Thesis supervisor: Marcell Gyula Gáspár
Location of studies (in Hungarian): Institute of Material Science and Technology Abbreviation of location of studies: ATI
Description of the research topic:
Due to increasing environmental standards for CO2 emissions, there is a growing demand in the automotive and vehicle industry for the widespread use of high-strength steels. The currently known ultra-high strength weldable steels have a yield strength above 1000 MPa, which is achieved by the combined effect of alloying, rolling and heat treatment. The novelty of these steels is also shown by the fact that current base material standards do not even include such strength categories (e.g. S1100, S1300). The resulting microstructure cannot be considered to be in equilibrium, which is problematic from a welding point of view because the welding heat cycle irreversibly changes the microstructure of the heat-affected zone (HAZ) and a dendritic structure crystallizes from the liquid state in the weld. There is a significant reduction in strength and toughness in the weld and HAZ of the welded joint compared to the mechanical properties of the base material, which can be compensated by the use of special welding techniques. With regard to welding processes, high energy density welding processes with low heat input (e.g. laser and electron beam welding) will come to the fore, and the use of beam technologies will open up the possibility of local post weld heat treatments (PWHT).
The research should focus on:
• The development and application trends of ultra-high strength weldable steels and their suitability for welding should be analysed;
• Optical and electron microscopic techniques should be used to investigate the non-equilibrium changes of ultra-high strength steels due to various welding thermal cycles with industrial realities;
• The temperature field formed during welding and the consequent metallurgical changes must be examined by finite element modelling (FEM), the most favourable weld structure must be determined on the basis of the obtained results;
• The microstructure and properties of the critical HAZ subzones must be analyzed by physical simulation;
• The relationship between the base material, HAZ and weld microstructure and mechanical properties should be investigated considering autogenous welds and also the application of filler metals;
• The possibilities of local PWHT and its’ theoretical background should be explored.
Research conditions: the equipment for physical simulation (Gleeble 3500 thermo-mechanical physical simulator) and the materials investigations (MTS electro-hydraulic universal material tester, hardness testers, instrumented impact tester, microscopes), as well as the numerical modelling (SYSWELD) are available at the University of Miskolc, and at the cooperating institutes.
Industrial background: the Institute of Materials Science and Technology provide a wide cooperation network in the industrial area (e.g. Fortaco Co., Ten Slovakia Ltd., automotive companies).
Part-time education abroad: the actuality and importance of the research work offer the possibility of part time research abroad (University of Oulu, Finland; Slovak University of Technology in Bratislava, Slovakia; Silesian University of Technology, Poland).
Additional expectations:
• Language: an adequate knowledge of the English language is essential for the study of the literature
• Preliminary studies:
good or excellent grade in the engineering field (MSc),
professional knowledge in the field of material science and material technologies,
experience in the use of (CAD, CAM, FEM) software is advantageous.
Recommended literature to the research work:
• Bhadesia, H. K. D. H, Honeycombe, R. W. K.: Steels Microstructure and Properties, Third Edition, Elsevier Linacre House, Hordan Hill, Oxford OX2 8DP, UK, 2006.
• Adonyi, Y.: Heat-affected zone characterization by physical simulations, Welding Journal, October 2006. pp. 42-47.
• Porter, D. A.: Weldable high-strength steels: challenges and engineering applications, Portevin lecture, IIW 2015 International Conference on High Strength Steels – Challanges and Applications, Helsinki, Finland, 2-3. July 2015, Paper IIW 2015 0102 13p.
• S. Błacha, M.S. Wȩglowski, S. Dymek, M. Kopuściański: Microstructural and mechanical characterization of electron beam welded joints of high strength S960QL and WELDOX 1300 steel grades, Archives of Metallurgy and Materials, . Vol. 62, pp. 627–634, 2017. https://doi.org/10.1515/amm-2017-0092.
• A. Lisiecki: Welding of thermomechanically rolled fine-grain steel by different types of lasers, Archives of Metallurgy and Materials. Vol. 59, pp. 1625–1631, 2014. https://doi.org/10.2478/amm-2014-0276.
• Sisodia, R.; Gáspár, M.: Experimental assessment of microstructure and mechanical properties of electron beam welded S960M high strength structural steel, Manufacturing Letters, Vol. 29., 2021. pp. 108-112. https://doi.org/10.1016/j.mfglet.2021.05.004
• Sisodia, R.; Gáspár, M.; Sepsi, M.; Mertinger, V.: Comparative evaluation of residual stresses in vacuum electron beam welded high strength steel S960QL and S960M butt joints, Vacuum, Vol. 184, Paper: 109931, 2021 https://doi.org/10.1016/j.vacuum.2020.109931
• Sisodia, R.; Gáspár, M.; Draskóczi, L.: Effect of post-weld heat treatment on microstructure and mechanical properties of DP800 and DP1200 high-strength steel butt-welded joints using diode laser beam welding, Welding in the World, Vol. 64 (4), 2020. pp. 671-681. https://doi.org/10.1007/s40194-020-00867-6
Number of students who can be accepted: 1 (one)
Number of students who can be accepted: 1
Deadline for application: 2023-06-30
2024. IV. 17. ODT ülés Az ODT következő ülésére 2024. június 14-én, pénteken 10.00 órakor kerül sor a Semmelweis Egyetem Szenátusi termében (Bp. Üllői út 26. I. emelet).
Login
