Analysis of fatigue crack properties of the weld metal of gas metal Arc welded 300WA steel

Abstract

Welded joints are major causes for concern in the engineering arena for two basic reasons. In the first instance the weld is known to be a region of weakness within a structure and is caused by residual and applied stress concentrations. Secondly, the behaviour of the stress patterns is somewhat difficult to predict accurately due to the difficulty of conforming to the geometry and process parameters. The experimental procedure in this work commenced with specimens being welded with a technique very commonly used in industry. The residual stresses generated by thermal fluctuations from the welding process cannot be predicted easily and is viewed as a problem as increased stress levels promotes failure. Residual stresses were then determined with the use of an ultrasonic stress measuring device. Strain gauges were used to measure strains in the welded specimens and these strains converted to stresses. The results of the two methods were compared and analysed. Compact tensile specimens were used to perform fatigue testing. The results confirmed findings from earlier research such as the proportion of cyclic life spent on initiating the crack. Hardness tests were performed to determine if any relationship existed between fatigue failure, yield strength and hardness. Finally metallurgical analysis revealed the phases and structures of the weld and heat-affected zones. The findings of this research indicate that close relationships exist between the cycles to crack initiation and ultimate fracture, the hardness, yield stress and the fatigue life of the weld as well as between the grain diameter and the yield stress. Furthermore it is shown that there was not enough information gathered in this research to conclude that the life expectancy of 300WA welded steel can be predicted. However recommendations are made for future research in the prediction of failure of the 300WA welded steel.