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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Here’s an ELI5. Steel is harder than wood, wouldn’t you agree? Like steel nail can scratch wooden plank, but a wooden shank won’t scratch a Steel sheet. That’s Mohs scale. But mohs scale does not account for geometry much. If you take a wooden block and hit it on a steel nail, the nail would bend as the resistance to bending depends upon the geometry of the nail itself in addition to its material properties. That’s why thinner nail is easier to bend than thicker nail.
When the razor blades are manufactured they are sharpened to a very thin edge. That makes them razor sharp, thus the phrase, but that sharp edge is inherently weak to bending because it’s so thin. When we use that blade, over time the edge starts to bend and the pointy sharp edge is rolled into a thick blunt edge. This blunt edge must be sharpened by some grinding tool like a grinding stone or sandpaper to scratch away the rolled metal on the edge to make it sharp again. At this stage Mohs scale comes into picture as you’re scratching the metal away.
To retain the sharpness for longer, knives and sword smiths do edge hardening to harden the metal at the edge and make it less susceptible to bending
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