Prevention of stress corrosion cracking in welded joint of type 304 stainless steel by laser peening

In order to prevent stress corrosion cracking (SCC) of austenitic stainless steel weldment, a novel technique -laser peening- has been introduced which is able to convert surface tensile stresses in the weldment to surface compressive stresses. In this paper, water-immersed welded specimens of type 304 stainless steel are peened by Q-switched Nd: glass laser with a wavelength of 1.06 mu m. A residual compressive layer is produced on the specimen surface by scanning laser pulse to cover the heat affected zone (HAZ) along the weld line. The residual compressive stress value based on X-ray measure is significant enough to prevent the initiation of stress corrosion cracking that is also validated by the finite element analysis. The SCC accelerated tests for comparing the potential against SCC of the specimens, which are unpeened and peened by laser pulse with different laser spot coverage, are carried on. The results show that stress corrosion cracks on the surface of unpeened specimen occur after immersion for 25 hours in boiling 42% MgCl2 solutions at 143 degrees C. In contrast, the specimen with 45% laser spot coverage cracks after immersion for 300 hours, while, cracks are observed on the surface of laser-peened specimen with 80% laser spot coverage after 985 hours of testing. The results show that laser peening is an effective technique for improving the residual stress distribution and the SCC resistance of 304 stainless steel weldment.