Metal Hardness

Checkline Europe's Technical Support 10 Jul 2026

A metal hardness number is only as good as the method behind it. Hardness correlates with tensile strength, wear resistance and heat-treatment state, which is why it is the fastest non-destructive check on the shop floor — but Rockwell, Vickers, Brinell and Leeb each measure a different response, and a value quoted without its scale and method is hard to defend. Where a metal hardness figure gets challenged, the cause is usually mundane — an unprepared surface, an under-supported specimen, or a scale conversion treated as if it were exact.

Most of the testing covered here is portable, on-site work — heat-treatment verification, weld inspection, material sorting and in-service monitoring on components that will never reach a laboratory bench. The sections below set out how the laboratory and portable methods differ and where each one fits.

1. Laboratory and Portable Methods

The laboratory scales differ by indenter and load — Rockwell reads indentation depth directly, while Vickers and Brinell measure an impression optically. The portable Leeb method instead fires a spring-loaded impact body at the surface and reports the ratio of rebound to impact velocity as an HL value, capturing the elastic and plastic response in one rapid reading. Leeb Rebound Hardness sets out the rebound principle, the impact-body types and their application ranges.

2. Testing in the Field

Portable testing is what makes a hardness check possible on a turbine rotor, a pipeline weld or a multi-tonne forging. It also introduces variables a bench tester never sees — surface preparation, specimen mass and rigidity, coupling and impact direction all govern whether the number is trustworthy. Portable Metal Hardness Testing covers surface preparation, coupling and positioning for reliable field results.

3. Reading Across Scales

Because a specification often names a different scale from the instrument in hand, HL values are routinely converted to HRC, HV or HB. Those conversions are empirical and material-group-specific — accurate within their intended alloy family, misleading outside it. Metal Hardness Scale Conversions explains the tables, their limits and how to report a converted value honestly.

4. Standards and Selection

Portable Leeb testing — the focus of this page — is governed by ASTM A956 and ISO 16859, with ASTM E140 providing the cross-scale conversion tables. The laboratory Rockwell, Vickers and Brinell methods are governed by their own standards, set out alongside the full framework in Hardness Calibration and Standards. To match an instrument, impact device and reporting scale to the work, the Metal Hardness Selection Guide walks through the choice.

5. Frequently Asked Questions

1. How accurate are portable Leeb testers compared with laboratory methods?

Portable Leeb testers typically achieve a repeatability of ±4–6 HL units (approximately ±0.5–1 HRC equivalent for steel). Laboratory Rockwell testers achieve ±0.5–1 HRC under controlled conditions. The difference reflects the additional variables inherent in portable, on-site measurement—surface condition, specimen mass, coupling quality and operator technique.

2. Can a Leeb tester be used on any metal?

Leeb testers can measure a wide range of metals—carbon and alloy steels, stainless steels, cast irons, aluminium, copper, brass and titanium alloys—provided the correct material group is selected for scale conversion. Materials that are highly elastic (returning most of the impact energy) may produce misleadingly high HL values. Very soft metals may be below the instrument’s useful range.

3. Is surface preparation always necessary?

Some degree of surface preparation is almost always required. As a minimum, the test area should be free from paint, scale, rust, oil and loose debris. For accurate results, grinding or polishing to a surface roughness of Ra ≤ 2 µm is recommended. The extent of preparation depends on the required accuracy and the condition of the original surface.

4. What minimum specimen mass and thickness are needed?

Requirements vary by impact device type. For the standard D-type impact device, a minimum specimen mass of approximately 5 kg is recommended, with a minimum thickness of 10–20 mm depending on the material. Thinner or lighter specimens can be tested if rigidly coupled to a heavy support mass using couplant paste or mechanical clamping.

5. Does a higher hardness number always mean a better metal?

No. Hardness tracks wear resistance and correlates with tensile strength, but pushing it higher usually trades away toughness — a very hard component can be more prone to cracking under shock or fatigue. The right target is the hardness the application and specification call for, confirmed on the correct scale, not the highest number the process can reach.

6. Glossary

Brinell hardness (HB)	A laboratory hardness scale using a spherical indenter under a high load, measuring the diameter of the impression; suited to coarse-grained and heterogeneous metals.
Impact body	The spring-loaded mass with a precision tip that strikes the specimen surface during a Leeb rebound hardness test.
Leeb hardness (HL)	A rebound hardness value calculated as (rebound velocity / impact velocity) × 1000, suffixed with the impact device type (e.g. HLD, HLC).
Rebound ratio	The ratio of the impact body’s rebound velocity to its impact velocity, the fundamental measurement underlying the Leeb hardness value.
Rockwell hardness (HR)	A laboratory hardness scale measuring indentation depth under a prescribed load cycle; Rockwell C (HRC) is the most common scale for hardened steels.
Scale conversion	The empirical process of converting a hardness value from one scale (e.g. HL) to another (e.g. HRC), using material-group-specific tables.
Surface preparation	Grinding, polishing or cleaning of the test area to ensure consistent and representative contact between the impact body and the specimen.
Vickers hardness (HV)	A laboratory hardness scale using a diamond pyramid indenter, measuring the diagonal of the impression; applicable across a wide range of metals and loads.