eli5 How does razor blade dull on hairs when razor blades are made of steel and they are much higher on mohs scale?
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This is actually not due to the material but due to the sharpness of the blade. As the blade becomes sharper, the contact area between blade and hair reduces where the force required to cut the hair stays the same. For the same force, a reduced contact area results in higher stress concentration across the contact area on the blade edge and this is sufficient to deform the material. Also as the area reduces, the strength of blade reduces which also helps in deformation of the blade. The angle of approach of this deformed blade towards the hair is changed (from perpendicular to parallel eventually) which causes difficulties in cutting the hair or dullness in blade.
Moh’s scale defines hardness but the dulling of blade happens due to lack of its tensile strength.
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