ARID ZONE JOURNAL OF ENGINEERING, TECHNOLOGY & ENVIRONMENT AZOJETE December 2020. Vol. 16(4):803-812 Published by the Faculty of Engineering, University of Maiduguri, Maiduguri, Nigeria. Print ISSN: 1596-2490, Electronic ISSN: 2545-5818 www.azojete.com.ng Corresponding author’s e-mail address: samorosada@gmail.com 803 ORIGINAL RESEARCH ARTICLE PARAMETRIC OPTIMIZATION AND DETERMINATION OF A SUITABLE WELDING PROCESS FOR STAINLESS STEEL-MILD STEEL DISSIMILAR METALS WELD S. O. Sada* and L. C. Enyi Department of Mechanical & Production Engineering, Faculty of Engineering, Delta State University. Oleh Campus, Nigeria *Corresponding author’s email address: samorosada@gmail.com 1.0 Introduction The increasing application of new structures with tailored engineering properties in the manufacturing industry has given rise to the joining of metals with entirely different materials and properties. This combination of different materials not only allows the use of metals with specific properties to be utilized in a more functional and efficient manner, but it also allows for a whole new structure possessing unique mechanical properties to be created. These materials often possess good compatibility in terms of properties as it relates to the service conditions necessities (Das et al., 2014; Kas et al., 2009). The joining of dissimilar metals cannot be compared to that of similar or identical metals (Bhattacharya et al., 2016; Satyanarayana et al., 2005). Many factors such as the dissimilar metals composition, its properties (chemical and metallurgical), the selection of suitable filler material, the joint design, and the welding process affects both the choice of the welding processes and the quality of the welded joints. Additionally, the proper selection of a suitable joining process, filler material, and process parameter, to an acceptable weld joint design is a major determinant for obtaining a reliable weld quality (Tusek et al., 2001). Electric arc welding, amongst which are: gas metal arc welding (GMAW), the gas tungsten arc welding (GTAW) and shield metal arc welding (SMAW), are the most prominent fusion welding processes employed for dissimilar metals (Lin et al., 2010). Martinsen (2015), Bang (2013) and Dong (2012), reported that the formation of brittle intermetallic compounds (IMC) resulting from the Heat Affected Zone (HAZ) and the molten pool is minimized with the use of arc welding process. Conversely, Kaewkuekool and Amornsin (2008), Kim (2009), and Wang (2012) revealed aside identifying a ARTICLE INFORMATION ABSTRACT Difficulties associated with dissimilar metals welding differ remarkably and can be minimized with the selection of a suitable joining process, modification of the joining technique, and the adoption of optimal process parameters. This study investigates the suitability of three fusion welding processes (gas tungsten arc welding (GTAW), gas metal arc weld (GMAW), and shielded metal arc welding (SMAW)) in the welding of stainless steel to mild steel plates based on their mechanical properties and observed weld defects. Gas tungsten arc welding (GTAW) process which turned out to be the most suitable of the three, recording the least imperfections, an efficiency in mechanical properties of 8% higher compared to the other processes, furthermore analyzed using the response surface methodology (RSM) to obtain a models of the input and output relationship, as well as the optimal process parameters was conducted. An optimal parameters of 461.88N/mm2 for the tensile strength and 31.65% for the Elongation was observed at the combined input parameters of 200 amp, 15 volt, 20 l/min, and 2.4mm for the weld current, arc voltage, gas flow rate and filler rod respectively. Therefore, the application of optimal process parameters along with a compatible weld process is recommended in the welding of dissimilar metals to guarantee excellent weld qualities. © 2020 Faculty of Engineering, University of