10Cr12Ni3Mo2VN超超臨界機組用葉片鋼熱變形行為HOT DEFORMATION BEHAVIOR OF BLADES STEEL 10Cr12Ni3Mo2VN FOR ULTRA-SUPERCRITICAL UNITS

利用Gleeble-1500熱模擬實驗機對10Cr12Ni3Mo2VN鋼進行壓縮實驗, 研究了變形溫度為 850~1200 ℃, 應變速率為 0.01~10 s-1條件下的熱變形行為. 結(jié)果表明, 隨變形溫度升高和應變速率降低, 再結(jié)晶晶粒尺寸增加. 變形溫度1200 ℃, 經(jīng)60%壓縮變形后, 應變速率較高時再結(jié)晶晶粒呈等軸狀, 應變速率較低時出現(xiàn)混晶. 通過傳統(tǒng)直線擬合方法和 Levenberg-Marquardt 算法分別建立了熱變形雙曲正弦本構(gòu)方程, 采用Levenberg-Marquardt算法可以一次性求解所有材料參數(shù), 求解步驟簡單, 結(jié)果可信, Levenberg-Marquardt算法所得本構(gòu)方程預測精度較傳統(tǒng)方法更高. 利用加工硬化率-應力(θ-σ)曲線, 通過二次求導, 準確測得臨界應變, 并建立了臨界應變、峰值應變與 Zener-Hollomon 因子(Z因子)之間的關(guān)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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