ADVANCES in NATURAL and APPLIED SCIENCES ISSN: 1995-0772 Published BYAENSI Publication EISSN: 1998-1090 http://www.aensiweb.com/anas 2017 April 11(4): pages 551-556 Open Access Journal Study And Analysis Of Microstructure And Mechanical Properties Of Weld During Underwater Wet Smaw 1 Kavitha K, 2 Arunkumar G, 3 Katturaja V 1 Assistant professor, Department of mechanical engineering, GCE Salem, 2 UG final year students, Department of mechanical engineering, GCE Salem, 3 UG final year students, Department of mechanical engineering, GCE Salem, Received 28 January 2017; Accepted 22 April 2017; Available online 1 May 2017 Address For Correspondence: Kavitha K,, Assistant professor, Department of mechanical engineering, GCE Salem, E-mail: kavitharaj31@gmail.com Copyright 2017 by authors and American-Eurasian Network for ScientificInformation (AENSI Publication). This work is licensed under the Creative Commons Attribution International License (CC BY). http://creativecommons.org/licenses/by/4.0/ ABSTRACT SMAW experiments were conducted under the water and in the air with PVA-alumina coated electrode. Influences of surrounding water on the weld geometry, weld microstructure and mechanical properties were studied. Fine granular pearlite and ferrite present in the wet weld. High amount of Acicular Ferrite (AF) in HAZ of wet weld and this amount is decreased by increasing the heat input, more ferrite content in the air weld. Two types of metal transfer mode has been observed, i.e. globular transfer mode and combined surface tension and repelled globular transfer mode. Mechanical properties like toughness and hardness has been studied. Mechanical properties improved at reduced cooling rate by increasing the heat flux. KEYWORDS: Underwater welding, PVA-alumina coated electrode, microstructure and metal transfer mode. INTRODUCTION The desire to repair damaged offshore structures as a result of corrosive defects, material fatigue and accident during assembly, construction errors, and excessive operational loads has brought the underwater welding. The first under water welding was done by British admiralty dockyard for the repair of leaking ship rivets. Most recently a lot of underwater welding activities have been going on for example the platform installation, pipeline welding, watercraft welding, seashore components and offshore structure welding. Offshore development has accelerated in recent years owing to the fact that more than 60% of undeveloped petroleum deposits are located under the ocean. In the offshore industry, oil and gas pipelines already a routine activity, the demand for under welding can produce the quality wet welding at greater depth and on variety of materials will continue to increase. Characterized by low cost, good adoptability, simple equipment the underwater wet welding is widely used. The most commonly used is shielded metal arc welding (SMAW). There are two types of underwater welding wet welding and dry welding. Wet welding occurs directly in aqueous environments with no mechanical barriers between the water and welding rod. It significantly low cost and simplicity of the process. The desired qualities of sound underwater are flexibility of operation in all positions, minimum electrical hazard,good visibility, reliable welds, less porosity of welds. However the increase in the carbon and oxygen content leads the tendency of cracking. The steel having higher carbon equivalent greater than 0.4% shows the poor weld ability and also the aqueous environment produce lot of disadvantages like loss of alloying metal, considerable amount of diffusion of hydrogen and the cooling rate is high ToCite ThisArticle: Kavitha K, Arunkumar G, Katturaja V., Study And Analysis Of Microstructure And Mechanical Properties Of Weld During Underwater Wet Smaw. Advances in Natural and Applied Sciences. 11(4); Pages: 551-556
552 Kavitha K et al., 2017/Advances in Natural and Applied Sciences. 11(4) April 2017, Pages: 551-556 MATERIALS AND METHODS In this project we chosen the low carbon steel having less carbon equivalent about 0.32 for Base material composition shown in Table I below. Table 1: Base material composition C Mg P S Si Cr Ni Mo V 0.2 0.4 0.035 0.035 0.1 0.4 0.4 0.15 0.08 A. Filler Rod: E6013 welding electrode selected for welding the mild steel specimens. Filler rod of electrode is made of mild steel. The composition of filler rod shown in table 2 below Table: 2 Filler Rod composition CONTENT WEIGHT PERCENTAGE Silicon 0.18 Magnesium 0.45 Phosphorus 0.014 Carbon 0.08 Sulphur 0.012 B. Water Proofing Electrode: In this paper, the coated electrode is used for wet welding process. For water proofing, the Commercial rutile electrode (E6013) is coated with poly vinyl alcohol and Nano alumina mixture by dip coating method A small amount of poly vinyl alcohol salt is taken in a beaker containing 100 ml of water. The solution is heated and mechanically stirred with help of glass rod for 5 minutes. After 5 minutes another small amount of poly vinyl alcohol added and stirred for 5 minutes. This process continues till formation of gel like adhesive polymer solution. After the gel like structure formed the solution allowed to cool to the room temperature. Then Nano alumina powder is mixed into the solution and stirred for 30 minutes for better dispersion of Nano particles into the polymer matrix. Now the electrode is dipped into the solution and removed slowly. After that electrode is placed in the oven for 15 minutes for drying. The electrode in the oven having thin layer PVA-alumina. The coating from the bottom of the electrode is removed by rubbing of abrasive sheet, for arc initiation purpose. Fig. 1: Electrode dipped in solution
