What Is Decarburisation?
Decarburisation depth determination is a test in which the carbon-loss layer formed on the steel surface during heat treatment or hot forming is measured on a metallographic section or via a microhardness profile.
Purpose of Decarburisation
The purpose is to verify that the surface carbon loss does not exceed the specification limit; the decarburised layer lowers surface hardness and fatigue strength.
Which Products Is Decarburisation Applied To?
- Spring steels
- Gear and shaft parts
- Hot-forged parts
- Heat-treated bar and wire
In Which Sectors Is Decarburisation Used?
Standards Related to Decarburisation
- ASTM E1077
- ISO 3887
- ISO 6507 (for microhardness profile)
Decarburisation Conditions
- Method
- Metallographic measurement or microhardness profile
- Section
- Perpendicular to the surface, at representative locations
- Etching
- Etchant that reveals the carbon-loss layer (typically nital)
- Measurement
- Full and partial decarburisation depths are reported separately
Equipment for Decarburisation
- Metallurgical microscope
- Microhardness testing machine
- Edge-retentive mounting rig
- Calibrated measurement system
Sample Requirements for Decarburisation
- The section must be taken perpendicular to the surface
- Edge retention is critical; rounding distorts the measurement
- Measurement must be performed at a sufficient number of locations
- The specimen surface must be unmachined before testing
Duration of Decarburisation
Typically 1–2 days.
Decarburisation Procedure
- 1A section perpendicular to the surface is taken and mounted with edge retention.
- 2The section is polished and etched.
- 3Depth is measured at the defined locations.
- 4A microhardness profile is taken if required.
- 5Maximum and average depth are reported.
Decarburisation Acceptance Criteria
The acceptance criterion is given in the product standard or specification as a maximum decarburisation depth.
Evaluation of Results
Full decarburisation (ferritic layer) and partial decarburisation are different depths; which one the specification limits must be clarified.
Decarburisation Report
- Standard and method applied
- Section locations
- Etching conditions
- Full and partial depth values
- Micro images
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 authorisationsRelated Regulations
- Product standards
Metal and Metallurgy Testing — What Does This Testing Field Cover?
The section below describes the field that the Decarburisation 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 Decarburisation
According to which standard is Decarburisation made?
Decarburisation is executed in scope ASTM E1077, ISO 3887 and ISO 6507 (for microhardness profile). The limit values and acceptance criteria to be applied are defined in the product standard; The version valid for your product is confirmed in writing at the offer stage.
Which products does Decarburisation apply to?
Mainly applied to Spring steels, Gear and shaft parts, Hot-forged parts and Heat-treated bar and wire. Whether your product is included in the scope is determined by examining its technical specifications and intended use.
Under what conditions is Decarburisation done?
The determining parameters are: Method — Metallographic measurement or microhardness profile, Section — Perpendicular to the surface, at representative locations and Etching — Etchant that reveals the carbon-loss layer (typically nital). The full terms are in the "Test Conditions" section on the page and vary depending on the product standard.
What kind of sample is needed for Decarburisation?
The section must be taken perpendicular to the surface, Edge retention is critical; rounding distorts the measurement and Measurement must be performed at a sufficient number of locations. The number of samples is determined according to the product standard and the scope to be reported.
How long does Decarburisation take?
Typically 1–2 days. This duration belongs to the experiment itself; sample preparation, queuing and reporting are also evaluated. A realistic schedule for your product is given in the offer.
What is the Decarburisation result called "appropriate"?
The acceptance criterion is given in the product standard or specification as a maximum decarburisation depth.