1College of Education, Shinshu University, Nagano
Stress corrosion behavior of Type 304 stainless steel wire in 2 kmol/m3 H2SO4-NaF at 368 K was examined as functions of both the amount of α' martensite induced by prestraining at various temperatures under a stress of 324 MPa and the NaF concentration of the test solutions.
Crack occurred when the steel containing a small amount of α' martensite induced at temperatures higher than 273 K was tested in a solution containing 1.9 kmol/m3 NaF, in which corrosion of solution annealed Type 304 steel was suppressed at early stages of testing. General corrosion, on the other hand, was observed when the steel contained a large amount of α' induced at temperatures below 273 K and/or when NaF concentrations of the test solution were below 1.5 kmol/m3, in which the decrease in corrosion rate of solution annealed Type 304 steel with time was small.
The above results have been interpreted in the same manner as in the previous work on Type 304 steel in H2SO4 aqueous solutions containing NaBr or NaI, that is, in terms of preferential dissolution of α' martensite and chemical stability of the protective layer of the corrosion product on the steel.
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