Maiduguri, Nigeria. All rights reserved. Submitted 2 May, 2020 Revised 23 November, 2020 Accepted 24 November, 2020 Keywords: Welding Dissimilar Metals Response Surface Methodology Tensile Strength mailto:samorosada@gmail.com http://www.azojete.com.ng mailto:samorosada@gmail.com Sada and Enyi: Parametric Optimization and Determination of a Suitable Welding Process for Stainless Steel-Mild Steel Dissimilar Metals Weld. AZOJETE,16(4):803-812. ISSN 1596-2490; e-ISSN 2545-5818, www.azojete.com.ng Corresponding author’s e-mail address: samorosada@gmail.com 804 suitable welding process, there is the need for compromise in the selection and combination of different process parameters. They reported that the selection of a filler material compatible with the base metal, the application of buttering, and the control of heat input was necessary in reducing the alloy element gradient and carbon migration, and the risk of corrosion. Monika et al. (2013) studied the effect of the heat input on the mechanical properties of a dissimilar (GMAW) welded joints. They observed that the hardness is directly proportional to the heat input but inversely proportional to the tensile strength of the weld. The authors concluded that the mechanical properties of materials with considerable difference in properties welded by the arc welding method, depends greatly on the input process control, the filler material used and the preheat and post-heating condition. Kaewkuekool and Amornsin (2012), carried out a study on the mechanical properties of a dissimilar metal weld between stainless (AISI 304) and low-carbon steel using gas metal arc welding (GMAW) technique along with three different filler metals; GFW304L, 308L [EN12073] and 316L [EN12072]). From the result obtained, the tensile strength and percentage elongation are greatly affected by the weld speed, weld current, as well as filler metal type. Khorrami et al. (2014) studied the suitability of applying filler metals, in the welding of AISI 430 ferritic stainless steel weld and plain carbon steel) using the GTAW process. They reported that a reasonable improvement in the mechanical properties (hardness and Ultimate tensile strength) was observed in the weld having filler metals compared to the autogenously weld. They reported further that applying a filler metal compatible to the dissimilar metals being joined enhances the mechanical properties of the joint. Mvola and Kah, (2017) in their study examining the effects and components of shielding gas mixtures in fusion welding, asserted that the appropriate selection of shielding gases and the control of the gas flow rate was capable of increasing productivity in the welding industry along with improving the quality of the weld. Chuaiphan et al. (2013) carried out a study to investigate the most suitable of the welding processes; gas tungsten arc welding (GTAW) and shield metal arc welding (SMAW) in terms of toughness for 15 mm thick stainless steel to carbon steel plates dissimilar welded joints. They reported that aside the pitting corrosion potential displayed by the GTAW welded joint, the SMAW weld had a higher weld metal toughness. Teker et al. (2011) pointed out that in the welding of ferrite steel and quenched, and tempered steel using GMAW-P and GMAW, a superior tensile strength, less grain growth, and a narrow heat affected zone was recorded in the GMAW_P welded compared to the GMAW welded joint. This they ascribed to the better heat control, a finer fusion zone, and higher fusion hardness attributes of the GMAW-P welding process. Kumar and Sundarrajan, (2009) applied the Taguchi method in determining the optimal mechanical properties of a (Al-Mg-Si) aluminum alloy welded using TIG welding process as well as the effect of the pulsed TIG welding parameters. Their findings which compared the TIG weld to the parent metal revealed had a lower notch tensile strength and impact toughness. The objective of this study is to compare three different welding processes in the joining of mild steel to austenitic stainless steel (304) plates (10mm thickness) and evaluate the optimal welding parameters for the selected weld process. 