Laser welding of low carbon steel and thermal stress analysis B.S. Yilbas n , A.F.M. Arif, B.J. Abdul Aleem Mechanical Engineering Department, KFUPM, Saudi Arabia article info Article history: Received 13 November 2008 Received in revised form 17 November 2009 Accepted 26 November 2009 Available online 21 December 2009 Keywords: Laser welding Temperature Finite element model abstract Laser welding of mild steel sheets is carried out under nitrogen assisting gas ambient. Temperature and stress fields are computed in the welding region through the finite element method. The residual stress developed in the welding region is measured using the XRD technique and the results are compared with the predictions. Optical microscopy and the SEM are used for the metallurgical examination of the welding sites. It is found that von Mises stress attains high values in the cooling cycle after the solidification of the molten regions. The residual stress predicted agreed well with the XRD results. & 2009 Elsevier Ltd. All rights reserved. 1. Introduction Laser is widely used as a thermal source for industrial applications. This is because of the local treatment, precise operation, and short processing time. One of the important industrial applications of laser processing is the laser welding, which offers considerable advantages over the conventional welding methods. High intensity laser beam melts and partially evaporates the welded material during the process. Attainment of high temperature gradient during the heating and cooling periods results in the development of high thermal stresses in the welding zone. Once the cooling period ends, the residual stress in the welding zone is resulted. This, in turn, influences the mechanical performances of the resulting welds. Consequently, investigation into thermal stress development and residual stress formation in the weld zone becomes essential. Considerable research studies were carried out to examine the laser welding process. An extensive review on laser welding and related process was carried out by Mackwood and Crafer [1]. They presented the applications laser welding processes under differ- ent welding categories such as laser spot welding, laser butt welding, etc. Nd:YAG laser repair welding of tool steels and microstructural changes in the welded region were examined by Vedani[2]. They indicated that heat affected zone was narrow and carbides dissolve during the heating phase of the welding process. Li et al. [3] studied the laser forming process using the finite element method. They showed that thermal expansion and contraction took place during the laser processing, which in turn allowed the thermo-mechanical forming of complex shapes. Laser welding and heating analysis were carried out by Papadakis and Tobias [4]. They examined the lap and fillet seam welds and measured the distortion during the processing. Moreover, the experimental findings were compared with the model predic- tions. A high speed laser pulse welding of metallic substrates was examined by Holtz et al. [5]. They demonstrated that an improvement in the structural integrity of the weld site was resulted for high speed pulsed contour welding than the seam welding process. The transient effects on the formation of laser produced weld pool were studied by Ehlen et al. [6]. They accommodated the Marangoni effect using a semi-empirical model for the temperature dependent surface tension gradient. The thermal stress developed during the lap welding of thermo- plastic films was examined by Coelho et al. [7]. They showed that the influence of thermal stresses and expansion and contraction forces played an important role on the achievement of strong welds; in which case, tensile strength improved 80% as compared to the original thermo-plastic substrate. The high power laser welding of construction steel was investigated by Engstron et al. [8]. They indicated that laser welding offered new design opportunities, which improved the manufacturing process by shortening lead and production times as well as reducing the amount of materials used. The metallurgical and residual stress evaluation of CO 2 laser welded super-austenitic stainless steel was carried out by Zambon et al. [9]. They showed that the residual stress was tensile and close to the yielding strength of the substrate material in the longitudinal direction in the weld bead while the stresses were compressive in the transverse direction in the base material. Laser welding of steel and residual stress ARTICLE IN PRESS Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/optlastec Optics & Laser Technology 0030-3992/$ - see front matter & 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.optlastec.2009.11.024 n Corresponding author. Tel.: + 966 3 860 4481; fax: + 966 3 860 2949. E-mail address: bsyilbas@kfupm.edu.sa (B.S. Yilbas). Optics & Laser Technology 42 (2010) 760–768