Effect Of Microstructure Change On Stress Corrosion Cracking Of 304 Stainless Steel

The relation between cold working and microstructure and corrosion resistance of 304 stainless steel(304SS) in MgCl2 solution has been investigated in this paper. The distribution of the dislocations was observed by transmission electron microscope and martensite phase content was determined using ferrmagnetometer. First, effect of cold working on microstructure of 304SS was studied. Specimen which had dislocation proliferation only was got by plastic deformation on 304SS at +180C and specimen which had dislocation proliferation and martensite phase was got by plastic deformation on 304SS at -70C. Second, effect of cold working on stress corrosion cracking(SCC) of 304SS in 42% boiling MgCb solution was studied by slow strain rate testing. Then, effect of cold working on pitting corrosion of 304SS in 0.5mol/L MgCl2 solution at 50 C was also studied by potentiodynamic polarization.The microstructure of 304SS was influenced by cold-working. The results showed that plastic deformation at -70 C and +180C both make the dislocation density of 304SS increase with the increase of deformation, and in 304SS deformed at -70 C, martensite phase transformation is induced and increases with the increase of deformation, whereas it is not at+180C.The SCC of 304SS was influenced by cold-working. The results showed that as the degree of drawing deformation at +180C increases, SCC susceptibility of 304SS in 42% boiling MgCl2 solution decreases, while as the degree of drawing deformation at -70 C increases, it decreases at first, then increases.The pitting corrosion of 304SS was influenced by cold-working. The results showed that as the degree of drawing deformation at +180C increases, the breakdown potential Eb of 304SS's passive film in 0.5mol/L MgCl2 solution at 50 C becomes a little more positive, while as the degree of drawing deformation at -70 C increases, it becomes more negative.The corrosion resistance of 304SS was influenced by cold-working. The results showed that martensite phase makes both SCC susceptibility and pitting susceptibility of 304SS increase.