The Effect of Welding Different Plate Thickness on Heat Affected Zone Microstructure and Hardness

The main purpose for this project is to research the effect of welding thickness with regard to heat affected zone (HAZ) microstructure and hardness. Welding cause heat that generates heat affected zone (HAZ) which change the properties of material. This generates the residual stresses cause failure to material performance in future. HAZ sizes are influence by several factors such as heat input, welding traveling and metal thicknesses. This research focus on welding thickness as parameters whilst the other parameters are keeps constant. Thickness parameter is chosen to observe the relationship between thermal diffusivity for different thickness. Theoretically, thicker material has high diffusivity. For this project, the material use is low carbon steel and equipment involved is welding machine, optical microscope, hardness testing tools and other suitable apparatus that needed to complete the task. The material were welded by using shielded metal arc welding and then sectioning, mounting, grinding, polishing and etching for metallographic examination. The different types of microstructure appear in comparison between affected and unaffected zone. The project further carried out by conducting hardness testing for different thickness. From the data acquired, one can know the information of welding parameters performing which affect the materials condition. The outcomes for different thickness plate towards HAZ size were influenced by thermal diffusivity of the material. Thicker material has higher thermal diffusivity and vise versa, hence less HAZ region due to fast rate cooling. For metallurgical region, the HAZ which adjacent to fusion boundary has lowest hardness compare to other region. Coarse pearlite microstructures were found in the area with small amount of ferrite. The hardness is increasing as distance from fusion boundary increased. For the conclusion, dissimilar parameters (different thickness) give different thermal diffusivity towards material which gives variety sizes of heat affected zone (HAZ) and hardness for HAZ is also increasing as the thickness of the material increased.