Definition of carbon equivalent and degree of eutecticity of cast iron in foundry production

Abstract

The issues related to the essence of the concepts of carbon equivalent, an indicator of the degree of eutecticity and the ratio of carbon content to silicon content for characterizing the chemical composition and properties of gray cast iron were analyzed. The results of studies of the carbon equivalent value, the degree of eutecticity and the C/Si ratio of the chemical composition of synthetic cast iron, which is used for the manufacture of brake pads and the «Khanin wedge» of railway rolling stock, are presented. Examples of different approaches and formulas for determining the limits and methods of using the carbon equivalent of the chemical composition of cast iron to characterize the weldability of steels, coefficient of friction, wear, other operational indicators of cast iron brake pads, and evaluation of the quality of cast iron as a whole are given and analyzed. Within the standards-regulated ranges of the content of chemical elements in cast iron, the value of its carbon equivalent in individual smelting batches of products can differ significantly (by 30 %). With certain ratios of the main elements in the chemical composition of cast iron, the values of the carbon equivalent can be the same, but the mechanisms of crystallization of cast iron and its properties do not coincide. The parameters of the distribution of the content of carbon, silicon, manganese, phosphorus, sulfur, carbon equivalent, and the degree of eutecticity in cast iron СЧ350, from which the friction «Khanin wedge» for railway rolling stock is made, were analyzed. Cleaning the factory arrays of indicators of chemical composition, hardness, carbon equivalent, degree of eutecticity of cast irons intended for the production of brake pads and the friction «Khanin wedge» from gross erroneous values practically did not affect the general characteristics of the statistical analysis, which indicates the reliability of the results. It is shown that when smelting in induction crucible furnaces gray synthetic cast iron intended for the production of brake pads and the «Khanin wedge», the ranges of variation in the content of C, Si, Mn, P, S are much narrower than those regulated by the standards for these foundry products. The fundamental possibility of introducing appropriate clarifications to the requirements of the standards regarding the content of chemical elements in synthetic gray cast iron intended for the production of brake pads of the «M» type and the friction «Khanin wedge» for railway rolling stock was noted, in particular, reducing the sulfur content to 0,05 % to increase stability of its quality. Keywords: cast iron, chemical composition, carbon equivalent, degree of eutecticity, properties, castings, brake pads, operational characteristics.