Influence of chemical composition and microstructure on thermal conductivity of alloyed pearlitic flake graphite cast irons

Abstract

Thermal conductivity is one of the most important properties of flake graphite cast iron, that decides the transient temperature and thermal stress distribution in the components which are subjected to elevated temperature applications. Such applications include cylinder heads, brake-drums, exhaust manifolds, ingot moulds, hot mill rolls and dies. Thermal conductivity values are experimentally measured in 23 flake graphite cast irons having an identical base iron composition. The irons selected can be classified into two groups: one with high carbon (3.93%) content and another with medium carbon (3.00%) content. The irons are alloyed with commonly used alloying elements such as molybdenum, chromium, vanadium, nickel, tin, antimony, copper and aluminium. Thermal conductivity values are determined up to the temperature range 40 to 500° C and values up to 40 to 700° C are presented by extrapolation. The present work has provided information regarding thermal conductivitiy of flake graphite cast irons which are used for thermal fatigue applications (where the temperature of the component usually reaches a maximum of 700° C). It is concluded that an increased amount of graphite carbon, an increased amount of type A graphite and an increased fineness of graphite increase thermal conductivity. Further, molybdenum increases thermal conductivity appreciably while nickel and copper increase it moderately. Aluminium and silicon considerably reduce thermal conductivity while chromium, vanadium, tin and antimony reduce it moderately.