of intercritical normalizing and tempering on mechanical properties and microstructure of microalloyed steel

通过光学显微镜（OM）、扫描电镜（SEM）和透射电镜（TEM）等分析手段,对不同热处理工艺下微合金化钢的显微组织与力学性能进行了研究,并分析了相应的作用机理。结果表明,直接正火态试验用钢的组织为针状铁素体,一次正火态和二次正火态试验用钢的组织分别多边形铁素体＋针状铁素体和板条状铁素体＋针状铁素体,回火处理后试验用钢的组织形态变化不大,在铁素体界面处析出了较多的M23C6型碳化物,且二次正火＋回火态试样中M23C6型碳化物的平均尺寸最小、数量密度最大;虽然两相区正火能够降低试验用钢的屈强比,但是两相区正火不一定会提高试验用钢的强塑性和冲击吸收能量,而只有二次正火才能有效提高试验用钢的强塑性和冲击吸收能量。

Microstructure and mechanical properties of microalloyed steel under different heat treatment processes were studied by means of optical microscope（ OM）,scanning electron microscope（ SEM） and transmission electron microscope（ TEM）,and the corresponding mechanism was analyzed. The results show that microstructure of direct normalized tested steels is acicular ferrite,and microstructure of step normalizing ＋ tempering and intercritical normalizing are polygonal ferrite ＋ acicular ferrite and lath ferrite ＋ acicular ferrite,microstructure of the tested steel changes little after tempering,and many M23C6 carbides are precipitated at ferrite interface,in which the tested steels with intercritical normalizing has the smallest average size and largest number density of M23C6 carbides. Although the normalizing in two-phase region can reduce the yield strength ratio of the tested steels,but not necessarily improve the strength plasticity and impact absorbed energy,while only intercritical normalizing can effectively improve the strength,plasticity and impact absorbed energy of the tested steels.