Hardness Testing: Brinell, Rockwell, Vickers Selection
"What's the hardness of this part?" — the answer could be HB, HRC or HV, all different numbers. All are hardness, but with different principles, applications and meanings.
Brinell (HBW)
Carbide ball indenter, fixed load, measure impression diameter. Large impression — measures bulk average hardness. Use: cast iron, non-ferrous, annealed steel, blanks. Not for thin parts or finished surfaces.
Rockwell (HRC/HRB/HRA)
Diamond cone (HRC) or steel ball (HRB), measure depth difference, direct readout in seconds. The workhorse of production floors. HRC for hardened steel (20~70); HRB for soft steel/non-ferrous; HRA for carbides. Requires flat surface; scales not directly convertible.
Vickers (HV)
Diamond pyramid, measure diagonal, load from grams to hundreds of kg — tiny impressions, continuous comparability across loads. Use: thin parts, carburized/nitrided layers, coatings, HAZ. Demands excellent surface prep.
Selection Table
| Method | Indenter | Impression | Speed | Use |
|---|---|---|---|---|
| HBW | Ball | Large | Slow | Cast iron, blanks |
| HRC | Cone | Small | Fast | Hardened steel |
| HRB | Ball | Small | Fast | Soft steel |
| HV | Pyramid | Tiny | Medium | Thin/micro |
Hardness vs. Strength
For the same steel, hardness roughly tracks strength (HB ≈ tensile/3.2 empirical), so hardness substitutes for strength on the floor — but the ratio varies by grade and heat treatment; don't guess across grades.
Summary
Brinell for macro/bulk, Rockwell for fast floor checks, Vickers for micro-zones. Soft thick → Brinell; hard fast → Rockwell; thin micro → Vickers. Right method, meaningful numbers.