ISO 4212:2023
(Main)Corrosion of metals and alloys - Method of oxalic acid etching test for intergranular corrosion of austenitic stainless steel
Corrosion of metals and alloys - Method of oxalic acid etching test for intergranular corrosion of austenitic stainless steel
This document specifies a method to test for intergranular corrosion (IGC) in austenitic stainless steels using an oxalic acid etch. This method can evaluate non-sensitization of austenitic stainless steels by observing the structure of the etched surface with a microscope after performing electrolytic etching (hereinafter called “etching”) on austenitic stainless steel in an oxalic acid solution.
Corrosion des métaux et alliages — Méthode d'essai de gravure à l'acide oxalique pour la corrosion intergranulaire de l'acier inoxydable austénitique
General Information
Overview
ISO 4212:2023 specifies an oxalic acid etching test for detecting intergranular corrosion (IGC) characteristics in austenitic stainless steels. The standard defines an electrolytic etching procedure and microscopic evaluation to determine whether a stainless steel specimen is non‑sensitized or suspected of sensitization. This method is a rapid, simple screening technique that complements ISO IGC tests (ISO 3651-1, ISO 3651-2, ISO 12732) and established practices such as ASTM A262-15 and JIS G0571.
Key Topics and Requirements
- Purpose: Screen for non‑sensitization or suspicion of sensitization by observing etched surface structure (does not by itself quantify sensitization).
- Test solution: Dissolve 100 g oxalic acid crystals in 900 ml deionized/distilled water (ISO 3696 Grade 3). For some Mo‑containing steels, ammonium peroxodisulfate (100 g/900 ml) may be used.
- Apparatus: DC power supply (example: 15 V, 20 A), variable resistor, ammeter, cathode (stainless beaker or plate), inert test vessel, holder and thermometer (±1 °C).
- Specimen preparation: Fine polishing (buffing with diamond suspension), isolation of non‑tested areas with insulating material; welded sections should include base metal, HAZ and weld metal where applicable.
- Etching conditions: Oxalic acid solution at 20–50 °C; etch as an anode for 90 s at 1 A/cm². For ammonium peroxodisulfate: 5–10 min at 1 A/cm².
- Microscopy: Examine entire etched surface; typical magnification 200×–500× for rolled, forged, cast products or weld zones.
- Etch classification:
- A (Step structure): orientation‑dependent step features.
- B (Dual structure): grooves at grain boundaries but no fully surrounded grains.
- C (Groove structure): one or more grains completely surrounded by grooves.
- Evaluation: A or B indicate no further ferric sulfate/65% HNO3/CuSO4/EPR testing required; C (grooved) indicates suspicion of sensitization and requires follow‑up testing (ISO 3651-1, ISO 3651-2, ISO 12732).
- Test report: Must reference ISO 4212:2023 and record steel grade, specimen details, sensitization heat treatment (if applied), solution and times, etching structure, solution temperature, deviations and anomalies, and test date.
Applications
- Rapid screening in corrosion laboratories and metal production QA/QC for austenitic stainless steel components.
- Weld and fabrication inspection to identify areas that may require further IGC testing.
- Material acceptance testing for manufacturers, fabricators, shipbuilding, chemical and power industry components where IGC risk is a concern.
- Metallurgists and corrosion engineers use it as a cost‑effective triage method before undertaking detailed IGC or electrochemical reactivation (EPR) tests.
Related Standards
- ISO 3651-1, ISO 3651-2 (detailed IGC corrosion tests)
- ISO 12732 (EPR double loop method)
- ASTM A262-15 Practice A (oxalic acid etch)
- JIS G0571:2003 (basis for ISO 4212)
Keywords: ISO 4212:2023, oxalic acid etching test, intergranular corrosion, austenitic stainless steel, sensitization, electrolytic etching, IGC screening, metallurgical inspection.
Frequently Asked Questions
ISO 4212:2023 is a standard published by the International Organization for Standardization (ISO). Its full title is "Corrosion of metals and alloys - Method of oxalic acid etching test for intergranular corrosion of austenitic stainless steel". This standard covers: This document specifies a method to test for intergranular corrosion (IGC) in austenitic stainless steels using an oxalic acid etch. This method can evaluate non-sensitization of austenitic stainless steels by observing the structure of the etched surface with a microscope after performing electrolytic etching (hereinafter called “etching”) on austenitic stainless steel in an oxalic acid solution.
This document specifies a method to test for intergranular corrosion (IGC) in austenitic stainless steels using an oxalic acid etch. This method can evaluate non-sensitization of austenitic stainless steels by observing the structure of the etched surface with a microscope after performing electrolytic etching (hereinafter called “etching”) on austenitic stainless steel in an oxalic acid solution.
