反应堆压力容器用SA508Gr.4N钢的热变形行为

利用Gleeble-1500D热模拟试验机,在温度为1050~1250℃、应变速率为0.001~0.1s-1、真应变量0.16的条件下,研究和分析SA508Gr.4N钢高温塑性变形及动态再结晶行为。结果表明:SA508Gr.4N钢的高温真应力-应变曲线主要以动态再结晶为特征,峰值应力随变形温度的降低或应变速率的升高而增加,属于温度和应变速率敏感材料;在真应力-应变曲线的基础上,建立材料热变形本构方程,较好地表征了材料高温流变特征,其热激活能为383.862kJ/mol;其硬化率-应力(θ-σ)曲线均呈现拐点且-dθ/dσ-σ曲线出现极小值;临界应变随应变速率的增大与变形温度的降低而增加,且临界应变(εc)与峰值应变(εp)之间具有一定相关性,即εc/εp=0.517;临界应变与Z参数之间的函数关系为εc=8.57×10-4 Z0.148。

Hot Deformation Behavior of SA508Gr.4N Steel for Reactor Pressure Vessels

The high-temperature plastic deformation and dynamic recrystallization behavior of SA508Gr.4N steel were investigated through hot deformation tests in a Gleeble1500D thermal mechanical simulator.The compression tests were performed in the temperature range of 1050-1250C and the strain rate range of 0.001-0.1s-1 with true strain of 0.16.The results show that from the high-temperature true stress-strain curves of the SA508Gr.4N steel,the main feature is dynamic recrystallization,and the peak stress increases with the decrease of deformation temperature or the increase of strain rate,indicating the experimental steel is temperature and strain rate sensitive material.The constitutive equation for SA508Gr.4N steel is established on the basis of the true stress-strain curves,and exhibits the characteristics of the high-temperature flow behavior quite well,while the activation energy of the steel is determined to be 383.862kJ/mol.Furthermore,an inflection point is found in the θ-σ curve,while the-dθ/dσ-σ curve shows a minimum value.The critical strain increases with increasing strain rate and decreasing deformation temperature.A linear relationship between critical strain (εc) and peak strain (εp) is found and could be expressed as εc/εp=0.517.The predicted model of critical strain could be described as εc =8.57 × 10-4Z0.148.