Hardness File Test — Glossary Entry

Hardness File Test is a quick, portable method for verifying the hardness of a heat-treated knife, using a set of calibrated files of known HRC values. The test is the standard quality-control check for slitter, shear and granulator blades.

How to perform the 5-point test

• Mount the knife on a flat surface
• Test 5 points: centre, two mid-radius, two edge points
• At each point, try the file one HRC above and one below the target
• The file that “skids” (slides without biting) on the surface defines the upper bound; the file that bites defines the lower bound

Interpretation

• All 5 points within ± 1 HRC of target: heat-treat is OK
• Edge points 2+ HRC soft: decarburisation, surface must be re-ground
• Centre 2+ HRC high: incomplete austenitisation, knife must be re-heat-treated
• All 5 points high: heat-treat temperature wrong, knife must be re-heat-treated

See also.