ASTM E18 is the ASTM International standard test method that defines Rockwell and Rockwell Superficial hardness testing of metallic materials, covering the equipment, indenters, procedure, verification and reporting requirements. It is published and maintained by ASTM International (Committee E28 on Mechanical Testing) and is one of the two globally referenced Rockwell standards, alongside ISO 6508.
What ASTM E18 covers
ASTM E18 specifies the Rockwell hardness test, in which the depth of penetration of a standardised indenter under a defined force is measured to produce a dimensionless hardness number. It applies to metallic materials across a wide hardness range and covers both:
- Rockwell hardness, total test force of 60, 100 or 150 kgf, with a 10 kgf preliminary force.
- Rockwell Superficial hardness, total test force of 15, 30 or 45 kgf, with a 3 kgf preliminary force, used on thin sections, sheet, coatings and small parts.
Two indenter families are used: a spheroconical diamond indenter with a 120 degree included angle and a 0.200 mm tip radius, and tungsten carbide ball indenters of 1/16, 1/8, 1/4 and 1/2 inch diameter. The scale letter (for example HRC, HRB, HRA, HR15N, HR30T) identifies the specific combination of indenter and total force used, and the hardness value has meaning only when reported with its scale.
The principle: a preliminary test force is applied to seat the indenter and establish a reference position; the additional force is then applied to reach the total test force, held for a specified dwell, and removed back to the preliminary force. The permanent increase in penetration depth h (in millimetres) is converted to a Rockwell number using scale constants, for the diamond and Rockwell scales, HR = 100 − (h / 0.002), and for the Superficial scales, HR = 100 − (h / 0.001). The result is unitless and always prefixed HR followed by the scale letters.
Why it matters for procurement
Institutional tenders for materials-testing laboratories, ITI/polytechnic workshops, engineering colleges and quality-control cells routinely specify Rockwell hardness testers “conforming to ASTM E18” or “IS 1586 / ISO 6508 / ASTM E18”. Writing the standard into the specification does three things: it fixes the indenter geometry and force tolerances, it forces the machine to be verifiable against certified reference blocks, and it makes results comparable across suppliers and laboratories.
Because ASTM E18, ISO 6508 and IS 1586 are technically harmonised (same principle, same scales, near-identical tolerances), a machine built to one is generally acceptable against the others provided the calibration certificate and reference blocks are traceable. Cross-referencing the equivalents in the BOQ avoids single-source objections during technical evaluation.
Equivalent international standards
| Region / Body | Standard | Title / Scope |
|---|---|---|
| USA / ASTM | ASTM E18 | Rockwell hardness of metallic materials |
| International / ISO | ISO 6508-1, -2, -3 | Test method, verification of machines, calibration of reference blocks |
| India / BIS | IS 1586 (Parts 1-3) | Indian adoption of the ISO 6508 series |
| Europe / CEN | EN ISO 6508 | European adoption of ISO 6508 |
| Japan / JIS | JIS Z 2245 | Rockwell hardness test method |
| China / GB | GB/T 230.1 | Rockwell hardness test, test method |
Testing procedure summary
- Select the scale. Choose the scale (for example HRC for hardened steels, HRB for softer steels and non-ferrous alloys, HR30N for thin hardened layers) based on material, thickness and expected hardness. The specimen thickness should be at least ten times the depth of indentation.
- Prepare the specimen. The test surface must be flat, clean and free of scale, oxide and lubricant. Support the specimen rigidly on a suitable anvil so that no movement occurs during the test.
- Apply the preliminary force. Bring the indenter into contact with the surface and apply the preliminary test force (10 kgf for Rockwell, 3 kgf for Superficial) within the tolerances given in the standard, then set the reference position.
- Apply the additional force. Increase the load smoothly to the total test force within 1 to 8 seconds and hold for the specified dwell (typically 1 to 5 seconds for materials without significant time-dependent behaviour; longer for materials that show indentation creep).
- Remove and read. Reduce the load back to the preliminary force, allow the reading to stabilise, and record the Rockwell number directly from the machine, together with the scale letters (for example 62 HRC).
- Verify and space indentations. Keep the centre-to-centre distance between adjacent indentations at least three (Rockwell) or two (Superficial) indentation diameters, and the distance from any edge at least two-and-a-half indentation diameters, per the standard.
Scientico compliance
Scientico India manufactures Rockwell and Rockwell Superficial hardness testers designed to be supplied against ASTM E18, ISO 6508 and IS 1586 specifications. Machines are offered with diamond and tungsten-carbide ball indenters of the geometries required by the standard, standard load ranges, and are supplied with certified hardness reference test blocks so that customers can perform the indirect verification of the machine at installation and at the intervals required by their quality system. Documentation, load tolerances and indenter certificates are provided to support technical evaluation in institutional tenders.
Related Scientico equipment
- Rockwell hardness tester (analogue and digital models)
- Rockwell Superficial hardness tester
- Combined Rockwell / Brinell / Vickers universal hardness tester
- Brinell hardness testing machine (ASTM E10 / ISO 6506)
- Vickers / micro-Vickers hardness tester (ASTM E92, E384 / ISO 6507)
- Certified hardness reference test blocks for machine verification
Related pages: Quality & certifications · Contact us for a CIF quote
Frequently Asked Questions
Who publishes ASTM E18?
ASTM International, through Committee E28 on Mechanical Testing, publishes and maintains ASTM E18. It is periodically revised; always cite the current year of issue in tender specifications.
What is the difference between ASTM E18 and ISO 6508?
Both cover Rockwell hardness of metallic materials and are technically harmonised on principle, scales and tolerances. ISO 6508 is issued in three parts (method, machine verification, reference blocks); ASTM E18 combines these into a single document.
Which Rockwell scale should I specify for hardened steel?
HRC (150 kgf, diamond indenter) is the standard scale for hardened and tempered steels above roughly 20 HRC. For thin hardened layers or case-hardened surfaces, use a Superficial N scale such as HR15N or HR30N.
Is IS 1586 acceptable in place of ASTM E18?
Yes. IS 1586 is the Indian adoption of the ISO 6508 series and is technically equivalent to ASTM E18. Institutional buyers commonly write “IS 1586 / ISO 6508 / ASTM E18” to keep the specification open.
How is a Rockwell hardness tester verified?
By indirect verification against certified hardness reference test blocks at the scales in use, at intervals defined by the standard and the user’s quality system, plus periodic direct verification of force, indenter geometry and depth-measuring system by an accredited laboratory.
Does Scientico supply calibration blocks with the machine?
Yes. Scientico’s Rockwell testers are supplied with certified reference test blocks and indenter certificates so the machine can be verified at installation and at routine intervals. Contact us for the current CIF quote on WhatsApp.
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