🔩 Depth of decarburization of steel — metallographic method (worst field or mean of four measurements), Vickers or Knoop microhardness profile, carbon content methods; PN-EN ISO 3887:2024-04 (ISO 3887:2023)

Materials and NDT PN-EN ISO 3887

Overview

WHAT THE STANDARD COVERS. Scope from the PKN card of PN-EN ISO 3887:2024-04, in full (our translation): "This document describes decarburization and specifies three methods of measuring the depth of decarburization of steel products." The card of the withdrawn Polish-language edition PN-EN ISO 3887:2005 was more detailed and narrower: "Decarburization is defined and three methods of measuring the depth of decarburization of non-alloy and low-alloy steels are specified (the metallographic method, the microhardness measurement method and the method of determining the carbon content)" (no full stop on the card). We read the content of the method in the sample extract of ISO 3887:2023 from the cover to clause 5.3.3, with the table of contents; we do not have clause 5.4 (methods of determining the carbon content), clause 6 (report) or Annex A (example microstructures).

ACCORDING TO THE TEXT OF ISO 3887:2023 (foreword, clauses 1–5.3). The standard was prepared by ISO/TC 17 "Steel", subcommittee SC 7 "Methods of testing (other than mechanical tests and chemical analysis)", together with CEN/TC 459 ECISS (Vienna Agreement); the fourth edition (2023-09) replaced the third (ISO 3887:2017), and the only change listed is a note in 5.2.1 on automatic image analysis. Scope (1): definition of decarburization and three methods of measuring its depth in steel products. References (2): ISO 4545-1 (Knoop hardness), ISO 6507-1 (Vickers hardness), ISO 9556 and ISO 15349-2 (total carbon and low carbon content — infrared absorption after combustion), ISO 14594 (electron probe microanalysis EPMA) and ISO 14707 (GD-OES). Definitions (3): decarburization — a decrease of the carbon content in the surface zone of steel; partial decarburization d3 — from the place at which the carbon content exceeds the solubility in ferrite (e.g. pearlite is visible) to the place where there is no longer a visible difference from the core; complete (ferritic) decarburization d1 — from the surface to the place up to which only ferrite occurs, determined from the microstructure; depth of functional decarburization d2 — to the place at which the carbon content or hardness reaches the level at which the properties of the product are not impaired (minimum from the product standard); total depth of decarburization d4 = d3 + d1, designated DD, in millimetres (e.g. DD = 0.08 mm); carbon content profile and hardness profile — as a function of the distance from the surface. Sampling (4): representative specimens, the location and number agreed by the parties; for the metallographic, microhardness and EPMA methods — a cross-section perpendicular to the axis of the product, which allows the variation around the circumference to be assessed; without corners, which may show abnormal decarburization, unless otherwise agreed; cross-sections up to about 2.5 cm in diameter are polished in full, larger ones — one or more specimens as agreed; for chemical analysis — chips or a milled surface. Choice of method (5.1): it depends on the degree of decarburization, the microstructure, the carbon content and the shape; the methods used for finished products are the metallographic method (5.2), Vickers or Knoop microhardness for hardened or quenched-and-tempered steels (5.3) and determination of the carbon content by chemical, spectrographic, EPMA or GDOES analysis (5.4); the specimen is tested in the as-delivered condition, and additional heat treatment may be applied only by agreement of the parties, protecting the carbon distribution (small specimen, short austenitization, inert atmosphere); the parties agree on the method in writing if the product standard does not specify it — without agreement the metallographic method shall be used. Metallographic method (5.2): only where changes in the carbon content are visible in the microstructure — especially in the annealed, normalized, as-rolled or as-forged condition, with reservations for hardened and tempered structures; automatic image analysis is permissible, preferably after its accuracy has been confirmed by an extensive correlation; polishing must not round the edges (mounting the specimen, clamping or a protective metallic coating applied electrolessly or electrolytically; automatic or semi-automatic preparation recommended); etching with nital (1.5–4 % nitric acid in ethanol) or picral (2–5 % picric acid in ethanol). The loss of carbon is assessed by the decrease in the amount of pearlite (ferrite with pearlite), of hypereutectoid carbides and/or pearlite, or of carbides dispersed in a ferritic matrix; the distance from the surface to the place where the structure does not differ from the core (total decarburization) is measured with suitably calibrated equipment; the magnification is chosen by the assessor — the highest at which the whole zone is visible, ×100 being recommended in most cases; first the whole circumference is examined at low magnification and the deepest uniform zone of decarburization is selected. Measurement by one of two methods, chosen by agreement: the worst-field method (one measurement in the deepest uniform zone) or the mean method (starting from the deepest zone the circumference is divided into equal parts and measurements are made at their ends — unless otherwise agreed, four measurements, and the result is their mean; points with surface defects are omitted). For carburized products the definition of the "core" must be agreed; the permissible depth of decarburization is specified by the product standard or by agreement of the parties. Microhardness method (5.3): Vickers (ISO 6507-1) or Knoop (ISO 4545-1) hardness profile along a line perpendicular to the surface (large and medium depths; a zigzag line gives denser points) or oblique to it (medium and small depths); only hypoeutectoid steels in the hardened, tempered or heat-treated condition and decarburized zones lying in the hardened layer; for low-carbon steels the method becomes inaccurate; the specimen is prepared as for metallography, but usually without etching; the load as high as possible, the spacing of the measuring points at most 0.1 mm, the distances between indentations according to ISO 6507-1 or ISO 4545-1.

