Hardness Measurement — ISO 6506 / ISO 6507 / ISO 6508 / ASTM E18

What Is Hardness?

Hardness measurement is a test in which the hardness value is determined by measuring the indentation resulting from pressing a defined indenter into the material surface under a defined load. Brinell (ISO 6506), Vickers (ISO 6507) and Rockwell (ISO 6508) are common scales.

Purpose of Hardness

The purpose is to quickly verify the material's heat-treatment condition and strength level.

Which Products Is Hardness Applied To?

Steel and cast iron
Aluminium and copper alloys
Heat-treated parts
Welded joints and coatings

In Which Sectors Is Hardness Used?

MetalSteelMiningMachineryOil & Gas

Standards Related to Hardness

ISO 6506 (Brinell)
ISO 6507 (Vickers)
ISO 6508 (Rockwell)
ASTM E10
ASTM E18
ASTM E384

Hardness Conditions

Indenter: Ball, diamond pyramid or diamond cone, depending on the scale
Load: Defined in the standard according to scale and material
Dwell time: Load-application duration defined in the standard
Number of measurements: A number of indentations defined in the standard; averaged

Equipment for Hardness

Brinell, Vickers and Rockwell hardness testing machines
Calibrated reference hardness blocks
Indentation-measurement optical system
Specimen-preparation bench

Sample Requirements for Hardness

The surface must be flat and of the roughness required by the scale
Specimen thickness must be the multiple of indentation depth defined in the standard
Indentations must be at a sufficient distance from the edge and from each other
The specimen must not move during measurement

Duration of Hardness

Minutes per measurement; short, together with specimen preparation.

Hardness Procedure

1The machine is verified with reference blocks.
2The appropriate scale and load are selected.
3The surface is prepared.
4The defined number of indentations is made and measured.
5The hardness value is calculated and averaged.

Hardness Acceptance Criteria

The acceptance criterion is given in the product standard or specification as a hardness range.

Evaluation of Results

Conversion tables between hardness scales (ASTM E140) are approximate; if the specification requires a value on a given scale, it must be measured on that scale. Microhardness or instrumented indentation is used for thin coatings.

Hardness Report

Applied standard and scale
Load and indenter
Instrument verification records
Individual indentation values and the average
Measurement positions

Accreditation

EUROLAB holds internationally recognised accreditation obtained from accreditation bodies party to the IAF and ILAC multilateral recognition arrangements, under ISO/IEC 17025 for laboratory testing, ISO/IEC 17020 for inspection and surveillance, and ISO/IEC 17021-1 and ISO/IEC 17065 for system and product certification. This chain ensures the reports and certificates issued are accepted worldwide.

Whether this test can be offered within accredited scope depends on your product and the standard applied; since accreditation is method-based, the scope is confirmed in writing at the quotation stage.

Scope and authorisations

Related Regulations

Product standards and manufacturing specifications

Metal and Metallurgy Testing — What Does This Testing Field Cover?

The section below describes the field that the Hardness test belongs to; the conditions and acceptance criteria of this particular test are given in the sections above. The scope specific to your product is confirmed in writing at the quotation stage.

Metal and metallurgical testing determines the load a metal or a welded joint can carry, how it fails and what its internal structure looks like. The output of this family is often not about the product itself but about the identity of the MATERIAL: is the steel really of the declared grade, does the weld seam deliver the strength the design assumes, does the casting contain an unacceptable internal defect?

The practical importance of the field comes from the fact that a metal part rarely fails gradually. A plastic part deforms, ages, cracks and usually gives warning. A weld seam or a fastener, by contrast, often breaks without warning — especially where fatigue and brittle fracture are involved. That is why in fields such as pressure equipment, lifting gear, structural steel and pipelines, material testing is a requirement of REGULATION rather than of design.

The family brings together three groups of methods, and each answers a different question. Mechanical tests quantify how the material behaves under load. Non-destructive examination looks for defects without damaging the part. Metallography and chemical analysis explain why the material behaves the way it does — through grain structure, phase distribution, inclusion content and alloy composition.

The acceptance criterion for these tests almost never comes from the test standard, and this is the key to understanding the field. The test standard says how the measurement is to be made; the acceptable values come from the product standard, the material grade or the fabrication code. ISO 6892-1 tells you how to run a tensile test; EN 10025 tells you what yield strength that steel must deliver. When reading a report, the product standard it was assessed against is essential.

Sampling is an inseparable part of the result in this field. Two specimens taken from the same heat may give different values depending on the direction and location they were taken from; in rolled products, specimens parallel and perpendicular to the rolling direction produce different results. Product standards therefore also govern sampling location and orientation, and the report must document this.

Method groups in this field

Mechanical tests
Tensile, compression, bending, notch impact (Charpy), hardness (Brinell, Vickers, Rockwell), fatigue, creep and fracture toughness. These give the behaviour of the material under load in numerical form.
Non-destructive examination
Radiography, ultrasonic examination, penetrant, magnetic particle and visual examination. It looks for surface and internal defects without damaging the part and is an indispensable step in welded fabrication.
Metallography
Specimen preparation, etching and microscopic examination. Grain size, phase distribution, inclusion content, case depth and the weld heat-affected zone are assessed.
Chemical analysis
Alloy composition is verified by optical emission spectrometry and wet chemistry; confirmation of the material grade runs through this step.
Corrosion behaviour
Salt spray, pitting and crevice corrosion and intergranular corrosion tests. In stainless steels these can indicate the quality of the heat treatment.

Commonly confused in this field

A material certificate (such as EN 10204 3.1) is not a test report; it is the manufacturer's declaration. In critical applications independent verification is carried out, and the two must not be confused.
ASTM and ISO tensile tests measure the same quantities but use different specimen geometries; the results are not treated as directly equivalent, and whichever the specification calls for is the one applied.
Conversion tables between hardness and strength are APPROXIMATE. Calculating yield strength from hardness is not sufficient evidence for material acceptance.
In non-destructive examination, "no defect found" does not mean there is no defect; defects below the detection limit of the method may be present. The report must state the method applied and the sensitivity level.
A weld seam passing does not show that the welder or the procedure is qualified; these are separate processes.

Which decisions these results support

Verifying the material certificate and accepting incoming material
Approving welded fabrication; welder and procedure qualification
Manufacturing control of pressure equipment and structural components
Failure analysis and determining the root cause of field damage
Verifying heat treatment and surface treatment processes

Related Tests

Frequently Asked Questions About Hardness

Can a Rockwell value be converted to Brinell?

ASTM E140 conversion tables give an approximate value but carry material-dependent deviation. If the specification requires a value on a specific scale, the measurement must be made directly on that scale.