The effect of residual thermal stresses on the fatigue crack growth of laser-annealed 304 stainless steels

Abstract

The fatigue crack growth behavior of AISI 304 stainless steels annealed by a CO2 laser was investigated in the study. For the laser-annealed specimen prior to introducing a notch, the residual tensile stress was obtained around the center of the laser-annealed zone (LAZ), and the residual stress field changed gradually from tensile into compressive stress with increasing the distance away from the centerline of LAZ. Based on the experimental result, the laser-annealed specimen tested under low K had a higher resistance to fatigue crack growth in the region preceding the LAZ after introducing a notch perpendicular to the LAZ. In contrast, the retardation of fatigue crack growth disappeared for the laser-annealed specimen stress-relieved at 850 ◦C for one hour. The presence of residual compressive stress field ahead of the crack tip resulted in the decreased fatigue crack growth rate (FCGR). Moreover, residual compressive stresses enhanced the effect of crack closure, and led to the formation of rubbed marks on the fatigue-fractured surface. As the fatigue crack propagated further into the LAZ, the residual tensile stress field ahead of crack tip did not accelerate the crack growth. The results indicated that tensile stress field ahead of the crack tip had little effect on the FCGR of the ductile 304 stainless steel