INCREASING THE PHYSICAL-MECHANICAL AND OPERATIONAL PROPERTIES OF HIGH MANGANESE STEELS BY IMPROVING THE TECHNOLOGICAL PROCESSES OF THEIR MELTING, MICRO-ALLOYING AND MODIFICATION

Procesi littâ, 2024, Vol 1 (155), 14-28

Abstract

The regularities of the influence of the pouring temperature and nitrogen modification of highmanganese steel on the formation of the primary dendritic structure and the quality of castings are shown, the influence of chemical-structural heterogeneity and metal density on the physical and mechanical properties of steels, and the regularities of the influence of the initial structural state on
the wear resistance of steel under shockabrasive wear conditions are determined. The influence of the cooling process of castings on the physical and mechanical properties of highmanganese steels is shown, taking into account their features and temperature regimes of casting. It is noted that in order to obtain highquality castings, the optimal temperature of the melt before pouring it into molds should be in the range from 1430 ºС to 1480 ºС depending on the wall thickness of the cast part and its overall dimensions. This temperature ensures high physical and mechanical properties and quality of castings with a wall thickness of up to 20 mm. Nitrogen modification significantly reduces the negative impact of the increase in the temperature of the melt before pouring into molds on the mechanical properties of steels. After heat treatment to austenite, modification with nitrogen provides a simultaneous increase in the strength and plasticity of the metal by 15...20% due to grain boundary strengthening and strengthening of austenite with solid nitrogen. It is shown that the degree of influence of nonmetallic inclusions on the properties of steel depends on their number, shape and distribution in the micro- and macro-volumes of the casting and does not depend on the reasons for their appearance in the metal. The sizes of nitrides in these steels do not exceed 2...8 μm, and silicate, oxide and sulfide inclusions in all steels – 12 μm, which does not significantly affect the properties of the metal in castings. Nitrogen modification, dispersive vanadium nitride hardening after nitrogen modification and vanadium microalloying provides a 1.5–3.0 times reduction in the index of contamination of steel with nonmetallic inclusions of various morphologies. The grain score of 4 standard steel increases to 6 after its modification with nitrogen and microalloying with vanadium, which contributes to an increase in strength by 15...17% and plasticity by 40...60% while maintain-ing a high level of steel viscosity. It is shown that tempering products made of high-manganese steels from the cast state in order to reduce their hardness and, as a result, improve the mechanical processing of the products, is impractical.