The aim of this laboratory experiment is to examine the tensile strength of three specimen of low, medium and high carbon steels is examined. The microstructure of the specimen is determined and calculations such as tensile strength, yield strength etc we
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INDEX Page ABSTRACT 1 INTRODUCTION 1 BACKGROUND 2-3 EXPERIMENTAL PROCEDURE 4 RESULTS 5-6 DISCUSION 7-8 CONCLUSION 8 ABSTRACT The aim of this laboratory experiment is to examine the tensile strength of three specimen of low, medium and high carbon steels is examined. The microstructure of the specimen is determined and calculations such as tensile strength, yield strength etc were clearly recorded. Also, the background theory was stated, the apparatus and procedure used to achieve the experiment was described. The main part of this lab report is the discussion on the results and how close they've been calculated to the original theoretical values by taking into consideration some external experimental errors. The last part of this report is the conclusion on the whole procedure. INTRODUCTION The main purpose of this lab report is by using a tensile testing machine (Hounsfield tensometer), to determine mechanical properties of three different plain carbon steel materials (low carbon steel, medium carbon steel and high carbon steel). Also, their grain structure is to be examined using a Metallurgical microscope. BACKGROUND The three different materials are the low-carbon, medium-carbon and high carbon steels. Their tensile strength is examined which by definition is explained as the amount of stress that a material can resist when a force pulls it along its length until a complete deformation takes place.
This force is measured (in kN) on a digital force meter which is connected to the machine. On the top there is a cylinder with a graph paper around it in order to sketch a graph of force against the extension of the specimen. This is done by moving the pointer on the graph paper by 0,5kN respectively and pointing on the graph each time the reading on the digital force meter increases by 0,5kN, for instance, if the reading reaches 1,0kN the pointer has to be pointing at 1,0kN and by the time that the reading is 1,0kN a point is sketched on the graph. (See figure 2 below) Figure 2. Furthermore, measurements of the length and cross-sectional area were taken before and after the test in order to determine the percentages of elongation and the reduction in area. The last part of the experiment is to examine the three micro-specimens given which is the exact same material and condition as the three materials used on the tensile machine and determine the percentage of the carbon content of their grain structure. This is done by using a Metallurgical Microscope. RESULTS The results of the experiment were calculated and recorded on a table as shown below: Test piece material % carbon content Yield strength (N/mm2) Ultimate tensile strength (N/mm2) % elongation % reduction in area Specimen A Low-carbon steel 0,1 315 430 37 66 Specimen D Medium-carbon steel 0,4 475 660 28 62 Specimen N High-carbon steel 0,8 932 960 13 30 All the specimens had normalized treatment conditions.
Also, from the tables plotted on the tensometer machine the load that every specimen could withstand, the elongation percentage and the reduction in cross-sectional area were different. By considering these values, low-carbon steels have the least amount of load before complete deformation and the most percentage on both reduction in cross-sectional and elongation of the three specimens. This means that low-carbon steels have the least amount of carbon. In addition, low carbon steels can be defined as ductile materials. Medium-carbon and high-carbon steels are less ductile have les percentage of elongation. This means that they are harder and they are applied more load in order for deformation to take place. Finally, the last part of the discussion is about the different yield point of the three specimens. If the graphs are considered, a sudden fall of the load appears to take place on the graphs of low and medium carbon steels during the procedure. This means that the two specimens faced a reduction in cross-sectional area (also known as necking). This doesn't seem to happen to the specimen of high-carbon steel which means that the deformation took place without having any noticeable reduction in cross-sectional area as the load was kept increasing. CONCLUSION In conclusion, the three specimens where tested and results were given. Since the calculated values meet the theoretical values, the experiment was successful. Discussion about the ductility and the main structure of the given specimens was made and also the differences between them were stated.
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