Hardness Testing Essay Example

a permanent increase in depth of penetration from the initial load. Removal of the additional load allows for partial recovery, reducing the depth of penetration. Resulting from the addition as well as removal of the additional major load is a permanent depth allows the Rockwell hardness number to be calculated by the testing machine. Figure1: The above figure shows the Rockwell hardness testing machine used. The Rockwell Hardness Test is the best to use when it comes to determining mechanical properties.

This being because this test is the easiest to perform and the hardness value is calculated whereas in the Brinell Hardness Test, the hardness is calculated. A downside to this test is if a material were needed to be tested in between scales; a proper hardness value would not be outputted. Procedure When it comes to testing the hardness of materials, two main tests called upon are the Brinell and Rockwell hardness tests. For our experiment, the Rockwell hardness test was used. This method consists of using a machine to calculate the hardness number.

This machine has a variety of scales that can be used to test a wide range of materials whether they are soft or hard. For our experiment, scales C and F were used. Scale C uses a diamond cone and it used for steels, hard cast irons, case hardened steel and other materials harder that 100 HRB. HRB refers to the hardness test scale B which consists of copper alloys, soft steels, aluminum alloys, etc. Scale F uses a 1/16” steel ball indenter and is typically used for annealed copper alloys and thin soft sheet metals. Each scale has its own minor,

major, and total load and needed to be set before beginning.

In our experiment, four separate steels and one stainless steel were used and hardness values were calculated; stainless steel being the hardest at 40HRC and 1020 steel being the softest at 25HRC. Alloys added to steel increase its strength, like carbon, nickel, and tungsten. Carbon can play a large role in determining hardness. The material will have a higher hardness when more carbon is added, as long as the amount is less than two percent. Higher carbon content existed in the stainless steel than that of the 1020 steel which is why we see stainless steel having higher hardness. The HRF scale is used for annealed copper lloys and thin soft sheet metals. For our experiment, soft steel, aluminum, and brass alloys were used and were penetrated by the 1/16” steel ball indenter. Many 6061 aluminum alloys were tested to compare between different heat treating adjustments and non-heat treated. Aluminum has a melting temperature of 660°C and a recrystallization temperature of 150°C. Since each of the heat treated aluminum alloys were heated well above its recrystallization temperature, the grains within the aluminum were able to mend themselves and reduce dislocations, producing higher tensile strengths.

As seen in Table 2, the hardness of the aluminum alloys increased as the time of heat treatment increased. Conclusion As stated previously, hardness measures the ability of a material to resist scratching, indentation, or penetration. Depending on the material used, hardness is going to be different. Base materials, non-heat treated, will determine the hardness and with alloying and annealing comes increased tensile strength and increased yield strength.