What is hardness?
What is hardness? |
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Hardness is a measure of how resistant a material is to changing its shape when pressure is applied. | |||
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For one object to be able to cut another, it needs to be harder. For example, a table knife can easily cut through butter, because the knife is harder than the butter. | |||
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If you used the same knife to try to cut a piece of stone, however, you would have a lot less success. This is because the stone is harder than the knife. | |||
Measuring hardness |
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Hardness is measured on the Mohs scale, and is given a number between 0 and 10, with 10 being the hardest. | |||
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Talc is a very soft substance, measuring only 1 on the Mohs scale. | |||
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You could easily cut into a piece of talc with your fingernail, which measures 2.5 on the Mohs scale. | |||
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Magnetite, the compound that is created during black oxide coating, has a hardness of 5.5 on the Mohs scale. | |||
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Steel also clocks in at 5.5 without any added alloying elements. | |||
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Chromium, the first of the two alloying elements used in the creation of the tool steel used in files, has a hardness of 8 on the Mohs scale. This is the first of two elements that increases the steel’s hardness. | |||
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The second alloying element, carbon, has a low hardness under normal conditions.
Graphite, a type of carbon used as lead in pencils, only has a hardness of 1 or 2. |
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However, when carbon is heated to a high temperature under high pressure, it crystallises into diamond, which tops the Mohs scale with a score of 10. | |||
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As carbon steel is heated, the carbon content of the material adds to the hardness, instead of subtracting from it. While it doesn’t make it as hard as diamond, it works with the chromium to bring it up to a hardness of around 9! | |||
Black oxide coating on steel files |
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As you can see, the steel used in files is much harder than black oxide, which is why it is not often used as a protective coating. The file is tougher than it is! | |||