ISO 4212:2023 is classified under the following ICS (International Classification for Standards) categories: 77.060 - Corrosion of metals. The ICS classification helps identify the subject area and facilitates finding related standards.
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Standards Content (Sample)
INTERNATIONAL ISO
STANDARD 4212
First edition
2023-02
Corrosion of metals and alloys —
Method of oxalic acid etching test for
intergranular corrosion of austenitic
stainless steel
Corrosion des métaux et alliages — Méthode d'essai de gravure
à l'acide oxalique pour la corrosion intergranulaire de l'acier
inoxydable austénitique
Reference number
© ISO 2023
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Published in Switzerland
ii
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 General principles . 2
5 Apparatus . 2
6 Sensitization heat treatment for test specimens. 2
7 Test specimens . 2
8 Test solution . 2
9 Test procedure .3
10 Evaluation of etching structure .4
11 Test report . 4
Bibliography . 6
iii
Foreword
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iv
Introduction
Intergranular corrosion (IGC) is a form of localized corrosion which occurs along grain boundaries. IGC
of stainless steel is attributable to grain boundary segregation and precipitates. When the formation
of chromium-rich grain boundary carbides occurs, it leads to continuous chromium depletion adjacent
to the grain boundary, and IGC occurs in certain corrosive media. This process is usually known
as sensitization. Sensitization of stainless steel can be evaluated by ISO IGC tests for austenitic
stainless steels: such as ISO 3651-1, ISO 3651-2, and ISO 12732. On the other hand, oxalic etching
tests (JIS G0571:2003 and ASTM A262-15 Practice A) cannot evaluate sensitization, however, they
can evaluate non-sensitized condition of austenitic stainless steels and suspicions of sensitization by
observing the etched surface of the stainless steels. This is because it does not etch chromium depletion
adjacent to the chromium-rich grain boundary precipitates but chromium-rich grain boundary carbides
themselves. If sensitization is suspected, IGC tests, ferric sulfate-sulfuric acid test (see ISO 3651-2),
65 % nitric acid test (see ISO 3651-1), copper sulfate-sulfuric acid test (see ISO 3651-2) or EPR test
(ISO 12732) should be conducted to evaluate sensitization of austenitic stainless steels.
The main benefits of these oxalic acid etching tests are that they are simple, easy and rapid. This
document is based on JIS G0571:2003.
v
INTERNATIONAL STANDARD ISO 4212:2023(E)
Corrosion of metals and alloys — Method of oxalic acid
etching test for intergranular corrosion of austenitic
stainless steel
1 Scope
This document specifies a method to test for intergranular corrosion (IGC) in austenitic stainless steels
using an oxalic acid etch. This method can evaluate non-sensitization of austenitic stainless steels by
observing the structure of the etched surface with a microscope after performing electrolytic etching
(hereinafter called “etching”) on austenitic stainless steel in an oxalic acid solution.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document
...
ISO 4212:2023 establishes a comprehensive framework for assessing intergranular corrosion (IGC) in austenitic stainless steels through an oxalic acid etching test. This standard is essential in the metallurgy sector, particularly for industries where corrosion resistance is critical. The document outlines a precise methodology to evaluate the non-sensitization of austenitic stainless steels, ensuring that these materials can withstand corrosive environments without compromising their structural integrity. One of the key strengths of ISO 4212:2023 is its focus on the electrolytic etching process using oxalic acid, which allows for a detailed examination of the surface structure of the stainless steel post-etching. By using microscopic analysis to observe the etched surfaces, the standard facilitates a clear assessment of the degree of intergranular corrosion present. This level of scrutiny is invaluable for manufacturers and engineers who need to ensure the reliability and longevity of stainless steel components. Moreover, ISO 4212:2023 is relevant not only for its methodology but also for its implications in quality control and material selection. The accuracy and reproducibility of the etching test provided by this standard help organizations maintain industry compliance and enhance overall product safety. As industries increasingly demand materials with superior corrosion resistance, the adoption of ISO 4212:2023 will support the development of robust austenitic stainless steels, aligning with global standards for quality and performance. In summary, ISO 4212:2023 is a critical document in the field of metallurgy, offering a standardized approach to testing for intergranular corrosion in austenitic stainless steels through the oxalic acid etching method. Its detailed scope, methodological rigor, and practical relevance underscore its importance for industries reliant on the performance of stainless steels in hostile environments.
