动态应变时效对18MND5低合金钢材料抗拉性能的影响分析及服役安全评价

Safety Evolution and Investigation of Dynamic Strain Aging Effect on Tensile Property of 18MND5 Low Alloy Steel Used in Nuclear Island Equipment

18MND5低合金钢凭借其良好的机械性能,被广泛应用于压水堆核电站核岛设备上。针对核岛设备用国产18MND5低合金钢钢板,在性能热处理状态和性能热处理+模拟消应力热处理两种状态下,进行了室温及100、125、150、175、200、250、300、350℃拉伸试验。基于上述试验结果,分析了动态应变时效对不同热处理条件下18MND5低合金钢材料抗拉性能的影响。结果表明,在室温~350℃温度范围内,随着温度的升高,18MND5低合金钢材料的抗拉强度呈先下降后上升的特征,抗拉强度谷值出现在150~200℃,发生了动态应变时效。采用两种热循环制度模拟18MND5低合金钢材料的封头成形工艺,分析了热循环制度对材料抗拉性能的影响。结果表明,18MND5低合金钢材料150℃下的抗拉强度仍低于350℃下的抗拉强度,动态应变时效的影响仍存在;经历热循环后18MND5低合金钢材料的抗拉强度未低于原始材料性能态的抗拉强度。此外,根据RCC-M中设备设计用抗拉强度Su的计算公式,对18MND5低合金钢材料在抗拉强度低谷的服役安全性进行了评价。结果表明,在动态应变时效影响下,18MND5低合金钢材料产生的抗拉强度的谷值仍处于材料安全使用范围内。

18MND5 low alloy steel has excellent mechanical properties,so it is widely used in nuclear island equipment of PWR nuclear power plant.In this paper,the tensile tests of 18MND5 low alloy steel plate under heat treatment condition and heat treatment then simulated stress-relieving heat treatment condition were respectively carried out at room temperature and 100,125,150,175,200,250,300,350℃.Based on the tensile test results of room temperature to 350℃,the dynamic strain aging(DSA)effect and heat treatment conditions on tensile properties were analyzed.The results show that the tensile strength of this material firstly decreases and then increases under DSA effect range from room temperature to 350℃.Two kinds of thermal cycle systems were used to simulate the forming process of 18MND5 low alloy steel.The results indicate that after thermal cycle system the tensile strength of this material is almost equal to tensile properties of heat treatment condition.The DSA effect still exists in 18MND5 low alloy steel plate,and the tensile strength of this material at 150℃is still lower than the one at 350℃.In addition,the test results of this material under DSA effect were evaluated according to the formula of tensile strength S u in RCC-M.Under the DSA effect,the minimum value of the tensile strength is still within the safe range.