The roles of Al addition and heat treatment temperature on chloride corrosion of 9Cr alloy steel

The effects of 0.7% Al and heat treatment temperatures on chloride corrosion of 9Cr alloy steel were investigated through potentiodynamic polarization measurement and salt spray test. Al promoted the formation of Al2O3-rich inclusions and AlN, thus reducing the pitting potential at initial stage. However, Al addition reduced weight loss after longer time by optimizing the alpha/gamma * value, compactness and element distribution of rust layer. The mechanism of corrosion resistance changing with heat treatment temperature was understood from the decrease in the pitting resistance equivalent number caused by (Fe, Cr)23C6 precipitation and the microgalvanic corrosion between fresh martensite and tempered martensite/ferrite.