MICROSTRUCTURE CHARACTERISTICS & MECHANICAL PROPERTIES OF DISSIMILAR TIG WELD BETWEEN STAINLESS STEEL AND MILD STEEL

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1 International Journal of Mechanical Engineering and Technology (IJMET) Volume 8, Issue 7, July 2017, pp , Article ID: IJMET_08_07_192 Available online at ISSN Print: and ISSN Online: IAEME Publication Scopus Indexed MICROSTRUCTURE CHARACTERISTICS & MECHANICAL PROPERTIES OF DISSIMILAR TIG WELD BETWEEN STAINLESS STEEL AND MILD STEEL Baljeet Singh Assistant Professor, School of Mechanical Engineering, Lovely Professional University, India. Pankaj Kumar School of Mechanical Engineering, Lovely Professional University, India. Dr. S.K. Kumara swamy ICMCB, CNRS, Bordeaux, France. Dr. Uday Krishna Ravella School of Mechanical Engineering, Lovely Professional University, India. Dr.Anil Midathda School of Mechanical Engineering, Lovely Professional University, India. ABSTRACT In this experiments, TIG welding parameters influence on weld-ability of both stainless steel304 and mild steel 1018 specimens with dimension of 150 mm long x 75 mm wide x 3 mm thick is investigated. This paper investigated the microstructure and mechanical properties of dissimilar materials such as SS and MS joints by tungsten inert gas (TIG) welding. Tungsten inert gas welding techniques is wildly used for joining both ferrous and non-ferrous metals. Performance of Tungsten inert gas (TIG) welding on between stainless steel 304 and Mild steel 1018 plate have been studied by optical microscope. The work aims at joining of dissimilar material are stainless steel and mild steel done by TIG welding with the various parameters like voltage, welding speed and gas flow rate. The filler metal grade ER309 employed for joining of these dissimilar metals. Optical Microscopic examination was carried editor@iaeme.com

2 Baljeet Singh, Pankaj Kumar, Dr. S.K. Kumara swamy, Dr. Uday Krishna Ravella and Dr.Anil Midathda Key words: TIG welding, Microstructure, Tensile strength, Hardness, Taguchi method (TM), analysis of variance (ANOVA) orthogonal array, S/N ratio. Cite this Article: Baljeet Singh, Pankaj Kumar, Dr. S.K. Kumara swamy, Dr. Uday Krishna Ravella and Dr.Anil Midathda Microstructure Characteristics & Mechanical Properties of Dissimilar Tig Weld Between Stainless Steel and Mild Steel. International Journal of Mechanical Engineering and Technology, 8(7), 2017, pp INTRODUCTION In the fabrication process equipment s made from stainless steels and mild steel such as pipe, automotive exhaust gas system, chemical industrial equipment, etc., an arc welding commonly used to join metal and its alloys. Arc welding using shielding gas is often used. Tungsten inert gas (TIG) welding is one of the mostly used welding methods. [1] Welding of dissimilar metal is frequently used to join stainless steels to other metal alloys. This joint is mostly used where high strength or performance are required. Below a certain temperature and pressure, however, low-alloy and low-carbon steels perform adequately, and a transition from stainless steel to other steels is often used for economic purposes. Most stainless steels can be successfully welded to low-alloy and low-carbon steels. The weld metal with the two base metals have different coefficients of thermal expansion in stainless steel and low-carbon or Mild Steel. [2] Tungsten Inert Gas (TIG) welding is also called the Gas Tungsten Arc Welding (GTAW). The Gas Tungsten Arc Welding (GTAW) or Tungsten Inert Gas (TIG) are most commonly used in fabrication industries for joining ferrous and non-ferrous metals and widely used in modern industry due to good weld bead surface finish obtained. TIG welding offers several advantages like joining of dissimilar metals, low heat affected zone, absence of slag etc. TIG weld quality is strongly characterized by weld bead geometry. A high penetration to width ratio means a narrow weld. This also means a good quality of the weld. [3] A non-consumable tungsten rod is used as the electrode with inert gas shielding both the molten metallic pool and red hot filler wire tip. TIG welding can be done commonly all position of metal thickness ranging from 1 to 6 mm is generally joint by TIG process. [4] During the TIG welding process thermal cycles in welding process cause the chemical composition and micro structural changes. These changes affect the mechanical properties of the welded joints. Mechanical properties like tensile strength, hardness are typically controlled by cross-sectional microstructure. [5] editor@iaeme.com

