| Popis: |
It has been stated that electrode shape and heat input relates to the arc motion, thermal cycles, the weld pool molten metal crystallization rate and deposited metal microstructure. Surfacing performed with perpendicular and longitudinal ribbon electrodes results in coarse-grained and non-uniform microstructure of the deposited metal. Surfacing made with wire and composite electrodes leads to the microstructure refinement, it becoming small-dispersed and uniform. The electrode shape is the main parameter determining the deposition process, since the arc moving along the butt end of the electrode gets concentrated when surfacing is made with wire and dissipates when surfacing is made with a ribbon electrode, according to its movement either along the longitudinal axis or transverse the weld pool. The arc movement determines heat input in the pool, heating and cooling rates of the molten metal and heat affected zone; surfacing regime being constant. This changes the crystallization conditions of the weld pool, diffusion processes, structural and phase transformations [1,2], and the deposited metal quality. However, the influence of the electrode shape on the deposited metal quality was not investigated properly. It has been proved both through experiments and calculations that when surfacing rate is high and heat input is low, heating and cooling rates increase, the number of crystallization centers grows too and they, lying in front of the growing crystals, slow down their further growth. Deposition rate increasing, the crystallization rate of the weld pool molten metal grows in proportion to it, microstructure gets reduced, welding stresses decrease, these processes resulting in the welded joints toughness increase as well as the cracking resistance of the deposited metal. The process of energy-saving high-speed deposition with low heat input, which provides increase in the heating, cooling and crystallization rates, microstructure reduction, welding stresses decrease and metallurgical equipment parts cracking resistance increase has been developed |