STATUS (as of 08.10.2026). The card of PN-EN ISO 3887:2024-04 (English version) has no withdrawal label: title "Steels -- Determination of the depth of decarburization" (our translation), publication 10-04-2024, 24 pages, price group M, Metallurgy Sector, KT 123 Testing of Properties of Metals, "Introduces: EN ISO 3887:2023 [IDT], ISO 3887:2023 [IDT]", "Replaces: PN-EN ISO 3887:2018-03 – English version", ICS 77.040.99. Card of PN-EN ISO 3887:2018-03 (English version): "Withdrawn and replaced by PN-EN ISO 3887:2024-04 – English version", publication 15-03-2018, withdrawal 10-04-2024, it introduced ISO 3887:2017. The last Polish-language edition, PN-EN ISO 3887:2005 (it introduced ISO 3887:2003; KT 262 Heat Treatment of Metals, 12 pages), was withdrawn on 15-03-2018. PKN search, term "ISO 3887" (08.10.2026): 7 items — five editions of the standard on decarburization (from PN-ISO 3887:1999 "Non-alloy and low-alloy steel -- Determination of the depth of decarburization" (our translation), which introduced ISO 3887:1976, to the current PN-EN ISO 3887:2024-04) and two editions of PN-EN 3887 (2002 and 2004) "Aerospace series -- Heat resisting alloy CO-WH4101 (CoCr20W15Ni) -- Filler metal for welding" (our translation), i.e. standards on a different subject. evs.ee catalogue: ISO 3887:2023 in force since 22.09.2023, in the history ISO 3887:2017 (since 17.11.2017).

HOW MANY LABORATORIES AND IN WHAT FORM (copy of the accreditation scope database and current PCA documents, read on 08.10.2026). In the current PCA documents (issues from 23.04.2025 to 22.09.2026) the standard appears in 9 entries at 8 laboratories; in the database copy in 12 records (the entry of AB 053 is split there into four records — Polish and English rows); no entry is suspended. Notation "PN-EN ISO 3887:2024-04" — AB 053 (with the addition "excluding clause 5.4"), AB 099 (two entries), AB 193, AB 342, AB 490; "PN-EN ISO 3887:2024:04" alongside PN-EN 13674-1+A1:2017-07 (railway rails) — AB 1449; without a year — AB 128 and AB 608. The entries of AB 053 and AB 342 have an asterisk (tests on the basis of which the laboratory formulates opinions and interpretations). The "Laboratories" tab (term "PN-EN ISO 3887") shows all 8 laboratories and 12 records; the term does not pick up standards with other numbers. Apart from these 8 laboratories, AB 369 (issue 29 of 17.12.2025), in the entry "Depth of decarburization, mm", metallographic method, for metal structural products and materials, writes "PN-EN 3887" alongside "PN-EN 13674" (entry not suspended) — under the designation PN-EN 3887 the PKN catalogue has an aerospace standard on a welding filler metal; we do not count this entry, and in the tab it becomes visible only under the term "PN-EN 3887".

WHAT THE LABORATORIES TEST (PCA documents). Quantity: depth of decarburization. Method: metallographic, i.e. optical microscopy — all laboratories; Vickers microhardness (AB 099: HV0.5 and HV1), Vickers and Knoop (AB 053) or the "hardness distribution method" (AB 128). AB 053 excludes clause 5.4, i.e. all methods of determining the carbon content. Subject: steel products and materials (AB 053), metallurgical products and castings (AB 099), products of iron alloys (AB 128), non-alloy and low-alloy steels (AB 193, AB 342), steel metallurgical and structural products (AB 490), steels (AB 608), steel products — alongside the standard for rails (AB 1449). The laboratories do not give numerical ranges of depth.

