SSRG International Journal of Mechanical Engineering (SSRG-IJME) – volume 2 Issue 9 – September 2015 ISSN: 2348 – 8360 www.internationaljournalssrg.org Page 79 Effect of Arc Welding Current on the Mechanical Properties of A36 Carbon Steel Weld Joints Asibeluo I.S, Emifoniye E. Department Of Mechanical Engineering, Delta State Polytechnic, Ogwashi-UKU, Delta State Abstract This research work focuses on the effect of temperature as a function of current toward the mechanical properties of a welded joint of A36 carbon steel using Shielded Metal Arc Welding (SMAW). With the melting point of A36 steel at about 1426- 1470 0 C, the range of the welding current was chosen from 70A -120A to give a varying amount of heat input. The hardness, impact and microstructure test were conducted to determine the mechanical properties of the welded joint. Increasing the current from 70A - 120A caused a corresponding increase in the temperature of the welded joint which affected the microstructure of the weld. The weld microstructure was controlled mainly by the cooling cycle. At 70A (i.e. with low level of current) the time for solidification was less. The rapid cooling promotes smaller grains. At 120A, the time required for solidification increases and therefore cooling rate slows down which yielded coarse grains. At 120A the grain size was most coarse with a hardness and toughness value of 60BHN and 11 Joules respectively indicating reduced strength and hardness. I. INTRODUCTION In manufacturing, welding is one of the important processes. It is used widely to join metals using metals or fillers. There are many types of welding such as Arc welding, Metal Inert Gas welding (MIG welding), oxy acetylene welding; Tungsten Inert Gas welding (TIG welding), laser welding and friction welding. Shielded metal arc welding is usually performed manually. According to the American Welding Society, common application includes construction, pipelines, machinery structures, ship building, job shop fabrication and repair work. It employs the use of a consumable electrode, electrode holder, source of an electrical power (AC or DC) and a welding Machine. It is a process which produces coalescence of metal by heating the with an arc between a covered metal electrode and the work. Shielding is obtained from decomposition of the electrode covering. Pressure is not used. Filler metal is obtained from the electrode. According to the steel construction manual 8 th Edition, ASTM A36 steel is the most commonly available of the hot rolled steel. It is generally available in round rod, square bar, rectangular bar as well as I beam, H beam, angle and channels. It finds its application in areas like, bridge, ship, machine frame, and railway constructions. The chemical composition of A36 mild steel by weight (wt %) is given as follow C-0.26, Mn- 0.75, Cu-0.2, P-0.04, S-0.05 and Fe. Welding Joint can be a difficult task in some industries with the problem of cracking, and altered mechanical properties compared to the parent material. Due to limited knowledge in effect of current towards weld, this research is therefore aimed at investigating the effect of temperature arising from changes in current values when using shielded metal arc welding (SMAW) on the mechanical properties such as hardness and impact strength of A36 low carbon steel with the aid of Charpy hardness testing procedures on welded joint. II. LITERATURE REVIEW Shielded metal arc welding is the most common metal fabrication technique in industry due to its reliability and capability of producing good quality welds. During operation, the bare metal end of the melting stick (opposite the welding tip) is clamped in the electrode holder that is connected to the power source, the holder has an insulated handle so that it can be held and manipulated by human welder. Current typically used in SMAW is 30-300A and voltage from 15 -45v. Shielded metal arc welding are usually performed manually. Common application includes construction, pipelines, machinery, structures, shipbuilding, job shop fabrication and repair work. The disadvantage of shielded metal arc welding as a production operation is the use of the consumable electrode stick. As the sticks are used up, they must periodically be changed. This reduces arc time with this welding process. Another limitation is the current level that can be used. Because the electrode length varies during the operation and this length affects the resistance heating of the electrode. Current level must be maintained within a safe range or the coating will overheat and melt prematurely when starting a new welding stick. Some of the AW (arc welding) process overcomes the limitations of welding stick length in SMAW by using a continuous feed wire electrode. A. Chemical Aspect Of Welding It is quite understandable that composition of base metal, electrode wire and flux impose profound effect on mechanical properties of the welded joint, which in turn depends on microstructure of weld metals and heat affected zone (HAZ). According to [14]. A Shielded Metal Arc(SMA)electrode consists of a metal