Hardness, Strength& Toughness
In the discipline of metallography and metal analysis hardness, toughness, and strength are three distinct properties yet also share some overlap. Together, the three properties make up what is commonly referred to as metal “strength.” Here’s how these three metal properties are different and how they also overlap and work together:
Hardness: A material’s ability to withstand friction, essentially abrasion resistance, is known as hardness. Diamonds are among the hardest substances known to man, it is incredibly difficult to scratch a diamond. However, while a diamond is hard it is not tough. If you took a hammer to a diamond it would shatter, which demonstrates that not all materials that are hard are also tough. In the world of metal tools, drill bits and grinding discs must be extremely hard to be able to handle high amounts of friction.
Strength: The amount of force necessary for a material to deform. The higher the force required to change the shape of the material, the stronger the material is. Steel is notoriously difficult to pull apart, hence it has a high strength. Silly putty, on the other hand, is not strong at all, and merely requires a child’s touch to quickly deform this material into all sorts of shapes..
Toughness: How well the material can resist fracturing when force is applied. Toughness requires strength as well as ductility, which allows a material to deform before fracturing. Do you consider silly putty to be tough stuff? Under these terms, believe it or not, it actually is relatively tough, as it can stretch and deform rather than break.