EPMA Test of Nitrogen in Stainless Steel Heat Exchanger Tube with Expansion Crack Failure

Cracks appeared in the expansion process of a 2205 duplex stainless steel heat exchanger tube. The failure causes of the heat exchanger tube were analyzed by electron probe micro analyzer (EPMA). The results show that the enrichment of local strong austenite forming element nitrogen led to abnormal microstructure distribution here. The single-phase zone of coarse austenite was formed at the position where the content of two-phase should be similar, and its plasticity and strength were worse than the normal microstructure. In the process of machining, microcracks initiated and eventually led to the expansion crack of the heat exchanger tube.