THE EFFECT OF TORCH DISTANCE ON WELDABILITY OF DISSIMILAR WELDING ASHAARI BIN IBRAHIM

Transcription

1 i THE EFFECT OF TORCH DISTANCE ON WELDABILITY OF DISSIMILAR WELDING ASHAARI BIN IBRAHIM A report submitted in partial fulfillment of the requirements for the award of the degree of Bachelor of Mechanical Engineering Faculty of Mechanical Engineering UNIVERSITI MALAYSIA PAHANG JUNE 2013

2 vii ABSTRACT This project presents the effect of parameter in welding process on the weldability of dissimilar welding. The parameters that have been focusing are torch distance or also known as arc length. Studies were made to investigate the effect of torch distance on weldability of dissimilar welding and also to find the optimize parameters for welding dissimilar metal between stainless steel and carbon steel. The experimental data was analyzed by using Taguchi method and also Analysis of Variance. The output of this research is the visual inspection, microstructure analysis, hardness test and also tensile test. The optimized parameter for hardness test and tensile test is obtained by using Taguchi method. The result obtained for this studies is the effect of torch distance is significant based on the four output, however if compare to others parameter it is the least significant. The optimized parameter for hardness test is 90 A, 26 V, 4 mm, 4 mm/s, while for tensile test is 95 A, 24 V, 2 mm, and 4 mm/s.

3 viii ABSTRAK Projek ini membentangkan kesan parameter dalam proses kimpalan pada kebolehkimpalan kimpalan berbeza. Pembolehubah yang telah diberi tumpuan adalah jarak obor atau juga dikenali sebagai panjang arka. Kajian telah dibuat untuk mengkaji kesan jarak obor pada kebolehkimpalan kimpalan berbeza dan juga untuk mencari pembolehubah optimum untuk kimpalan logam berbeza antara keluli tahan karat dan keluli karbon. Data eksperimen dianalisis dengan menggunakan kaedah Taguchi dan juga Analisis Varian. Hasil kajian ini adalah pemeriksaan visual, analisis mikrostruktur, ujian kekerasan dan juga ujian tegangan. Parameter optimum untuk ujian kekerasan dan ujian tegangan diperolehi dengan menggunakan kaedah Taguchi. Keputusan yang diperolehi untuk kajian ini adalah kesan jarak obor adalah penting berdasarkan keputusan eksperimen, tetapi jika dibandingkan dengan lain-lain parameter ia adalah yang paling kurang penting. Parameter optimum untuk ujian kekerasan adalah 90 A, 26 V, 4 mm, 4 mm / s, manakala bagi ujian tegangan adalah 95 A, 24 V, 2 mm, dan 4 mm/ s.

4 ix TABLE OF CONTENTS TITLE PAGE EXAMINER S DECLARATION SUPERVISOR S DECLARATION STUDENT S DECLARATION ACKNOWLEDGEMENTS ABSTRACT TABLE OF CONTENTS LIST OF TABLES LIST OF FIGURES LIST OF EQUATION ABBREVIATIONS PAGE ii iii iv v vii ix xiii xiv xvi xvii CHAPTER 1 INTRODUCTION 1.1 BACKGROUND STUDY PROBLEM STATEMENT OBJECTIVES SCOPE 2 CHAPTER 2 LITERATURE REVIEW 2.1 OVERVIEW STAINLESS STEEL Typical Stainless Steel Application Austenitic (200 and 300 series) LOW CARBON STEEL 5

5 x Typical Mild Steel Application METAL INERT GAS (MIG) Advantage of MIG welding DISSIMILAR METAL WELDING Weld metal Risk of bimetallic corrosion to dissimilar welding WELDING PARAMETER CONSIDERATION Parameter of welding s torch Filler Wire Selection for Dissimilar Metal Buttering Process Butt Joint Shielding Gas DESIGN OF EXPERIMENT Taguchi Method Analysis of Variance TENSILE TEST HARDNESS TEST Vickers hardness test TOUGHNESS TEST Charpy s test WELDING DEFECT Crack Porosity Undercut Distortion Lack of Fusion Incomplete Penetration 17 CHAPTER 3 METHODOLOGY OVERVIEW 19

