Optimization of gas metal arc welding process parameters in ultra-high strength steels based on prediction
Alves Netto, Alnecino (2019)
Alves Netto, Alnecino
School of Energy Systems, Konetekniikka
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The search for materials to manufacture products with the aim of reduction weight and higher strength has been carried out during many years for many companies to fulfill requirements of lighter and safer products. The ultra-high strength steel (UHSS) is a complex and sophisticated material that came to be possible to develop products with properties that allows reduction of weight with increased strength due to the properties of the material, assisting for example, the automotive industry to save fuel of the vehicles and decreasing its emission. The gas metal arc welding (GMAW) has been used in several applications based on UHSS and may be considered as a well-established welding process. The welding of UHSS has a high level of complexity, mainly due to the higher quantity of alloys and the heat treatments applied to the material, which result in a microstructure with a higher sensitivity to the welding. The main purpose of the current thesis is to select the best parameters of GMAW to welding the S960 material based on prediction methods. To achieve the expected results, it was used finite element analysis (FEA) to simulate and evaluate the results comparing with experimental results obtained by welding a butt weld joint. The purpose of the use of a computational method is to approximate to the real condition and evaluate different structural and thermal behaviors. As a result, was found that the welding parameters and consequently the heat input derived from it has a great effect on the UHSS microstructure. The GMAW welding process achieved satisfactory results to weld the material and thickness analyzed, however, it was observed that some features such as pulse and laser welding along a specific joint shape must be considered to minimize the effect of heat input. By using FEA it was possible to estimate the extension of the heat affected zone (HAZ), the peak temperature and even the effect of the distortion and shrinkage. Those results are useful to predict a desirable behavior, or a microstructure based only on changes on the welding parameters. At last, could be observed that the new generation of UHSS achieved results with excellence on welded structures, though the number of grades is still a challenge that requires early analysis in order to obtain a prediction even closer to the real condition.