Three cast irons with different graphite morphologies were austempered in order to investigate how some important material properties are affected. The cast irons had similar chemical compositions so valid comparisons could be made between morphologies and between as-cast and austempered samples. The cast irons were austenitized for 2h at 900°C and austempered at 350°C for five different times, resulting in coarse ferrite needles. Microstructure, hardness, scuffing resistance, ultimate tensile strength (UTS) in bending and thermal properties was investigated for both as-cast and austempered samples. The hardness increased by about 25% after 110 min austempering while the thermal conductivity dropped about 30%, for all three morphologies. Scuffing resistance increased significantly when austempering lamellar graphite cast iron but was slightly reduced for both the compacted and nodular graphite morphologies. After 110 min austempering, the ultimate tensile strength was reduced for the lamellar and compacted samples, but was slightly increased for the nodular morphology.

Understanding how alloying elements and amounts affect the shape and size of graphite in compacted graphite cast irons could be of great importance. Some important material properties that are affected by the graphite shape are tensile strength and thermal conductivity. Knowing the effect of alloying additions could be of assistance when trying to optimise material for a specific application. In order to determine how graphite changes depending on alloying additions the microstructure of nineteen CGI materials were investigated. All melts were based on one chemical composition and alloying elements were added to obtain melts with variation in magnesium, silicon, copper, tin, chromium and molybdenum. Some of the more important microstructure features that were analysed are the amount and size of different graphite particles. The result from this analysis should give an indication on what features each alloying element affect and how these features varies with alloying amount.

Nineteen compacted graphite cast irons were investigated in order to determine how alloying additions affect the thermal transport properties and microstructure. All melts were based on one chemical composition and alloying elements were added to obtain melts with variation in magnesium, silicon, carbon, copper, tin, chromium and molybdenum. Increasing amounts of magnesium resulted in a further compaction of the graphite particles, reducing the thermal conductivity. Large amounts of silicon resulted in a fully ferritic metal matrix. Silicon also formed solid solution with iron which had a deteriorating effect on the thermal conductivity, i.e. the larger amount of silicon the lower the thermal conductivity. Copper and tin promoted formation of pearlite that had worse thermal properties compared to ferrite. Increasing amount of ferrite generally had a positive influence of the thermal conductivity. Chromium and molybdenum were carbide forming elements and carbides had a negative influence on the thermal conductivity.

The thermal conductivity of various grades of pearlitic cast iron has been modelled with good results by means of regression analysis. The experimental thermal conductivity data, which the modelling is based on, were obtained by the laser flash method. The microstructure was investigated by digital image analysis combined with a colour etching technique. The model developed takes the carbon content, the silicon content, the nodularity as well as the fraction of cementite into consideration. The graphite morphologies of the samples investigated were lamellar, compacted and spheroidal.

A model describing the thermal conductivity of compacted graphite iron (CGI) was created based on the microstructure analysis and thermal conductivity measurements of 76 compacted graphite samples. The thermal conductivity was measured using a laser flash apparatus for seven temperatures ranging between 35 C and 600 C. The model was created by solving a linear regression model taking into account the influence of carbon and silicon additions, nodularity, and fractions of ferrite and carbide constituents. Observations and the results from the model indicated a positive influence of the fraction of ferrite in the metal matrix on the thermal conductivity. Increasing the amount of carbon addition while keeping the CE value constant, i.e., at the same time reducing the silicon addition, had a positive effect on the thermal conductivity value. Nodularity is known to reduce the thermal conductivity and this was also confirmed. The fraction of carbides was low in the samples, making their influence slight.  A comparison of the thermal conductivity values calculated from the model with measured values showed a good agreement, even on materials not used to solve the linear regression model.