Preparation effect of mould systems on microstructure and mechanical properties of spheroidised graphite iron
This study is based on evaluation of microstructure and mechanical properties such as tensile strength, Brinell hardness and Charpy impact test of as-cast spheroidal graphite iron using sandwich techniques in different mould systems viz. green sand mould, dry sand mould and CO2 sand mould under varying cooling rates.
Effect of Graphite Microstructure on their Physical Parameters and Wettability Properties
To produce castings of titanium, nickel, zinc, copper and many other metal alloys, graphite molds can be used. Using graphite molds has many advantages, including that no lubricate or coating layers are needed, a high cooling rate, and ease of production of complex shapes. However, for high quality castings, high quality graphite is required with high mechanical properties and a high heat transfer coefficient. Since there is no room for adjusting the chemical composition of graphite molds, the most important factor determining the properties of the molds is their production process. Thus, in the present study, mechanical properties of two different types of graphite are investigated. The two types of graphite were produced by different technological processes: a typical process of graphite production from isotropic coke, and an electrolytic method of production. The research included mechanical testing and structural investigation by scanning electron microscopy. Chemical analysis was performed by Energy Dispersive x-ray Spectroscopy, and x-ray phase analysis was performed by XRD. Mechanical properties were determined by compression and three-point flexural testing at room temperature. It was found that the porosity of graphite is the key parameter determining its mechanical properties. In addition, it was found that mechanical anisotropy of graphite is dependent on the production method where the size and distribution of pores play an important role.
Experimental study of the eutectoid transformation in spheroidal graphite cast iron
The decomposition of austenite to ferrite + graphite or to pearlite in spheroidal graphite cast iron is known to depend on a number of factors amongst which are the cooling rate and microsegregation of alloying elements (Si, Mn, Cu,...) issued from the solidification step. This present study was undertaken in order to deepen the understanding of the effect of alloying with low levels of Mn and/or Cu on the eutectoid reaction. For this purpose, differential thermal analyses were carried out where samples were subjected to a short homogenization treatment designed to smooth out the microsegregations. The effect of the cooling rate on the temperature of the onset of the growth of ferrite and pearlite and on the overall growth kinetics was investigated. A description of the conditions for the growth of ferrite and of pearlite is given and shows that the reactions can develop only when the temperature of the metal is below the lower boundary of the related ferrite + austenite + graphite or ferrite + austenite + cementite tri-phasic domain. The experimental results might then be conveniently understood when the appropriate reference temperature is used to express the effect of the cooling rate on the undercooling of the reaction. The effect of the cooling rate on the temperature of the onset of the ferrite growth is thus found to be alike what is observed for the eutectic reaction, with a measured undercooling which can be extrapolated to a zero value when the cooling rate is zero. Concerning pearlite, it is found that its growth undercooling takes values which are in agreement with similar data obtained on silicon steels