Influence of Surface Ultrasonic Rolling on Microstructure and Corrosion Property of T4003 Ferritic Stainless Steel Welded Joint

Abstract

In this paper, the effect of surface ultrasonic rolling treatment (SURT) on surface properties of T4003 cold metal transfer (CMT) welded joints was studied. Surface topography and microstructure changes of the welded joint surface before and after SURT were observed by optical microscope and scanning electron microscope. The hardness and residual stress distribution of welded joint were measured by a microhardness tester and X-ray diffractometer. The change of corrosion resistance of welded joints was studied by electrochemical polarization curve measurement. The results show that surface roughness (Ra) of the weld zone, heat affect zone (HAZ), and base metal after SURT was reduced to 0.320 μm, 0.156 μm, and 0.227 μm, respectively, and surface morphology became smooth. The plastic deformation layer and working hardening layer were formed at the welded joint. The degree of plastic deformation of the weld zone was more serious than that in the base metal, and grains in weld zone was obviously refined. The thickness of plastic deformation layer was about 100 μm. The surface hardness in the weld zone was highest, which is about 420 HV. The refinement of grains and the increase of surface hardness can improve the fatigue life of welded joint. After SURT, the residual stress in the welded joint changes from residual tensile stress to residual compressive stress, which can also improve fatigue life of the welded joint. Surface corrosion resistance of welded joints after SURT was improved due to smooth surface and the formation of fine grains layer.

Ultrasonic Surface Rolling Process: Properties, Characterization, and Applications

“…Below the top layer, a second layer is present, a region of extensive deformation showing many deformation structures. Below that layer is a region that contains unaffected matrix material [40,48]. The degree of grain refinement, the extent of plastic deformation, the depth of SPD layers, etc.…”

“…In this manner, the severity of the USRP process can be enhanced. Liu et al [48] studied residual stress before and after USRP treatment on T4003 ferritic SS welded joints. The authors used an X-ray diffractometer to determine the residual stress distribution at the welded junction.…”

“…The authors summarized that improved surface finish, higher surface hardness, and introduction of RCS induced by USRP significantly enhanced corrosion fatigue and fretting properties. Liu et al [48] studied the influence of USRP on microstructure and corrosion property of T4003 ferritic SS welds using electrochemical polarization curve measurement. The authors observed increased corrosion potential in the weld zone after USRP treatment compared to the untreated specimen.…”

“…The specimen is subjected to multiple weld thermal cycles during welding, resulting in the poor surface finish in the weld fusion zone and heat-affected zone. Liu et al [48] revealed that USRP on T4003 ferritic SS weld joints reduced the surface roughness significantly and changed the surface morphology. They used another nomenclature named surface ultrasonic rolling treatment (SURT), which is similar to USRP.…”

“…heat-affected zone. Liu et al [48] revealed that USRP on T4003 ferritic SS weld joints re-duced the surface roughness significantly and changed the surface morphology. They used another nomenclature named surface ultrasonic rolling treatment (SURT), which is similar to USRP.…”