Comparative Results of Tribotechnical Tests of Rollers for a Pendulum Mill Made of IChKh28N2 Wear-Resistant Cast Iron and ShKh15SG Steel

Abstract

The purpose of the work was a comparative analysis of the results of metallographic and tribotechnical properties of industrial working rollers made of ShKh15SG steel (before and after operation) and IChKh28N2 wear-resistant cast iron (before operation) to select the material of the rollers and increase the service life of pendulum mills. Metallographic studies were performed on IM7000 optical microscopes with a Thixomet image analyzer and a microvizo-MET microimage. Microhardness measurements were carried out automatically using the Vickers method at a load of 50 g over the entire cross section of industrial rollers. Tribotechnical tests were performed on a SMC-2 friction machine according to the “roller–abrasive roller” scheme (rotation speed 500 rpm, load 45 N, test time 2 h) with an assessment of the coefficient of friction, wear, and surface roughness. It was found that ShKh15SG steel in its initial state had a homogeneous structure of low-pressure martensite with a carbide heterogeneity of (Cr,Fe)₃C (HV 828) with an average hardness of HV 630. After 3 months of operation, under the influence of softening processes (temperature and plastic deformation), martensite was transformed into tempering troostite in the subsurface layers, and bands with martensitic and martensitic–troostite structures were formed with an average hardness of HV 443, which is 1.5 times less than the hardness (HV 630) in the initial state. Internal arc-shaped cracks were found. IChKh28N2 cast iron had a white pre-eutectic cast iron structure consisting of alloyed austenite (670–750 HV), cementite-type carbides (Cr,Fe)₃C (856 HV), and complex carbides (Cr,Fe)₇C₃ (1389 HV). The average hardness of the cast iron was HV 781, which is 1.2 times higher than the hardness of the steel in its initial state. Tribotechnical tests have shown that cast iron had a lower coefficient of friction (0.58 versus 0.68–0.85 for steel), 1.7 times less wear (214 mg versus 358 mg for steel) and the ability to run in under friction (reducing the roughness of R_a by 3.7 times). Based on the structural characteristics, hardness, and tribotechnical properties, IChKh28N2 wear-resistant cast iron is recommended as a material for the manufacture of rollers of pendulum mills operating under conditions of intense abrasive wear, which will increase their service life.