A new approach to improve the ductility of non-penetrating laser-welded lap joints of cold-rolled 301LN stainless steel
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RESEARCH PAPER
A new approach to improve the ductility of non-penetrating laser-welded lap joints of cold-rolled 301LN stainless steel Xiangzhong Guo 1 & Wei Liu 1
&
Xiqing Li 1 & Jiafei Fan 1 & Zhikun Song 1
Received: 4 January 2020 / Accepted: 15 September 2020 # International Institute of Welding 2020
Abstract The aim of this work is to improve the fracture ductility of non-penetrating laser-welded lap joints. The 1.5 + 2.0 and 2.0 + 2.0 lap plates of cold-rolled 301LN stainless steel tilted 15° in the load direction and in the reverse load direction were welded by a vertical laser beam to prepare a positive-tilt weld (PTW) and negative-tilt weld (NTW). The tilt weld had a regular geometry, and the solidification centerline was tilted by approximately 15°. The laser-welded 301LN stainless steel was solidified by the primary ferritic mode with good resistance to thermal cracking, and the weld metal with ultrafine grains had excellent plasticity. The main weld in the penetrating plate of the NTW joints has a greater bending moment than that of PTW joints under tensile loading conditions, so the plastic deformation of the NTW is due to uniform bending, while that of the PTW is due to approximate parallel stretching. The bending deformation of the main weld of the NTW joint leads to a greater tensile stress ratio (decomposed normal stress to shear stress) in the interfacial weld metal than that of the PTW joint, so the interfacial fracture ductility of NTW joints is much greater than that of PTW joints. Keywords Tilt plate laser welding . Weld geometry . Decomposed stress . Interfacial fracture ductility
1 Introduction Lightweight railway passenger cars made of 301LN coldrolled plates have been widely used in subways and intercity express transportation systems, and laser welding is replacing resistance spot welding in vehicle body manufacturing due to its superior performance [1–4]. Non-penetration laser lap welding is an assembling method for the side facade panels of passenger cars, which can improve corrosion resistances and provide vehicle bodies with a weld-free appearance. The requirement for no heat discoloration on the outer surface of the side facade panel limits the welding penetration depth and interface welding width, which results in the low ductility interfacial fracture of the laser-welded lap joint, especially Recommended for publication by Commission XV - Design, Analysis, and Fabrication of Welded Structures * Wei Liu [email protected] 1
School of Mechanical, Electronic and Control Engineering, Beijing Jiaotong University, Beijing 100044, China
for laser-welded high-strength plates [5]. Research efforts devoted to improving the tensile properties of laser-welded lap joints with a lower weld hardness have shown that the weld width has a substantial influence on the fracture strength and ductility [6–8]. Therefore, it is necessary to develop a method to increase the interface welding width of laser-welded lap joints without increasing the penetration rate. Laser fiber welding can prepare de
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