Journal of Advanced Processes in Materials Engineering
Year:2009 | Volume:2 | Issue:7|Papers Count:8

One of the problems in continuous casting of steel is that low melting point phases from binders are developed and reacted with both permanent and consumable layers of tundish, leading to interdiffusion and sintering of layers and making difficulties in deskulling and destroying the permanent layer. In this study three different complex silicate, phosphate and sulphate binders are employed. SEM and XRD experiments have shown that magnesium sulphate is the best. It provides low temperature adequate strength, but no high temperature melting and sintering. By using this binder, deskulling is easily performed and permanent layer is not deteriorate.

In this research the changes of microstructures of HAZ (Heat Affected Zone) and weld metal of a 316 stainless steel was studied using proper heat transfer and fluid flow numerical model. With respect to the heat input extent, maximum grain size in heat affected zone have changed in the range of four to two times greater than that of base metal. Studying of microstructure of weld metal showed that temperature gradient and cooling rate have important effects in prospecting the solidification morphology and grain size of weld metal.

Modeling of sheet metal forming is an effective tool in analysis of metal forming and prediction of effective parameters in this process. Most of present models do not take into account the thickness changes and friction phenomena during forming process and using 2D models, they can not predict the real situation of the drawing process. The new 3D model presented in this research considers changes in sheet thickness and friction in drawing and show better agreement with the experimental results.

In this research, 70-30 brass containing 0.25% Mn was prepared using a controlled atmosphere furnace and cast in a copper mould. Samples with 5×10×50 mm dimensions were cold rolled in order to reach 65% reduction. Then specimens were isothermally annealed at three different temperatures (600, 700 and 800oC) with different holding times between 2-60 minutes and were then cooled in 20oC water. Microstructural studies were executed using optical microscope. The average grain area of 200-450 grains was measured using Clemex image analyzer software. Results showed that addition of Mn to 70-30 brass had an impact on grain boundaries atmosphere and also decreased its activation energy and consequently accelerated grain growth. Calculation of growth activation energy within 500 and 700oC showed that growth activation energy of Mn free brass was 171 kJ/mol while that for Mn containing alloy was 22.35 kJ/mol.

In this paper, effect of time and temperature of aging on hardness and microstructure of 60 Nitinol (nickel - titanium alloy with 60% wt. nickel) has been studied. After hot working, the specimens were solution treated for 6 h at 1100oC and then aged at various temperatures between 400 to 900oC for 30-480 min. The microstructures of the specimens were studied by scanning electron microscopy (SEM). The results showed that with increasing aging time at a constant aging temperature, an almost a constant hardness was obtained. The hardness decreased as the aging temperature increased to about 700oC. Further increase in aging temperature increased the hardness of the samples. At a constant aging temperature, with increasing aging time, the size of precipitations was increased.

In this study, the adhesion strength of 316 L stainless steel coating deposited on the surface of 1.1248 steel by methods of flame spraying and electro - spark deposition (ESD) was investigated. For measuring adhesion and also bending strengths, the required samples according to Standard Numbers ASTM C633-01 ASTM B 489-85 were prepared, respectively. The characterization of deposited layers on the samples by the two methods was performed using the X-ray diffraction (XRD) and scanning electron microscopy (SEM) techniques. The results also reveal that adhesion strength of the coating deposited by electro - spark is much higher than that of flame spraying coating. No crack was created on coated layers by ESD, during the bending tests.

The effect of Al content on grain growth behavior of 70-30 brass containing iron was studied. The results showed that grain growth behavior was different in various temperatures. At low temperatures, abnormal grain growth occured but normal grain growth occured at higher temperatures. Also the amounts of Al content affect this transition and so with increasing Al the transition temperature was decreased. Occurrence of Abnormal grain growth at lower temperatures and transform to normal grain growth at higher temperatures may be attributed to solute drag effects.

Hydroxyapatite powder was prepared by burning bone and heat treating the obtained bone ash at 600, 700, 800 and 1100oC in an air furnace. The black ash was converted to a white powder after heat treatment. X-ray diffraction analysis and Fourier transform infra - red spectroscopy indicated that the white powder was hydroxyapatite and did not contain any organic components of the bone. Furthermore, phase transformation of the resulted hydroxyapatite to other calcium phosphate phases did not occur up to 1100oC. The resulted material was found to be thermally stable up to 1100oC. The density of natural hydroxyapatite heat treated at 800°C was measured to be 3.187 g/cm3.