2. Materials and Methods 2.1 Materials The base metals selected for the experiment are stainless steel and mild steel plates with dimensions of 20 mm x 10 mm x 6 mm, along with the following input parameters; weld current (200-240amp), arc voltage (15-25Volts), filler rod (2.0-2.4mm) and gas flow rate (20- 24lit/min). Based on the physical, chemical and mechanical-technological properties comparable to those of the base material, 302 stainless steel with chemical composition as shown in Table 1, was selected as the filler material (Hatifi et al., 2014). http://www.azojete.com.ng mailto:samorosada@gmail.com Arid Zone Journal of Engineering, Technology and Environment, December, 2020; Vol. 16(4):803-812. ISSN 1596-2490; e-ISSN 2545- 5818; www.azojete.com.ng Corresponding author’s e-mail address: samorosada@gmail.com 805 Table 1: Chemical Compositions (wt. %) of the Base Metals and Filler Metal Designation Fe C Si Mn S P Mo Cr Ni Stainless Steel 71.43 0.058 0.35 1.32 0.007 0.032 0.94 18.52 8.28 Mild Steel 99.31 0.2 0.14 0.4 0.05 0.04 0.24 0.21 Filler Material 0.03 0.6 1.8 0.15 23.4 13 2.1.2 Welding Process The electric arc welding process comprises of different types, amongst which are the gas tungsten arc, gas metal arc and the sheilded arc welding processes. The gas tungsten arc welding (GTAW) is performed by means of an electric arc generated by the welding machine along with a non-consumable tungsten electrode (Sathish et al., 2012). The gas metal arc welding (GMAW) process on the other hand makes use of an arc along with a servo wire electrode which is automatically feed as it melts into the weld puddle. They both make use of an inert gas, or a gas mixture such as argon, helium, and mixtures of these gases. The shielded metal arc welding (SMAW) process unlike the gas shielded welding processes mentioned above, makes use of a consumable electrode and does not require a shielding gas. However, its covered electrode serves as a source of protection from harmful oxidation. A display of the GTAW and GMAW welding machines is presented in Figures 4a, and 4b respectively. Figure 4a: GTAWWelding Machine Figure 4b: MIG/MAG Welding Machine 2.2 Method The workpiece interface (stainless steel and carbon steel) was bevelled, to conceal the nickel content effect associated with the austenitic stainless steel, and to allow for sufficient application of filler metal, before fitting the metals together to form a groove as shown in Figure 1. Figure 1: Schematic Representation of the Welded Joint The labels ά, represent the bevel angle, d; the gap, and t; the thickness. The experiment was performed using the three different welding techniques: gas metal arc welding (GMAW), the gas tungsten arc welding (GTAW), and shielded metal arc welding (SMAW) with argon gas as the inert gas with a bevel angle of 90° and gap of 2 mm. The welded specimens from each of file:///C:/Users/user/Downloads/azojete143/www.azojete.com.ng mailto:samorosada@gmail.com Sada and Enyi: Parametric Optimization and Determination of a Suitable Welding Process for Stainless Steel-Mild Steel Dissimilar Metals Weld. AZOJETE,16(4):803-812. ISSN 1596-2490; e-ISSN 2545-5818, www.azojete.com.ng Corresponding author’s e-mail address: samorosada@gmail.com 806 the welding processes were subjected to visual inspection and tensile tests to ascertain the performance of the different welding processes. Observations for surface defects made with the naked eye and x-ray flaw detector were obtained and tabulated as shown in Table 2. Prior to the experiment, the base materials were grouped into three (A, B, and C), for the three welding processes GTAW, GMAW, and SMAW respectively. And with the application of the central composite design of the response surface methodology using the Design Expert Software, thirty (30) experimental runs were generated. 