Based on the software Visual-Environment, Finite element method (FEM) was performed on the dissimilar butt-joint between Q345 and 2Cr13 steel aiming at the welding residual stress. The main contents in the paper were different current intensity was applied to modeling the welding process of Q345/2Cr13 dissimilar steel and the law of residual stress field were discussed. Based on the result, different current intensities have little effect on the lateral residual stress, while the longitudinal residual stress and the initial and end of the weld have a great influence. The physical properties of the dissimilar plates lead to uneven distribution of residual stress, and the current intensity should be smaller

B. Xu

H. Fu

Q. Xiao

S. Bian

S. Li

T. Kang

X. Zhang

English

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163METALURGIJA 59 (2020) 2, 163-166H. FU, B. XU, Q. XIAO, S. LI, X. ZHANG, S. BIAN, T. KANG  EFFECT OF CURRENT INTENSITY ON RESIDUAL STRESS OF Q345/2Cr13 DISSIMILAR STEEL PLATESReceived – Primljeno: 2019-08-28Accepted – Prihvaćeno: 2019-11-15Original Scientific Paper – Izvorni znanstveni radH. Fu, B. Xu (e-mail: boxuchina@163.com), College of Metallurgy and Energy, North China University of Science and Technology, Tangshan, Hebei, ChinaQ. Xiao, S. Li (e-mail: lishengli@ustl.edu.cn), Key Laboratory of met-allurgical engineering, University of Science and Technology Liaoning, Anshan, Liaoning, X. Zhang, S. Bian, ChinaT. Kang, 725 Research Institute of China Shipbuilding Heavy Industry Group Corporation, ChinaBased on the software Visual-Environment, Finite element method (FEM) was performed on the dissimilar butt-joint between Q345 and 2Cr13 steel aiming at the welding residual stress. The main contents in the paper were different current intensity was applied to modeling the welding process of Q345/2Cr13 dissimilar steel and the law of resid-ual stress field were discussed. Based on the result, different current intensities have little effect on the lateral re-sidual stress, while the longitudinal residual stress and the initial and end of the weld have a great influence. The physical properties of the dissimilar plates lead to uneven distribution of residual stress, and the current intensity should be smaller.Keywords: steel plates, dissimilar steel welding, current intensity, numerical simulation, residual stressINTRIDUCTIONWith the advancement of science and technology and the development of modern industry, people have put for-ward higher requirements for the comprehensive perfor-mance of welded components [1]. Therefore, in various modern engineering structures, the welding of dissimilar steel has received more attention [2]. The transient stress generated during the welding process and the residual stress formed by the completely cooled after welding lead to uneven distribution of the residual stress of the entire workpiece after welding, and the residual stress af-fects the working strength of the welded component to some extent [3]. In dissimilar plate welding, the differ-ence in physical properties, chemical properties and tis-sue composition between metal materials results in a large difference in soldering to the same material [4]. Mainly, there are four differences: the chemical composi-tion of the fusion zone of dissimilar materials is not uni-form which carbon migration occurs in the joint fusion zone [5]; the metallographic structure of the welded joints of dissimilar materials is uneven, and it is easy to produce weld cracks and brittle fractures, especially the coarse grain in the fusion zone, which becomes the weak-est area of dissimilar metal welded joints [6]; the grain in the heat-affected zone is relatively coarse, and its compo-sition and properties are not uniform, resulting in a sig-nificant decrease in the ductility and toughness of the ISSN 0543-5846METABK 59(2) 163-166 (2020)UDC – UDK 669.15/621-41:621.791.057/620.1:537.3:531.79:620.16=111heat-affected zone [7]; the heat-affected zone is also the main part of stress concentration, and its stress-strain dis-tribution is uneven, which is easy to produce welding re-sidual stress and welding deformation after welding [8,9]. Therefore, the residual stress distribution after welding of dissimilar plates has important research sig-nificance, and the welding numerical simulation technol-ogy allows people to better predict and control the weld-ing residual stress [10-12].In this paper, the variation of temperature field and strain field of Q345/2Cr13 dissimilar steel during weld-ing is analyzed by changing the welding current inten-sity. The purpose of this paper is to analyze the variation behavior of Q345/2Cr13 dissimilar steel welding resid-ual stress and provide theoretical guidance for actual welding engineering.Experimental processIn this paper, the model-meshing software visual-mesh in visual-environment is used to establish the model and mesh. There are two 50 mm × 200 mm × 4 mm plates were built by visual-mesh, and the welding model of the plate is established. The schematic dia-gram of the model is shown in Figure 1, in which the weld width is set to 5 mm. Plate 1 is low alloy steel Q345, plate 2 is martensitic stainless steel 2Cr13, and the filling material of the weld is 2Cr13. The chemical composition of the two materials is shown in Table 1.Keep the voltage constant and change the current in-tensity to change the heat input acting on the unit length of the weld:qw = g/vWhere: qw is the effective power of the arc; v is the welding speed.164H. FU et al.: EFFECT OF CURRENT INTENSITY ON RESIDUAL STRESS OF Q345/2Cr13 DISSIMILAR STEEL PLATE METALURGIJA 59 (2020) 2, 163-166The experimental scheme uses three different cur-rent intensities for numerical simulation. The specific welding parameters are shown in Table 2. The speed of welding is 5 mm in each case.Table 2 Numerical simulation projectsComputing scheme Amp / A Vol / V Line power/ (J / mm)Case 1 140 15 294Case 2 150 15 315Case 3 160 15 336The welding process includes many complex physi-cal and chemical metallurgical phenomena such as heat conduction, convection, radiation, evaporation and melt solidification [13,14]. Therefore, the following assump-tions are made in the numerical simulation process [15]:1)  Assume that surface deformation does not change heat transfer and mass transfer between the weld-ing arc and the workpiece.2)  Ignore the fuzzy area where the solid-liquid two phases coexist in the molten pool.Simulation results and analysisFigure 2 shows the lateral residual stress distribution at different current intensities. It can be seen from the figure that the residual stresses in the three cases in the central weld zone are approximately the same. The lat-eral stress distribution in the figure shows a certain ir-regularity. The direct cause of the lateral residual stress is the lateral contraction of the workpiece. The indirect cause is the longitudinal contraction of the workpiece. Under the action of the lateral contraction and longitu-dinal contraction of the workpiece, the stress distribu-tion is certain irregularity. In addition, it can be seen that the residual stress of the heat affected zone of the panel 1 is less than the residual stress of the panel 2, and the edge portion of the panel 1 is significantly smaller than the residual stress of the panel 2.This is mainly due to the fact that during the welding process, the material properties of the two plates are different and the heat transfer is inconsistent. The comparison shows that as the current intensity increases, the lateral residual stress increases, but the growth rate is not obvious. Therefore, the change in current intensity has little effect on the lateral residual stress.Figure 3 shows the residual stress distribution at the weld position at different current intensities. By com-parison, it can be found that the residual stress at the weld position is approximately the same, and the in-crease of the current intensity leads to a small increase in the residual stress of the weld. At the welding start end and the arc end, the longitudinal residual stress gra-dient is large. This is caused by the arc being unstable in arcing and arcing, and the instability of the arc causes uneven stress distribution at the beginning and end of the welding. The residual stress curves at the middle of the weld at the three current intensities are relatively straight, indicating that the stress distribution in the middle of the weld is uniform and the arc is stable. It can be seen that different current intensities have little effect on the residual stress distribution at the weld.Figure 4(a) and (b) shows the longitudinal residual stress distribution in the heat-affected zone of the two plates at different current intensities. By comparison, it Figure 1 Model schematicTable1 Chemical composition of Q345 and 2Cr13C Si Mn CrQ345 0,12 - 0,18 0,5 1,7 0,302Cr13 0,16 - 0,25 1,0 043 0,12 - 0,14Mo V Ni S P0,10 0,15 0,5 0,045 0,050- - 0,60 0,030 0,010Figure 2 Lateral residual stress comparisonFigure 3 Weld residual stress165H. FU et al.: EFFECT OF CURRENT INTENSITY ON RESIDUAL STRESS OF Q345/2Cr13 DISSIMILAR STEEL PLATEMETALURGIJA 59 (2020) 2, 163-166is known that, similar to the residual stress distribution at the weld, the longitudinal residual stress gradient is large at the welding start end and the arc end. By calcu-lating the average post-weld residual stress in the weld-ing stabilization stage, the residual stress at the current intensity of 140 A on plate 1 is 488,54 MPa, 150 A is 491,77 MPa, and 160 A is 493,24 MPa, which is 0,67 % and 0,92 % larger than 140 A, respectively. The residual stress of plate 2 at 140 A is 586,41 MPa, 150 A is 614,87 MPa, and 160 A is 636,62 MPa, which is 4,85 % and 8,56 % larger than 140 A, respectively. It is found that the longitudinal residual stress in the heat-affected zone is asymmetrically distributed on both sides of the weld line, and the stress gradient on the side of the 2Cr13 base metal is larger than that on the Q345 base material side, indicating that the welding temperature field is the main factor determining the welding stress field. The thermal conductivity of 2Cr13 is small, resulting in a large temperature gradient, and the yield strength of 2Cr13 is large, resulting in a large residual stress ampli-tude after welding, indicating that the yield strength is the main factor affecting the residual stress amplitude, which explain that yield strength is the main factor af-fecting the magnitude of residual stress. At 160 A, the residual stress after welding is large, while at 140 A, the residual stress after welding is the smallest, and the welding process is also stable. Therefore, for the weld-ing of Q345/2Cr13 dissimilar steel, it is better to use smaller current strength welding in terms of reducing residual stress.SUMMARYThe change in current intensity results in a change in the weld line energy, but has little effect on the lateral residual stress distribution during the dissimilar plate welding process.The thermal conductivity and yield strength of the material are the main factors affecting the post-weld re-sidual stress. Leading to dissimilar plate welding, dif-ferent current intensity has a great influence on the re-sidual stress of the heat affected zone, there is a certain residual stress amplitude difference, and Q345 is obvi-ously smaller than 2Cr13.For Q345/2Cr13 dissimilar steel welding, in order to reduce residual stress after welding, a small current in-tensity should be used when the voltage is constant.Acknowledgments This work was financially supported by Opening Fund for National Key Laboratory of Metallic Materials for Marine Equipment and Application (SKLMEA-K201801), Liaoning Province Natural Science Fund Project (201602385), 2017 Provincial Key Laboratory Opening Project of Liaoning University of Science and Technology (USTLKFSY201709), Liaoning Provincial Department of Education Innovation Team Project (LT2016003)REFERENCES[1] M. A. Derakhshi, J. Kangazian, M. Shamanian. 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Effect of current intensity on residual stress of Q345/2Cr13 dissimilar steel plates

Effect of current intensity on residual stress of Q345/2Cr13 dissimilar steel plates

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