Structural transformations and their impact on the mechanical and antifriction properties in the process of alloying graphitized hypereutectoid steel with copper

Abstract

The purpose of the work is to develop a cast antifriction material based on an iron-carbon alloy with a high copper content for use in large, heavy duty sliding friction units. Using the casting method in self-hardening liquid glass mixtures, two specimens of hypereutectoid graphitized steel with different copper contents (0.09 and 8.76 wt.%) were produced. To obtain graphite in the steel structure, modification with the silicocalcium (SiCa) was used. The microstructural examination was carried out using optical metallography, SEM and TEM methods. The impact of copper on the structure as well as the mechanical and antifriction properties of graphitized hypereutectoid steel was studied. It was found that adding 8.76 wt.% of copper to the steel composition leads to an increase in the Brinell hardness level of the material from 250 to 300 HB, ultimate tensile strength from 250 to 380 MPa and compressive strength from 1050 to 1200  MPa, which is associated with an increase in the microhardness of pearlite from 350 to 420 HV. To assess the impact of copper on the sliding friction coefficient of graphitized hypereutectoid steel, a curve of sliding friction coefficient vs applied load was plotted; the experiment was carried out according to the liner-on-disk scheme. The wear resistance of materials under sliding friction conditions was also assessed using this method. Copper alloying has a positive effect on the wear resistance of graphitized hypereutectoid steel by increasing the mechanical properties of the material and also by reducing the level of the sliding friction coefficient under boundary lubrication conditions.