Negus material training text book in mechanical

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1. P resented By : Nigus Ayalew Advisor: Dessalegn Ahmed Yeshanew (Ph. D.) September , 2025 G.C Addis Ababa, Ethiopia 10/1/2025 Prepared by: Negus Ayalew 1 Optimization of Micro-Structure and Mechanical Properties of Heat Affected Zone in Submerged Arc Welding Of Mild Steel AISI 1020

2. The quality of a weld joint is highly influenced by depth of penetration. Hence, accurate prediction and maximization of depth of penetration is highly essential to ensure a good - quality joint. In this study, was to investigate the Microstructure and Mechanical Properties of Heat Affected Zone in Submerged Arc Welding of AISI 1020 Mild Steel. In this study, was to investigate the effect of various welding parameters like, the welding current, arc voltage, welding speed, heat input rate are chosen as welding parameters. The methodology was used in this study a combined approach of experimental and analytical methods to analyzing a micro-structure and mechanical properties in terms heat affecting zone for the selected welding parameters on the selected welding process. The depth of penetrations were measured for each specimen after the welding operation on closed butt joint and the effects of welding speed and heat input rate parameters on depth of penetration, hardness, tensile strength were investigated. This study was also get by experimental investigation the optimal effect of submerged arc welding in micro structure and mechanical properties of weld metal such as tensile strength, impact strength, micro-hardness and micro-structure in submerged arc welded metal are to evaluate. Finally based on the investigation, optimized the effects of submerged arc welding in micro structure and mechanical properties was showed porosity and luck of fusion/joint of penetration were defects in the flat welding positions. Key Words: Submerged Arc Welding, welding parameters, Micro Structure, Mechanical Properties and Heat Affecting Zone 10/1/2025 Prepared by: Negus Ayalew 2 ABSTRACT

3. Background of the study Submerged arc welding (SAW) is a method of joining metals through coalescence. The method is broadly utilized in the heavy welding industry for the fabrication of pipelines, fuel cylinders, shipbuilding, mining, large industrial shed construction, pressure vessel and boiler industries, automobile companies, large shape constructing corporations, garage tanks, and rail system industries and mineral processing equipment, and many others. A wide spread problem encountered by the manufacturers in the case of the SAW process is setting the process parameters to attain the best overall performance of the process. The SAW process is characterized by deep penetration and high deposition rates, making it suitable for applications in industries such as shipbuilding, structural steel fabrication, and heavy machinery manufacturing. The heat generated during welding creates a Heat Affected Zone (HAZ) around the weld, where micro-structural changes occur due to thermal cycling. These alterations can significantly affect the mechanical properties of the material, making the HAZ a critical area of study for ensuring the integrity and performance of welded structures. 10/1/2025 Prepared by: Negus Ayalew 3 CHAPTER ONE INTRODUCTION

4. SAW process is characterized by using multiple input parameters which include wire feed rate, electrode stick out, traverse speed, welding current, arc voltage, contact tip-to-plate distance, wire diameter, flux type, and so on. These input parameters significantly affect the responses such as weld bead geometry, tensile strength, hardness, impact value, deposition rate, penetration of weld, etc. However, a process parameter setting determined in this way is commonly far from optimum. Therefore, an urge to achieve more optimum values of output parameters has recommended the researchers use of optimization techniques for the selection of input process parameters of SAW [2]. In SAW the weld quality is mainly influenced by independent variables like welding current, wire feed rate(𝑤𝑓), electrode stick (𝑠0𝑢𝑡) out and traverse speed (𝑆) and these are also represented the strength and hardness of weldment. So, in this study was necessary to control these input parameters for quality welding, more ductility and strength within the weld while it welded with the aid of SAW. 10/1/2025 Prepared by: Negus Ayalew 4 Statement of the problem

5. In this study were rising the following research questions according to the investigation of researcher context: 1. What the major factors of a Mechanical Properties in submerge arc welding process? 2. What the major factors of a Microstructure of the HAZ are in submerge arc welding process? 3. What are the relationship of Mechanical with Microstructure Properties in submerge arc welding process? 4. How to now the proper welding practices in submerge arc welding process? 10/1/2025 Prepared by: Negus Ayalew 5 Research questions

