热处理对42CrMoVRE钢强韧化机制的影响

Effect of heat treatment on strengthening and toughening mechanism of 42CrMoVRE steel

采用扫描电镜、拉伸和冲击试验机等研究了42CrMoVRE钢经不同工艺热处理后的显微组织、力学性能与冲击韧性。结果表明:油淬+高温回火后实验钢的组织为回火索氏体,正火+油淬+高温回火后的显微组织为回火索氏体+少量针状铁素体,而正火+油淬+低温回火后的组织为回火马氏体;淬火前的正火处理可有效地细化铁素体晶粒和碳化物,进而提高细晶强化和析出强化对强度的贡献;较低的回火温度显著提高了实验钢的强度,其主要强化机制是细晶强化和位错强化,但严重牺牲了冲击韧性;油淬+高温回火后实验钢中的多边形铁素体较好地抑制了裂纹的扩展,冲击韧性较高,正火+油淬+高温回火后实验钢的针状铁素体具有较小的裂纹扩展阻力,导致冲击韧性降低,正火+油淬+低温回火后实验钢中的回火马氏体具有较高的残余应力,导致裂纹容易萌生和扩展,所以冲击韧性最低。

Microstructure,mechanical properties and impact toughness of 42CrMoVRE steel after heat treatment by different processes were studied by means of scanning electron microscopy,tensile and impact testing machines.The results show that the microstructure of the experimental steel after oil quenching+high temperature tempering is tempered sorbite,the microstructure after normalizing+oil quenching+high temperature tempering is tempered sorbite+a small amount of acicular ferrite,and the microstructure after normalizing+oil quenching+low temperature tempering is tempered martensite.The normalizing treatment before quenching can effectively refine the ferrite grains and carbides,thus improving the contribution of fine grain strengthening and precipitation strengthening to strength.The lower tempering temperature significantly increases the strength of the experimental steel,and the main strengthening mechanism is fine grain strengthening and dislocation strengthening,but seriously reduces the impact toughness.The polygonal ferrite in the experimental steel after oil quenching+high temperature tempering can better inhibit the crack growth,and the impact toughness is high.The acicular ferrite in the experimental steel after normalizing+oil quenching+high temperature tempering has a small crack propagation resistance,resulting in a reduction in the impact toughness.The tempered martensite in the experimental steel after normalizing+oil quenching+low temperature tempering has a high residual stress,resulting in easy crack initiation and propagation,so the impact toughness is the lowest.