Effect of quantity of martensitic transformation on fatigue behavior in type 304 stainless steel

The effects of strain-induced martensitic transformation on the fatigue behavior of type 304 stainless steel were studied. Rotating bending fatigue tests have been conducted in laboratory air and in 3%NaCl solution using specimens subjected to tensile-prestrains at ambient temperature and -25 degrees C. Martensitic transformation developed more extensively at -25 degrees C than at ambient temperature. In laboratory air, the fatigue strengths of the prestrained specimens increased with increasing prestrain and the specimens subjected to the same prestrains at each temperature exhibited similar fatigue strength in spite of the different amount of martensitic phase. This suggests that the increase in fatigue strength of the prestrained specimens is primarily attributed to work hardening. In 3%NaCl solution, the fatigue strengths of the prestrained specimens at -25 degrees C decreased significantly compared to those in laboratory air. EBSD analysis revealed that the strain-induced martensitic transformation took place within slip bands but the crack initiated in austenitic phase in laboratory air. On the other hand, in 3%NaCl solution, corrosion pits generated at slip bands, from which crack initiation took place. Based on these results, it was confirmed that the strain-induced martensitic transformation exerted a large influence on the fatigue behavior in 3%NaCl solution. (C) 2011 Published by Elsevier Ltd. Selection and peer-review under responsibility of ICM11