热老化对20Cr25NiNb不锈钢冲击韧性的影响研究

Effect of Thermal Aging on Impact Toughness of 20Cr25NiNb Stainless Steel

针对长时间高温下合金力学性能退化问题,开展超临界气冷堆候选包壳材料的热老化研究。对改进型气冷堆用原型20Cr25NiNb不锈钢和添加不同元素的改进型合金,开展650℃下3000 h热老化试验。组织和性能结果表明,所有合金的冲击吸收能量(KV_(2))均随热老化进行而下降。这种塑性降低与高温下第二相演化密切相关。沿晶界先后析出M_(23)C_(6)和G相导致原型合金冲击韧性先下降再缓慢上升。添加W和Mo元素后,沿晶界析出Laves和σ相,引起KV_(2)下降更快;B元素可细化晶界σ相,使得冲击韧性下降幅度小于不含B元素。加入Al元素后,合金基体中析出大量Laves和NiAl相,同时晶界σ相快速粗化,导致材料脆化严重。

In view of the degradation of alloy mechanical properties under prolonged high temperature exposure,the thermal aging study of candidate cladding materials for supercritical gascooled reactor was carried out.The prototype 20Cr25NiNb stainless steel for advanced gas-cooled reactor (AGR) reactor and improved alloys with different elements were subjected to thermal aging test at 650°C for 3000 h.The results of microstructure and properties showed that the impac absorbed energy (KV_2) of all alloys decreased as the thermal aging proceeded.This plasticity decrease was closely related to the evolution of second phases at high temperature.The precipitation of M_(23)C_(6) and G phases along grain boundaries led to a decrease and then a slow increase in the impact toughness of the prototype alloy.The addition of W and Mo elements brought the precipitation of Laves andσphases at grain boundaries,causing a faster decrease in KV_2;B elemen refinedσphase and made the impact toughness decrease less than that of the alloy without B.After adding Al,a large number of Laves and NiAl phases precipitated in the matrix,while theσphase a grain boundaries coarsened rapidly,leading to severe material embrittlement.