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在DIL805膨胀仪上测量了X70管线钢在连续冷却过程中的热膨胀曲线。根据试验结果,分析比较了两种奥氏体-铁素体相变开始温度模型,并通过对JMAK方程采用逆向回归法确定了铁素体相变分数的关键性参数,从而确定了连续冷却过程中的相变动力学。结果表明,不同冷却速率下的最佳n值和k值可通过JKMA公式逆向回归得出,模型分别采用时间指数n为0.5、1、1.5、1-0.5X2的4种取值方法计算铁素体相变动力学曲线,通过与试验数据的对比发现,用相变体积分数X的函数表征n值的方法计算精度更高,与试验结果吻合更好。模型Ⅰ由于对铁素体体积形核功ΔGV的取值有局限性,使得模型在大冷却速率下的预测结果会出现一定偏差,而模型Ⅱ仅涉及两个参数,适用性强,对于X70管线钢铁素体相变开始温度与冷却速率变化趋势为:Ts=Ae3-39.1440φ0.4020。
The thermal expansion curve of X70 pipeline steel during continuous cooling was measured on DIL805 dilatometer. According to the experimental results, two kinds of austenite-ferrite transformation start-up temperature models are analyzed and compared, and the key parameters of the ferrite transformation fraction are determined by using the reverse regression method on the JMAK equation, so as to determine the continuous cooling process In the phase transition dynamics. The results show that the optimum values of n and k at different cooling rates can be obtained by inverse regression of the JKMA formula. The model uses four kinds of values of time index n of 0.5,1,1.5,1-0.5X2 respectively to calculate the ferrite Compared with the experimental data, it is found that the method of characterizing the n value by the function of the phase transition volume fraction X is more accurate and in good agreement with the experimental results. Because of the limitation of the ΔGV value of the ferrite bulk nucleation power, the model Ⅰ has a certain deviation in predicting the cooling rate of the model. However, the model Ⅱ only involves two parameters and has strong applicability. For the X70 pipeline The trend of initial temperature and cooling rate of ferrite transformation is: Ts = Ae3-39.1440φ0.4020.