Low alloy steels are one of the most used materials in structural applications owing to their excellent properties such as ease of manufacturing, good toughness, and high strength. Among the available material joining methods, welding is undoubtfully the most suitable. This has led to significant research amongst scientists over the past years with the aim of improving the manufacturing processes. Generally, there are different types of welding whose application depends on the types of material and the intended application. Consequently, the microstructures and mechanical properties of these welds affect the properties and functionality of the materials and their entire structures in general.
Recent studies have shown significant improvements in the investigation of the joint performance of high strength steels using the residual stress, microstructure and weld pool flow. Unfortunately, considering the different nature of the arc welding and marine welding, the aforementioned criteria are insufficient to assure high-quality welding in marine manufacturing.
To this note, Huazhong University of Science and Technology scientists: Dr. Youmin Rong, Ting Lei, Dr. Jiajun Xu, Professor Yu Huang, Professor Chunming Wang assessed the distribution of residual stresses in laser welding in marine high strength steel EH36. In particular, a finite element model was designed by taking into consideration the solid transformation based on thermodynamics. Their research work is currently published in the journal, International Journal of Mechanical Sciences.
Briefly, the research team assessed the phase transformation and its effects of the residual stress by further taking into account the response of the microstructure to strain in laser welding marine high strength steel. Next, the distribution of the temperature was investigated using a heat source model while on the other hand, thermodynamics of the solid phase transformation was used in determining the microstructure fractions. To actualize their study, the research team experimentally verified the prediction accuracy of the designed model based on the residual stress, microstructure and weld profile.
The authors uncovered the usefulness of the index increment double cone method in fitting the penetration resulting from laser welding. As such, they recorded prediction errors of 11.06%, 10.24% and 6.69% in UW, MW, and BW respectively. On the other hand, a prediction error of 10.372% and 5.6435 were observed in the microstructures of the laser-welded EH36 and in particularly for martensite and ferrites. This was attributed to the influence of the weld microstructures on the strain and residual stresses of the material. However, it was worth noting that the heat affected zone, and not the center of the fusion zone, produced the maximum stress.
Therefore, the Huazhong University scientists successfully proposed a finite element model for not only accurately predicting the residual stresses in laser welded EH36 steels but also providing a basis for minimizing the welding associated stresses. Furthermore, considering the stability if the plastic strain without the need for external forces, the study will advance marine manufacturing through high-quality welds.
Rong, Y., Lei, T., Xu, J., Huang, Y., & Wang, C. (2018). Residual stress modelling in laser welding marine steel EH36 considering a thermodynamics-based solid phase transformation. International Journal of Mechanical Sciences, 146-147, 180-190.Go To International Journal of Mechanical Sciences