6 xi 3.2 PROCESS FLOWCHART EXPERIMENT PREPARATION Raw Material Carbon Steel Austenic 304 stainless steel filler wire WELDING PROCESS DESIGN OF EXPERIMENT Taguchi Method ANOVA SPECIMEN PREPARATION MECHANICAL PROPERTIES TEST 24 PREPARATION Tensile test preparation Hardness test preparation METALLURGY PROCESS Surface analysis 27 CHAPTER 4 RESULT AND DISCUSSION OVERVIEW VISUAL INSPECTION Example for visual inspection Summary of visual inspection MICROSTRUCTURE ANALYSIS Microstructure analysis under Inverted 35 Microscope Microstructure analysis under SEM Optical Measurement View MECHANICAL TEST Vickers Hardness Test 44

7 xii Tensile Test TAGUCHI ANALYSIS Optimize parameter for hardness test Optimized parameter for tensile test VALIDATION TEST Hardness test Tensile test 57 CHAPTER 5 CONCLUSION AND RECOMMENDATION OVERVIEW CONCLUSION RECOMMENDATIONS 59 REFERRENCES 60 APPENDICES 61

8 xiii LIST OF TABLES Tables No. Title Page 2.1 Example of carbon steel application carbon steel chemical composition Austenitic 304 stainless steel chemical composition ER 308 filler wire chemical composition Taguchi method parameters Dimension for ASTM standard of E Variables value for Vickers hardness test The visual inspection Hardness test result Tensile test findings (Force, Displacement, Stress, Strain and 46 Yield Strength) 4.4 Result of experiment Optimized parameter for hardness test Regression analysis (Hardness) Optimized parameter for Tensile test Regression analysis (Tensile) 55

9 xiv LIST OF FIGURES Figures No. Title Page 2.1 Metal Inert Gas IMC layer of aluminium-steel joint MIG welding parameters Electrode extension Contact tip to work distance Butt joint stress strain curve Welding defect MIG machine Automated welding table Shear machine ASTM E Vickers Hardness Tester MMT-X7 Matsuzawa Cold mounting machine Grinding process Polishing process Etching process Inverted Microscope IM Scanning Electron Microscope SU The view for visual inspection A, B, C, D, E is a spot of the picture of microstructure Microstructure at the base metal for carbon steel at magnification x 4.4 Microstructure at the base metal for SS at magnification 100x Microstructure between weldment and HAZ (CS) for specimen 2 36 at magnification 100x 4.6 Microstructure between weldment and HAZ (SS) at 100x Microstructure of weldment at magnification 100x 37

10 xv 4.8 Defect inspection from the view of microscope Fusion zone with 5 µm magnification Base metal (stainless steel) with 10.0 µm Corrosion occur at the fusion zone with 2.00 µm Optical measurement view for specimen Optical measurement view for specimen Optical measurement view for specimen Vickers hardness result The Tensile Strength graph Tensile test result Main effects plot for means and SN ratios(hardness) Main effects plot for means and SN ratios (tensile) Hardness validation result Tensile validation test result 57

11 xvi LIST OF EQUATION Equation No. Title Page 4.1 Regression equation of Hardness Regression equation of Tensile 55

12 xvii LIST OF ABBREVIATIONS ASME ASTM ANOVA BM C Cr CS Cu DOE FKM Fe FZ HAZ IMC MIG Mn Ni OA SEM Si SS American Society of Mechanical Engineers American Society for Testing and Materials Analysis of Variance Base Metal Carbon Chromium Carbon Steel Copper Design of Experiment Fakulti Kejuruteraan Mekanikal Ferrous Fusion Zone Heat Affected Zone Intermetallic Compounds Layer Metal Inert Gas Manganese Nickel Orthogonal Arrays Scanning Electron Microscope Silicon Stainless Steel

