70Cr3Mo钢支承辊热处理断裂的原因分析

对于尺寸较大的高碳合金钢轴(辊)类件而言,外圆表层在快速加热喷冷淬火时,一定深度的表层部分会因为相变而产生体积膨胀,从而使心部承受拉应力。加热温度越高、冷却越激烈,则淬硬层越深,心部拉应力就越大。但喷淬过程中心部温度尚处于较高状态,可以通过应变使这种应力得到协调或松弛,因而一般不会造成开裂。心部的这种开裂常常发生在热处理后的放置过程中,即所谓"置裂"。本文运用常规金相分析的方法,确定70Cr3Mo钢支承辊的断裂属于置裂并具体指出该支承辊发生置裂的主要原因是:最后热处理加热温度偏高,导致淬层马氏体粗大、残余奥氏体增多。

Modeling Flow Stress of 70Cr3Mo Steel Used for Back-Up Roll During Hot Deformation Considering Strain Compensation

A constitutive model incorporating the influence of strain developed based on the Arrhenius equation by considering the variation of material constants as a fifth polynomial function of strain is presented. Materials con- stants are fit to data from hot compression tests of 70Cr3Mo steel used for back-up roll at the temperatures from 1 173 to 1 473 K and strain rates from 0.01 to 10 s ~ by using a Gleeble-1500D thermo-mechanieal simulator. The de- veloped constitutive model is then used to predict the flow stress under all the tested conditions. The statistical pa- rameters of correlation coefficient and average absolute relative error are used to analyze the predictable efficiency and the values are 0. 997 and 3. 64%, respectively. The results show a good agreement between experimental stress and predicted stress.

70Cr3Mo钢热变形行为及加工图

采用Gleeble-1500热模拟实验机研究了70Cr3Mo钢在不同变形条件下的高温压缩热变形行为，变形温度850-1150 ℃, 应变速率0.01-10 s-1。依据实验数据，分析了应力、应变间的关系，建立了流变应力本构方程和加工图。由应力、应变曲线可以得出：变形温度一定时，应力峰值随着应变速率的增加而增加；应变速率一定时，应力峰值随变形温度的增加而降低。计算分析了真应变为0.5的加工图，结果表明，70Cr3Mo钢在热压缩过程中存在两个失稳区：（1）变形温度为850-940 ℃、应变速率为0.01-1.6 s-1；（2）变形温度为975-1150 ℃、应变速率为1-10 s-1。并获得了最佳的工艺参数：变形温度为1000-1150 ℃、应变速率为0.01-0.36 s-1。