6. The general objectives of this thesis was investigated a Microstructure and Mechanical Properties of Heat Affected Zone in Submerged Arc Welding of AISI 1020 Mild Steel. Specific Objectives The specific objectives of this thesis was: To evaluate the mechanical properties of the HAZ To analyze the micro structural changes in the HAZ To correlate the microstructure with mechanical properties To provide recommendations for optimizing welding parameters 10/1/2025 Prepared by: Negus Ayalew 6 General Objectives of the study

7. The significance of this study is fabrication in its potential to contribute to the understanding of how welding processes affect material properties, particularly in the critical HAZ. By providing data and insights, this research can help improve welding practices, enhance product quality, and ensure the safety and reliability of welded structures. Furthermore, the findings may serve as a foundation for future research in welding technology and materials science. Scope of the study This study focuses on the submerged arc welding process applied to mild steel. It encompasses the analysis of the microstructure and mechanical properties of the HAZ resulting from various welding parameters, including heat input and welding speed. The research will utilize a combination of experimental techniques, including microscopy for micro-structural analysis and standardized mechanical testing methods. While the study was provide valuable insights into the HAZ characteristics, it was primarily concentrate on mild steel, leaving the exploration of other materials and welding techniques for future investigations. 10/1/2025 Prepared by: Negus Ayalew 7 Significance of the study

8. Introduction In this chapter will present the literature review part of the study focusing on the basic concepts submerged arc welding process and its working principles. Then a review of the related literature was presented on the investigation of micro structure and mechanical properties of mild steel where the research will be conducting. Submerged Arc Welding Submerged arc welding (SAW) process uses heat generated by an electric arc established between a bare consumable electrode wire and the work piece. Since in this process, welding arc and the weld pool are completely submerged under cover of granular fusible and molten flux therefore it is called so. During welding, granular flux is melted using heat generated by arc and forms cover of molten flux layer which in turn avoids spatter tendency and prevents accessibility of atmospheric gases to the arc zone and the weld pool. 10/1/2025 Prepared by: Negus Ayalew 8 CHAPTER TWO LITERATURE REVIEW

9. Principle of Submerged Arc Welding According to the researchers [6 and 7] Sub Arc welding requires a continuously fed tubular or consumable solid electrode and may be fully automatic or semi-automatic. The arc is flat and is maintained between the end of a bare wire electrode and the weld. The electrode is constantly fed into the arc and as it is melted, a layer of granular flux provides a protective cover beneath which the welding occurs. The submerged-arc welding (SAW) process is similar to MIG where the arc is formed between a continuously-fed wire electrode and the work piece, and the weld is formed by the arc melting the work piece and the wire. However, in SAW a shielding gas is not required as the layer of flux generates the gases and slag to protect the weld pool and hot weld metal from contamination. Flux plays an additional role in adding alloying elements to the weld pool [14]. 10/1/2025 Prepared by: Negus Ayalew 9 Cont ….

10. Submerged Arc Welding Equipment Power Source Welding Gun Electrode Flux handling Protective equipment Welding Parameters and their Effects Electrode polarity Welding current Electrode Diameter Arc voltage Welding speed Electrode extension Electrode angle and Flux depth 10/1/2025 Prepared by: Negus Ayalew 10 Cont ….

11. Methodology The main objectives of this chapter was to investigate the optimization of welding parameters and mechanical properties on heat affected zone in submerged arc welding process for AISI 1020 mild steel. This study was used a scientific research methodology presented by identifying a research approach, research design, data collections, sampling techniques with sampling size and data analysis tool to implementing the proposal work. Materials The material use for this experimental investigation was used AISI 1020 mild steel. This material is used to applicable in different steel work due to its sustainability, availability and least cost. AISI 1020 steel is one of the steel grades widely used in different industries like; construction, transport, automotive, power, etc. The chemical composition and mechanical properties of the AISI 1020 mild steel of work piece material is given in table 3.1 and table 3.2. 10/1/2025 Prepared by: Negus Ayalew 11 CHAPTER THREE RESEARCH METHODOLOGY AND MATERIALS