553 Kavitha K et al., 2017/Advances in Natural and Applied Sciences. 11(4) April 2017, Pages: 551-556 Fig. 2: PVA-alumina mixture Fig. 3: Polyvinyl Alcohol salt Table 3: Welding parameters Parameters Air Water 1 Water 2 Current 120A 150A 180A Voltage 35V 33V 31V Speed 1.6x10-3 m/s 1.42x10-3 m/s 1.48x10-3 m/s Table 4: Heat input conditions Power(W) Heat input(kj/m) Air 4200 2100 Water 1 4950 2021 Water 2 5580 2186 Fig. 4: Schematic diagram
554 Kavitha K et al., 2017/Advances in Natural and Applied Sciences. 11(4) April 2017, Pages: 551-556 Weld Charecteristics: A. Weld Bead Appearance: Good weld bead appearance was obtained in the air welding and poor weld bead appearance was obtained in the underwater weld due to the metal transfer affected by surface tension. Fig. 5: Air welding bead appearance Fig. 6: wet welding bead appearance In the air welding, the globular mode of metal transfer taken place. In this mode of metal transfer molten metal from the electrode transferred drop by drop to the base metal In underwater wet welding, combined surface tension and globular mode of metal transfer taken place. Surface tension transfer affects transfer of molten metal from the electrode, so poor weld bead appearance obtained. B. Joint Preparation: Underwater welding butt joints resulted in the lower penetration only 2mm in the 5mm depth of specimen. Fig. 7: Square butt joint Poor penetration To have the good penetration, the edges are prepared with V grooves at angle of 30 o to the depth of 4mm. V weld joint made under the water having higher penetration shown in figure below. Fig. 8: Cross section of V weld joint made Analysis Of Microstructure: A. Microscopic Examination: Microscopic images were captured with the help of Metallographic Microscope. The specimen etched with the nital (etchant used for steels) solution is placed on the stage of the microscope, so that its surface is perpendicular to the optical axis. A metallurgical microscope has a system of lenses, so can achieve the different magnifications (25X to 1000X). The images captured at 400X magnification.
555 Kavitha K et al., 2017/Advances in Natural and Applied Sciences. 11(4) April 2017, Pages: 551-556 4.2 Microstructures of Specimen: Fig. 9: Microstructure of specimens Figure a shows the more ferrite (75%) and less pearlite (25%) content in weld zone of air welding with larger grain size and also special side plate ferrites. Figure b shows the acicular ferrite content reduced and pro-eutectoid ferrite formed at increased heat input specimen Figure c shows Fine granular ferrite and pearlite structure were observed in underwater wet welding of lower heat input due to High solidification rate of weld metal. Time provided for grains to grow is very less due to higher cooling rate. This grain size is increased by increasing the heat input. Figure d shows Heat affected zone of underwater wet at low heat input contains higher amount of acicular ferrite Mechanical Testing: A. Rockwell Hardness Test: The Hardness tests were conducted on the specimen in Rockwell hardness testing Machine. Fig. 10: Hardness Distribution
556 Kavitha K et al., 2017/Advances in Natural and Applied Sciences. 11(4) April 2017, Pages: 551-556 Hardness distribution of specimen given in the figure 10 above, the low heat input underwater weld specimen (water 1) having less hardness due to the formation of fine grains in the weld zone. Also heat affected zone having higher hardness because it s having higher amount of acicular ferrite shown in figure 9(d) The hardness values are reduced considerably in high heat input underwater welding specimen (water2). B. Impact Test: Specimen Dimensions of 5x10x55 mm with V notch to 1mm as per ASTM A370 Standard prepared for Impact tests on CHARPY V NOTCH TESTING MACHINE. Fig. 11: Impact strength at various condition Conclusion: Microstructure and Mechanical properties studied for the specimens made in Shielded Metal Arc Welding carried under water at different heat input condition. The following conclusions were made by analysing surrounding water effects on specimen. The cooling rate affecting properties of the weld joint. This cooling rate can be reduced by increasing the heat input. Fine granular structure Produced in weld zone of underwater welding at lower input underwater welding condition. Increased heat input result in increased size of granular structure by reducing cooling rate. Higher amount of acicular ferrite were observed in the heat affected zone of underwater welding at lower heat input condition. The amount of acicular ferrite content reduced by increasing the heat input. REFERENCES 1. Cui, L., X. Yang, D. Wang, X. Hou, J. Cao, W. Xu, 2014. Friction taper plug welding for S355 steel in underwater wet conditions: welding performance, microstructures and mechanical properties. Mater. Sci. Eng. A 611: 15-28. 2. Yin, Y., X. Yang, L. Cui, F. Wang, S. Li, 2015. Material flow influence on the weld formation and mechanical performance in underwater friction taper plug welds for pipeline steel. Mat., 88: 990-998. 3. Di, X., S. Ji, F. Cheng, D. Wang, J. Cao, 2015. Effect of cooling rate on microstructure, inclusions and mechanical properties of weld metal in simulated local dry underwater welding. Mater., 88: 505-513. 4. Gao, W., D. Wang, F. Cheng, C. Deng, Y. Liu, W. Xu, 2015a. Enhancement of the fatigue strength of underwater wet welds by grinding and ultrasonic impact treatment. J. Mater. Process. Technol., 223: 305-312. 5. Guo, N., W. Guo, Y. Du, Y.L. Fu, J. Feng, 2015a. Effect of boric acid on metal transfer mode of underwater flux-cored wire wet welding. J. Mater. Process. Technol., 223: 124-128. 6. Guo, N., D. Liu, W. Guo, H. Li, J. Feng, 2015b. Effect of Ni on microstructure and mechanical properties of underwater wet welding joint. Mater., 77: 25-31. 7. Guo, N., C. Xu, Y. Du, M. Wang, J. Feng, Z. Deng, D. Tang, 2016. Effect of boric acid concentration on the arc stability in underwater wet welding. J. Mater. Process. Technol., 229: 244-252.