OBRABOTKA METALLOV

The influence of parameters of laser melting of gray cast iron SCh20 on the surface topography, microstructure and microhardness is investigated. Parts of centrifugal electric submersible pumps (ESP) for oil production are made of gray cast iron. According to the chemical composition, the analyzed material is gray cast iron. But due to the rapid cooling during casting the material in its initial state has the structure of white cast iron. The rapidly cooled from the melt cast iron (chilled iron) has a high hardness and wear resistance due to the presence of ledeburite in the structure. However, it is of interest to further increase the surface hardness by laser melting. Usually white iron is slightly hardened by laser melting. However, in this case the cast iron observed significant hardening. Samples were cut from the part obtained by casting in a metal mold, and had the form of 3 mm thick plates. Laser surface melting was carried out using a fiber laser with the 1.07 mm radiation wavelength and a circular cross-section laser beam. The varied parameters were: a speed of beam movement v, a spot size d, and a power of the laser beam P. Microhardness was measured with a load of 50 grams. Laser melting in this case does not change the type of structure. However, the dispersion of the microstructure increases significantly. As a result of structure refinement, the microhardness increased from 500 to 770…850 HV_0,05. When a spot size of 0.2…0.5 mm periodic relief is formed on the surface. The relatively smooth surface of the track is formed by laser beam with spot size of 2…4 mm. Simultaneously, in this case, the material has a maximum microhardness. Before and after laser treatment, the samples were weighed. Mass change Dm per unit of length of the laser tracks is determined. It is shown that the value of Dm well approximated by a quadratic dependence on the value of P/(d*v)^0.4. It is known that the value of P / (d * v) 0.4 is proportional to the size of the laser melting zone. Previously, during a study of laser melting of austenitic Ni-Resist cast iron with flake graphite, it was found, that Dm is in linear dependence on the value of P/(d*v)^0.4.

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