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13. Research approach The research approach for this study will collect and analyze significant data for the purpose of the study and the research approach for this research will use both qualitative and quantitative approach. Quantitative approach will use to investigating the study by the help of needed data and the qualitative research approach of study will also concerning with the expressing way of the exiting situations under study investigation. Sampling techniques Sampling is the act, process, or technique of selecting a representative part of a material for the purpose of determining characteristics of the different materials on the study. In order to fulfill these experimental work samplings of AISI 1020 mild steel materials is mandatory. The sampling methods will use for this experimental work is by using purposive sampling method for the materials of AISI 1020 mild steel plates within the selecting thickness and positions to analyzing the micro-structure and mechanical properties on the heat affected zone in submerged arc welding process. 10/1/2025 Prepared by: Negus Ayalew 13 Cont …

14. Data Collection methods In this study was used both the primary and secondary data collection methods. The primary data was used to collect through direct observation by visual inspection and through unstructured interview with concerned person in order to identify the mechanical properties and micro structure on heat affecting zone of submerged arc welding. Primary Data Collection In this study the primary data was used collect through direct observation by visual inspection in order to investigate the optimization of welding parameters and mechanical properties on heat affected zone upon, submerged arc welding. The second method of primary data collection was used through unstructured interview with concerned person about originated of the welding parameters. Secondary data Collection In this study the secondary data collections was collected from different types literature review like published journal, and different types of welding books. This reference was used to know how to happen different characters with in applying in AISI 1020 mild steel welding operations. 10/1/2025 Prepared by: Negus Ayalew 14 Cont ….

15. In this study the data analysis tools was used like Pareto chart in order to investigate the major constituents of the problems, Cause and effect or Fish Bone Diagram to identify the root cause of the welding defects, Tauguchi methods to identify the optimal quality welds, Microstructure analysis by using metallographic examination/testing and Experimental analysis for mechanical properties investigation by using tensile and hardness testing. 10/1/2025 Prepared by: Negus Ayalew 15 Data Analysis

16. Welding was carried out on submerged arc welding Machine on the AISI 1020 mild steel of the dimensions 250 x 100 x 10 mm welded with closed butt joint. Submerged arc welding (SAW) is carried out on these specimens using automated welding machine with consumable electrode E2062, 4mm dia. Granulated flux powder was also used to submerge the arc process. 10/1/2025 Prepared by: Negus Ayalew 16 Experimental Conditions

17. A properly prepared metal specimen by using the following point: Selection of specimen Cutting of the specimen Obtaining flat specimen surface Intermediate and fine grinding Fine polishing and Etching 10/1/2025 Prepared by: Negus Ayalew 17 Specimen preparation

18. Test sample were prepared by butt welding AISI 1020 Mild steel specimens by using a welding electrode made from the same material. SAW (manual/automatic) welding process was used. First of all, trial runs were conducted to find out the Current (I) range to be used and three set of SAW parametric combinations were decided, because of well-established fact that among all the welding variables in SAW welding processes welding Current (I) is the most influential variable since it affects the Current (I) density and thus the melting rate of the filler as well as the base material. The heat input from the welding process plays a major role in the heating and cooling cycles experienced by the weld and parent plate during welding. For a given plate thickness, a high heat input is likely to result in a slower cooling rate than a low heat input, and will therefore produce a softer microstructure in the HAZ. 10/1/2025 Prepared by: Negus Ayalew 18 Welding procedure

19. 10/1/2025 Prepared by: Negus Ayalew 19 Experimental Procedural

20. Testing Tensile strength, micro Hardness and impact strength tests were performed on as welded specimen. Tensile Test It is also called tension test and is used to determine, Tensile strength of the material when subjected under uni -axial loading. Hardness test This method consists of indenting the test material with a diamond cone or hardened steel ball indenter. The indenter is forced into the test material under a preliminary minor load F0 usually 150kg. 10/1/2025 Prepared by: Negus Ayalew 20 Cont…

21. In this chapter data collected by different methods like observations, questionnaires and interviews are presented. The collected data also analyzed and presented through cause and effect diagram, Pareto charts and experimental investigation using tensile and hardness testing on SAW welding effects through charts. This study deals with the analysis and discussions of the experimental findings of micro structure and mechanical properties on heat affected zone welded at different welding parameters i.e , current, voltage, and welding speeds. The specimens prepared under different welding speeds, heat input rates with different current and voltages are having different effects. Finally, the analyzed data are interpreted, discussed and the findings are put in the summary form. 10/1/2025 Prepared by: Negus Ayalew 21 CHAPTER FOUR DATA ANALYSIS AND DISCUSSIONS

