ASTM E384
Standard Test Method for Microindentation Hardness of Materials
Test method for Knoop and Vickers microindentation hardness of materials with test forces from 1 gf to 1 kgf (9.8 mN to 9.8 N), including specimen preparation, indentation measurement, spacing and verification.
What ASTM E384 specifies
ASTM E384 is the method for hardness measurements too small for Rockwell or Brinell — case-depth traverses, thin coatings, individual phases. A Vickers (136° square pyramid) or Knoop (elongated rhombic pyramid, 172.5° and 130°) diamond is pressed into a polished, mounted section with a force of 1 to 1000 gf; the diagonals of the indentation are measured optically and converted to HV = 1854.4 × F/d² or HK = 14229 × F/d² (F in gf, d in µm). The method sets requirements for specimen flatness and polish (ASTM E3), dwell (10–15 s), indentation spacing (at least 2.5 diagonals between impressions and from an edge for Vickers), measuring-system resolution and periodic verification of the tester with certified blocks. Case-hardening specifications (AMS 2759/6 and /7, SAE J423, ISO 2639) rely on HV 0.5 or HK 500 traverses at 0.05–0.1 mm steps to find effective case depth.
ASTM E384 types and classes
Every designation the document defines, with the thickness it requires and the tests it imposes.
| Designation | Meaning | Requirement / test |
|---|---|---|
HV (Vickers) | 136° square-based diamond pyramid; HV = 1854.4 × F/d² with F in gf and d the mean diagonal in µm. HV 0.1 to HV 1 are typical for case-depth traverses; the number is nominally force-independent on homogeneous material. | Verification with certified Vickers test blocks at the force used |
HK (Knoop) | Elongated rhombic pyramid (172.5° / 130°); HK = 14229 × F/d² with d the long diagonal in µm. Shallow indentation suits thin layers, coatings and brittle materials; HK 500 is common for case depth (542 HK500 corresponds to 50 HRC). | Verification with certified Knoop test blocks at the force used |
Tests and the drawing call-out
Tests the document imposes
- Indirect verification with certified Vickers / Knoop reference blocks at the forces used, daily or before use
- Direct verification of force, indenter geometry and measuring system at fixed intervals
- Specimen preparation: mounted, polished cross-section per ASTM E3 with edge retention
- Indentation spacing and edge-distance checks (at least 2.5 diagonals)
- Repeat measurements (typically five) with reported mean and range
How to cite it
Drawing call-out
EFFECTIVE CASE DEPTH 0.6–0.9 MM TO 513 HV 0.5 PER ASTM E384 TRAVERSE (SAE J423)Angle brackets mark the choices the drawing must make; every finish page shows a completed example.
Heat treatments specified to ASTM E384
| Treatment | Role | Cost |
|---|---|---|
Age C17200 (Beryllium Cu) is a precipitation-hardening condition for C17200 and C17300. | Test method | $$$ |
Carbonitriding diffuses both carbon and nitrogen into low-carbon steel in the austenitic range, then quenches and tempers the surface to martensite. | Test method | $$ |
Carburizing diffuses carbon into low-carbon steel at austenitizing temperature, then quenches and tempers the enriched surface into a hard martensitic case. | Test method | $$$ |
Cryogenic treatment cools a previously hardened alloy below room temperature to transform retained austenite and improve dimensional stability. | Test method | $$ |
Flame hardening rapidly austenitizes selected steel surfaces with an oxy-fuel flame and immediately quenches them to martensite. | Test method | $$ |
Gas nitriding diffuses nitrogen into finished ferrous parts below the transformation temperature, producing a hard compound layer and diffusion zone without quenching. | Test method | $$$$ |
Induction hardening uses an alternating magnetic field to austenitize selected steel surfaces, followed immediately by quenching. | Test method | $$ |
Ferritic nitrocarburizing diffuses nitrogen and carbon into ferrous surfaces below the transformation temperature. | Test method | $$$ |
Plasma nitriding uses a glow discharge to clean, heat, and diffuse nitrogen into ferrous surfaces. | Test method | $$$$ |
ASTM E384 — frequently asked
HV or HK for a case-depth traverse?
Both work. Knoop's long, shallow indentation lets you get closer to the surface and space points more tightly (its short diagonal sets the spacing limit); Vickers gives numbers that convert more directly to HRC through ASTM E140 (513 HV = 50 HRC, 542 HK500 also 50 HRC). Choose one, state the force (HV 0.5 or HK 500 are typical) and keep it, because results at different forces are not interchangeable.
Why does E384 insist on polish quality?
A 500 gf Vickers indentation on 600 HV steel has a diagonal of only about 39 µm; scratches, relief or edge rounding of a few micrometres change the read diagonal and shift the result by tens of HV. Sections must be mounted, ground and polished scratch-free with the edge retained (ASTM E3), and etched only after the hardness measurements if microstructure is also needed.
How close to the surface can the first indentation be?
About 2.5 diagonals from the edge — roughly 0.1 mm for HV 0.5 on a hard case — so the first traverse point sits 0.05–0.1 mm below the surface. Nitrided and other thin cases use lower force (HV 0.1, HK 100) or Knoop to approach within 20–30 µm; state the traverse start and step in the test plan.
Can microhardness replace the surface hardness check?
It measures the case itself rather than the composite response, so it is the right tool for compound layers and cases below about 0.3 mm. For acceptance the drawing should state which method governs, because a 900 HV nitrided layer only 15 µm thick reads lower on a superficial Rockwell scale as the indenter senses the diffusion zone beneath it.
ASTM E384 is copyrighted by ASTM International. This page explains the document so a drawing can be read; it does not reproduce the standard. Purchase the current edition from the publisher. Official source ↗