Effect of carbides on the corrosion resistance of industrial corrosion resistant alloys
Date of Issue2009
School of Materials Science and Engineering
This report will cover the steps taken, the tests to be conducted and the equipment to be used to investigate the effect of the amount of chromium carbides on the corrosion resistance ability of AISI 316L weld overlay. Austenitic stainless steels are susceptible to intergranular corrosion when sensitized during welding or improper heat treatment process. Embrittlement eventually occurs if intergranular corrosion persists due to the lack of passivity at the grain boundaries. The usage of low carbon content austenitic stainless steel counteracts sensitization but total elimination of chromium carbides is not possible. Small amount of chromium carbides is believed not to have any significant effect on the corrosion resistance of the weld overlay. AISI 316L weld overlay specimens were heat treated, at various temperatures, for a period of 5 hours followed by water quenching. The amount of chromium carbides precipitated was evaluated using microscopic examination and point count method. The specimens were subjected to ASTM A262 Practice B for corrosion rate quantification. The effect of preservation of corrosion resistance was evaluated by conducting bend test, reference to ASTM A262 Practice E. Results indicated that the amount of chromium carbides decreases with increasing temperatures. Various amounts of chromium carbides were achievable with the designed heat treatment, without any failure to the specimens. The corrosion rate reduced with amount of chromium carbides and the two parameters showed a linear correlation. Absence of cracks and fissures were observed for low volume fraction of chromium carbides. Positive results from the various tests indicate the insignificant effect on the corrosion resistance of AISI 316L weld overlay with 3% of chromium carbides and below.
Final Year Project (FYP)