ISO 6507 and ISO 6508 — Vickers and Rockwell hardness testing

Scope — and what it does not cover

ISO 6507 specifies the Vickers hardness test — a diamond pyramid indenter, with the result reported as HV plus the test force, for example 320 HV 0.3 — and ISO 6508 specifies the Rockwell test (HRC, HRB and the superficial N and T scales). Between them they cover the two measurements that decide whether a heat-treated fastener sits in its property class. They specify the machine, indenter, force, surface preparation and reporting. They do NOT tell you which hardness your part should have — that comes from ISO 898-1, the drawing or the customer specification — and they do not make HV and HRC interchangeable, because scale conversions are approximations.

Standards are copyrighted documents. We explain scope, intent and practical application in our own words; obtain the current edition from ISO, ASTM, DIN or your national standards body.

What actually bites in production

• 1The test force is part of the result. 320 HV 0.3 and 320 HV 30 are not the same measurement, and on a thin case only the low-force result is valid.
• 2Rockwell needs material under the indenter. On small screws, thin washers and shallow cases, Vickers with an appropriate low force is the honest choice.
• 3Surface preparation is not cosmetic. A decarburized skin, a plated layer or a rough face will all move the reading, usually downwards.
• 4ISO 898-1 uses Vickers at HV 0.3 for the surface-versus-core comparison, with a 30-point limit, precisely because the low force resolves the near-surface layer.
• 5Conversions between HV, HRC and HB are approximate tables built for particular material families. Report the scale you actually measured and let the drawing state which one governs.
• 6Indentation spacing, edge distance and specimen thickness rules exist to stop the material flowing or the anvil supporting the indentation. On small parts they are the rules most often broken.

What to write on the drawing or PO

• The scale AND the test force: "45 ± 3 HRC" or "550 HV 1", never just "hardness 550".
• Where the measurement is taken: surface, mid-radius, core, or a defined distance below the surface.
• How many pieces per lot and how many indentations per piece.
• Whether the part is measured before or after coating, and whether the coating is removed for the test.
• Which scale governs if two are reported, so that a conversion argument cannot start.

What goes wrong when it is cited loosely

• Converting a case hardness measured at HV 0.3 into HRC and then rejecting the lot against an HRC limit.
• Testing HRC on a thin part and effectively reading the anvil through it.
• Measuring on an as-received rolled or plated surface without preparation.
• Specifying a hardness minimum with no maximum on a class-controlled fastener.