不同温度回火低合金钢缺口拉伸性能的预测

Notch Tensile Properties Prediction of Low-alloy Steel Processed by Different Tempering Temperatures

使用电子背散射衍射技术和扫描电镜观察在不同温度回火的35CrMo低合金钢的微观组织和应力集中系数不同的缺口试样拉伸断裂形貌,研究了回火温度对其拉伸性能、损伤机制和力学性能的影响。结果表明:淬火态和回火温度为150~200℃的35CrMo钢,其显微组织均为回火板条状马氏体;在400℃回火的试样其组织为均匀的屈氏体组织;缺口试样的断裂形式均为韧性和脆性混合断裂。两种应力集中系数(K_(t)=3,5)的试样其缺口抗拉强度随回火温度变化的趋势相同,随着回火温度的升高缺口抗拉强度先升高后降低。K_(t)=3回火温度为150℃的试样其抗拉强度最高为2626 MPa;K_(t)=5回火温度为200℃的试样其抗拉强最高为2450 MPa。缺口的敏感度都>1,即在不同温度回火后都发生缺口强化效应,且缺口敏感性随着回火温度的升高有下降的趋势。随着应力集中系数的增大在不同温度回火的试样其缺口强化效果都呈现出先上升后下降的趋势,在400℃回火的缺口试样其强化效率最显著。基于硬度与缺口抗拉强度的关系提出一种快速预测缺口抗拉强度的方法,预测结果的误差<8%。

The microstructure and notch tensile fracture morphologies at different stress concentration factors of the low alloy steel 35CrMo for the head cover bolts of the pump turbine of a storage power station were investigated by electron backscatter diffraction microscopy and scanning electron microscopy.The effects of tempering temperature on the relationship between tensile properties,damage mechanism and mechanical properties of 35CrMo steel were studied.The results show that the microstructures of tempered state at 150~200oC and quenched state are composed of lath martensite.After tempering at 400oC,the microstructure of tempered troostite is more uniform.The final fracture of the notched specimens is a mixture of ductile and brittle fracture.At the two stress concentration factors(K_(t)=3,5),the notch tensile strength has the same changing trend with the tempering temperature.With the tempering temperature increasing,the notch tensile strength first increases and then decreases.For K_(t)=3,the highest tensile strength is 2626 MPa at tempering temperature of 150oC;when K_(t)=5,the highest tensile strength is 2450 MPa at tempering temperature of 200oC.Notch sensitivity ratio(NSR)is greater than 1,that is,notch strengthening effect occurs after different tempering temperatures,and notch sensitivity tends to decrease with the increase of tempering temperature.With the increase of stress concentration factor,the notch strengthening effect of specimens treated at different tempering temperatures shows an increasing trend first and then a decreasing trend,and the notch strengthening efficiency was the most obvious when tempering at 400oC.Finally,based on the relationship between hardness and notch tensile strength,a fast prediction method of notch tensile strength was proposed,and the prediction error was less than 8%.