GCr15轴承钢在不同加热速率下的奥氏体转变研究

加热速率对GCr15轴承钢铸坯表面组织有较大影响。利用DIL805A热膨胀仪进行热模拟试验,通过分析GCr15轴承钢在连续加热过程中的热膨胀曲线,研究了不同加热速率下的奥氏体转变过程,分析了加热温度对奥氏体转变温度和奥氏体转变量的影响,分析了不同加热速率下奥氏体转变规律和大断面铸坯表面组织。结果表明:GCr15轴承钢中珠光体转变为奥氏体,温度范围约为760~810 ℃;(Fe,Cr)₃C_Ⅱ向奥氏体中的溶解,温度范围约为810~1 100 ℃;奥氏体的成分均匀化温度大于1 100 ℃。若GCr15大断面铸坯表面过热度大,相变后晶粒粗大,相对于内部组织其表面的耐磨性和抗疲劳性下降,且铸坯表面奥氏体浓度均匀性差,后续液析碳化物溶解过程受阻碍,碳化物溶解浓度不均匀,表面的组织性能受到影响。根据J-M-A方程,计算了模型参数,GCr15轴承钢激活能Q约为7.156×10⁵ J/mol,n=0.52,k₀=75。

Study on austenite transformation of GCr15 bearing steel under different heating rates

The heating rate has a great influence on the surface structure of GCr15 bearing steel billet. Thermal simulation experiments were carried out using DIL805A thermal dilatometer. By analyzing the thermal expansion curve of GCr15 bearing steel during continuous heating, the austenite transformation process under different heating rates was studied. The effects of heating temperature on austenite transformation temperature and austenite transformation amount were analyzed, and the austenite transformation law and surface structure of large section slab under different heating rates were analyzed. The results show that the temperature range for the transformation of pearlite to austenite of GCr15 steel is about 760-810 ℃. (Fe,Cr)₃C_Ⅱdissolves into austenite at a temperature range of about 810-1 100 ℃. The composition homogenization temperature of austenite is higher than 1 100 ℃. The large section slab of GCr15 has coarse grains after phase transformation under large superheat. Compared with the internal structure, the wear resistance and fatigue resistance of the surface were reduced, and the uniformity of austenite concentration on the slab surface is poor. The subsequent liquid precipitation carbide dissolution process is hindered, the carbide dissolution concentration is uneven, and the microstructure and properties of the surface are affected. According to J-M-A equation, the activation energy Q of GCr15 steel is about 7.156×105 J/mol, n=0.52, k₀=75.