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14 1 CHAPTER 1 INTRODUCTION 1.1 BACKGROUND STUDY Carbon steel and stainless steel are the most metal that used in the manufacturing world field. Carbon steel has used worldwide in manufacturing industry, because of their properties that is malleable, have a good strength, can be bent, and also anti-corrosion. Carbon steel also used in the oil and gas industry for piping because of it has high end durability. The other metal that use frequently in the world of industry is, stainless steel. That is because, stainless steel is anti-corrosion and dirt, easy to handle, and ideal for many applications. Both metal is used worldwide and absolutely have experience in the joining process like welding. Welding is a technique to join two or more types of metals. Welding is operation in which two or more parts are united by means of heat or pressure or both, in such a way that there is continuity in the nature of the metal between these parts. There is much type of welding like, laser welding, spot welding, arc welding, TIG welding and the most used in manufacturing industry is MIG welding. Metal Inert Gas welding (MIG welding) is a welding process that uses shielding gas to cover the arc. The arc is between a weld metal and filler wire.this process is not using the application of a pressure. In this welding process, the parameter is very important. Parameter like voltage, current and wire feed rate can give huge influence in the welding result. Therefore this research focus on the torch distances parameter. The torch distance is the distance between the tip of the filler wire and the metal face. This research is to study the effect of torch distance on the weldability of the dissimilar metal using MIG welding process. Weldability is the capability of a material

15 2 to be welded under the imposed fabrication conditions into a specific, suitably designed structure and to perform satisfactorily in the intended service. In other word, weldability is a term used to determine whether easy or not to weld some metal. To test the weldability, several test need to conduct, like, Charpy s test, tensile test and the microstructure analysis. It is easy to weld the metal if the weldability is high. 1.2 PROBLEM STATEMENT Welding dissimilar metal is difficult because of the difference compositions that lead to difference chemical properties. The dissimilar welding will form intermetallic compound. Therefore to make a good compound, two metals with filler wire should have mutual solubility. (Cary & Helzer, 2005). Dissimilar metals have different chemistries, so they have different physical properties such as melting temperature. Many who have involved with joining metal with different melt temperature experience frustration. The difficulties was arise when someone try to melt metal together at same weld temperature. For example mild steel and stainless steel, obviously in nature these materials have different melting point. Besides that, to get the good welding result, the parameters also give the influence. The joining of two dissimilar metals fail due to wrong parameter. If the parameter like torch distance too far and too close, the dissimilar joint will not successfully. 1.3 OBJECTIVE To investigate the effect of MIG torch distance on weldability of dissimilar welding To evaluate weld properties through the Hardness, Tensile, and Microstructure analysis 1.4 SCOPE Here, scope act as the guidance that permits this research is doing without loss the focusing. It is capable to bring the project to their objective without run out by doing work that not relate to the objective. Welding process has done using MIG welding machine. The controlled parameter such Voltage, Wire feed, current and Gas flow rate

16 3 was selected which respect to the welding standard and machine capability. The main parameter that needs to study for this research is the torch distance. Material used is mild steel and (AISI 304) stainless steel with both thickness 3 mm. the joint design was single groove butt joint with flat position by MIG welding filler wire (ER308). Specimen was prepared according to AWS and ASTM respectively to study the mechanical properties such state in the objective. Other variables are not mention here become a limitation of this project scope. To choose the right parameter, the design of experiment used is Taguchi Method. Then, the data is collect and analyze by using ANOVA.

17 4 CHAPTER 2 LITERATURE REVIEW 2.1 OVERVIEW This chapter is state the literature review from the past researches. From this literature review, there is much information that will be useful to operate the project. This literature review is from journals, handbooks and articles. 2.2 STAINLESS STEEL Stainless steel also known as anti-corrosion steel is one of the most useful steel in the manufacturing industry. Stainless steel is steel that have many addition element, like titanium, niobium, nickel, chromium, and molybdenum. Stainless steel has three main types, martensitic, austenitic, and ferritic Typical Stainless Steel Application Stainless steels are used in many applications. That is because, stainless steel is one of the metals that most easily to be welded (Wahab et al. 1998). These applications include an extremely diversified range of uses, including nuclear reactor vessels, heat exchangers, oil industry tubular, components for chemical processing and pulp and paper industries, furnace parts, and boilers used in fossil fuel electric power plants Austenitic (200 and 300 series) Stainless steel also known as corrosion-resisting steels because of its anticorrosion steel (Ibrahim et al. 2012). Austenitic stainless steels are used worldwide because of their properties that very good anti-corrosion with excellent mechanical

