THE EFFECTS OF ELECTRIC POWER ARC INPUTS ON THE MICROSTRUCTURE AND MECHANICAL PROPERTIES OF 0.4%C STEEL

Abstract

An investigation of the effect of electric arc power inputs on the microstructure and mechanical properties of welded 0.4% carbon steel was studied using shielded metal arc welding (SMAW) process with E6013 electrode. The as-received ribbed steel form was firstly cut and machined to  standard configurations for both tensile, hardness and impact tests. The power inputs controlled  by the welding current, arc voltage, welding speed and electrode diameter were used in this  investigation. The current was varied while maintaining a constant arc voltage of 40 volts, welding speed of 3.2mm/sec and electrode gauge of 3.2mm. The currents were varied at 100A low heat
input, dual current of 100A & 125A for medium heat input and 125A for high heat input to give a varying amount of heat inputs. Microstructural analysis and mechanical tests were carried out on the specimens forboth the welded and the controlled specimens to determine the mechanical properties of the specimens. The results showed that the selected welding parameters hadsignificant influence on the mechanical properties and micro-constituent of the welded samples.
Increasing the welding current from 100A-125A caused a corresponding increase in the temperature of the welded joint which affected the microstructure of the welds. The weld microstructure was controlled mainlyby the cooling cycle. At 100A (i.e. with low level of current) the time for solidification was less. This rapid cooling promoted smaller grains. At 125A, the time required for solidification increases and therefore cooling rate slowed down which yielded coarse grains. On the mechanical properties, the results indicated that the joints made by using low heat input exhibited higher tensile strength (515.90 Mpa) and from scanning electron microscopy (SEM) of tensile test fractured surface exhibited ductile failure, higher hardness strength (179.5 HRC) andimpact toughness value of (6.5 Joules) than those welded with medium and high heat inputs respectively which exhibited brittle failure as the heat inputs increases as shown from the SEM image