Effect of Cold Working on Hot Corrosion Behavior of 9 Cr–1 Mo Ferritic Steel in 75 wt% Na2SO4 + 25 wt% K2SO4 Molten Salt Environment at 900 °C

Abstract

The hot corrosion behavior of as received (0 %), 10, 30 and 50 % cold rolled T-91 (9 Cr–1 Mo) ferritic steels has been studied in salt 75 wt% Na2SO4 + 25 wt% K2SO4 atmosphere under cyclic heating conditions at a temperature of 900 °C for 50 cycles. Each cycle consisted of 1 h heating at 900 °C followed by 20 min of cooling in air. Oxidation kinetics was studied using thermogravimetric technique by recording the weight gain at the end of each cycle. Oxidation kinetics of cold rolled sample with 10 and 50 % reduction followed parabolic rate law while cold-worked with 30 % showed accelerated rate of weight gain compared to the other cold worked samples as well as un-worked sample. 30 % cold worked sample in salt atmosphere was fully oxidized after 50 cycles and only fragmented thick scale remained. X-ray diffraction and scanning electron microscopy were utilized for characterizing the oxide layer. Cold rolled steel sample with 10 % was found to be more oxidation resistant compared to other cases.