2.2.1 Tensile test To evaluate the transverse tensile properties (tensile strength and percentage elongation) of the stainless steel/mild steel dissimilar welds, the welded plates were machined to a tensile specimen shape according to ASTM standards and thereafter tested for tensile strength, and percentage elongation using a Universal Testing Machine (UTM) according to their groups (GTAW, GMAW, and SMAW). 2.2.2 Response surface methodology (RSM) The response surface methodology is employed on the concept of identifying the relationship between the response or dependent variable "y" and the relevant input or independent variables x1, x2,…,xk (Hicks 1993). The response surface is expressed as shown in Equation (1) on the assumption that the variables are continuous, controllable and measurable not ignoring a level of negligible error ε. y = f (x1, x2, x3...,xk ) + ε (1) With the Response surface methodology (RSM), the experimental data was used in developing the empirical models for the experiment, establishing the independent and response variable relationship with the aid of the second order quadratic model given in Equation (2). y = βₒ + i=1 βᵢxᵢ� + j=1 k βᵢᵢxᵢ2� + ij k βᵢⱼxᵢxⱼ�� + ε for i < j (2) The coefficient of the polynomial denoted by “β” is estimated using the least squares method. 2.2.2.1 Analysis of variance ANOVA The ANOVA test is performed to establish the suitability of the model, with the following parameters R2 representing coefficient of determination, Adjusted R2, the P value required to be < 0.05 identifies the significant model terms. 3. Results and Discussion For visual inspection and radiographic test, seven (7) of the welded samples from the different welding processes were observed for surface defects with the naked eye and an x-ray flaw detector and their results tabulated as shown in Table 3. http://www.azojete.com.ng mailto:samorosada@gmail.com Arid Zone Journal of Engineering, Technology and Environment, December, 2020; Vol. 16(4):803-812. ISSN 1596-2490; e-ISSN 2545- 5818; www.azojete.com.ng Corresponding author’s e-mail address: samorosada@gmail.com 807 Table 2: Visual Inspection and X-ray Radiographic Test Results. GTAW GMAW SMAW Samples Visual Inspection X-ray radiographic Visual Inspection X-ray radiographic Visual Inspection X-ray radiographic 1 No imperfection No imperfection No imperfection No imperfection incomplete penetration Undercut porosity 2 Blow hole Spatter porosity No imperfection No imperfection incomplete penetration spatter lack of fusion 3 No imperfection No imperfection Spatter incomplete penetration incomplete penetration spatter lack of fusion 4 No imperfection No imperfection incomplete penetration Undercut porosity incomplete penetration Undercut porosity 5 Spatter incomplete penetration incomplete penetration Undercut porosity incomplete penetration Undercut porosity 6 No imperfection No imperfection incomplete penetration Lack of fusion incomplete penetration Lack of fusion 7 No imperfection No imperfection incomplete penetration Undercut porosity incomplete penetration Undercut porosity The results from the visual inspection and x-ray radiographic test shows that there was little or no defects observed on the GTAW welded plates compared to the other two processes. However, defects like lack of penetration, undercut at both the root and the face, a lack of sidewall fusion, blowhole, porosity, etc. were observed in the GMAW welds and higher in the shield metal arc welded plates. 