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Welding of materials for the production of energy devices with laser and laser-MIG hybrid technology, hybrid welding
Mrňa, Libor ; Šebestová, Hana ; Novotný, Jan ; Beran, D.
Laser welding technology is known more from the automotive field, where it is used for fast and high-quality welding of thin body sheets. The production of power equipment is specific both in the materials used (mainly martensitic stainless steels) and in the significantly larger thicknesses of the welds. Research into the weldability of these materials using laser welding technology and laser-MIG hybrid technology is being conducted at the ÚPT. The article describes experiences with the general weldability of these materials with laser and hybrid laser-MIG, as well as practical applications of welding parts of steam turbines. Finally, the possibility of welding stellites using hybrid laser-MIG technology is also discussed.
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Microstructure modifications of Al-Si-coated press-hardened steel 22MnB5 by laser welding
Šebestová, Hana ; Horník, Petr ; Mika, Filip ; Mikmeková, Šárka ; Ambrož, Ondřej ; Mrňa, Libor
Weld microstructure depends on the characteristics of welded materials and parameters of welding technology, especially on the heat input that determines the peak temperature and the cooling rate. When the coated sheets are welded, the effect of the chemical composition of the coating must be also considered even though its thickness is only a few tens of microns. During 22MnB5+AlSi laser welding experiments, the ferrite-stabilizing elements of coating modified the weld metal microstructure. Ferrite appeared in a quenched weld metal. The rapid cooling rate accompanying welding with a focused beam limited the homogenization of the weld metal which resulted in the formation of ferritic bands in the regions rich in Si and especially in Al. On the other hand, a high level of homogenization was reached when welding with the defocused beam. The ferritic islands uniformly distributed in the weld metal were formed at 0.4 wt% and 1.6 wt% of Si and Al, respectively. The doubled heat input reduced the Al content to 0.7 wt% insufficient for the ferrite formation at still relatively high cooling rates. Predicting the distribution of ferrite in the weld metal is challenging due to its dependence on various factors, such as cooling rate and the volume of dissolved coating, which may vary with any modifications made to the welding parameters.
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