Abstract:The surface of X70 pipeline steel welded joint was strengthened with the technology mechanical shot peening

the tensile mechanical properties of X70 pipeline steel substrate

welded joint in primitive state and the processed sample by shot peening treatment were analyzed through the tensile test

the fracture morphologies were observed with Scanning Electron Microscopy (SEM)

and the fracture mechanisms were analyzed. The experimental results show that the substrate of X70 pipeline steel has the continuous yield feature

no significant yield platform

its elongation rate is 38％

the tensile fracture appears the layered cracking. After the X70 pipeline steel is welded

its yield strength

tensile strength

shrinkage are obviously less than those of the substrate

and the tensile strength

yield strength and elongation rate of X70 pipeline steel welded joint have increased significantly after shot peening treatment. The plastic deformation is produced on the welded joint surface

and the decrease of holes and cracks is the main factor of improving the tensile strength of X70 pipeline steel welded joint after shot peening.