10Cr12Ni3Mo2VN超超临界机组用叶片钢热变形行为HOT DEFORMATION BEHAVIOR OF BLADES STEEL 10Cr12Ni3Mo2VN FOR ULTRA-SUPERCRITICAL UNITS

利用Gleeble-1500热模拟实验机对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 Levenberg-Marquardt 算法分别建立了热变形双曲正弦本构方程, 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, Levenberg-Marquardt算法所得本构方程预测精度较传统方法更高. 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 do 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 thermal-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 appeared after compressed 60% at 1200 ℃ with high and low strain rates respectively. A new method of establishing the hot deformation hyperbolic sine constitutive equation by Levenberg-Marquardt algorithm was proposed. Parameters of the constitutive equations established by traditional linear fitting and Levenberg-Marquardt algorithm have a similar value, and both of the constitutive equations 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 recrystallization initiation were determined from the work hardening rate-strain curves and a model related to Zener-Hollomon parameter for predicting critical and peak strain under different deformation paraments was established.

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