22. The data analysis for this experimentally investigation work is done by using the following procedures: Out of 10 questionnaires distributed, 8 workers responded to the questionnaires and considered as essential sources for the study. According to the respondents of question number 1 eight of them responded that they do all check current while using SAW process. However, for the given questions the responses are analyzed by using graphically as follows as shown in the following figure 4.1. 10/1/2025 Prepared by: Negus Ayalew 22 From the questionnaire

23. In the material preparation case of this experiment used plates were seriously clamped to the welding jig or work piece holding devices to avoid any misalignment, movements or thermal distortions during welding. Table 4.3. SAW welding parameters for flat welding positions. 10/1/2025 Prepared by: Negus Ayalew 23 SAW Welding Parameters

24. A Pareto chart are based on the Pareto principle also known as the 80/20 rule as it states that 80% consequences occur as a result of 20% of known causes. Pareto chart along with cause and effect analysis serve as extremely useful tools to study the causes of problems and determine which ones are most vital or serious and what are the reasons for their occurrence. It helps to interpret and decide which variations to control. 10/1/2025 Prepared by: Negus Ayalew 24 Pareto Chart

25. From this Pareto chart porosity and luck of fusion are more dominant compare to the rest of welding defects on submerged arc welding process in the company. Porosity is a collective name describing cavities or pores caused by environmental gas and non-metallic material entrapment in molten metal during solidification stage. Porosity classified in to two internal porosity and surface porosity. Small cavities or holes caused by trapped gas bubbles in the weld metal. It mostly caused by contaminated flux or base metal( rust, oil, moisture), improper flux coverage, high moisture content in flux, excessive welding speed and dirty or oxidized surfaces. Then the effects of this type of defects are reduces weld strength and fatigue resistance and may cause leakage in pressurized application. 10/1/2025 Prepared by: Negus Ayalew 25 Cont…

26. The other more dominate defects in this type of welding process was a luck of fusion or incomplete joint penetration is an incomplete bonding between weld metal passes. It mostly caused by low welding current or voltage (insufficient heat input), excessive travel speed, incorrect electrode angle or misalignment and poor joint preparation. Then the effects of this type of defects are creates weak zones prone to cracking and may lead failure under load. The un-penetrated and un-fused area is a discontinuity described as incomplete joint penetration. Incomplete joint penetration may result from insufficient welding heat, improper joint design (e.g., thickness the welding arc cannot penetrate), or improper control of the welding parameters. Due that the way of prevention in submerged arc welding are pre-dry flux, optimize parameters (like current, voltage and speed), ensure proper joint fit up and cleaning, and use backing bars for thin materials. 10/1/2025 Prepared by: Negus Ayalew 26 Cont …

27. As the experimental data indicated that mostly porosity problems occurred when welding travel speed is too fast. If the welding speeds too fast not allowing enough time for the shielding gas or flux ingredients to do their job, because solidification needs time. Due to those reason the weld puddle expose to surrounding gas like oxygen and hydrogen and incorrect setting of current also affected the welding quality so too low and too high current is one of the root cause for porosity since excessive current create wide weld pool shielding gas cannot protect the environmental gas as match as possible. 10/1/2025 Prepared by: Negus Ayalew 27 Fish bone diagram

28. So, the researcher investigate the causes and effect or fish bone analysis for welding defects of incomplete of penetration/ Luck of fusion. When we create fish bone diagrams of this defects, the researcher uses and applies 5M. These 5Ms are Method, Manpower, Material, Machine, and Measurement (environment), should be clarified and discussed in detail with relate to those welding parameters such as welding current, welding speed, angle of electrode, type of electrode, electrode diameter, welding position and material thickness. So first let construct the fish bone diagram for the causes of surface crack problems which shown in the figure 4.7 below. 10/1/2025 Prepared by: Negus Ayalew 28 Cont…

