ABSRACT The impact of Post-Weld Heat-Treatment (PWHT) on the hardness and microstructure of of 0.165% carbon steel was determined in this study after welding operation. Autodesk Inventor Simulation CFD 2015 Application Software for Visual Style-Wire Frame and Visual Style-Shaded Mesh was used to simulate the Heat Affected Zone (HAZ) and welded pool on three planes (YZ, XZ, XY). The welded samples were subjected to normalizing, annealing and quench hardening in different media (water, palm oil,

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... uartz 5000 Total Engine oil, and Groundnut oil). The prepared samples (PWHTs and as-welds) were subjected to hardness and microstructure tests and were compared with non-heat treated as-weld to determine their hardness and observed microstructure. The results obtained showed significant differences in the microstructure and mechanical properties of the different PWHT samples. Results also showed that specimens annealed and quenched in water and palm oil had lowest Brinnel Hardness Numbers (BHN) at welded pool, that is 62.105BHN, 84.06BHN and 69.835BHN, while the specimens normalized, annealed and quenched in palm had the lowest hardness values at HAZ , that is 82.25,73.365 and 88.13BHN. Hardness values of 100.77BHN for welded pool and 133.735BHN for HAZ were highest for samples quenched in Quatz 5000 Engine oil. The normalized and annealed samples had values of 89.695 and 62.105BHN at welded pool, and 82.25BHN and 73.365BHN at HAZ compared with untreated as-weld low carbon steel samples with 106.855BHN at welded pool and 100.97BHN at HAZ. Normalizing PWHT sample yielded a microstructure of better quality than annealing and quench hardening in the different media used. It was deduced that the reduction in hardness values was a consequence of an increase in ductility and toughness in normalized and annealed samples. This improved the properties of the low carbon steel and reduced mechanical hazard. It was concluded that improved mechanical behaviour of welded low carbon steel is achieved by post-weld normalizing and annealing operations.