回火温度对铁基合金组织与力学性能的影响

Effect of tempering temperature on microstructure and mechanical properties of iron-base alloy

将真空烧结的铁基合金奥氏体化、油淬后，在600~700℃温度下进行回火处理，保温1 h，空冷。测试回火后合金的硬度和冲击韧性，并用金相显微镜、X 射线衍射（XRD）、扫描电镜（SEM）观察和分析合金的组织、结构与断口形貌，研究回火温度对铁基合金组织与力学性能的影响。结果表明：随回火温度升高，第二相碳化物粒子M23C6的含量（质量分数）基本保持不变，约为3.5%；碳化物M6C的数量大幅减少，平均尺寸明显减小，碳化物M6C的第二相强化效果降低，硬度下降，同时基体组织软化，冲击吸收功增大。回火温度为675℃时，铁基合金保持较高的硬度40 HRC，冲击韧性较回火前提高11%。回火处理后的铁基合金断口形貌为典型的沿晶断裂。

Vacuum sintering iron-base alloy was tempered in the temperature range of 600~700℃for 1 h following by air cooling after austenitizing and oil quenching. Hardness and impact toughness were tested at different tempering temperature. Microstructure and fracture morphology examination were conducted by optical microscope, X-ray diffraction, scanning electron microscope and energy disperse spectroscopy. The results show that the mass fraction of the second phase carbide M23C6 remains fairly static about 3.5%. The amount of carbide particles M6C decreases sharply and the average size of M6C refines obviously. The effects of second phase strengthening of carbide particles M6C turn deteriorated, a decreasing on hardness occurs with increasing the tempering temperature, while the matrix structure is softened, an increasing on impact toughness also happens with increasing the tempering temperature. When the tempering temperature is 675℃, the iron-base alloy presents hardness of 40 HRC, and impact toughness is increased by 11%. The fracture surface of the iron-base alloy is a typical intercrystalline fracture.