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.
Highlights
In recent years, with the increasing of train capacity, material property for truck bodies are increasingly high [1,2]
This paper studies the effect of surface ultrasonic rolling treatment (SURT) on surface properties of a T4003 stainless steel welded joint
After the surface ultrasonic rolling test, surface microstructure and rolling surface morphology of welded joint were analyzed by Zeiss Supra field emission gun scanning electron microscope (FEG-SEM, Carl Zeiss, Jena, Germany)
Summary
With the increasing of train capacity, material property for truck bodies are increasingly high [1,2]. The disadvantages of CMT is that a large residual tensile stress in a welded joint is formed after welding treatment. According to previous research results, surface peening technology can change the residual stress of the surface. The increase of surface roughness can cause stress concentration and affect the properties of materials. Surface ultrasonic rolling treatment (SURT) can greatly improve surface hardness, corrosion resistance, reduce surface roughness, and change surface residual stress distribution. The research about influence of surface ultrasonic rolling treatment (SURT) on the performance of welded joint is less common. This paper studies the effect of SURT on surface properties of a T4003 stainless steel welded joint. An electrochemical corrosion test was used to study the change rule of surface corrosion resistance of welded joint before and after SURT. The research results can lay a foundation for the application of ultrasonic rolling treatment technology
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