Improvement of microstructure and surface behaviors of welded S50C steel components under electropulsing assisted ultras
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-Zhu Kure-Chu Department of Chemistry and Bioengineering, Iwate University, Iwate 020-8550, Japan
Guolin Song Advanced Materials Institute, Graduate School at Shenzhen, Tsinghua University, Shenzhen 518055, People’s Republic of China
Zhiyan Sun and Guoyi Tanga) Advanced Materials Institute, Graduate School at Shenzhen, Tsinghua University, Shenzhen 518055, People’s Republic of China, Key Laboratory for Advanced Materials of Ministry of Education, School of Materials Science and Engineering, Tsinghua University, Beijing 100084, People’s Republic of China (Received 16 January 2016; accepted 14 March 2016)
The effect of electropulsing assisted ultrasonic surface modification (EUSM) on microstructure and surface properties of S50C steel welded components is investigated. Compared with conventional ultrasonic surface modification (USM) process, EUSM process achieves significant improvements in microstructure, including deeper strengthened layers and gradient microstructure on the surface. The EUSM-induced microstructure results in higher levels of surface compressive residual stress and greater surface microhardness and its effective depth. Conventional USM process is inevitably accompanied by some plastic damages, such as pit and crack defects. The damages, however, can be eliminated to some extent during the EUSM process. These enhancements may be attributed to the thermal and athermal effects caused by electropulsing treatment, which accelerates the mobility of dislocations in the dynamic recrystallization process.
I. INTRODUCTION
Welded components have been widely used in the industry. Welding, however, is a rapid heating and cooling nonequilibrium process. Some defects and welding residual stress inevitably appear in the joints due to nonhomogeneous mechanical, thermal or plastic misfits,1,2 resulting in loss of mechanical properties. Therefore, improving the quality and properties in joint surface is demanded and urgently required. Many mechanical surface processing techniques have been reported to improve the surface mechanical properties effectively, such as surface mechanical attrition treatment,3,4 shot peening,5 laser shock peening,6,7 and ultrasonic surface modification (USM).8–10 USM dates back to 1970s and is invented by Statnikov.8 Compared with the techniques mentioned above, USM is a more effective and controllable method to enhance material Contributing Editor: Jürgen Eckert a) Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2016.127
properties. The USM method involves deformation treatment of the weld toe superposed by ultrasonic treatment at a frequency of 27 kHz. At beginning, USM method is used for relieving the stress concentration in ship components. It can convert the residual tensile stress into residual compressive stress, and hence to improve the performance.8,9 Moreover, it can not only refine the surface microstructure but also improve the surface microhardness. Previous studies8–11 have shown that surface nanocrystallization and severe plast
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