Effect Of Surface Strengthening On Corrosion Behavior Of Welded Joints

Welded joint becomes the weak link of the component because the microstructure and performance are not uniform caused by the welding process with rapid heating and cooling.In this paper,High Energy Shot Peening(HESP)was used to improve the microstructure and properties of Commercial pure titanium(CP-Ti)welded joint and X70 pipeline steel welded joint.By means of open circuit potential,polarization curves and AC impedance test,the electrochemical corrosion behavior of the two materials were studied.Combined with weight loss method,Mott Schottky curve and XPS techniques,the corrosion mechanism of CP-Ti welded joint was investigated,and the following results were obtained:HESP processing realized the surface grain refinement of CP-Ti welded joint and X70 pipeline steel welded joint and a gradient distribution structure from the surface to matrix grain size ascending were obtained.The surface hardness of CP-Ti welded joint was improved simultaneous.The welding residual tensile stress was eliminated,and the compressive residual stress was introduced.HESP processing realized the uniformity of surface microstructure,hardness and residual stress in different regions of the welded joint.Surface strengthening treatment can improve the corrosion resistance of CP-Ti welded joints in 10% HCl and 0.2% Na F solution,the optimal processing parameters in two kinds of solution were 0.2 MPa-60 min and 0.4 MPa-40 min;The passivation film thickness after surface strengthening treatment is greater than untreated one,and the passivation film after surface strengthening treatment is more compact than untreated one.Surface strengthening treatment promotes the formation of compact and thickpassive films on the surface of material.The weight loss test showed that the surface strengthening treatment reduced the corrosion rate of the material in the corresponding environment.The passive film formed on the surface of the material hinders the further corrosion and reduces the overall corrosion rate.Shot peening treatment can change the corrosion properties of pipeline steel,the corrosion resistance was declined after shot peening for 15 min,30 min compared with the untreated sample.The corrosion resistance performance of the weld and base metal has been significantly improved than the untreated sample after shot peening for 60 min.