10Cr12Ni3Mo2VN超超临界机组用叶片钢的热变形行为

HOT DEFORMATION BEHAVIOR OF BLADES STEEL 10Cr12Ni3Mo2VN FOR ULTRASUPERCRITICAL UNITS

利用Gleeble-1500热模拟试验机对10Cr12Ni3Mo2VN钢进行压缩实验,研究了变形温度为850～1200℃,应变速率为0.01～10 s-1条件下的热变形行为.结果表明,随变形温度升高和应变速率降低,再结晶晶粒尺寸增加.变形温度1200℃,经60%压缩变形后,应变速率较高时再结晶晶粒呈等轴状,应变速率较低时出现混晶.通过传统直线拟合方法和LevenbergMarquardt算法分别建立了热变形双曲正弦本构方程,2种方法建立的本构方程均具有较高预测精度.采用Levenberg-Marquardt算法可以一次性求解所有材料参数,求解步骤简单,结果可信.利用加工硬化率-应力（θ-σ）曲线,通过二次求导,准确测得临界应变,并建立了临界应变、峰值应变与Zener-Hollomon因子（Z因子）之间的关系方程.

10Cr12Ni3Mo2VN steel is mainly made by forging and usually used to make last stage blades of ultra-supercritical unit, demanding strict standards of microstructure property because of its hard service environment, so it is necessary to conduct deep research on its hot deformation behavior. The hot deformation behavior of 10Cr12Ni3Mo2VN steel was investigated through high temperature compression tests on the Gleeble-1500 ther- mal-mechanical simulator at 850-1200 ℃ and strain rate range of 0.01-10 s^-1. The results show that dynamic recrystallization becomes more prone to happen and recrystallized grain size increases with increasing temperature and decreasing strain rate. Isometric crystal and mixed structure appear after compressed 60% at 1200 ℃ with high and low strain rate respectively. A new method of establishing the hot deformation hyperbolic sine constitutive equation by Levenberg-Marquardt algorithm is proposed. Parameters of the constitutive equations established by traditional linear fitting and Levenberg-Marquardt algorithm have a similar value, and both of the constitutive equa- tions have a high prediction precision, so the method of establishing constitutive equation by Levenberg-Marquardt algorithm is credible. However, Levenberg-Marquardt algorithm can get all parameters at the same time with fewer and simpler steps compared to traditional linear fitting. In addition, the values of critical strain for dynamic recrys- tallization initiation are determined from the work hardening rate-strain curves and a model related to Zener-Hollo- mon parameter for predicting critical and peak strain under different deformation paraments is established.