New sights on intergranular corrosion resistance mechanism of type 304 austenitic stainless steel by adjusting carbon contents
Liming Mou, Tiantian Bian, Shaohua Zhang, Baosheng Liu, Pengpeng Wu, Jinling Zhang, Yanchong Yu, Yuezhong Zhang, Xinchao Wang
Abstract
IGC mechanisms and/or corresponding IGC resistance mechanisms of 304 and 304L ASSs by adjusting carbon contents were systematically investigated by microstructure characterization, electrochemical and IGC tests. The results reveal that a maximum IGC degree of 304 ASS is observed at an aging temperature of 660 °C for 10 h based on a continuous precipitation of Cr-carbides along grain boundaries. The roles of precipitated Cr-carbides are concluded as two aspects, involving an occurrence of Cr-depleted regions and a destruction of film stability along grain boundaries. However, this IGC behavior is not linearly relevant with precipitation behavior of Cr-carbides, and a co-segregation mechanism of Cr and C atoms before a nucleation of carbides plays a decisive role in this current study. In comparison, 304L ASS (by adjusting carbon contents) exhibits a superior IGC resistance after a long-term aging treatment, which is mainly attributed to simultaneously restricting a precipitation of Cr-carbides and ensuring a continuous supply of Cr atoms toward Cr-depleted regions.