Low-Temperature Plasma Generator with Direct Arc for Plasma Remelting
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MA INVESTIGATIONS
Low-Temperature Plasma Generator with Direct Arc for Plasma Remelting M. Kh. Gadzhieva, *, M. V. Ilyicheva, A. S. Tyuftyaeva, and M. A. Sargsyana aJoint
Institute for High Temperatures, Russian Academy of Sciences, Moscow, 125412 Russia *e-mail: [email protected] Received February 28, 2020; revised February 28, 2020; accepted March 10, 2020
Abstract—An efficient low-temperature plasma generator with direct arc for plasma remelting was developed and studied with direct and reverse polarity. It has an expanding nozzle channel and the remelted metal acts as a second electrode. An efficiency of ≈90% and a long service life with a current strength of up to 200 A were obtained. It is shown that the nozzle increases arc stability at an opening angle of 12°. It is established that a super-equilibrium nitrogen content (up to 0.22%) in the molten metal can be obtained. DOI: 10.1134/S0018151X20040033
INTRODUCTION Low-temperature plasma is increasingly used in material-processing technologies, such as welding, cutting, hardening, sputtering, surfacing and remelting, steel alloying with nitrogen from an arc plasma, the deoxidization of magnetic alloys with argonhydrogen plasma, the production of steels with a particularly low carbon content, metal purification from nonmetallic inclusions, desulfurization, and other refining processes [1–3]. The requirements for the mechanical and corrosive properties of metals have increased in recent years. One of the most promising areas for the creation of high-strength, corrosion-resistant high-alloy steels is nitrogen alloying [4–6], which has a beneficial effect on the properties and structure of austenitic and austenitic-ferritic steel (it acts as an austenite stabilizer and increases the mechanical characteristics of this steel: hardness, range of fluidity and strength) [7–9]. In addition, nitrogen is a cheap replacement for nickel (the ability of nitrogen to form austenite is 20 times higher, and it hardens steel without a significant change in its ductility or corrosion resistance). The effect of nitrogen on the ductility and strength of the material is characterized by the form of its presence in the steel. For example, the effect of nitrogen in a solid solution (in austenite) is to slow down dislocations or to create distortion fields that dislocations must overcome during movement [10, 11]. The effect of hardening with nitrogen is manifested when nitrogen is present in its atomic form in solid solution or in the composition of carbonitride phases [12–14]. Thus, in the creation of new nitrogen-containing steels and methods for their production, it is important to take into account the characteristics of the behavior of nitrogen during its interaction with the liquid melt during crys-
tallization and recrystallization phases, which determine the efficiency of alloying steel with nitrogen. Of all the existing methods to produce nitrogen steel (smelting in steelmaking units at normal atmospheric pressure, plasma-arc remelting, electroslag remelting under pressure, me
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