3 Microstructure Characteristics & Mechanical Properties of Dissimilar Tig Weld Between Stainless Steel and Mild Steel Figure 1 Diagram of TIG welding plates The materials used for dissimilar welding were SS-304 and MS-1018, nominally 3 mm in thickness. The chemical compositions of Specimen SS-304, MS-1018 and filler rod 309 are shown in Tables I, II and III respectively. Table 1 Chemical compositions of SS-304 % C Mn S P Si Ni Cr Cu Table 2 Chemical compositions of MS-1018 % Fe C Mn S P Table 3 Chemical compositions of Filler Rod 309 % C Mg Si Mo Ni Cr Before welding, the samples were prepared and welding can be done. Transverse crosssections were observed by optical microscopy (OM). The specimens for optical microscopy were cut perpendicular to the welding direction using an electrical discharge machine. The Vickers hardness profile of the weld was measured on the cross-section perpendicular to the welding direction. The tensile strength are performed on universal testing machine (UTM). [6] 2. METHODOLOGY 2.1. Taguchi Method Taguchi method is used to plan the experiments. Taguchi technique is importance of studying the productivity using the signal-to-noise (S/N) ratio, resulting in minimization of quality characteristic variation due to uncontrollable parameter. The S/N ratio used for this type response is given by [7] There are three Signal-to-Noise ratios of common interest for optimization editor@iaeme.com

4 Baljeet Singh, Pankaj Kumar, Dr. S.K. Kumara swamy, Dr. Uday Krishna Ravella and Dr.Anil Midathda (1) Smaller The Better:- n = -10 Log10 [mean of sum of squares deviation] (2) Higher The Better:- n = -10 Log10 [mean of sum squares of deviation] (3) Nominal The Best:- n = 10 Log10 [square of mean variance] [8] Taguchi L-9 Orthogonal Array Taguchi L9 Orthogonal array was used, which has nine rows corresponding to the number of tests, with three columns at three levels. L9 OA has eight DOF, in which 6 were assigned to three factors (each one 2 DOF) and 2 DOF was assigned to the error. For this purpose of observing the degree of influence of the process parameters in GTA Welding As per DOE in table 3, nine samples were made by pulsed GTAW process which are shown in table. [7] Table 3 Standard Taguchi l-9 orthogonal array Specimen No. Welding Current Gas Flow Rate A B C D E F G H I Welding Speed Table 4 Sequence experiment done by Taguchi method on specimen Specimen No. Welding Current (amp) Gas Flow Rate (l/min) Welding Speed (mm/sec) A B C D E F G H I editor@iaeme.com

5 Microstructure Characteristics & Mechanical Properties of Dissimilar Tig Weld Between Stainless Steel and Mild Steel 2.2. Work Material Using dimensions of work-piece 75 mm long x 75 mm wide x 3 mm thick of different material such as stainless steel and mild steel can be used for work material as shown in figure II. Figure 2 Diagram of TIG welding work material plates TIG welding experiments are performed using the Polarity Direct Current Electrode Negative [DCEN]. TIG welding using the process parameters are welding current (70, 80, 90) amp, Gas Flow Rate (10, 15, 20) L/Min & Welding speed (1.5, 1.7, 2.3)mm/sec. Constant parameters are Frequency 60Hz, Voltage 16V, Electrode diameter 1.6 & Electrode to workpiece distance 2mm. Table 5 Shows level and parameters Levels 3. EXPERIMENTAL RESULTS Welding Current Gas Flow Rate Welding Speed Level-i Level-ii Level-iii Microstructure Microstructures for all the welded samples have been studied and the photographs are taken in weld and HAZ regions, for each of the samples by the metallurgical microscope. Base metal microstructure has also been studied. Typical TIG welding microstructure was identified in all the welds with the help of metallurgical microscope. All the welds produced by varying the process parameters were analyzed for microstructural appearance. Samples of size 15 mm x 15 mm at the joint interface were sectioned and mounted the samples such that the advancing side of the weld was always to the right. The mounted samples were prepared according to the standards given in metallography and microstructure. Metal has removed by filing to a depth of approximately 1 mm during preparation of the specimen. Sand paper of 220, 600, 1000, 1500 grits are used for cleaning to make the surface finished. Diamond paste has been used for finishing purpose to obtain as like mirror image surface. Alumina (Al2O3) was also used during cleaning the specimen on velvet paper which was mounted on the disc. After cleaning the specimen etching process has been used to obtain microstructure characteristics. Etchant editor@iaeme.com

