Effects of Laser Premelting Treatment on Microstructure and Mechanical Properties of High-Strength Steel Weld Obtained b
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JMEPEG https://doi.org/10.1007/s11665-020-05084-2
Effects of Laser Premelting Treatment on Microstructure and Mechanical Properties of High-Strength Steel Weld Obtained by Laser-MAG Hybrid Welding Yanqing Li, Shuangyu Liu, Qiushi Zhang, Yongsheng Ma, Fulong Zhang, and Genzhe Huang (Submitted January 8, 2020; in revised form July 14, 2020) Experimental research is performed on ultra-high-strength steel using a 4-kW Nd:YAG laser and a metal active gas (MAG) welding facility providing two processes, namely laser-MAG hybrid welding (LMHW) and laser premelting + laser-MAG hybrid welding (LPLMHW). The study shows that LPLMHW produces joints with a fine lath martensite and excellent mechanical properties. Additionally, there is a certain random crystallographic orientation between the martensite laths by using the LPLMHW process. The microstructure within the martensite laths is refined and many high-angle lath boundaries are formed, which contribute to the enhancement of the impact energy of the joints obtained using the LPLMHW process. This interlaced high-angle grain boundary of martensite laths can significantly improve the tensile strength and toughness of the weld. The impact energy of the welded joints by LPLMHW is higher than that obtained by LMHW. The tensile strength and impact energy of the welded joints by the LPLMHW process reach 1313 MPa and 21.2 J, respectively. The impact energy of the welded joints by LPLMHW is double than that obtained by LMHW. Keywords
laser-MAG hybrid welding, mechanical properties, microstructure, premelting treatment, ultra-high-strength steel
1. Introduction Generally, steel with a tensile strength greater than 1200 MPa is termed as ultra-high-strength steel. Ultra-high-strength lowalloy steel, made by a quenching and tempering process, is widely used in the manufacture of mining equipment, construction machinery and pressure vessels because of its excellent properties of strength and toughness (Ref 1, 2). Although this kind of steel has excellent mechanical properties, if the welding process is not strictly controlled, the weld performance will still be unstable. Because the content of alloy elements is high, cold cracks can easily appear in the welding process of high-strength steel (Ref 3). To avoid cold cracks during welding, an austenite or ferrite wire is commonly used in the welding of an ultra-highstrength steel plate. A previous investigation (Ref 4) into the effect of a filler metal (yield strength less than 650 MPa) on the cold cracking susceptibility of ultra-high-strength steel (Ultimate tensile strength UTS Rm = 1500 MPa) showed that the preheating temperature and the heat input directly affect the crack Yanqing Li, Qiushi Zhang, Fulong Zhang, and Genzhe Huang, College of Mechanical and Electrical Engineering, Changchun University of Science and Technology, 7089 Weixing Rd., Changchun 130022, PeopleÕs Republic of China; Shuangyu Liu, School of Mechanical Engineering, Yancheng Institute of Technology, Yancheng 224051, PeopleÕs Republic of China; Yongsheng Ma, Department
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