By: Bahredin Ali Muzeyin
Materials Engineering Department Adama Science and Technology University
Deferent carbon content steel examined to determine the microstructure, concentration and hardness of the specimens. 0.2% C, 0.4% C and 1.0% C steel specimens were prepared by cutting. Abrasive cutter was used to cut the steels. Furnace was used for heat treatment at 900°C to make the phases separate when seen by microscope. Mounting press was use to mount the specimen to make it suitable for handling at the time of grinding and polishing. Different kind of sand paper was used to grind and make smooth the spacmens and finally polishing cloth with diamond suspension was used to remove the extra scrachs . to diffrantiate the grain boundaries it was etched by nital solution. Finally the first observation was taken made by optical microscope and scanning electron microscope.
This paper contains some important experiment results concerning metals properties. The main aim of the laboratory experiment was to examine and to compare the microstructure and hardness of different carbon content metals, starting from 0.2%C, 0.4%C, 1.0C% content metals with different heat treatment and cooling mechanism. The experiment was started from the preparation of the samples. At the first step the samples was prepared by cutting in appropriate size by the abrasive cutter. After cutting of the specimens, the experiment was held heat treatment under 900Cº for one o’clock. For 0.4%C different mechanism of cooling (i.e. air cooling, furnace cooling and water quenching) was used. After proper cooling mounting was the next step. Hot press mounting machine was used for mounting the sample in order to make suitable for handling and to make the surface flat and zero slope for the next steps. After the mounting the next step was grinding with different sand papers (i.e. #400,#800,#1200and 2000#) mechanically(by hand) using water as a suspension until flat fine mirror like surface is gotten. And to remove extra scratches the specimen was polished with polishing clothes using diamond suspension in polishing machine for about 50 minute. Finally before the microstructure testing the samples was etched by nital (solution of ethanol, HNO3 and alcohol) solution for about ten seconds to make the grain size visible under optical microscope. After the preparation of specimens the first step to examine was microstructure examination under optical microscope. Standard optical microscope with magnification of 50Χ and 100Χ was used. The experiment result was taken from the optical microscope by using installed camera connecting with computer. To make the result more accurate it was taken five times in each step and for each samples of the experiment. And using the microphotograph grain size was determined; using ASTM method formula. N = 2n-1
For determining the volume fraction of perlite simply glide line in Microsoft power point was used to simplify the worthy. After optical microscope test Vickers hardness tester was used as the next experiment. This machine is the simplest and as well as the poorest machine and also it is cheap. It tests actually the hardness of the samples, but since the samples are iron (steels) and its hardness properties are related with its strength. The machine was automatic to calculate the hardness of the materials. But also it can be used using Hall-Peach equation also.
0.102 Χ F(sin136º/2)/d2 1.2 hall-peach equation
Using this machine it is easy to see that how the content of carbon in iron can affect the hardness property and also its...
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