The grain size of the austenitic stainless steel affects the rate of intergranular attack at high temperatures. While the effect of grain size has been studied for 18-8 chromium-nickel austenitic steels, little work has been done on chromium-nickel-manganese austenitic steels. It is the purpose of this investigation to correlate intergranular attack with grain size in these steels.
A commercially available alloy (AISI Type 201) was selected for study. Effect of four different grain sizes (ASTM Grain Size Numbers 1, 2, 3 and 5) at four different sensitization times and four temperatures was studied. Results obtained in terms of weight loss in the boiling nitric acid test and through photomicrography were used to correlate intergranular attack with grain size.
Best resistance to corrosion was obtained at a sensitization temperature of 800 F (426 C) for all grain sizes. At elevated temperatures [1000 and 1200 F (537 and 649 C)] corrosion rate increased with increasing sensitization time. Upon comparison of sensitization behavior at 1400 F (760 C) for all grain sizes it was found that exposure for 48 hours produced less severe corrosive attack than did the 16-hr exposure. This was explained in terms of increase in size of carbide particles.
