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本文研究了国产7021马氏体时效钢(18Ni)焊接接头在3.5%NaCl 水溶液中的应力腐蚀行为。结果表明,在峰值温度为1280℃左右的热影响区中焊接热循环并不影响断裂韧性,但严重降低对应力腐蚀的抗力,使该区成为焊接接头的薄弱环节。其原因可能与焊接,过程钛、钼等合金元素在晶界的偏聚和晶粒长大有关。焊后经820℃×1h 固溶处理,临界应力腐蚀强度因子K_(ISCC)得到一定提高,双重固溶处理可进一步改善,而三次900℃×20min 水冷处理效果最显著,晶粒明显细化,应力腐蚀裂纹由沿晶破坏转变为穿晶塑性破坏。但上述固溶处理对焊缝的作用与热影响区不同。一次或二次固溶有使焊缝K_(ISCC)降低的趋势,只有多次固溶可保持较好的水平并能与热影响区性能相匹配。
In this paper, the stress corrosion behavior of domestic 7021 martensitic steel (18Ni) welded joint in 3.5% NaCl aqueous solution was studied. The results show that the welding heat cycle does not affect the fracture toughness in the heat affected zone with the peak temperature of 1280 ℃, but seriously reduces the resistance to stress corrosion and makes the zone a weak link in welded joints. The reason may be the welding, the process of titanium, molybdenum and other alloying elements in the grain boundary segregation and grain growth related. After heat treatment at 820 ℃ for 1h, the critical stress corrosion strength K_ (ISCC) is increased, and the double solution treatment can be further improved. However, the effect of three times 900 ℃ × 20min water cooling is the most obvious, the grains are obviously refined, Stress corrosion cracking transforms from the destruction of intergranular to transgranular ductile damage. However, the effect of the solution treatment on the weld is different from that of the HAZ. The primary or secondary solution has a tendency to reduce the weld K_ (ISCC), and only the multiple solution can maintain a good level and match with the performance of the heat-affected zone.