Hardness Testing Methods
Animated demonstration of three workshop hardness tests
File Testing Method 1
A hardened file of standardized hardness is lightly pressed against the part and pushed with a slow forward motion over the surface. The tester feels the “bite” or “slip” of the file through the fingers. If the file does not bite, the part is considered “file hard” — as hard as, or harder than, the file itself.
By using a set of files hardened in five-point increments from 40–65 HRC, the operator works from a hard file (which bites) down to softer files until one slips. The workpiece hardness lies between the file that marks and the file that slips.
Rockwell Testing (C Scale) Method 2
The Rockwell C scale is the most common hardness test for heat-treated tooling over 40 HRC. A 330-lbf (150-kgf) load is pressed into the workpiece through a spheroconical diamond penetrator. The depth of indentation — not the diameter — is the basis for the Rockwell hardness number.
Always take at least four readings; omit the first (seating). If three are within ±1 HRC, the result can be averaged. Never retest in the same indentation.
Brinell Testing Method 3
The Brinell test forces a hard ball (10-mm / 0.39-in. diameter) under a specified load — typically 6,600 lbf (3,000 kgf) — into the surface of the material. After the load is removed, the diameter of the impression is measured with a measuring microscope (graduated to 0.005 mm) and converted into a Brinell hardness number (HB).
Best suited for material in the annealed or low-hardness range (≤ 375 HB). Material over 375 HB (≈ 40 HRC) should be tested with Rockwell C instead.
- Apply load: Ball is pressed into the surface under 3,000 kgf.
- Hold (dwell): Load is maintained to form a full impression.
- Remove load: Ball is retracted, leaving a spherical indentation.
- Measure: Diameter of impression is read with a microscope → converted to HB.