| After obtaining two different distribution of austenite, fibrous and dispersed structure, in the ferrite matrix by changing the heat treatment paths, the amount of austenite, growth process of austenite, tensile properties and stress corrosion cracking(SCC) resistance of Fe-22Cr-7Ni-3Mo duplex stainless steel were investigated. The procedures of austenite formation from ferrite single phase appeared to the following sequence : 1) formation of austenite film along the grain boundaries of ferrite 2) growth of spike-like austenite from the ferrite grain boundaries to the grain interiors 3) formation of rod-like austenite at the ferrite grain interiors. The strength and elongation of the duplex stainless steel with fibrous structure were superior to those with dispersed structure. With increasing ferrite content, the increase in yield strength for the specimen of fibrous structure was remarkable. The SCC resistance of the duplex stainless steel was closely related to ferrite content. The SCC resistance of the dispersed structure in the duplex stainless steel appeared to superior compared to that of fibrous structure. With decreasing pH in 3.5% NaCl Solution, the SCC resistance decreased down to pH 5. On the other hand, the SCC resistances were nearly unchanged below pH 5. |
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