Studies on the Oxidation and Spalling Resistance of Austenitic Stainless Steels

Abstract

Studies were made on austenitic stainless steel types AISI 304, 310, 316 and 321, to determine their, resistance to cyclic oxidation and to scale spalling and shedding. Oxidation was carried out in air at 950°c for 30 h each cycle, to a maximum of seven cycles; the specimens after each cyclic oxidation were then rapidly cooled to specified ambient temperatures. Resistance to oxidation as well as to spalling was found to be in the following order: 310 > 316 > 304 > 321. In all cases the separation of initially formed protective scale resulted in the re-formation of less protective scales insubsequent cycles. The re-formed scales exhibited an increasing tendency to cracking and shedding instead of to clean spalling. Internal oxidation, porosity, and stratification in scales increased with the number of cycles, particularly in the 304 and 321 type steels. Grain boundary attack was more evident in 310 and 316 steels. Spalling and shedding of scales was a function of alloy composition, of scale thickness and composition,and of the severity of thermal shock.