Wear Resistance of the Ductile Cast Iron Increasing

Abstract

Problem. Ductile cast irons with spheroidal graphite are increasingly used for heavy and medium-loaded machine parts operating under conditions of friction and wear. Providing the necessary wear resistance is hampered by the structural and chemical heterogeneity of cast iron, which are formed in the process of its production. The properties can be improved by heat treatment or alloying, a combination of alloying with heat treatment. Goal - Investigation of the effect of complex microalloying on the structure and properties of high-strength cast irons, selection of the optimal composition with sufficient strength and wear resistance. Method. Used cast irons modified with iron-zo-silicon-magnesium alloy, alloyed with different amounts of nickel and molybdenum. The structure was investigated using metallographic and electron microscopes, the distribution of elements on a X-ray spectral microscope analyzer. Determination of wear resistance was carried out on a standard SMZ-2 friction machine. Results. Alloying ductile iron with nickel and molybdenum first leads to an increase in the amount of a high-carbon component (pearlite) in the structure, and then even to the appearance of troostite and bainite in cast iron. The location of troostite and bainite along the boundaries of eutectic grains is due to the distribution of the main elements in the cast iron matrix, and significantly increases the strength and wear resistance of cast iron. The maximum wear of cast iron 1 is 0.719 g, and the pads – 0.362 g. The maximum wear of cast iron 2 is 0.471 g, and the pads – 0.182 g. The maximum wear of cast iron 3 is 0.210 g, and the pads – 0.090 g.  Cast iron 3 with the largest number of alloying elements (0.75% Ni, 0.58% Mo) have the highest wear resistance. The lowest wear resistance has undoped cast iron 1. Due to the change in the structure of the matrix and its compliance with the Charpy principle, the complex microalloying with nickel and molybdenum makes it possible to significantly increase the wear resistance of high-strength cast iron. Cast iron with the highest amount of alloying elements is the least susceptible to wear. Scientific novelty. Establishing the nature of the distribution of chemical elements (silicon, magnesium, nickel, molybdenum) in the matrix of high-strength cast iron and the corresponding processes of structure formation. In particular, the formation of troostite and bainite along the boundaries of eutectic grains in the studied cast irons is explained by the oversaturation of these boundaries with nickel and molybdenum. Practical significance. The optimal composition of cast iron is determined. Reducing the wear of high-strength cast iron does not cause a corresponding increase in wear of the connected parts.