TR 35024; 2011-2014
The subject of this project is improvement of the welding technology for micro-alloyed steels, in order to increase productivity and improve the quality of welded joints. It will be evaluated the following welding processes: a) SMAW, b) GMAW-MIG/MAG, c) FCAW-G with mixture of external shielding medium (Ar, CO2 and O2) and d) FCAW-S. In the mixtures of shielding gases the content of Ar, CO2 and O2 would be different, because the preliminary investigations executed in Fac. of Mech. Eng. in Belgrade showed that the appropriate choice of the shielding gas mixture composition can significantly affect the quality of the weld metal, and therefore the welded joint as a whole. Therefore, it is planned that the Project precisely defines the mix of shielding gases and to compare the obtained quality of welded joints with the quality of joints made by SMAW process. It was planned to made joints by FCAW-S process that is currently increasingly used worldwide in this area. It is also planned to investigate the influence of applied welding technologies on the properties of welded joints by different experimental methods: mechanical testing, metallographic examination and fractographic examination.
micro-alloyed steels, gmaw-mig/mag, fcaw-s, microstructure, fractography, toughness
Micro-alloyed steels are vastly used in the process industry, for making pipes and cylindrical and spherical storage tanks for gas and oil. Hence, it was very important to provide high quality welded joint of structural elements made of micro-alloyed steel. Improving of the welding technology for micro-alloyed steels, is in the accordance, and practically follow the development of welding procedures. Preliminary research indicates that the properties of weld metal are affected by many factors like the type of shielding atmosphere, used additional material, heat input. The influence of the shielding medium composition on the properties of weld metal will be accompanied by oxygen equivalent Oeq, which is calculated by empirical expressions available in the literature. Special attention will be devoted to study the impact of shielding gas on weld metal toughness and the formation of different morphology of ferrite in microstructure, which directly affect the properties of welded joints. Besides microstructural investigation and impact toughness testing also hardness measurement, tensile testing and fractographic investigation will be carried out. After detailed analysis of results of above-mentioned experimental research and testing Project will provide experimental welding of micro-alloyed steel by self-shielded flux cored arc wire process (FCAW-S), which was increasingly used in the world. In this Project it was also planed to determine the effect of welding parameters. Because of this, within this part of the project, in addition to the standard mechanical tests, special attention will be paid to detailed microstructural investigation of joints made with self-shielded flux cored wire.
Expected key results
Great efforts are directed worldwide in order to achieve high quality micro-alloyed steel welds . However, by selecting the optimal parameters of welding, and above all, by selecting the appropriate mix of shielding gas it is possible to get the optimum weld metal microstructure, which is one of the objectives of this Project. It is also important to determine the relationship between the parameters of welding with self-shielded flux cored wire and weld metal quality. Verification of the results of this Project will take place even during its preparation. It will be also possible, by comparing the results of numerous destructive tests, to determine which combination of welding processes and parameters provides the best weld quality. Also, it will be possible to find the optimum combination of diametrically opposite indicators: lower production costs and good quality of products.
Participants from Singidunum University:
prof. dr Dragan Cvetković