18 5 properties (toughness and strength), have low carbon levels, and nitrogen alloying for increasing their mechanical strength (Ibrahim et al. 2012). Welding stainless steels can make the imperfection like hot cracking. To overcome this problem, ensure the formation of ferrite in the weld deposit. The filler wire that most used for welding stainless steels is, 347, AWS E/ER 308, 308L. However to join the stainless steel with other metal like carbon steel, 309 filler wire is the best choice. The stainless steels in the austenitic group have same characteristics but different compositions and properties.they can be hardened by cold working, but not by heat treatment. In the annealed condition, all are nonmagnetic, although some may become slightly magnetic by cold working (Arivazhagan et al. 2006). 2.3 LOW CARBON STEEL Carbon steel is the no one metal that used in the manufacturing industry. This is because it is cheap, easy to handle, can be bent, and also high in toughness. The amount of element in carbon steel usually 0.25% Carbon and 0.4%-0.7% manganese, 0.1%- 0.5% Silicon and addition of other element Typical Mild Steel Application Mild steel is an important category of materials due to their wide range of industrial applications. It is used in many industries due to its excellent mechanical properties. It is used in industries as pipelines for petroleum industries, storage tanks, reaction vessels and chemical batteries (Nascimento et al. 2001). Weldability of carbon steels depend on the content of carbon. Weldability will decrease if the carbon content is increase. However, with the high content of carbon, the steel hardenability will also high, but it will be more prone to cracking.

19 6 Table 2.1: Example of carbon steel application Types Application Low Carbon Steel (Mild Steel) Use for component that no need high strength, like component in machine (nut, bolt, sheet, etc) Medium Carbon Steel High Carbon Steel Use for component that need higher strength than low carbon steels. For example, equipment from agriculture part, automotive part, and machine parts. Use for higher strength, like kitchen utensil, cable, medical equipment and cutting tools. Source: K. Serope and S. Steven (2006) 2.4 METAL INERT GAS (MIG) MIG welding is widely used in many industry applications such as automotive, oil and gas, agriculture, and construction. Metal inert gas welding (MIG) is a welding process that employs continuous consumable solid filler wire that shield by inert shielding gas which causes flow of current to generate the thermal energy in the partially ionized gas (Petrov et al. 2006). From the end of the melting filler wire, the heat is concentrated to the molten weld pool. Therefore the heat will melt the both base metal and filler wire at the weld pool (Podder et al. 2012). Their versatility, rapid, economical, capable in all weld position, technique, speed and high deposition is the reason why it most used. MIG welding can operate with semiautomatic or automatic and work with most metal. MIG welding does not require particular skill level and it is capable to be carried out by fresh welder with some basic instruction. Hence, it is provided with semiautomatic mode which is appropriate to reduce the human factor error that contributes to weld quality as well as to acquire the better result. In weld a dissimilar metal, MIG welding is twice better than SMAW in term of productivity from deposition of the welt metal on the base metal, and good consumable utilization (Lenin

20 7 et al. 2010). MIG welding produce high quality weld at high speed without the used flux and limited post weld cleaning. It is very desirable for both small and high production metal joining. It frequently replaces other joining process such as riveting, brazing, silver-soldering, or resistance welding. MIG welding is better than friction welding in term of flexibility because friction welding constraint for round billet shape or pipe only. There are two main factors influencing the metal transfer for the arc welding which are the arc voltage and the welding current. Filler wire Figure 2.1: Metal Inert Gas Source: Miller et al, Advantage of MIG welding There are some of the advantages of MIG processes (Sack & Bohnart, 2005): - Good penetration and smooth weld bead - Good weld appearance - Easy to weld and give high quality process - The welding process is fast - Distortion is reduced because the heat is being concentration during welding

21 8 2.5 DISSIMILAR METAL WELDING The definition for dissimilar metal welding is joining two difference metals together. It is not easy because difference metal have difference properties. However with good combination of two metal and filler wire, the metal can join successfully. This welding method can join any metals together to get the good function and appearance. Nowadays, welding dissimilar metal is use worldwide around the world, and many new methods has evolved to join dissimilar metal like friction stir welding and other method like involving laser process (Sathiya et al. 2010). However, joining two dissimilar metals can lead to some defect like brittleness, crack and porosity. Defects that usually found in dissimilar metal welding are crack, porosity, overlap, undercut and distortion lack of fusion and incomplete penetration. This is because intermetallic phases found in fusion zone. Intermetallic compound is metal compound that mix with the base metal and the filler wire. Therefore, before start selecting material to join together, the phase diagram of two metal needs to investigate. The welding will be success if two metals have mutual solubility (Sathiya et al. 2010). From the past research, (Hendrerieckx et al. 2009) most of the service failures are reported is at the weld region.. Figure 2.2: IMC layer of aluminium-steel joint Source: Lin et al, 2009