6 Baljeet Singh, Pankaj Kumar, Dr. S.K. Kumara swamy, Dr. Uday Krishna Ravella and Dr.Anil Midathda used that having contains 5.0gm of picric acid, 5 ml of hydrochloric acid, and 100 ml of ethanol. In total 9 specimen has taken for the microstructure evolution at the welded region. All microstructure images has taken at 0.50μm or at 400x resolution. One representative base metal microstructure is shown in Figure III. Figure 3 Metallographic view of base metal In general, austenitic grains are revealed under the microscope, in which precipitation of ferrite is also present. In Figure IV in the weld region columnar grains of ferrite have been seen though out the structure. Austenite grains are elongated, in Figure some of the portions, precipitated carbide has been found. In almost all the samples, traces of δ- ferrite are observed in HAZ under the microscope. Dispersed carbide phases are found in HAZ region of sample number B-1. This sample shows lowest UTS in tensile test. In most of the samples columnar-dendritic grain growths are observed in the weld microstructure, as shown in figure. In sample number C-1, full austenitic structure with small or fine grain has been observed. This sample has shown highest UTS. In general, more or less uniform distribution of austenite grains of equal size are seen throughout the structure, in which precipitation of carbide is revealed. In the weld-haz transition region, in some samples more amount of δ-ferrite is precipitated, because, dilution-less weld metal cannot reach to the base metal. So, base metal is quickly melted and solidified. As solidification time is less, δ-ferrite cannot get enough time for total transformation into complete austenitic structure. Microstructures developed at different regions of the weld beads are dependent on the compositions of base and filler materials, dilution, heating and cooling cycles and many other factors. A little bit of variation found in the microstructures among nine samples, may be linked with the above factors, particularly with heating and cooling cycles. Varied parametric combinations during welding, influence heat input, heat input rate and cooling cycle. This, in turn, influences microstructures. Figure 4 Metallographic view of 9 sample editor@iaeme.com

7 Microstructure Characteristics & Mechanical Properties of Dissimilar Tig Weld Between Stainless Steel and Mild Steel 3.2. Tensile Strength Now tensile test specimens are made by machining the welded samples. Photographic view of a tensile test specimen is shown in Figure V. Figure 5 Photographic view of the tensile test specimen Tensile test specimens are tested on universal testing machine and photographic view of tensile test specimen after testing as shown in figure VI. Figure 6 Photographic view of the tensile test specimen after testing 3.3. Results of Tensile Test Tensile test has been performed on universal testing machine, to examine the regions from where fracture has occurred and to find important mechanical properties of the welded samples. The results of tensile tests are given in Table VI. The tensile test results indicate that for most of the samples, tensile strength is satisfactory. It is generally desired that failure does not occur within the weld region. From Table it is found that under some parametric conditions of current, gas flow rate and welding speed, ultimate tensile strength are remarkably good. For sample numbers 1, 2, 3, 4, 5, 6, 7, 8, 9, it is within the range of 480 MPa 520 MPa. For the sample number 3, ultimate tensile strength is maximum and for the sample number 2, ultimate tensile strength is minimum. Ex.No. Welding Current(Amp) Table 6 Tensile test results Gas Flow Rate (L/Min) Welding Speed (mm/sec) Tensile Strength (N/mm2) S/N Ratio A B C D E F G H I editor@iaeme.com

