加氢反应器不锈钢堆焊熔合区氢剥离行为的分析

针对309L+347L双层不锈钢带极堆焊工艺,采用高温、高压釜试验方法进行了氢剥离试验研究,试验发现氢剥离裂纹萌生于紧靠熔合区硬化带的纯奥氏体晶界并沿平行于硬化带的奥氏体晶界扩展.结果表明,氢剥离的主要机制是H原子在硬化带与奥氏体不锈钢结合界面高度聚集,造成紧靠硬化带的纯奥氏体晶界脆化,在结合界面高剪应力的作用下,裂纹萌生和扩展.采用较小的焊接热输入,抑制309L堆焊层奥氏体晶粒过分长大并保证铁素体含量;采用合理的焊后热处理,减小硬化带厚度及控制加氢反应器停运的冷却速度是防止氢剥离的有效措施.

Analysis on hydrogen induced peeling behavior in fusion zone between base metal and austenitic stainless steel overlayer in hydro-processing reactors

Hydrogen induced peeling in the fusion zone between base metal and austenitic stainless steel overlayer is the main problem of hydro-processing reactors in practical operation. Focused on the widely applied 309L+347L austenitic stainless steel overlaying process,the simulation experiments in the high temperature autoclave indicated the peeling crack germinated at the pure austenitic grain boundaries close to the hardening zone (the microstructure in this region is very complex as a consequence of carbon migration during PWHT(post weld heat treatment) and incomplete mixing of melted base metal and stainless steel fillers) of fusion zone between base metal and austenitic stainless steel overlayers and propagated along the austenitic grain boundaries. Based on the experimental investigation,it is the embrittlement of austenitic grain boundaries induced by the hydrogen accumulation and the high residual shearing stress at the overlay interface that cause the hydrogen induced peeling. The experimental results showed that smaller heat input for 309L overlaying,appropriate PWHT and smaller cooling rate of hydroprocessing reactors are all helpful measurements to prevent hydrogen induced peeling.