Effects of Laser Shock Processing on The Mechanical Properties of Welded Joints(Ⅱ)

The welded zones of GH30 and 1Cr18Ni9Ti were shock-processed by pulse laser in last paper,the results showed that the limit strength of GH30 welded joints was increased by 12% but the effect on fatigue life was not obvious,at the meantime,the limit tensile strength of 1Cr18Ni9Ti welded joints was increased by only 5% but the fatigue life was increased by more than 300%.For further investigations,the distribution of microhardness and residual stress of welded zones were measured and the fatigue fractures were analyzed by SEM. After laser shock processing,the limit strength of GH30 welded joints and the microhardness in the surface layer were increased,surface residual compress stress was improved.Fatigue initiation and crack growth were held back and crack growth rates were reduced in the strengthened zones,but the shock spot did not cover the welded joints or HAZ entirely,unshocked zones did harm to the fatigue properties; martensite phase was formed in plasma welding 1Cr18Ni9Ti,which reduced the effect of strain deformation martensite induced by laser shock processing on the microhardness,so laser shock processing had less effect on the strength of 1Cr18Ni9Ti welded joints,but the surface residual compress stress gained by laser shock processing could obviously improve the fatigue life of 1Cr18Ni9Ti welded joints.