3.1 Tensile Strength The transverse tensile properties (tensile strength and percentage elongation) of the stainless steel/mild steel dissimilar welded specimens were evaluated according to their groupings (GTAW, GMAW and SMAW), and the results along with the average is presented in Table 3. Figure 2 shows the GTAW welded dissimilar metal joint before and after the tensile test. Figure 2: Mild steel/stainless steel dissimilar welded Joint before and after tensile test file:///C:/Users/user/Downloads/azojete143/www.azojete.com.ng mailto:samorosada@gmail.com Sada and Enyi: Parametric Optimization and Determination of a Suitable Welding Process for Stainless Steel-Mild Steel Dissimilar Metals Weld. AZOJETE,16(4):803-812. ISSN 1596-2490; e-ISSN 2545-5818, www.azojete.com.ng Corresponding author’s e-mail address: samorosada@gmail.com 808 Table 3: Expérimental data Table 4 shows the results for the tensile test of the welded plates. It was observed that average tensile strengths and elongations were 485.5 N/mm2 and 30.6% for the GTAW welds, 483.2 N/mm2 and 29.1% for the GMAW welds, and 480.8 N/mm2 and 28.4% for the SMAW welds. The results show that the weld performance of the GTAW process, performed better with a weld strength and elongation 0.5% and 5.2% respectively, compared with GMAW having 1.2% and 7.7% respectively compared to the SMAW techniques. 3.2 Optimization In developing the optimal equations in terms of actual factors for maximizing the responses, experimental data obtained as recorded in Table 3, was employed. The results were further analyzed using the response surface methodology (RSM), and mathematical models of the responses as shown in equations 1 and 2 were obtained. Exp No GTAWWELDED JOINTS GMAW WELDED JOINTS SMAW WELDED JOINTS Tensile Strength (Mpa Percentage Elongation Tensile Strength (Mpa) Percentage Elongation Tensile Strength (Mpa) Percentage Elongation 1 494.0 29.9 496.5 28.4 490.2 27.6 2 496.3 28.3 494.6 26.8 490.4 26.0 3 496.4 25.8 495.6 24.3 491.0 23.5 4 495.9 36.0 494.6 34.5 490.2 33.7 5 496.3 32.8 495.2 31.3 490.7 30.5 6 496.2 31.0 495.1 29.5 490.6 28.7 7 496.8 33.5 494.2 32.0 490.5 31.2 8 489.9 29.5 489.0 28.5 484.4 27.3 9 485.9 33.5 484.8 32.0 480.3 31.2 10 483.4 27.6 481.1 26.1 477.2 25.3 11 462.3 33.6 460.3 32.1 466.3 31.3 12 490.0 28.9 488.2 27.4 484.2 26.6 13 480.3 33.0 481.3 31.5 475.8 30.7 14 495.0 35.0 478.2 33.5 481.6 32.7 15 468.7 33.9 467.5 32.4 473.1 31.6 16 469.6 29.9 468.7 28.4 469.2 27.6 17 460.3 30.0 459.1 28.5 464.7 27.7 18 486.3 31.3 485.4 29.8 480.8 29.0 19 494.6 30.1 493.3 28.6 488.9 27.8 20 496.1 29.0 495.2 27.5 490.6 26.7 21 472.3 29.7 473.3 28.2 467.8 27.4 22 488.1 30.4 480.1 28.9 479.1 28.1 23 477.8 29.2 475.4 27.7 473.6 26.9 24 490.0 29.0 472.9 27.5 476.5 26.7 25 485.0 29.3 485.5 27.8 480.5 27.0 26 475.7 31.5 475.8 30.0 470.7 29.2 27 492.3 30.0 491.1 28.5 486.7 27.7 28 482.1 33.0 481.2 31.5 479.5 30.7 29 486.3 28.0 485.5 26.5 480.9 25.7 30 480.2 27.0 478.2 25.5 478.2 24.7 AVE 485.5 30.6 483.2 29.1 480.8 28.4 http://www.azojete.com.ng mailto:samorosada@gmail.com Arid Zone Journal of Engineering, Technology and Environment, December, 2020; Vol. 16(4):803-812. ISSN 1596-2490; e-ISSN 2545- 5818; www.azojete.com.ng Corresponding author’s e-mail address: samorosada@gmail.com 809 TENSILE STRENGTH = +660.26227 − 3.24914 ∗ X 1 + 12.10708 ∗ X 2 + 1.23333 ∗ X 3 + 2.24479 ∗ X 4 + 0.018083 ∗ X 1 ∗ X 2 + 0.124375 X 1 ∗ X 3 + 0.225521 ∗ (X 1 ∗ X 4 − 0.419375 ∗ X 2 ∗ X 3 − 1.58125 ∗ X 2 ∗ X 4 − 1.67187 ∗ X 3 ∗ X 4 − 0.001745 ∗ X 1 2 − 0.057083 ∗ X 2 2 − 0.134896 ∗ X 3 2 + 4.98698 ∗ X 4 2 (1) PERCENTAGE ELONGATION = +159676 − 0.186620 ∗ X 1 − 4.77625 ∗ X 2 − 5.58333 ∗ X 3 + 0.760417 ∗ X 4 + 0.002542 ∗ X 1 ∗ X 2 + 0.008437 X 1 ∗ X 3 − 0.067188 ∗ (X 1 ∗ X 4 + 0.021875 ∗ X 2 ∗ X 3 + 0.928125 ∗ X 2 ∗ X 4 − 0.742188 ∗ X 3 ∗ X 4 + 0.000287 ∗ X 1 2 + 0.031833 ∗ X 2 2 + 0.125521 ∗ X 3 2 + 1.153646 ∗ X 4 2 (2) The variables X1, X2, X3, and X4 in the équations, represent the process parameters; weld current, arc voltage, filler rod diameter and gas flow rate respectively. The strength of the models was analyzed using analysis of variance (ANOVA) test, the results as shown in Figure 3, shows that the models are significant and that the tensile strength and elongation is greatly influence by the weld current. This mostly attributable to its influence on the bead shape, the depth of penetration, the