8 Baljeet Singh, Pankaj Kumar, Dr. S.K. Kumara swamy, Dr. Uday Krishna Ravella and Dr.Anil Midathda 3.4. Main Effect of Tensile Strength Based on the data in Table VI main effect plots for UTS have been obtained. From these plots one can predict the nature of the relationship between UTS and input parameters. With increase in current, UTS increases. Thus trend is clear and definite. However, with increase in both gas flow rate and welding speed, UTS first decreases and then increases beyond the 2nd level. Thus trends between i) gas flow rate and UTS and ii) welding speed and UTS are not consistent. Figure VII indicates that change in the levels of the input parameters influences UTS, but not always in a consistent manner. Factors like environmental condition, some impurities present in the base metal may influence the process. Figure 7 Main effect plots for mean of UTS The Table VII shows the results of analysis of variance for tensile strength. If P value is less than 0.05, the corresponding factor is said to have significant influence on the response, at 95% level of confidence. On examining the P values it is observed that gas flow rate is the most significant factor because corresponding P value is the lowest and it is below Welding speed is also significant factor because its value is also less than Thus gas flow rate is the most significant factor followed by welding speed. Current is not a very significant factor which influences UTS. The determination factor (R-Sq) indicates the goodness of fit of the model. The value of R-Sq of this model is 99.69% which is greater than 80 %. This implies that at least 99.69% of the variability in data for the response is explained by the model. This indicates that the proposed model is adequate. Table 7 shows the results of analysis of variance for tensile strength Source DF Adj SS Adj MS F-Value P-Value Regression Current gas flow rate Welding speed Error Total S R-Sq R-Sq(adj) R-Sq(Pred) % 93.81% editor@iaeme.com

9 Microstructure Characteristics & Mechanical Properties of Dissimilar Tig Weld Between Stainless Steel and Mild Steel 4. CONCLUSION In the present work, butt welding of austenitic stainless steel AISI 304 and mild steel AISI 1018 has been done by tungsten inert gas (TIG) welding, at varied levels of current, gas flow rate and welding speed. The responses considered are tensile strength and hardness. Austenitic grains are revealed under the microscope, in which precipitation of ferrite are also present. Coarser grains found in HAZ than in base metal. Small amount of δ-ferrite is observed in the microstructure of HAZ. In single objective optimization by Taguchi, the objective is to maximize tensile strength individually i.e. separately. Taguchi s S/N ratio concept is utilized and it is found that optimum condition for maximum UTS is A3 B3 C1 i.e. current = 90 A, gas flow rate = 20 liter/min, welding speed = 1.5mm/sec Increase in current with increase the tensile strength of the material. REFERENCES [1] Ahmet Durgutlu. (2004):Experimental investigation of the effect of hydrogen in argon as a shielding gas on TIG welding of austenitic stainless steel. Materials and Design, 25(19 23). [2] Cheng-Hsien Kuo; Kuang-Hung Tseng; Chang-Pin Chou. (2011): Effect of activated TIG flux on performance of dissimilar welds between mild steel and stainless steel. Key Engineering Materials Vol. 479 pp [3] Vikesh; Jagjit Randhawa; N M Suri. (2013): Effect of a-tig welding process parameters on penetration in mild steel plates. International Journal of Mechanical and Industrial Engineering, ISSN No , Vol-3, Iss-2. [4] Dheeraj Singh; Vedansh Chaturvedi; JyotiVimal. (2013): Parametric optimization of TIG process parameters using Taguchi and Grey Taguchi analysis. International Journal of Emerging Trends in Engineering and Development, ISSN [5] Venkatasubramanian, G.; Sheik Mideen, A.; Abhay K Jha (2013): Microstructral characterization and corrosion behaviour of top Surface of TIG welded 2219 T87 Aluminium alloy. International Journal of Engineering Science and Technology, Vol. 5 No.03,ISSN : [6] Prashant Kumar Singh; Pankaj Kumar; Baljeet Singh; Rahul Kumar Singh (2015): A review on TIG welding for optimizing process parameters on dissimilar joints. Int. Journal of Engineering Research and Application ISSN: , Vol. 5, Issue 2, (Part -5), pp [7] Anoop C A; Pawan Kumar. (2013): Application of Taguchi Methods and ANOVA in GTAW Process Parameters Optimization for Aluminium Alloy International Journal of Engineering and Innovative Technology, Volume 2, Issue 11, ISSN: [8] J. Pasupathy; V.Ravisankar. (2013): parametric optimization of TIG welding parameters using taguchi method for dissimilar joint Low carbon steel with AA1050. International Journal of Scientific & Engineering Research, Volume 4,ISSN [9] K. Subbaiyan, V. Kalaiyarasan and M. AbdulGhaniKhan, Experimental Investigations and Weld Characteristics Analysis of Single Pass Semiautomatic TIG Welding with Disimilar Stainless Steels, International Journal of Mechanical Engineering and Technology, 8(5), 2017, pp editor@iaeme.com