Numerical Modeling of Cooling Rate and Hardness Prediction in Axi-Symmetric Flash Butt-Welded C45 Steel Circular Long Bars

Abstract

FE investigation into the effect of welding variables on the cooling rate, Δt8/5 (cooling time from 800 to 500 °C), around the weld and heat affected zone (HAZ) areas of C45 steel was carried out. Weldment material hardness property changes was examined using Brinell hardness test method, variation in hardness at known distances from the weld line in the HAZ arising from different cooling rates was the main focus. There exists in literature empirical correlations that relate cooling rates and hardness vis-a-vis welding variables, these were used for the computational evaluation of hardness. To establish the effects of welding variables on the cooling rate, a computer programme was written with Matlab. Generalized numerical prediction of temperature distribution, peak temperature, cooling rate and thermal cycles in solid bars joined by butt arc welding process was carried out and subsequently used to predict hardness of C45 steel. Increase in arc duration reduced the cooling rate, which consequently reduced the hardness by as much as 47%. The cooling rate decreased with increase in preheat, results in a significant decrease in hardness of the HAZ by as much as 49%. The results also indicated that the cooling rate increased slightly with an increase in coefficient of convection and caused an insignificant increase in hardness. It was discovered from the results that metal pre-heat temperature prior to welding has minimal effect on the cooling rate. Simulated weldment hardness obtained was in good agreement with the experimental value within 9 %.