29. Tensile strength is the maximum stress that a material can sustain in tension. Tensile test was conducted on sub size the sample made as per AISI 1020 mild steel cut from Adjacent to the weld bead using a hydraulic extensometer with prepared machined specimen dimensioned 250 mm x 50 mm x 10mm. Tensile samples were prepared by milling of the top and bottom surfaces to remove flashing and other surface irregularities. The standard shape is obtained using milling machine as shown in the Figure 4.11. 10/1/2025 Prepared by: Negus Ayalew 29 Data analysis by using tensile testing

30. As Figure 4.11, shows that the tensile strength of AISI 1020 mild steel on sample 9 (nine) at current, voltage, welding speed, heat input and penetration was 600A, 32 V, 775 mm/min, 1486 J/mm and 5 mm respectively welded by E 2065 the lowest average tensile strength value which about 56.66 N/mm 2 and the highest average tensile strength value of 73.56 N/mm 2 on sample 3 (three) at current, voltage, welding speed, heat input and penetration was 600A, 32 V, 375 mm/min, 3072 J/mm and 8.2 mm respectively welded by E 2065. This expressed that as the welding penetration increased; the tensile strength in welding area was also increased and welding speed decrease the tensile strength was increased. The result is will similar to other researchers [24-27]. The relationship is that as the welding current increase, the welding heat input also increase and decrease in tensile strength on the weld metal. The decrease in strength may be associated with the presence of void and other defects occurring as a result of increasing current. 10/1/2025 Prepared by: Negus Ayalew 30 Cont …

31. Generally to be conclude the tensile strength of the experimental work presented that from the above nine welding samples in an 10mm thickness of AISI 1020 mild steel welded by the welding electrode of E 2065 shows that the lowest average tensile strength value which about 56.66 N/mm 2 at sample 9 (nine) and the highest average tensile strength value 73.56 N/mm 2 at sample 3 (three) and also the lowest elongation of the sample 9 (nine) for AISI 1020 mild steel was 3.26 % and the highest elongation of the sample 9 (nine) for AISI 1020 mild steel was 4.16% at sample 3 (three). 10/1/2025 Prepared by: Negus Ayalew 31 Cont …

32. Hardness is the ability of materials to resists penetration, abrasion, scratching or cutting. It is the property by which material resists permanent deformation. 10/1/2025 Prepared by: Negus Ayalew 32 Hardness Testing

33. According to in the figure 4.16, shows that the highest average hardness Brinell (HRB) value sample for AISI 1020 mild steel was recorded 51.03 HRB in the 4 th sample and the lowest average hardness value sample was recorded 46.76 HRB in the 3 rd sample of the welding spacemen. When the welding speed was increased from 200 mm/min to 450 mm/min the average Rockwell hardness (HRB) value is decrease from 51.03 HRB to 46.76 HRB respectively. The relationship is that as the welding speed increase, the welding current, voltage also increases and reduces the hardness of the weld metal. 10/1/2025 Prepared by: Negus Ayalew 33 Cont …

34. The heat affected zones (HAZ) in the selected flat butt welded significantly vary from that obtained during single pass welding process because of the multiple reheats. In different welding enable a variety of weld joints and plate thicknesses to be welded with the same procedures and materials. According to the figure 4.17, shows that the highest Average Hardness Brinell (HRB) value heat affected zone (HAZ) hardness value was recorded 40.63 HRB on the 2 nd sample for AISI 1020 mild steel welded by E 2065 electrode and the lowest Average Hardness Brinell (HRB) value heat affected zone (HAZ) hardness value was recorded 35.33 HRB on the 9 th sample for AISI 1020 mild steel welded by E 2065 electrode. In this study when the welding Speed was increased from 200 mm/min to 775 mm/min the average Rockwell hardness (HRB) value decrease from 40.63 HRB to 35.33 HRB respectively. The relationship is that as the welding speed increase, the welding heat input also increases and reduces the hardness of the weld metal. This result is similar to research conducted by several other researchers [17-20]. 10/1/2025 Prepared by: Negus Ayalew 34 Heat Affected Zone (HAZ)

