EFFECTS OF Al ELEMENT ON MICROSTRUCTURE AND MECHANICAL PROPERTIES OF HOT-ROLLED 316L STAINLESS STEEL

316L stainless steel is applied to high temperature environment because of an attractive combination of mechanical properties and corrosion resistance in various aggressive environment. However, the corrosion resistance of 316L was reduced in a particular environment such as water vapor, aggressive sulfur gas which was attributed to the Cr2O3 protective scales formed in 316L. The Cr2O3 scales are compromised by water vapor due to the formation of volatile Cr oxy-hydroxide species. The Al2O3 is more thermodynamically stable in these enviroment than Cr2O3. In this work, the effects of Al element on the microstructure, mechanical properties and corrosion resistance of hot rolled 316L were investigated. Microstructure evolution was observed by OM, EPMA and XRD. Mechanical properties were measured by tensile tests. The resistances to intergranular and uniform corrosion of hot rolled 316L with different Al content were investigated by means of soaking method at 65%HNO3 and 5%H2SO4, respectively. The results show that microstructure has changed from single gamma to alpha+-gamma double phase. With the increase of Al content in 316L, the yield strength and ultimate tensile strength increased but the ductility decreased. The fracture morphology of tensile was observed by SEM. Which indicated that the fracture mechanism behaved in ductile fracture. Corrosion rate of intergranular and uniform corrosion decreased remarkly as the Al content increased. The optimum Al content in terms of corrosion rate curve was about 2%. Improvment of corrosion resistance was mainly due to Al2O3 scale formed in 316L.