EFFECTS OF SENSITIZATION HEAT-TREATMENT ON SCC OF TYPE-316L STAINLESS-STEEL IN HOT LITHIUM HYDROXIDE SOLUTION

This paper describes the effect of extended sensitization heat treatment (650-degrees-C) and applied potential on the corrosion behavior and the stress corrosion cracking (SCC) of low-carbon AISI 316L (UNS S31603) stainless steel (0.02%C) in a concentrated lithium hydroxide solution at 95-degrees-C. The results are compared to the behavior of solution-annealed material under the same conditions. In general, there is a fairly clear effect of prolonged heat treatment times on the material, and its susceptibility to intergranular attack (IGA) and SCC, as determined in slow strain rate tests, increases with increasing times of sensitization heat treatment. When the heat treatment extends to 100 h or more, the potential range in which IGA is observed extends to lower potentials (-300 m V SCE, open-circuit conditions) compared to the solution-annealed material. On the other hand, SCC is observed on both materials in approximately the same potential ranges (i.e., above approximately -100 m V SCE). However, both intergranular and transgranular cracking occur with the heat-treated specimens. Moreover, transgranular SCC, not intergranular SCC, is even the predominant fracture mode when the heat treatment time is increased to 200 h, if the applied potential is sufficiently high (+100 m V SCE). No such phenomenon has been observed with the solution-annealed material. A possible explanation for these different results and for the effects of sensitization treatment is provided based on the electrochemical and the surface-chemical behavior of the alloy.