Influence of technological parameters on nitriding rate in obtaining metal powders by plasma centrifugal spraying

Abstract

Increase in metal operational properties is ensured by introduction of a certain set and amount of alloying elements into it. These elements include nitrogen, the interest in which is constantly growing. As many works have shown, nitriding with gaseous nitrogen is used, among other things, in plasma-arc remelting. The data is given on metal alloying with nitrogen at the stage of obtaining granules and powders. However, the latter process requires further study. The process of obtaining nitrogen-containing metal microgranules from EP741NP alloy by plasma centrifugal spraying was studied in this work. Metal powders are obtained by melting the end of a rotating workpiece with a stream of ionized gas (mixture of gases). The technology makes it possible to obtain nitrogen-alloyed fine metal powders of multicomponent spherical alloys with a minimum number of satellites that do not differ in size and chemical composition. Investigation of the nitriding rate is of great interest, especially in the production of powder metal. One of the parameters that affect the degree of metal saturation with nitrogen is time spent by liquid melt under nitrogen-containing plasma and crystallization time of the metal drop. The paper presents a technique that allows one to quantify the role of these parameters on the absorption of nitrogen by the metal during powder production. It is known that the kinetic parameters of the nitriding process are determined by the contact area of ​​two metal – gas phases. In the case of obtaining a powder, this parameter depends on the size of a powder speak. In this connection, the paper presents a calculation method that allows estimating the average fractional composition of metal powders depending on a number of technological factors. The obtained values ​​were compared with the data of semi-industrial heats. It is shown that the fractional composition of microgranules depends on the rotation speed and diameter of the workpiece being remelted, the density of the alloy, and the force of surface tension. It was established that with an increase in the rotation frequency of the consumable electrode, it is possible to achieve a decrease in the fineness of metal powders.