|MadSci Network: Engineering|
Hi Nicola, In a word, the answer to you question is "wear". Every material has its own hardness. Tungsten steel, as you have rightly pointed out, is quite tough and hard. Hair, in comparison is softer. However, over a period of time, even hair is able to form microsopic scratches on the steel and cause it to lose its sharpness. No matter how large the differance between hardness of any two materials, the harder one will eventually wear out. However, the greater the differance in the hardness, the longer the harder material lasts before it wears out. This is applicable not only to hair and steel, its applicable in most of the things you see around you. Carpenters sharpen their tools made of Tool steel even though they use it to cut wood (much softer). Kitchen knives are used to cut vegetables and meats. Thus, no matter how large the differances in hardness, eventually the harder material will wear out. Hope I've cleared your doubt. If not, feel free to contact me. Nauzad
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