Abstract
Tension-tension fatigue tests were carried out to investigate the effect of secondary austenite (γ2) on the fatigue behavior of S32750 super duplex stainless steel (SDSS). Stress-life curves were fitted and analyzed in detail. It was demonstrated that γ2 deteriorates the fatigue resistance of SDSS. To further study the role of γ2 in fatigue deformation, fracture surfaces were examined. γ2 increased the probability of ferrite as a crack initiation source, which could be attributed to the combined variation of the ferrite/austenite interface relationship and alloying elemental distribution. γ2 increased the ratio of Kurdjumov-Sachs/Nishiyama-Wassermann crystallographic orientation, making the slip systems crossing the ferrite/austenite boundaries easier to affect the formation of fine-scaled dislocation structure in ferrite. Moreover, segregation of N enhanced the strength of γ2, thus leading to the earlier plastic deformation of partial ferrite in the fatigue deformation process.
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