Characterization of austempered ductile and vermicular graphite high simo and alsimo alloyed cast iron

Every year, tightening emission standards causing a reduction in engine volumes however desire for obtaining high power from an engine does not reduce. All the concepts meet and come up with simple consequence; light-weigthing the vehicle without causing a security flaw. Conventional engine materials such as aluminum alloys and cast irons are already ligther than their stronger steel equivalents however, increasing firing temperatures and pressures make them on the limit of utilization. Besides, not only hot systems of an automobile, but also every other component suffer from emission regulations because they all need to be lighter and lighter every year, including the windows, polymer consoles or any cast parts. Another big fraction of the heaviness of a vehicle comes from power train parts. For the same purpose, they also need to be shrink without creating weakness. Cast stainless steels are too heavy and austenitic cast irons are too expensive for being an automobile material. Briefly, automotive industry needs a new alloy that can satisfy both consumer and producer. The aim of this study is investigating a special kind of heat treatment of a recently very popular alloy, high aluminium added SiMo cast iron or with the other saying high AlSiMo cast iron. This alloy have very wide potential to be used in automotive and many other heavy industries. From previous investigations, it was observed that aluminum give rise to the A1 eutectoid line and thus retard the austenitization transformation. Other from that aluminum forms thermodynamically stable aluminosilicates (Al2SiO5) and ironaluminates (FeAl2O4) at the surface of the material, which provides high temperature oxidation resistance. Theoretical calculations and modellings had a good agreement with the experimental results. This alloying phenomenon is a pre-production treatment to enhance material`s properties in working conditions. However, in this study a post-production treatment is considered, austempering heat treatment of AlSiMo alloy. Nowadays, ADI (austempered ductile iron) is a very popular material in heavy industry. It brings high strength and wear resistance along with the ductility. ADI's specific acicular ferritic bainite structure give rise to the fracture toughness of material. Its tempered martensite relatives suffer from brittleness and require two-step heat treatment for production. Enhanced mechanical properties make high AlSiMo material suitable for being vehicle components. Especially considering the reducible excess weight of components in order to provide enough sectional strength. In the light of such informations, it is decided to investigate microstructural response of the material to the austempering treatment in the presence of aluminum, mechanical properties of aluminum alloyed austempered cast irons and the phase transitions take place during the heat treatment. In consequence of investigations, it is found that aluminum has a bainitic bay expander property and with the gradual addition of aluminum, samples get martempered. 5 % Al (by wt.) addition makes impossible to fully austenitize the sample even at high temperatures as 1100o C, due to its ferrite stabilizer properties and as a result dual matrix microstructures are obtained. Other from that, a new kappa phase suggested according to thermodynamical modellings and also observed in micrographs. High austenitizing temperatures are promoted to dissolve most of the graphite volume in the matrix, in fully austenitized samples. Thus, in some samples high carbon concentration stabilized austenite phase presented which have larger fraction than ausferritic structure. Those are tought to have very high fracture toughness properties. However, in samples that cannot fully austenitize (ie. have less carbon solubility) graphite diffusion along the grain boundaries is observed from one of its kind micrographs.