In the work the bimodal heat source model in the description of the temperature field is presented. The electric arc was treated physically as one heat source, whose heat was divided: part of the heat is transferred by the direct impact of the electric arc, but another part of the heat is transferred to the weld by the melted material of the electrode. Computations of the temperature field during SAW surfacing of S355 steel element are carried out. The macrographic
and metallographic analysis of the weld confirmed the depth and shapes of the fusion line and HAZ defined by the numerical simulation

E. Gawrońska

J. Winczek

English

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225METALURGIJA 55 (2016) 2, 225-228J. WINCZEK, E. GAWROŃSKATHE MODELING OF HEAT AFFECTED ZONE (HAZ) IN SUBMERGED ARC WELDING (SAW) SURFACING STEEL ELEMENT Received – Primljeno: 2015-03-06Accepted – Prihvaćeno: 2015-09-15Preliminary Note – Prethodno priopćenjeISSN 0543-5846METABK 55(2) 225-228 (2016)UDC – UDK 621.791.052:621.72:536.5:620.18=111J. Winczek, E. Gawrońska, Faculty Mech. Eng. and Comp. Science, Czestochowa University of Technology, PolandIn the work the bimodal heat source model in the description of the temperature field is presented. The electric arc was treated physically as one heat source, whose heat was divided: part of the heat is transferred by the direct im-pact of the electric arc, but another part of the heat is transferred to the weld by the melted material of the elec-trode. Computations of the temperature field during SAW surfacing of S355 steel element are carried out. The mac-rographic and metallographic analysis of the weld confirmed the depth and shapes of the fusion line and HAZ de-fined by the numerical simulation.Key words: SAW, HAZ, modeling, temperature, microstructureINTRODUCTION In the modelling of the temperature field of welding processes a single-distributed heat source model is gen-erally assumed, reflecting the direct impact of the elec-tric arc on the surfaced object. This approach is found in the description of the temperature field during SAW surfacing using analytical and numerical methods [1-4]. The shape of the fusion lines during surfacing by weld-ing often exhibit shape irregularity that is difficult to restore by means of the description of the temperature field obtained by using the single-distributed heat source model.MODEL OF TEMPERATURE FIELDThe part of the heat generated by the electric arc is consumed to heat and melt the electrode or the addi-tional material, and then transferred by the cooling weld material to the surfaced object. This gives a justification for the division of the heat generated by an electric arc. The proposed model assumes physically one heat source – an electric arc, and the heat transfer to the sur-faced object is divided into the heat transferred directly through the electric arc and through molten material in the form of drops, that under the influence of electro-magnetic forces are detached and transferred to the forming weld. The proposed solution of the temperature field is summing temperature fields caused by the heat of direct impact of an electric arc and the heat trans-ferred to the surfaced object through the molten elec-trode material. It was assumed that the volume of the weld reinforcement and the heat accumulated there are approximately equal to the volume of molten electrode wire and the amount of the heat consumed for melting the electrode. This allows the formulation of the tem-perature field in the form: T (x, y, z, t) – T0 = Ta (x, y, z, t) + Tw(x, y, z, t) (1)where: Ta(x,y,z,t) and Tw(x,y,z,t) are tempera-ture fields caused respectively by the heat of direct impact of an electric arc and by the heat of the weld reinforcement (consumed to melt the electrode).The shape of the weld face is determined mainly by the forces of surface tension. On the basis of experi-mental research Hrabe and others [5] have proposed a parabolic shape of the face. Lower limit of the imposed metal is defined by the surface shape of surfaced mate-rial. In the solution the parabolic model was adopted. Then the geometry of the weld is presented in Figure 1, where hw is the height of the weld (weld reinforcement – the part of the weld above the surface of the surfaced material), dp is the depth of material thickness loss (e.g. depth of wear zone), and l results from considering the volume of material supplied from the electrode.Figure 1 Geometry of the weld226J. WINCZEK et al.: THE