Effect of Laser Welding Process Parameters on Microstructure and Mechanical Properties on Butt Joint of New Hot-Rolled Nano-scale Precipitation-Strengthened Steel
来源期刊：Acta Metallurgica Sinica2014年第3期
论文作者：Min Zhang Xiaonan Wang Guangjiang Zhu Changjun Chen Jixin Hou Shunhu Zhang Hemin Jing
文章页码：521 - 529
摘 要：A 4 kW fiber laser was chosen to weld the new hot-rolled nano-scale precipitation-strengthened steel with a thickness of 4.5 mm. The effect of laser power, defocusing distance, and welding speed on the welded joint appearance was examined, and the microstructure and mechanical properties on the typical butt joints were investigated. Results showed that increasing laser welding power may cause faster downward flow of molten metal to produce greater root humping. With the welding speed increasing, the average welding seam（WS） width decreased, and the average WS and heat-affected zone（HAZ） hardness increased. The microstructures of WS, fusion line, and coarse grain heat-affected zone were lath martensite, but the growth direction of the original austenite grain boundaries was significantly different. The microstructures of fine grain heat-affected zone were ferrite and martensite, and the microstructure of mixed grain heataffected zone contained ferrite, massive M/A island, and a small amount of martensite. The micro-hardness values of WS,HAZ, and base metal（BM） were 358, 302, and 265 HV, respectively. The butt joint fracture at the BM far from the WS and the welded joint tensile strength are observed to follow proportional relationship with hardness.
Min Zhang1，Xiaonan Wang2，Guangjiang Zhu3，Changjun Chen1，Jixin Hou2，Shunhu Zhang2，Hemin Jing3
1. Laser Processing Research Center, School of Mechanical and Electrical Engineering, Soochow University2. Shagang School of Iron and Steel, Soochow University3. School of Materials Science & Engineering, Anhui University of Technology
摘 要：A 4 kW fiber laser was chosen to weld the new hot-rolled nano-scale precipitation-strengthened steel with a thickness of 4.5 mm. The effect of laser power, defocusing distance, and welding speed on the welded joint appearance was examined, and the microstructure and mechanical properties on the typical butt joints were investigated. Results showed that increasing laser welding power may cause faster downward flow of molten metal to produce greater root humping. With the welding speed increasing, the average welding seam（WS） width decreased, and the average WS and heat-affected zone（HAZ） hardness increased. The microstructures of WS, fusion line, and coarse grain heat-affected zone were lath martensite, but the growth direction of the original austenite grain boundaries was significantly different. The microstructures of fine grain heat-affected zone were ferrite and martensite, and the microstructure of mixed grain heataffected zone contained ferrite, massive M/A island, and a small amount of martensite. The micro-hardness values of WS,HAZ, and base metal（BM） were 358, 302, and 265 HV, respectively. The butt joint fracture at the BM far from the WS and the welded joint tensile strength are observed to follow proportional relationship with hardness.
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