New sights on intergranular corrosion resistance mechanism of type 304 austenitic stainless steel by adjusting carbon contents

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.