Materials Science and Metallurgy Engineering, 2013, Vol. 1, No. 2, 22-26 Available online at http://pubs.sciepub.com/msme/1/2/2 © Science and Education Publishing DOI:10.12691/msme-1-2-2 Reliability Level of Welding Voltage Dependence of Heat Affected Zone (HAZ) Hardness of Selected Metallic Weldments Cooled in Groundnut Oil C. I. Nwoye 1,* , C. C. Nwogbu 2 , A. O. Agbo 3 , J. U. Odo 1 , S. O. Nwakpa 1 1 Department of Metallurgical and Materials Engineering, Nnamdi Azikiwe University, Awka, Nigeria 2 Science Technical Vocation Schools Management Board 3 Department of Metallurgical and Materials Engineering, Enugu State University of Science & Technology, Enugu, Nigeria *Corresponding author: nwoyennike@gmail.com Received August 30, 2013; Revised September 12, 2013; Accepted September 15, 2013 Abstract This paper showcases the reliability level associating welding voltage dependence of heat affected zone (HAZ) hardness of aluminium, cast iron and mild steel weldments cooled in groundnut oil. These materials were welded using shielded metal arc technique and the HAZ hardness of the various groundnut oil cooled weldments determined. Three models were derived and used as tools for the empirical analysis of the influence of welding voltage on the HAZ hardness of the weldments. The results of the analysis show that the HAZ hardness of weldments is significantly and reliably affected by the operational welding voltage. Results evaluations largely show that on welding aluminium, cast iron and mild steel, and similarly cooling their respective weldments in groundnut oil, an empirical was used to predict aluminium weldment HAZ hardness as equivalent of HAZ hardness interaction between cast iron and mild steel. Aluminium weldment HAZ hardness was evaluated as a product of a multiplication operation between the general voltage product rule (GVPR) ((β a β m + β a β c )/ β c β m ) 0.2396 and the ratio; HAZ hardness product of cast iron and mild steel/ HAZ hardness sum of cast iron and mild steel ( ŋ ɤ /( ŋ + ɤ )). Predicted values of the HAZ hardness of cast iron and mild steel were comparatively analyzed and also found very reliably dependent on the GVPR which is a collective function of their respective welding voltage. The validity of the model was rooted on the core model expression; (β a /β c + β a /β m ) = (ζ /ɤ + ζ / ŋ) 4.1737 where both sides of the expression were correspondingly equal. Computational analysis of generated results shows that aluminium, cast iron & mild steel weldment HAZ hardness per unit welding voltage as evaluated from experiment and derived model were 1.4714, 4.1818 & 2.3318 (VHN)V -1 and 1.4714, 4.1821 & 2.3319 (VHN)V -1 respectively. Deviational analysis indicates that the maximum deviation of model-predicted HAZ hardness from the experimental results is less than 0.006%. This translates into over 99.99% operational confidence and reliability level for the derived models and over 0.9999 reliability coefficient for the welding voltage dependence of HAZ hardness. Keywords: analysis, hardness, heat affected zone, aluminium, mild steel, cast iron, groundnut oil cooling Cite This Article: C. I. Nwoye, C. C. Nwogbu, A. O. Agbo, J. U. Odo, and S. O. Nwakpa, “Reliability Level of Welding Voltage Dependence of Heat Affected Zone (HAZ) Hardness of Selected Metallic Weldments Cooled in Groundnut Oil.” Materials Science and Metallurgy Engineering 1, no. 2 (2013): 22-26. doi: 10.12691/msme-1- 2-2. 1. Introduction It has been widely accepted that applicability of a particular metal and alloy in the construction and fabrication industries is largely dependent on their respective weldability. Furthermore, the strength and hardness of the heat affected zone (HAZ) (in metals and alloys weldments) are significantly important weldability parameters that go a long way determining where these materials can be exactly useful when carrying out design for fabrication. The extent of formation of cold cracks in the coarse-grained region (adjacent to the fusion zone) of the HAZ depends on the hardness of the region. These cracks are formed as the weld cools and resides in the HAZ even before the section is put into service. Studies [1,2] have reported that even though cold cracks formation must be avoided, HAZ can be limited by specification. The hardening allowed in HAZ depends on several factors: the hydrogen level (determined by the welding process used), joint preparation and work piece thickness, and most importantly the metal composition, specifically the equivalent carbon content. Apart from formation of cold cracks, the corrosion sensitivity of the HAZ is also dependent on its hardness. The growing need in design and fabrication practice to develop reliable methods of calculating HAZ hardness level has lead to the derivation of some semi-empirical models [3,9]. These models were based on regression analysis and there are a lot of uncertainties regarding their respective applicability.