ASSESSMENT OF THE CORROSION BEHAVIOR OF SS 304L IN NITRIC-ACID ENVIRONMENTS - AN ALTERNATIVE APPROACH

Stainless steel (SS) 304L is widely used as a construction material in industries requiring corrosion resistance in nitric acid environments . Representative samples from 20 heats of SS 304L products were subjec ted to a testing procedure consisting of testing as per the rapid scre ening test (Practice A) and the Huey test (Practice C) of ASTM A 262, Practices for Detecting Susceptibility to Intergranular Attack in Aust enitic Stainless Steels. The presensitization heat treatment of 677 de grees C for 1 h and the modified heat treatment of 677 degrees C for 2 0 min were used for characterizing the microstructures in Practice A, whereas only the former presensitization heat treatment was used for P ractice C. The percent duality after the two heat treatments has been correlated with the corrosion rate obtained in Practice C. A chemical composition based parameter, Cr effective = [% Cr - 0.18 (%Ni) - 100 ( %C)], was calculated for all the heats and correlated with the percent duality after the two heat treatments as well as the corrosion rate i n Practice C. It is observed that the SS 304L heats with Cr effective >14.0 and <50% grain boundary coverage after the modified heat treatme nt (Practice A) show low corrosion rates in Practice C. This eliminate s the need for carrying out the lengthy Practice C of ASTM. Examples o f heats of SS 304L are given to show that the modified presensitizatio n heat treatment has better efficiency in screening materials and also exhibited better correlation with the results obtained in the Practic e C. Guide rules for selection of SS 304L heats for nitric acid servic e are also suggested.