METHOD OF DETERMINING THE OPTIMAL CONCENTRATION OF NANOSTRUCTURED POWDERS IN SHIELDING GAS

The paper presents the theoretical and experimental studies to determine the optimal concentration of nanostructured powders in the shielding gas. The objective of this study is the development of a defi nition technique for optimal concentration of nanostructured powders in the shielding gas during welding by consumable electrode in the argon medium. Molybdenum nanopowder (NP Mo) was used to confi rm the calculations used in the experimental studies. The injection of the powder into the weld bath was carried out through the special device. The surfacing of samples was carried out in a pilot plant, which consisted of a welding head GSP-2 with the developed device, the power supply had rated current of 300 A. For surfacing of steel samples (austenitic steel with chemical composition: C – 0.12 %, Cr – 18 %, Ni – 10 %, Ti – 1 %) the welding wire with diameter of 1.2 mm was used (chemical composition: C – 0.12 %, Cr – 18 %, Ni – 9 %, Ti – 1 %,). To ensure the quality of the welded joint during welding, the dimension parameters of dendrites should tend to a minimum. A stable welding process is caused by the transition of electrode metal droplets from the end of the welding wire into the weld bath. Therefore, the volume of the electrode metal droplet should also tend to a minimum. Before the start of the optimization of nanostructured powders concentration in the shielding gas, the eff ect of welding mode parameters by consumable electrode in the argon medium on the microstructure of the weld metal was established. The results of the investigations have shown that the minimum grain size is observed at a current strength of 240 – 260 A and arc voltage of 28 – 30 V. In these modes, the studies were conducted to select the optimum concentration of nanostructured powders in the shielding gas. It was found that the optimum concentration of nanostructured powders-modifi ers in the shielding gas is 20 mg/m of the welded joint. It was established that the use of diff erent concentrations of nanostructured powders in the shielding gas makes it possible to obtain a diff erent microstructure of the weld metal. The most lightly branched dendrites and the equilibrium structure according to the dendrites size are achieved at a concentration of nanostructured powder in the shielding gas of 20 mg/m of the weld. When adding nanostructured powders-modifi ers to a liquid weld bath, the mechanical properties of the welded joints increase as compared to the welding process, without the addition of a powder-modifi er at +20 °C by 7.5 %, at +500 °C by 6.5 %.

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