🔩 Vickers hardness (forces 1 gf–120 kgf) and Knoop hardness (1 gf–2 kgf) of metallic materials — requirements for hardness testers, indenters, test blocks and the test procedure; ASTM E92

Materials and NDT ASTM E92

Overview

WHAT THE STANDARD COVERS (ASTM page: sections 1 and 4). The test methods cover the determination of the Vickers hardness and Knoop hardness of metallic materials on the principle of pressing in a Vickers or Knoop indenter; the standard gives requirements for hardness testers and the test procedure. Mandatory annexes: A1 — verification of hardness testers, A2 — standardizing machines, A3 — standardization of indenters, A4 — standardization of test blocks, A5 — correction factors for Vickers tests on spherical and cylindrical surfaces; non-mandatory appendix X1 — examples of determining uncertainty. Vickers hardness is tested with forces from 9.807 × 10⁻³ N to 1176.80 N (1 gf–120 kgf), Knoop hardness — from 9.807 × 10⁻³ N to 19.613 N (1 gf–2 kgf); guidance for the microindentation range (forces up to 1 kgf) is given in ASTM E384. The standard gives forces and lengths in SI units, but for historical reasons the results are usually referred to kgf and gf; with the force in newtons it is divided by 9.80665 N/kgf. The principles, procedure and verification are essentially the same for both methods; they differ in the geometry of the indenter, the way the hardness number is calculated and the fact that Vickers can be used at higher forces. Note 2: the procedures are also suitable for other materials (ceramics — ASTM C1326 and C1327).

SIGNIFICANCE AND LIMITATIONS (section 4 on the ASTM page). Vickers and Knoop hardness is used for the evaluation of materials, quality control of manufacturing processes and research work; although empirical, for many metals it correlates with tensile strength and indicates wear resistance and ductility. Microindentation hardness makes it possible to test materials too thin or too small for macro tests and individual phases and zones. Because both methods reveal hardness inhomogeneity, a single result may not represent the hardness of the whole material. The Vickers indenter usually gives the same hardness number at all forces in a homogeneous material, except at very small forces (below 25 gf) and for indentations with diagonals smaller than approx. 25 µm; in isotropic materials both diagonals of the indentation are equal. The Knoop hardness number increases as the force decreases, more markedly in harder materials and at forces below 50 gf. The Knoop indenter has the shape of an elongated rhombus in which the longer diagonal is 7.114 times longer than the shorter one; it gives narrower and shallower indentations than the Vickers pyramid, so the indentations can be placed closer together — with the shorter diagonal in the direction of the hardness gradient.

EDITIONS AND STATUS (ASTM pages, read on 27.10.2026). In the ASTM list of versions the active edition is E92-26 (DOI 10.1520/E0092-26); the E92-23 page (DOI 10.1520/E0092-23) is marked "Historical" (both with the update date 27.08.2026), earlier editions are E92-17, E92-16 and E92-82 with versions (R03, R97). The text of sections 1 and 4 on the E92-23 and E92-26 pages is identical (comparison of both pages on 27.10.2026: no differences); the page does not state what changes the 2026 edition introduced. ASTM E92 has no Polish edition — it is a document of ASTM International. In the iTeh catalogue (read on 27.10.2026) ASTM E92-23 has the status "Published", and E92-17 and E92-16 — "Historical"; the catalogue did not yet list the 2026 edition.

HOW MANY LABORATORIES AND IN WHAT FORM (copy of the accreditation scope database refreshed from the production server on 27.10.2026 and current PCA documents downloaded on that day). Number E92 appears in 7 records at 6 Polish laboratories: AB 001, AB 205, AB 792, AB 1489, AB 1700 (two entries) and the calibration laboratory AP 045. The standard is in all 6 current PCA documents; no entry is suspended. All write "ASTM E92-23"; AB 792 also has "ASTM E92-17" in the same entry, and alongside — ASTM E384-22 and PN-EN ISO 6507-1:2024-04. The ISO Vickers standard PN-EN ISO 6507-1:2024-04 is held in the same entries by AB 205, AB 792 and AB 1700, and AB 1700 also has PN-EN ISO 9015-1:2011 for welded joints. The "Laboratories" tab ("ASTM E92") shows 13 laboratories: these 6 Polish ones and 7 Czech ones (tab query on labcoda.pl, 27.10.2026).

