INVESTIGATING THE PROCESS OF QUENCHING AND HARDENABILITY OF THE ХГС - GRADE STEEL BALLS

Abstract

Acecrding to the results of analysis of domestic and foreign literature, and also acecrding to ГОСТ 7524-89 and ГОСТ 5950-2000, it is shown that for grinding non-ferrous metal ores, balls with a diameter of 120 mm are mainly used, especially those made of steel grade ХГС. To ensure high productivity, the surface of the ball, up to half of the radius, must have a martensitic structure (HRC 55...58), and the core must be bainitic (HRC 45…48). It is quite a difficult task, that is the reason why, in this work, an attecnpt is made to use an aqueous solution of the nairit latex instead of mineral oil, which changes the rate of cooling of the metal at temperatures below 300⁰C and makes it possible to obtain a bainite structure in the core. The temperature of quenching (Т=830...850⁰C), the optimal percentage of the nairit latex (1,0…1,5%) and the temperature of the cooling environment (20…30⁰C) have been obtained dy mathematical modeling. To have a bainitic structure in the core, the correct concentration of the nairit latex is determined at which the cooling velocity in between 300…225⁰C is slow enough to cross the C-shaped curves. This process, as a result, provides a bainitic structure in the core (HRC 45…48) and martensitic structure on the surface (HRC 55...58). When quenching balls at a temperature of 850°C, the amount of retained austenite fluctuates within 15...16%, and the grain size reaches - 11...10 points, which makes it possible to reduce the deformation to a minimum. With an increase in the quenching temperature to 925°C, the content of retained austenite increases to 20%, and the grain size increases to 8...9 points, which explains the production of coarse-acicular martensite. On the contrary, as the temperature decreases to 775°C, the content of retained austenite decreases to 8...10%. Tempering at a temperature of 160...180°C for τ = 1,0...1,5 h reduces the content of the retained austenite to 1,0...1,5%, increasing the hardness by 1,5...2,0 HRC units.