MODELING OF HEAT AFFECTED ZONE (HAZ) IN SUBMERGED ARC WELDING (SAW)... METALURGIJA 55 (2016) 2, 225-228Analytical description of the temperature field caused by the direct impact of the electric arc with Gaussian heat distribution (Figure 2) is shown in [6], whereas considering the heat stored in the liquid metal imposed on the surface is presented in [7].For accepted scheme of the single-pass surfacing (Figure 3), where:  = x – vt – x0 and x0 is the coordinate of the start of the weld, the temperature field (1) is de-fined as follows:- for time t  tc , where tc is the total time of making of the weld:  (2)- for time t > tc:   (3)where tc = l / v (4)  (5)  (6)  (7)  (8)  (9)  (10)  (11)  (12)a - thermal diffusivity / m2 s-1, Cp - specific heat / J kg-1 K-1,  - density / kg m-3, x0 / m and l / m are the co-ordinates of the start and length of the weld respective-ly. Quantity t0 / s characterizes surface heat source dis-tribution whereas r2B = 4at0 [8] (compare Figure 2). Functions G1 – G4 and F1 – F4 are solutions of integrals using Gauss-Legendre quadrature [7].Figure 2 Gaussian distribution of heat sourceFigure 3 Surfacing scheme227J. WINCZEK et al.: THE MODELING OF HEAT AFFECTED ZONE (HAZ) IN SUBMERGED ARC WELDING (SAW)...METALURGIJA 55 (2016) 2, 225-228= 748 °C have been calculated taking into account the effect of heating rate on the temperature [10, 11].EXPERIMENTAL WORKThe attempts were made at submerged arc surfacing of a square plate measuring 200 mm x 200 mm and thick-ness of 30 mm, made of steel S355J2G3, with the follow-ing parameters: U = 30 V, I = 400 A and v = 0,5 m min-1. The photograph of a metallographic macrosection in the middle cross section is shown in Figure 6. Dimensions of the weld: height of the weld reinforcement – 2,5 mm, width of the weld – 18 mm, depth of fusion in the weld axis – 3,4 mm. Calculated solidus isotherm 1 493 °C (so-lidification temperature of steel) - black line - corre-sponds to the fusion line obtained in an experiment. Bright line corresponds to the calculated temperature limit of the full transformation of austenite A3. The metallographic analysis is performed confirm-ing the identification of the highlighted areas: fusion and the full austenite transformation zones. Results are compared with the structure of the parent material. In the reinforcement of the weld and in the fusion zone (Figure 7) there is visible dendritic, ferriticpearlitic structure with Widmanstätten structure near the fusion line (Figure 8). The heat affected zone (Figure 9) is characterized by fine-grained, ferritic-pearlitic struc-ture. The parent material structure is presented in Fig-ure 10.CONCLUSIONSTaking into account the heat of the molten metal in the descriptions of the temperature field in the surfacing processes allows the reproduction of the shapes and di-mensions of the fusion lines formed in surfacing prac-The total amount of the heat qv contained in the ma-terial of melted electrode is presented by formula [9]:  (13)where qsolid – the heat required to heat the electrode from the initial temperature to the melting point, qf – the heat used to melt the electrode (heat of fusion), qliq-uid – the heat used to heat melted material to the tem-perature, where a drop of metal falls onto the surface of the surfaced object.The initial value of the outputted from the welding head electrode temperature is determined on the 100 °C. Accordingly:  (14)where L is the heat of solidification /J kg-1,  (15)where: d is the diameter of the electrode, ρe is the den-sity of the electrode material and ve is wire feed speed.EXAMPLE OF CALCULATIONCalculations of the changeable in time temperature field for a square steel element with the side length 0,2 m and thickness of the plate 0,03 m made from steels S355J2G3 have been conducted. Thermal proper-ties of welded subject material and electrode have been determined by a = 8·10-6 m2s-1, Cp = 670 J kg-1 K-1,  = 7 800 kg m-3 and L = 268 kJ kg-1.Numerical simulation has been conducted for the welding heat source of power 3 500 W with Gaussian power density distribution determined by t0 = 0,13 s and z0 = 0,008 m. The source power corresponds to welding parame-ters (U = 30 V, I = 400 A,  = 0,95) used in the welding experiment. Likewise in the experiment in calculations there were assumed welding velocity v = 0,007 m s-1, electrode wire diameter d = 3,5 mm, wire feed speed ve = 0,031 m s-1 and bead dimensions hw = 2,5 mm and ww = 22 mm (dp = 0). The initial value of temperature of electrode