22 9 Melting temperature is one of the most importance factors that need to consider in welding process. It is because, difference metal have difference melting temperature. If the difference is too high, the one part of the metal will molten faster than other metal. So the third metals must take a place in joining process which may help to avoid this kind problem. For example, if steel melting point is around C, while aluminium alloy melting around C, so the third metal which is filler metal, its melting point must be somewhere in the middle of those two base metals. There is another method to join the dissimilar metal, it is coated the metal like steel by zinc or aluminium layer, to improve the filler wire s wetting and inhabit the IMC layer growth (Lin et al. 2009) Weld Metal Material such carbon steel and stainless steel are widely used in many applications such as construction, power plant, petrochemical, offshore, automotive industry, piping system and more. Carbon steel is low carbon steel that easy to form and has excellent weldability meanwhile stainless steel has popular as resistant to corrosion material and weldable with various application (Sathiya et al. 2010). Carbon steel and austenic steel (AISI 304) is a great affiliation of mechanical properties, formability, weldabiliy, and resistance to corrosion (Kim et al. 2003). According to (Karadeniz et al. 2007) joining carbon steel to stainless steel can be done by welding with the filler wire AISI Risk of bimetallic corrosion to dissimilar welding Although stainless steel is good corrosion resistance, with the joining with the carbon steel it is difficult to survive in the high corrosion environment like in seawater. This problem can easily overcome by applied coating like painting to avoid the corrosion. 2.6 WELDING PARAMETER CONSIDERATION Welding parameters like current, voltage and wire feed rate can give influences in the welding process and welding result. Welding current is factor that will determine

23 10 the penetration. If the value of welding current increase, then the value of depth of penetration will also increase. Welding speed and arc voltage also influence by the depth of penetration (Allen et al. 2001). Therefore, the parameter need to choose carefully, and the pre- experiment need to conduct to find the right welding parameter. From the previous study with an MIG or GMAW welding process, it observed that the depth of penetration increased when the welding current is increased but decreased with decrease in voltage and the penetration increased when arc travel rate decreased until it attained a minimum value depends on the arc power (Benyounis & Olabi, 2008). However, because of the big influences of the welding parameter in the weldability, these researches try to investigate the other parameter, torch distance. Torch distance is the distance between the tips of filler to the base metal face. To make a good possible welding condition the combinations factor like types of base metal, welding process and the geometry of welded part need be as good as possible (Tusek & Suban, 2000). The investigation of GMAW process and relationship between process variables and bead geometry was carried and the results showed the arc current has the greatest effects on bead geometry. Investigation in the weld deposit area and presented that the effects of electrode polarity, diameter and extension, arc voltage, welding current, power source setting, travel speed and flux on the weld deposit area (Jang et al. 2005). The perfect arc will be achieved if all the welding parameters in conformation. These parameters consists of arc welding current, arc voltage, welding speed, torch angle, free wire length, torch distance, nozzle distance, welding position and direction and lastly the flow rate of gas (Kim et al. 2003). These parameters influence the quality, productivity and cost of welding. Figure 2.3: MIG welding parameters Source: Jeff Nadzam et al, 1995

24 Parameter of welding s torch Electrode extension is the electrode extended from the end of the contact tip to the arc (figure 2.4). It is just the length of the electrode, and not includes the arc length. This term is use for the semiautomatic welding. Contact tip to work distance is the length measured from the end of the contact tip to the work piece (figure 2.5) Figure 2.4: electrode extension Source: Nadzam et al, 1995 Torch length is also known as arc length is the length from the tip of electrode filler to the surface of workpiece. It also can derive with the length of electrode extension subtract the contact tip to work distance (CTWD). Figure 2.5: Contact tip to work distance Source: Nadzam et al, 1995