Effect of Heterogeneous Surface Structure on Mechanical Properties of Interstitial-Free Steel Subjected to Laser Surface

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JMEPEG https://doi.org/10.1007/s11665-020-05136-7

Effect of Heterogeneous Surface Structure on Mechanical Properties of Interstitial-Free Steel Subjected to Laser Surface Treatment Xiaowei Cheng, Xiaojin Lian, Linjiang Chai, Ling Zhang, Pengzhan Cai, Tingting Wang, Zongqiang Feng, and Guilin Wu (Submitted May 30, 2020; in revised form July 22, 2020) To investigate the effect of heterogeneous gradient surface structure on mechanical properties of metals, a Ti-added interstitial-free steel with coarse-grained matrix and ultrafine-grained matrix were applied and were treated by laser surface treatment using liner-scanning. The distances between the scanning lines were modified to alter the space between the hard-treated zone and soft matrix. The laser-treated zone contains a melting zone, comprised of fine grains, and a heat-affected zone featured by coarse columnar grains grown radically from the laser beam center. For coarse-grained matrix sample, after proper laser surface treatment significant improvement (about 100%) in yield strength and moderate improvement (22.8%) in ultimate tensile strength were achieved with little loss in elongation. For ultrafine-grained matrix sample, gradual decrease in strength together with recovering of elongation was realized. Electron channeling contrast imaging was applied to investigate the structure of the sample which was then compared with the untreated one to reveal the origin of the mechanical behavior of the laser surface-treated steel. Keywords

gradient microstructure, IF steel, laser surface treatment, mechanical properties

1. Introduction There are increasing evidences that significant improvement of overall properties of metals and alloys can be fulfilled by surface modification (Ref 1-4), through the introduction of gradient structure into metals by, such as surface mechanical attrition treatment (SMAT) (Ref 4), surface mechanical grinding treatment (SMGT) (Ref 5), shot peening (Ref 6), ultrasonic shot peening (Ref 7), laser-shock peening (LSP) (Ref 8) and laser surface treatment (LST) (Ref 9-14). Formation of highly developed dislocation structures, grain refinement and desired compressive residual stresses offer significant hardening in the surface layers of the treated materials, resulting in better Xiaowei Cheng, Xiaojin Lian, and Pengzhan Cai, International Joint Laboratory for Light Alloys (MOE), College of Materials Science and Engineering, Chongqing University, Chongqing 400045, PeopleÕs Republic of China; and Linjiang Chai and Tingting Wang, College of Materials Science and Engineering, Chongqing University of Technology, Chongqing 400054, PeopleÕs Republic of China; Ling Zhang and Zongqiang Feng, International Joint Laboratory for Light Alloys (MOE), College of Materials Science and Engineering, Chongqing University, Chongqing 400045, PeopleÕs Republic of China; and Electron Microscopy Center of Chongqing University, Chongqing University, Chongqing 400044, PeopleÕs Republic of China; and Guilin Wu, International Joint Laboratory for Light Alloys (MOE), College of Mat