WHAT THE LABORATORIES TEST (database copy and PCA documents). Vickers hardness only: HV10 in products of metals and alloys and in welded joints (AB 001, Laboratory Testing Department in Poznań, also at the location indicated by the customer), HV 10 in cast steel and cast iron castings and metallurgical products (AB 205), HV 0.1 and HV 10 in metallic materials and products (AB 792), HV 0.1; 0.3; 0.5; 1; 5; 10; 30 in metals and alloys (AB 1489), HV10 in welded joints and metallurgical products (AB 1700). AP 045 calibrates Vickers hardness testers according to this standard in the range 100–1000 HV for scales from HV 0.05 to HV 30, with the smallest uncertainty (CMC) from 1.4 % (HV 10) to 5.1 % (HV 0.05). Knoop hardness according to ASTM E92 is not in any Polish entry; Knoop hardness HK is in the scope of AB 053 — according to PN-EN ISO 4545-1:2024-04.

WHERE A SEEMINGLY CORRECT RESULT IS EASY TO GET. First — edition: the scopes cite E92-23, which ASTM now marks as "Historical"; with a dated reference the laboratory works according to the edition in the scope, and the ASTM page does not describe the changes of the 2026 edition. Second — units: the hardness number is defined with the force in newtons, but in practice it is given in kgf and gf; with the force in N it must be divided by 9.80665 N/kgf — omitting the conversion changes the result approx. 9.8 times. Third — small forces: Vickers at forces below 25 gf or indentations smaller than approx. 25 µm, and Knoop at forces below 50 gf give numbers dependent on the force; only results with the same force can be compared (e.g. HV 0.1 with HV 0.1, not with HV 10). Fourth — a single indentation may not correspond to the hardness of the whole material, because the method detects inhomogeneities. Fifth — curved surfaces: for Vickers tests on spherical and cylindrical surfaces the standard has correction factors (Annex A5). Sixth — ASTM E92 and PN-EN ISO 6507-1 are two different documents; three laboratories have both in the same entry, so the report should indicate according to which one the test was carried out.

WHAT WE DO NOT GIVE. We did not have the text of the standard (the E92-23 preview in the iTeh catalogue was unavailable, the ASTM page provides only sections 1 and 4). We do not give the requirements for hardness testers and indenters, the force application time, the spacing between indentations and from the edge, the formulas for calculating HV and HK, the factors from Annex A5 or the uncertainty examples.

Method principle

A Vickers indenter (square-based pyramid) or a Knoop indenter (elongated rhombus, diagonals in the ratio 7.114 : 1) is pressed into the surface of the material with a specified force — for Vickers from 1 gf to 120 kgf, for Knoop from 1 gf to 2 kgf — and the hardness number HV or HK is calculated from the dimensions of the indentation; the principles, procedure and verification of machines are essentially the same for both methods (ASTM E92, sections 1 and 4 according to the ASTM page). WE DO NOT GIVE the formulas and the procedure.

Applications

• Metallic materials — Vickers hardness (1 gf–120 kgf) and Knoop hardness (1 gf–2 kgf), also microindentation hardness up to 1 kgf (with a reference to ASTM E384)
• Quality control, evaluation of materials and zones (phases, hardness gradients — especially by the Knoop method)
• Verification and standardization of hardness testers, indenters and test blocks (Annexes A1–A4)
• In accreditation scopes: 5 testing laboratories (HV only) and a laboratory calibrating Vickers hardness testers

Key parameters

Standard

Standard number

ASTM E92-26 (wydanie aktywne; E92-23 — „Historical”)

Title (PL)

Metody badań twardości Vickersa i twardości Knoopa materiałów metalowych (tłumaczenie tytułu nasze; norma ASTM nie ma polskiego wydania)

Title (EN)

Standard Test Methods for Vickers Hardness and Knoop Hardness of Metallic Materials

Step-by-step procedure

1. Choice of method and force

   Vickers 1 gf–120 kgf or Knoop 1 gf–2 kgf; for forces up to 1 kgf guidance in ASTM E384; force in N converted with 9.80665 N/kgf (points 1.4–1.6).

2. Verification of the hardness tester

   According to Annex A1, with test blocks standardized according to A4 and an indenter according to A3. WE DO NOT GIVE details.

3. Making the indentations

   Pressing in the indenter and measuring the diagonals of the indentation; for spherical and cylindrical surfaces the factors from Annex A5. WE DO NOT GIVE times and spacings.

4. Result

   HV or HK with the force symbol (e.g. HV 10); a single result may not correspond to the hardness of the whole material (point 4.3). ASTM E92-26 active, E92-23 — "Historical" (27.10.2026).

Required equipment and apparatus

Health and safety (OHS)

• The standard does not address safety issues; safety, health and environmental practices are established by the user (point 1.8)
• TECHNICAL NOTE: only results with the same test force can be compared — at small forces the hardness number depends on the force

Frequently asked questions