WHERE A SEEMINGLY CORRECT RESULT IS EASY TO GET. First — which depth is given: the standard distinguishes partial decarburization d3, complete (ferritic) d1, functional d2 and total d4 = DD; the metallographic method measures the depth to the place where the structure does not differ from the core, and d1 is determined from the microstructure — a result without a designation of the type of decarburization is ambiguous. Second — the measurement method: the worst field and the mean of four measurements give different numbers; the choice is made by agreement of the parties. Third — the test method: metallographic, microhardness and carbon methods are different methods; the parties agree on it in writing, and without agreement the metallographic method is used. Fourth — limits of microhardness: only hypoeutectoid steels in the hardened, tempered or heat-treated condition and zones in the hardened layer; for low-carbon steels the measurement is inaccurate — for non-alloy and low-alloy steels the laboratories declare the metallographic method. Fifth — the specimen: test in the as-delivered condition, cross-section, without corners (they may show abnormal decarburization), with an edge that polishing must not round. Sixth — exclusions and notation: AB 053 excludes the carbon content methods (5.4), AB 1449 writes the edition as "2024:04", AB 128 and AB 608 write the number without a year, and AB 369 cites "PN-EN 3887", i.e. the designation of another standard — a report with such a citation does not indicate the standard on decarburization.

WHAT WE DO NOT GIVE. We do not have clause 5.4 — the determination of the carbon content by chemical, spectrographic, EPMA and GDOES analysis and the interpretation of their results — clause 6 (report) or Annex A (example microstructures of decarburization). The standard leaves the values of the loads for microhardness to choice ("as high as possible") — WE DO NOT GIVE specific ones.

Method principle

Decarburization is a decrease of the carbon content in the surface zone of steel. Its depth is measured on a cross-section of the product by one of three methods: metallographic — after etching with nital or picral, as the distance from the surface to the place where the structure does not differ from the core (measurement in the worst field or the mean of four points on the circumference); microhardness — from a Vickers or Knoop hardness profile along a line perpendicular or oblique to the surface, with a spacing of points of up to 0.1 mm, only for hypoeutectoid steels that are hardened, tempered or heat-treated; or from the carbon content profile (chemical, spectrographic, EPMA, GDOES analysis) (ISO 3887:2023, clauses 3–5).

Applications

• Steel products — depth of decarburization by the metallographic method; in the current accreditation scopes 8 laboratories
• Hardened and quenched-and-tempered steels — Vickers or Knoop microhardness profile (AB 053, AB 099, AB 128)
• Non-alloy and low-alloy steels, metallurgical, structural and cast products, railway rails (AB 1449, alongside PN-EN 13674-1)
• Acceptance of products for which the permissible depth of decarburization is specified by the product standard or by agreement of the parties

Key parameters

Standard

Standard number

PN-EN ISO 3887:2024-04 (wersja angielska; wprowadza EN ISO 3887:2023 [IDT] i ISO 3887:2023 [IDT])

Title (PL)

Stale — Określanie głębokości odwęglenia

Title (EN)

Steels — Determination of the depth of decarburization

Step-by-step procedure

1. Agreement

   The parties agree in writing on the method (if the product standard does not specify it), the location and number of specimens and the way of measuring (worst field or mean); without agreement — the metallographic method (4, 5.1, 5.2.3).

2. Sampling

   Cross-section perpendicular to the axis of the product, in the as-delivered condition, without corners; up to about 2.5 cm in diameter — the whole cross-section, larger ones — one or more specimens as agreed (4, 5.1).

3. Preparing the section

   Polishing without rounding the edges (mounting, clamping or a metallic coating), etching with nital or picral; for microhardness usually without etching (5.2.2, 5.3.2).

4. Metallographic measurement

   Examination of the circumference at low magnification, selection of the deepest uniform zone, measurement at about ×100 from the surface to the place where the structure does not differ from the core — one measurement (worst field) or four and the mean (5.2.3).

5. Microhardness measurement

   Vickers or Knoop profile along a perpendicular or oblique line, points at most every 0.1 mm, spacing of indentations according to ISO 6507-1 or ISO 4545-1; only for hypoeutectoid steels that are hardened, tempered or heat-treated (5.3).

6. Result and report

   State the type of decarburization (d1, d3 or DD), the method and the way of measuring, in millimetres; WE DO NOT GIVE the content of the report from clause 6.

Required equipment and apparatus

Reagents, media and consumables

Health and safety (OHS)

• The etching reagents contain nitric acid (nital) or picric acid (picral) in ethanol — handle them according to the safety data sheets of these substances
• TECHNICAL NOTE: a result without the type of decarburization (d1, d3, DD), the method and the way of measuring (worst field or mean) is ambiguous; microhardness only for hypoeutectoid steels that are hardened or quenched and tempered

Frequently asked questions