Corrosion failure investigation of seamless stainless steel tube used in die-casting machine of Mg alloy

The examination of a corrosion failure type 316 austenitic stainless steel tube, installed in one of the Mg alloy die-casting machines, is described. The metallographic examination manifested a large amount of sigma phase was related to the corrosion failure. A comparison is made with samples taken from the far end of corrosion pit of the failure tube, which operated at a same process. No precipitates were found in the contrastive samples. The results illustrated that the sigma phases were not formed during the operation process instead of the production process of the steel tube. The results are discussed in terms of the contribution of sigma phase to the corrosion performance. In addition, the corrosion mechanism of AISI 316 stainless steel with sigma phase was also discussed in details. In high temperature supercritical atmosphere environment, it exhibited an obvious intergranular corrosion and pronounced oxide spallation.