35. The heat affected zone (HAZ) of a weld was that part of the welded joint which has been heated to a temperature up to solidus of the parent material resulting in varying welding speed, current and voltage was influence on microstructure which can result in change in mechanical properties as a consequence of heating and cooling cycle. The cooling rate of weldments depends on the heat input by the welding arc. Heat input is controlled by three variables, namely: current, voltage and travel speed. It is generally believed that travel speed affects heat input and heat input affects the cooling rate. With higher heat input the cooling rate is faster and vice versa. 10/1/2025 Prepared by: Negus Ayalew 35 Cont …

36. In submerged arc welding process the properties of AISI 1020 mild steel depend on the microstructure. As shown below in fig.4.18, the light colored region of the microstructure is the ferrite and the dark colored regions are the pearlite . Decrease in the size of grains and decrease in the amount of pearlite improves the strength, ductility and toughness of the steel whch shown in the figure 4.18. Figure : Microstructure of welded specimen at HAZ According to the figure 4.18, above shows that ferrite and pearlite structures are formed and traces of acicular ferrite can also be found in the heat affected zone. The light colored region of mild steel is the ferrite. Grain boundaries between ferrite grains can be seen quite clearly, dark regions are called Pearlite . 10/1/2025 Prepared by: Negus Ayalew 36 Micro structure of AISI 1020 Mild Steel

37. Based on the results of the present study, the following conclusions are drawn: Porosity was occurred when welding travel speed is too fast. If the welding speeds too fast not allowing enough time for the shielding gas or flux ingredients to do their job, because solidification needs time. Incomplete penetration created when welding metal deposition is low and improper filling of the root gaps. Inadequate gap in the root face which means that too large root face, root gap, beveling problems and improper joint design leads to this type of defect. 10/1/2025 Prepared by: Negus Ayalew 37 CHAPTER FIVE CONCLUSIONS AND RECOMMENDATIONS

38. The highest average tensile strength value 73.56 N/mm 2 at sample 3 (three) and the lowest average tensile strength value which about 56.66 N/mm 2 at sample 9 (nine) and also the lowest elongation of the sample 9 (nine) for AISI 1020 mild steel was 3.26 % and the highest elongation of the sample 9 (nine) for AISI 1020 mild steel was 4.16% at sample 3 (three). The highest average hardness Brinell (HRB) value sample for AISI 1020 mild steel was recorded 51.03 HRB in the 4 th sample and the lowest average hardness value sample was recorded 46.76 HRB in the 3 rd sample of the welding spacemen. When the welding speed was increased from 200 mm/min to 450 mm/min the average Rockwell hardness (HRB) value is decrease from 51.03 HRB to 46.76 HRB respectively. The relationship is that as the welding speed increase, the welding current, voltage also increases and reduces the hardness of the weld metal. The highest Average Hardness Brinell (HRB) value heat affected zone (HAZ) hardness value was recorded 40.63 HRB on the 2 nd sample for AISI 1020 mild steel welded by E 2065 electrode and the lowest average Hardness Brinell (HRB) value heat affected zone (HAZ) hardness value was recorded 35.33 HRB on the 9 th sample for AISI 1020 mild steel welded by E 2065 electrode. 10/1/2025 Prepared by: Negus Ayalew 38 Cont …

39. The optimum parameters for smaller bead width and higher bead Hardness was in welding Current (I) 600 I, Voltage (V) 32 V, Welding Speed (S) 275, and average hardness test vale of 40.63 HRB. As observed in micro structure finding when decrease in the size of grains and decrease in the amount of pearlite improves the strength of the steel. The microstructure using submerged arc welded component depends on the cooling rate from nearly 800 to 500 °C. 10/1/2025 Prepared by: Negus Ayalew 39 Cont …

40. According to the study the following recommendations are made for the next scholars: For SAW process, technique and skill is very crucial in order to gain the best end result the welding parameters from the material to be welded was need to be pay attention to give similar heat input. Thus, it is better to have qualified personnel to perform the welding process. Qualified welder has received training and they continuously involved in this matter. Hence, average person skill needs to be reduced as much as possible for accurate result. To get more precise results of the experimental work, investigation on the effect of welding parameters and other welding variables need in depth analysis to get optimum micro structure and mechanical properties of any selected material heat affected zone of different welding process. 10/1/2025 Prepared by: Negus Ayalew 40 Recommendations

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