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Experimental Investigation on the Influence of Alloying Elements on Heat Affected Zone Toughness of Welded Mild Steel Joints

C. O. Izelu, B. U. Oreko, B. A. Edward

This research work investigates the influence of alloying elements on Heat Affected Zone (HAZ) toughness of welded mild steel joints by identifying the alloying elements and experimentally determining their influence on the strength property of the weld. The ten V- notch impact test specimens made from all weld metal were used to conduct Charpy impact energy test. The chemical compositions of each of the all weld metals were determined. A relationship was established between the chemical compositions and their Charpy impact energy absorbed. The significance of alloying elements on the impact of the absorbed energy is explained by the theory of coefficient of variation. Small coefficient of variation means that the element considered is expected to have a high reliability. The coefficient of variation calculated and presented shows that Si, Cu and Mn have low reliability in term of toughness since the coefficient of variation in these elements is high (positive or negative). Also Mn is less reliable than Si. The implication of this is that the increase in the addition of Mn alloying elements would deteriorate the toughness profile of the weld as well as its Heat Affected Zones (HAZ). Other alloying elements such as C, P, Ni, Cr, Nb and V have high reliability; therefore these elements would tend to improve the HAZ toughness.