Title: Microstructure examination of steel DOCX

Title	Title: Microstructure examination of steel
Author	Ashan Dissanayake
Pages	9
File Size	877 KB
File Type	DOCX
Total Downloads	613
Total Views	676

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Title: Microstructure examination of steel. Objective: To observe the composition, structure and properties of metals and their alloys by means of an optical microscope. Introduction: In solid form, metals are crystalline in structure. The arrangement of the atoms which are in order and in three dimensional pattern are internal structures and known as crystalline structure, which in this experiment is of solid metal steel. A collective of many very small crystals exists in normal metallic materials of polycrystalline and these crystals are known are grains. Normally, these grains are very small in size and impossible to observe with bare naked eyes. There for these structural features are observed usually by an optical microscope or if possible by an electron microscope with magnification above hundred times. These structures which require this type or range of magnification for their examination are called microstructures. The internal structure of any material is evidentially very important in any engineering material aspect. And the structure of any material is associated with its arrangement, properties, and performance. And it very important to understand the composition and other discussed factors of any material's structure in real life applications. And in this experiment gives us an idea of how to observe the internal structure of steel and will help in the understanding of how to observe in other materials as well. Theory: Before examining the steel specimen, there are some before in hand procedures to follow for a better observation. Initially the specimen should be prepared for the examination; Mounting: Is done for the ease of holding the specimen during the grinding and polishing process. Here, in one process, cold mounting is conducted where using two components resins which are liquid to start with but which set solid shortly after mixing. Cold mounting requires very simple equipment consisting of a cylindrical ring which serves as a mold and a flat piece which serves as the base of the mold. The sample is placed on the flat piece within the mold and the mixture poured in and allowed to set. Cold mounting takes few hours to complete. Another method is hot-mounting which uses a heating method. Grinding: Is done using rotating discs covered with silicon carbide paper and water. There are a number of grades of paper, with 180, 240, 400, 1200, grains of silicon carbide per square inch. 180 grade therefore represents the coarsest particles and this is the grade to begin the grinding operation. We should always use light pressure applied at the center of the sample. Continuation of this grinding should be carried out until the blemishes are removed. Polishing: Is done to get a mirror like surface to clearly observe the structure here it is being polished by polishers which has rotating discs covered with soft cloth impregnated with a pre-prepared slurry of hard powdery alumina particles (Al2O3, the size ranges from 0.5 to 0.03 μm). This is done due to fact that the surface unevenness will be removed. The specimen should be put in acid in which the acid will attack the grain boundaries taken into a reaction. Etching: Is done due to Grinding and polishing operations produce a highly deformed, thin layer on the surface which is removed chemically during etching. Secondly, the etchant attacks the surface with preference for those sites with the highest energy, leading to surface...