Effect of tempering temperature and time on the corrosion behaviour of 304 and 316 austenitic stainless steels in oxalic acid

Abstract

The effect of different tempering temperatures and heat treatment times on the corrosion resistance of austenitic stainless steels in oxalic acid was studied in this work using conventional weight loss and electrochemical measurements. Typical 304 and 316 stainless steel samples were tempered at 150°C, 250°C and 350°C after being austenized at 1050°C for 10 minutes. These samples were then immersed in 1.0M oxalic acid and their weight losses were measured at every five days for 30 days. The results show that corrosion of both types of ASS samples increased with an increase in tempering temperature and time and this was due to the precipitation of chromium carbides at the grain boundaries of these metals. Electrochemical results also confirm that the 304 ASS is more susceptible to corrosion than 316 ASS in this medium. This is attributed to the molybdenum in the composition of the latter. The metallographic images of these samples showed non-uniform distribution of precipitated chromium carbides at the grain boundaries of these metals and unevenly distributed carbides and retained austenite phases which cause galvanic effects in the medium.