Rockwell hardness

The Rockwell test is the fast, push-button workhorse of the hardness world. Instead of measuring the width of a dent with a microscope, the machine measures how DEEP the indenter sinks and prints a number straight off a dial or screen. Press, read, done — a few seconds per part with no optics and little skill needed, which is why Rockwell testers sit in almost every metals workshop.

It works by depth difference under two loads. A small preload seats the indenter and cancels surface roughness; then the main load is applied and removed, and the machine reports how much deeper the tip went under the main load. A harder material lets the tip sink less, so it scores higher. Different scales pair an indenter with a load: the C scale (HRC) uses a diamond cone at 150 kgf for hard steels (a hardened tool steel reads around 60 HRC), while the B scale (HRB) uses a 1.6 mm steel ball at 100 kgf for softer metals like brass and mild steel. You must always state the scale, because 60 HRC and 60 HRB are wildly different hardnesses.

Rockwell's speed and small, shallow indent make it perfect for production quality control and for finished parts. Its cautions: each scale has a valid range and they are not interchangeable, so you pick the scale to suit the material, and a badly supported or thin specimen gives false readings because the depth measurement is fooled by any give underneath. It reads hardness directly but, unlike Brinell and Vickers, does not translate into an area-based stress, so strength estimates usually go via a conversion table.