The Effects of Composition on the Hardness Property of Metals: An Experimental Study - Pro, Lab Reports of Materials science

Download The Effects of Composition on the Hardness Property of Metals: An Experimental Study - Pro and more Lab Reports Materials science in PDF only on Docsity! 1 The Effects of Composition on the Hardness Property of Metals by Dan Schwarz School of Engineering Grand Valley State University Laboratory Module 4 EGR 250 – Material Science & Engineering Section 01 Instructor: Dr. P.N. Anyalebechi February 21, 2006 2 Abstract Hardness is the quality of a material that allows it to withstand deformation. A variety of relative scaling methods such as the Rockwell hardness scale can be used to quantify the hardness of a material. Composition, microstructure and processing conditions of a material all contribute to its hardness but the following hardness experiment is only aimed at establishing a relationship between the composition and hardness characteristics of several metal samples. The metal samples are tested using the Rockwell B scale and the material compositions are compared with the resulting hardness values. Ferrous materials such as cast irons and steels were found to be generally harder than non-ferrous materials such as aluminum alloys, copper alloys, and titanium. Overall, the metals were hardened by increased amounts of alloying materials. Introduction In the context of material science, hardness is a mechanical property which allows a material to resist “localized plastic deformation”. [1] The hardness of a material is commonly quantified using Rockwell, Brinell, and Vickers methods. In general, these methods define the hardness of a material in terms of the amount of deformation produced by a loaded indenter that is harder than the test specimen. Hardness testing produces relative hardness values since different indenters and loading methods create unique indentations on the same test specimen. Engineering materials exhibit a wide range of hardness values that depend on their composition, microstructure, and processing methods. The main objective of the following experiment is to explore the relation between hardness and composition of thirteen metallic engineering materials. These materials have a wide range of compositions that can be divided into ferrous and non-ferrous categories with subgroups that contain various alloys. Obtaining hardness values for each material with the Rockwell B test provides a framework for comparing material compositions to their respective hardness properties. Experimental Procedure The Rockwell hardness tester was set to the B scale by selecting a test load of 100kg and by using a 1.588mm diameter ball indenter. A standard material with a known value of 89.3±1.0 5 harder than all of the cast irons. Consequently, steel hardness changes quickly with respect to iron when small changes are made in its composition. Cast irons are harder relative to one another as their carbon content increases. Ductile cast iron is the hardest iron with a carbon content of 3 to 4 wt. % C and 99 RB. White cast iron is the softest with a carbon content of 2 to 2.9 wt. % C and 94 RB leaving Grey iron in the middle. Steels appear to be hardened by the addition of carbon since C1045 has a higher carbon content and hardness than C1018. However, the addition of chromium seems to soften or negate the hardness of carbon in the steel. For example, 4140 has approximately the same amount of carbon as C1045 yet it is softer than C1018 with 0.8 to 1.1 wt. % chromium. Stainless steel has more chromium than 4140 making it the softest of the four steels with a hardness of 86 RB. The three subgroups of non-ferrous materials include aluminum alloys, copper alloys, and titanium. Titanium is the hardest of the three non-ferrous materials. Titanium’s hardness value of 85 RB made it almost as hard as stainless steel. Aluminum alloys where consistently soft with hardness values ranging from 52 to 78 RB. However, aluminum seems to harden by copper since AA2024 has 3.8 to 4.9 wt. % copper and a hardness of 77 RB whereas AA2024 only has 0.15 to 0.4 wt. % copper and a hardness of 52 RB. Copper alloys have the widest range of values that were both lower and higher than aluminum. Pure copper is by far the softest material with a hardness value of 31 RB. Large amounts of zinc make the copper harder but the hardest copper alloy was produced by small amounts of tin. The wide range of copper hardness suggest that the hardness of copper is heavily dependant on it composition. In order to gauge the accuracy of the experiment, Table 4 compares the measured experimental results with other published values. The error column shows the discrepancy between the measured and reported hardness for each material. The discrepancy may be caused by errors in the experimental process or by differences in the materials such as processing methods or composition. Table 4 : A comparison of the experimental results with published values. 6 Metal Sample Measured Mean Values Reported Hardness Values Condition of Reported Material Source of Reported Hardness Difference Error Ductile Cast Iron 99.1 98 Grade A Matweb 1.1 Grey Cast Iron 98.7 96 Untreated Atlas foundry co. 2.7 White Cast Iron 94.5 104 Unalloyed Mesa castings inc 9.5 C1018 91.8 78 Cold rolled Small parts inc 13.8 C1045 100.7 95 Cold Drawn, Annealed Efunda.com 5.7 4140 92.5 98 Cold Drawn, Annealed Metals depot 5.5 Stainless Steel 86.7 88 S304L Annealed Ask ZN .com 1.3 AA2024 77.1 75 Untreated ASM aerospace inc 2.1 AA6061 52.8 60 Tempered Matweb 7.2 Pure Copper 31.0 37 Cold drawn Matweb 6.0 Brass 62.7 56 Phosphorized, tempered Matweb 6.7 Phosphorous Bronze 79.6 80 H10 Matweb 0.4 Titanium 85.1 80 Grade 2 Matweb 5.1 Most of the materials have discrepancies of about 5 to 6 RB which may be caused by experimental errors such as testing materials that have slants or ridges in the test surface. This problem could be remedied by more careful preparation of the test samples. Smaller discrepancies in the vicinity of 1 RB may be caused by the Rockwell tester itself. Recalibration of the Rockwell tester may be able to eliminate these minor errors. On the other hand, large discrepancies in the vicinity of 9 to 13 RB may be caused by different material processing methods that change the hardness characteristics of the material. Conclusions 1) Ferrous metals are generally harder than non-ferrous metals. 2) Low carbon and low alloy steels are softer than cast irons. 3) Medium carbon steels are harder than cast irons. 4) Higher carbon levels produce harder cast irons and carbon steels. 5) The addition of chromium seems to soften or negate the hardness of carbon in the steel. 6) Titanium is one of the hardest non-ferrous materials. 7) Aluminum seems to harden by increased copper content. 8) Pure copper is one of the softest non-ferrous materials. 9) Large amounts of zinc produce a brass alloy that is harder than pure copper. 10) Small amounts of tin produce a bronze alloy that is even harder than brass. 11) The hardness of copper is heavily dependant on it composition. 7 References [1] Callister, William D. Fundamentals of Materials Science and Engineering : An Inegrated Approach. 2nd ed. New Jersey: John Wiley and Sons Inc., 2005.