【摘要】 研究了高温形变热处理对60Si2Mn弹簧钢室温至-196℃的单轴拉伸变形特性,断裂韧性、解理断裂应力,疲劳裂纹扩展速率和门坎值的影响。结果表明:和普通热处理相比,一定形变量的高温形变热处理,可以提高60Si2Mn钢室温至-196℃的断裂塑性,断裂韧性、解理断裂应力,并降低解理断裂温度和疲劳裂纹扩展速率,而提高其门坎值。试验证明:解理断裂应力是一个材料常数,它和断裂韧性、裂纹尖端塑性区的大小以及材料的显微组织之间有一定关系;此外,它可以根据其它力学性能数据或碳化物粒子的直径进行计算。对淬火和回火状态的组织形态及拉力和解理断口的金相观察表明:高温形变热处理对60Si2Mn钢断裂特性的这种良好影响,是和断口中韧窝区扩大,准解理断裂区减少相一致;断口形貌的这种变化,是高温形变热处理使钢的淬火组织中片状马氏体明显细化,板条马氏体量增多,从而使回火状态的碳化物变细,分布均匀的结果。分别用所测得的断裂韧性和疲劳裂纹扩展速率值,计算了不同处理工艺后材料的使用应力和疲劳寿命的变化,其结果与高温形变热处理提高电振机板簧使用寿命的趋势一致。更多还原

【Abstract】 Effect of HTMT on the uniaxial tensile deformation characteristics at +20～ -196℃, fracture toughness, the cleavage fracture stress, fatiguecrack propagation rate as well as fatigue threshold stress intensity of 60Si2Mn spring setel has been investigated. The results showed that in comparison with conventional heat treatment, HTMT of 60Si2Mn spring steel will increase its fracture plastic property at +20～-196℃, fracture toughness, cleavage fracture stress and reduce cleavage fracture temperature and fatigue-crack propagation rate, whereas raise fatigue threshold stress intensity. The tests proved that cleavage fracture stress is a material constant and it can be related to the fracture toughness, the size of plastic zone ahead of the crack tip and the microstructure of materials, besides, it can be calculated by using the values of other mechanical properties or the diameter of carbide particles. Metallographic observation of the structures and the fracture surfaces of uniaxial tensile and cleavage fracture specimens denoted that the beneficial effect of the HTMT coincident with the enlargement of dimple zone and the dimination of the quasi-cleavage zone on the fracture surface, while the change in fracture mode is due to refinement of the plate martensite and the increase in lath martensite content in the quenched structure of the HTMT steel, so that the carbides in the tempered condition become fine and finely dispersed. Using the measured fracture toughness and fatigue crack propagation rate respectively, the working stress and fatigue life of the flat spring after different heat treatment processes were calculated. The calculated results agree with the experimental results of the service life of the flat spring used in the electro-magnetieal vibration machine.更多还原