Te = 100 °C (a temperature of contact tip with the welding head). Computations have been made for middle cross-section of the surfaced element.In Figure 4 maximum temperature distribution in cross section has been presented. The calculted iso-therm 1 493 °C determines the fusion line and isotherms A3 and A1 determine the partial and full austenitization zones (Figure 5). The temperatures A3 = 920 °C and A1 Figure 4 Maximum temperature fieldFigure 5 Calculated heat affected zones.Figure 6  Comparison of numerical results and image of metallographic section228J. WINCZEK et al.: THE MODELING OF HEAT AFFECTED ZONE (HAZ) IN SUBMERGED ARC WELDING (SAW)... METALURGIJA 55 (2016) 2, 225-228[4] A. Ghosh, N. Barman, H. Chattopadhyay, S. Hloch, A study of thermal behaviour during  subm erged arc welding, Strojniški vestnik – J. Mech. Eng. 59 (2013) 5, 333-338[5] P. Hrabe, R. Choteborsky, M. Navratilova, Influence of weld-ing parameters on geometry of weld deposit bead, Proceed-ings, Int. Conf. on Economic Engineering and Manufacturing Systems, Brasov, 2009, Regent 10, 27, pp. 291-294[6] J. Winczek, Analytical solution to transient temperature field in a half-infinite body caused by moving volumetric heat source, Int. J. Heat Mass Transfer 53 (2010), 5774-5781[7] J. Winczek, New approach to modeling of temperature field in surfaced steel elements, Int. J. Heat Mass Transfer, 54 (2011) 4702-4709[8] P. R. Vishnu, W. B. Li, K. E. Easterling, Heat-flow model for pulsed welding, Mat. Sci. Tech. 7 (1991), 649-659[9] P. J. Modenesi; R. I. Reis, A model for melting rate phe-nomena in GMA welding, J. Mater. Proccess. Tech. 189 (2007), 199-205[10] W. Piekarska, M. Kubiak, Z. Saternus, Numerical simula-tion of thermal phenomena and phase transformations in laser-arc hybrid welded joints, Arch. Metall. Mater. 56 (2011), 409-421[11] J. W. Elmer, T. A. Palmer, W. Zhang, B. Wood, T. DebRoy, Kinetic modeling of phase transformations occurring in the HAZ of C-Mn welds based on direct observations, Acta Mater. 51 (2003), 3333-3349Note:  The responsible translator for English language is Izabela Mish-chil, Częstochowa, Polandtice. The macrographic inspections of the weld confirm the depth and regular shapes of the heat affected zone defined by the numerical simulation. The metallograph-ic analysis shows the material structure characteristic for the identified zones (dendritic structure in the rein-forcement of the weld and the fusion zone, fine grain structure in fully austenitic transformation). The direc-tion for further research is to analyze the correlation be-tween the parameters of the heat source model and tech-nological parameters of the process and their impact on the temperature distribution (dimensions and shapes of the fusion lines and also the heat affected zones) as well as the kinetics of phase transformation.REFERENCES[1]  R. Parkitny, A. Pawlak, W. Piekarska, Thermal model of submerged arc welding process , Mat. Sci. Tech. 8 (1992), 841-843[2] V. Gunaraj, N. Murugan, Prediction of heat-affected zone characteristics in submerge d arc welding of structural steel pipes, Weld. J. 81 (2002), 94s-98s[3] A. K. Pathak, G. L. Datta, Three-dimensional finite ele-ment analysis to predict the different zones of microstruc-ture in submerged arc welding, Proc. Inst. Mech. Eng. B, 218 (2004), 269-280Figure 7  Weld, Nital Etch, 100x, pearlitic-ferritic, dendritic structureFigure 8  Weld near fuison line, Nital Etch, 100x, pearlitic-ferritic, Widmanstätten structureFigure 9  Heat affected zone, Nital Etch, 100x, fine-grained, ferritic-pearlitic structureFigure 10 Parent material, Nital Etch, 100x, ferritic-pearlitic structure

The modeling of heat affected zone (HAZ) in submerged arc welding (SAW) surfacing steel element

In the work the bimodal heat source model in the description of the temperature field is presented. The electric arc was treated physically as one heat source, whose heat was divided: part of the heat is transferred by the direct impact of the electric arc, but another part of the heat is transferred to the weld by the melted material of the electrode. Computations of the temperature field during SAW surfacing of S355 steel element are carried out. The macrographic and metallographic analysis of the weld confirmed the depth and shapes of the fusion line and HAZ defined by the numerical simulation

The modeling of heat affected zone (HAZ) in submerged arc welding (SAW) surfacing steel element

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