Structure formation of steel castings depending on the temperature-time parameters of melting and crystallization

Abstract

The paper highlights modern ideas about the features of the processes of crystallization and structure formation in the volume of steel castings, depending on the temperature and time conditions for cooling the melt and cooling the castings, as well as the technological prehistory of charge materials. The analysis of the influence of modification and thermokinetic conditions of crystallization and cooling of steel castings is carried out, taking into account the chemical composition of steels at each stage of the technological cycle for producing cast products. At the stage of selecting charge materials, the conditions for preserving certain metallogenetic features of the initial charge in the structure of steel castings are considered, the existence of an equilibrium temperature (Te), when overheated above which heredity is lost, is considered. Due to this, the possibility of using secondary metal to improve the casting properties without changing their chemical composition is shown. The influence of temperature and time parameters in the pre-crystallization period, namely, the melt overheating temperature, the duration of isothermal treatment and the rate of its subsequent cooling, on the structure formation and properties of steel castings, including taking into account the metallogenetic features of the initial charge, is analyzed. Regularities of the influence of the temperature-time conditions of crystallization in the temperature range of the solid-liquid state on the nature of nucleation and structure formation during the crystallization of steel castings are shown. The features of structure formation and the formation of properties in steel castings under conditions of temperature-kinetic influence after their hardening are determined. And also considered the prospects for obtaining castings with a gradient structure to improve the special properties of cast products. The considered approaches to improve the quality and properties of steel castings open up the prospect of creating new technological solutions and automating technological processes for producing cast products with a predictable set of properties at or above the level of properties of similar rolled products. Keywords: castings, charge, heredity, equilibrium temperature, modification, crystallization, cooling rate, thermal treatment.