Deformation-induced Martensitic Transformation in Welded Plates of SUS304 Fatigued at Room Temperature in Air

Abstract

The present study has investigated deformation-induced martensitic transformation in fatigue of welded SUS304 plates. Martensitic transformation occurred in welded SUS304 plate specimens fatigued at room temperature in air. Ferrite scope reading of the central portion of welded specimens ranged 10 to 15%, indicating the existence of ferromagnetic ferrite phase produced during the welding process. Modified ferrite scope reading ξ, 1.37 times ferrite reading, showed a slight decrease after the application of cyclic stress, then remained almost a constant value of 15 to 17% irrespective of applied stress range Δσ for the most part of fatigue life, and finally showed sudden increase to about 28% to cause fracture. The spatial distribution of ξ in the welded specimens varied with the number of stress cycles N: i.e., continued cycling of stress made α' transformation localized near the central portion of specimens where the ξ value reached as high as 18-21%. This value is higher than the highest ξ_α' value found in the tensile tests of SUS304 at room temperature. Small edge cracks were found in the high ξ value regions of the welded SUS304 specimens. These results imply that the measurement of ξ in fatigued SUS304 weldments can detect crack initiation sites and predict residual fatigue life.