The refractory materials used in the wall of the furnaces for glass melting can be prepared from mullite-zirconia composite material. The composite of mullite/zirconia was synthesized from Iraqi kaolin, γ-alumina, and zirconia using thermal decomposition with reaction sintering at 1600 °C. Several batches were prepared with various ratios of kaolin, γ-alumina, and zirconia, and the composite compositions were selected from the Al 2 O 3-SiO 2-ZrO 2 phase diagram. The mullite-zirconia composite was prepared with different steps beginning with milling the starting materials, semi-dry uniaxial pressing, and then reactive sintering at various temperatures (1200, 1400, and 1600 °C). The predicted phases ZrO 2 and Al 6 Si 2 O 13 were identified by X-ray diffraction patterns according to the phase diagram for all the batches. The lower amount of the zirconia added to mullite reduced porosity and improved the bulk density of the mullite/zirconia composite. The thermal expansion coefficient slightly increased with the addition of zirconia. It also enhanced the thermal shock resistance of the composite. Finally, the mechanical properties were improved by increasing the amount of zirconia particles in a matrix of mullite due to the phase transformation of zirconia from tetragonal to monoclinic phase.

One of ways to improve properties of materials without changing the product shape toobtain the desired engineering applications is heating and cooling under effect of controlledsequence of heat treatment. The main aim of this study was to investigate the effect ofheating and cooling on the surface roughness, microstructure and some selected propertiessuch as the hardness and impact strength of Medium Carbon Steel which treated at differenttypes of heat treatment processes. Heat treatment achieved in this work was respectively,heating, quenching and tempering. The specimens were heated to 850°C and left for 45minutes inside the furnace as a holding time at that temperature, then quenching process wasperformed in four types of quenching media (still air, cold water (2°C), oil and polymersolution), respectively. Thereafter, the samples were tempered at 200°C, 400°C, and 600°Cwith one hour as a soaking time for each temperature, then were all cooled by still air. Whenthe heat treatment process was completed, the surface roughness, hardness, impact strengthand microstructure tests were performed. The results showed a change and clearimprovement of surface roughness, mechanical properties and microstructure afterquenching was achieved, as well as the change that took place due to the increasingtoughness and ductility by reducing of brittleness of samples.

The current study shows the effect of various heat treatments on the cutting force and surface finishing of machining for medium carbon steel (0.522C) with different cutting conditions have been investigated. In this research, samples have been divided into two groups. Samples of the first group were heated to austenitizing temperature and quenched in a polymer solution (Polyethylene glycol M. W.400), followed by tempering. Tempering process is to reduce brittleness and relieve residual stresses. In this treatment, the samples were heated again to 450 ○ C, held for one hour at that temperature (soaking stage), then cooled in still air. Samples of the second group were heated to austenitizing temperature and cooled by air (normalizing process). The cutting force and other properties were evaluated before and after heat treatment. The results showed a direct effect of heat treatments on cutting force and machinability. In other words, a correlation between the machinability and the heat treatment of specimens was established.

In this paper, quenching and tempering effects on the machining conditions of medium carbon steel were investigated. The samples were quenched in a saltwater and polymer solution after heated to austenitizing temperature at 870°C, then, the tempering process of the samples were conducted to reduce internal stresses and hardness. In the tempering process the samples were heated again to 400°C with a soaking time was one hour, so cooled in still air. So the samples were machined by lathe machine with selected cutting conditions. The results appeared the effect of heat treatments on hardness, surface finishing, cutting force and microstructure that were evaluated before and after heat treatment with various cutting conditions.