Engineering Manufacture OCR R109 Practice Test

Hardness is what keeps a cutting edge from wearing away under load. When a tool cuts, the edge endures repeated contact and abrasion with the workpiece, so it needs to resist local plastic deformation and scratching. A harder edge resists being shaved or smeared, helping the apex stay sharp longer. Ductility would cause the edge to deform and roll, dulling it more quickly, while conductivity doesn’t affect wear, and toughness mainly helps resist cracking rather than edge wear. So hardness best explains why the edge remains sharp.