On uniqueness of thermophysical properties and prospects of cast iron with vermicular graphite for internal combustion engines

Abstract

The article is devoted to the problem of implementation new cast irons into mechanical engineering, namely, cast iron with vermicular graphite (CGI) for the manufacture of parts for engines operating under thermomechanical stress. The article presents the results of the analysis of the CGI modern situation. It is shown that the serial production of engineering products in the world began relatively recently due to the development of reliable technology of cast iron modifying for vermicular graphite (VG) only by the end of the XX century. The use of CGI in mechanical engineering in Russia is extremely limited mainly because of outdated inaccurate and even erroneous information about its properties. The data of own research of microstructure, thermal conductivity and strength of cast iron obtained with the use of modern methods and techniques of control are presented. It is shown that the thermal conductivity of CGI may significantly differ within the grades regulated by the obsolete domestic standard GOST 28394-89 which, inter alia, requires reworking for this reason. All investigated microstructures of CGI have thermal conductivity in the temperature interval from 22 °C to 300 °C varying within no more than 5 %. At high and irregular share of sphere graphite (SG) with temperature growth thermal conductivity can grow a little, with decrease of SG share its growth slows down, and since ~200 ºС it starts to fall. At a high share of VG more than 90 % the thermal conductivity starts to fall from ~100 °С, but by 300 °С the fall is no more than 10 %, which is much less than the fall in the same temperature range of the thermal conductivity of lamellar graphite iron (GI) more than 30 %. The difference in thermal conductivities between the perlitic gray cast iron and CGI with a low and medium share of SG already at temperatures higher than 200 °C becomes commensurate with the error of measurement, and at 300 °C practically disappears. At the same time, in the presence of a high SG share in the structure of CGI its thermal conductivity at 300 °С remains considerably lower than that of the perlitic gray cast iron, the difference being ~30 %.