deposition rate, and the rate at which electrode is melted (Sada 2018). Figure 3: ANOVA of the Responses The mathematical model obtained in Equations 1 and 2, were further employed in carrying out the prediction of the responses. Predicted values obtained of the responses were compared to that of the experimental values by performing a plot of the predicted response against the observed values for each of the responses as shown in Figure 4a and 4b. file:///C:/Users/user/Downloads/azojete143/www.azojete.com.ng mailto:samorosada@gmail.com Sada and Enyi: Parametric Optimization and Determination of a Suitable Welding Process for Stainless Steel-Mild Steel Dissimilar Metals Weld. AZOJETE,16(4):803-812. ISSN 1596-2490; e-ISSN 2545-5818, www.azojete.com.ng Corresponding author’s e-mail address: samorosada@gmail.com 810 Figure 4a: Plots of predicted versus Figure 4b: Plots of predicted versus actual values of tensile strength actual values for percentage elongation The straight-line graph shows that the errors are uniformly distributed. An indication that there’s a significant correlation between the experimental and predicted response values (Sada 2018). 3.3 Numerical optimization To ascertain the desirability of the overall model, numerical optimization was performed using the design expert software. The responses were optimized and their corresponding optimum input process parameter values were determined. Figure 5 shows the Ramp Results of the optimal response parameters. Figure 5: Ramp showing the optimal response parameters 4. Conclusions Comparative study of the different welding processes based on the tensile properties; tensile strength and Percentage elongation, showed that the GTAW weld performed better with higher tensile strength and elongation while the shielded had the least output. The experiment not only confirms the GTAW welding process as the most suitable technique for the welding of stainless steel to mild steel dissimilar metals in comparison to the gas metal arc welding and shielded metal arc welding processes. It also confirms that stainless steel filler metal is an appropriate filler material for the joining of mild steel to stainless steel. Further analysis of the GTAW weld process using the response surface methodology showed that the weld current is the most significant model term and the optimal tensile strength of 491.49N/mm2 and Elongation of 32.31% can be obtained at a welding current of 200 amp, voltage 15 volt, gas flow rate 24 l/min and filter rod of 2.4mm. http://www.azojete.com.ng mailto:samorosada@gmail.com Arid Zone Journal of Engineering, Technology and Environment, December, 2020; Vol. 16(4):803-812. ISSN 1596-2490; e-ISSN 2545- 5818; www.azojete.com.ng Corresponding author’s e-mail address: samorosada@gmail.com 811 5. Acknowledgement The author would like to acknowledge the staffs and head of the Department of Welding and Fabrication, Petroleum Training Institute, Effurun, Delta state for their support with the equipment. Reference Bang, H., Bang, H., Song, H. and Joo, S. 2013. Joint properties of dissimilar Al6061-T6 aluminum alloy/Ti-6%Al-4%V titanium alloy by gas tungsten arc welding assisted hybrid friction stir welding. Materials and Design, 51: 544-551. Bhattacharya, A. and Sanchit, S. 2016. Dissimilar GTAW between AISI 304 and AISI 4340 steel. multi-response optimization by analytic hierarchy process. Proceedings of the institution of mechanical engineers. Part E; Journal of Processing Mechanical Engineering, 231(4): 824-835. Chuaiphan, W., Somrerk, C., A., Niltawach, C. and Sornil, B. 2013. Dissimilar welding between AISI 304 stainless steel and AISI 1020 Carbon Steel Pates. Applied Mechanics and Materials, 268: 283-290. Das, C., Bhaduri, A., Srinivasan, G., Shankar, V. and Mathew, S. 2009. 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International Journal of Minerals, Metallurgy and Materials, 19(6): 518-524 http://www.azojete.com.ng mailto:samorosada@gmail.com