ISO 4212:2023は、オーステナイト系ステンレス鋼の間隙腐食（IGC）を評価するための方法を規定しています。この標準の特徴は、オキサリック酸を用いたエッチング試験を通じて、オーステナイト系ステンレス鋼が非感作状態にあるかどうかを検証できる点にあります。具体的には、エッチング処理を施した後に顕微鏡でエッチング表面の構造を観察することで、腐食の程度を分析します。 ISO 4212:2023の強みは、間隙腐食の早期発見と評価を可能にする明確な手順を提供していることです。この標準は、材料科学や腐食工学の分野において、オーステナイト系ステンレス鋼の信頼性を高めるための重要なツールとなります。また、これにより、産業界の品質基準の向上にも寄与することが期待されます。 さらに、ISO 4212:2023はグローバルな規格であり、多様な業界で広く適用可能です。この標準を採用することで、企業は製品の耐久性を評価し、顧客に対して信頼性の高い製品を提供することが可能となります。したがって、間隙腐食の評価に関する好適な基準として、ISO 4212:2023はその関連性が高いと言えるでしょう。
ISO 4212:2023 표준은 오스테나이트 스테인리스 강의 간섭 부식(IGC)에 대한 시험 방법을 규정하고 있습니다. 이 문서는 옥살산 침식법을 사용하여 오스테나이트 스테인리스 강의 간섭 부식을 평가하는 방법을 명확하게 제시합니다. 이 표준의 목적은 비감작화된 오스테나이트 스테인리스 강의 구조를 전해침식 후 관찰하여 평가할 수 있도록 하는 것입니다. ISO 4212:2023의 강점은 정밀한 시험 방법론을 통해 간섭 부식을 명확히 규명할 수 있다는 점입니다. 이 표준은 전해침식 과정에서 발생하는 미세한 구조 변화를 현미경을 통해 관찰할 수 있게 하여, 소재의 부식 저항성을 정량화하는 데 기여합니다. 따라서, 이 방법은 제조업체와 엔지니어들이 오스테나이트 스테인리스 강의 품질을 보장하고, 신뢰할 수 있는 부식 방지를 위해 필수적인 참고 자료로 자리 잡을 수 있습니다. 또한, ISO 4212:2023은 산업 전반에 걸쳐 오스테나이트 스테인리스 강을 사용할 때의 표준화 촉진에 큰 역할을 할 것으로 기대됩니다. 이 표준이 제공하는 체계적이고 과학적인 접근은 금속과 합금의 부식 시험에서 신뢰성을 높이는 데 기여하며, 관련 산업에 실질적인 이점을 제공합니다. 결국, ISO 4212:2023은 오스테나이트 스테인리스 강의 부식 저항성 평가에서 중요한 기준을 마련하고 있으며, 금속 및 합금의 부식 연구에 있어 필수적인 문서로서 그 중요성을 강조할 수 있습니다.
La norme ISO 4212:2023 se concentre sur la corrosion des métaux et des alliages, en spécifiant une méthode d'essai à l'acide oxalique pour détecter la corrosion intergranulaire (CIG) dans les aciers inoxydables austénitiques. Cette norme est essentielle pour les professionnels de l'industrie métallurgique car elle fournit une approche systématique pour évaluer la résistance à la corrosion des aciers inoxydables austénitiques, un aspect critique dans de nombreuses applications où la durabilité et la longévité des matériaux sont primordiales. L'une des forces majeures de la norme ISO 4212:2023 est sa capacité à éliminer l'incertitude liée à la sensibilité des aciers inoxydables à la corrosion intergranulaire. En utilisant un procédé d'attaques électrolytiques avec de l'acide oxalique, cette méthode permet d'observer avec précision la structure de la surface attaquée à l'aide d'un microscope, fournissant ainsi des résultats fiables et reproductibles. Cette précision est cruciale non seulement pour la recherche et le développement, mais également pour les contrôles de qualité dans le secteur industriel. L'application de cette norme est particulièrement pertinente dans des domaines tels que l'aéronautique, l'industrie chimique, et les équipements médicaux, où la performance des matériaux est soumise à des conditions sévères. De plus, la norme ISO 4212:2023 contribue à la minimisation des risques associés à la corrosion, favorisant ainsi la sécurité et la confiance des consommateurs dans les produits finis. En résumé, la norme ISO 4212:2023 est un outil indispensable pour les professionnels cherchant à évaluer la sensibilité à la corrosion intergranulaire des aciers inoxydables austénitiques. Sa méthodologie éprouvée et sa portée pertinente renforcent son utilité dans divers secteurs industriels, faisant d'elle une référence incontournable pour la gestion de la corrosion des métaux.
Die ISO 4212:2023 ist ein bedeutendes Dokument, das einen methodischen Ansatz zur Untersuchung der interkristallinen Korrosion (IGC) bei austenitischen Edelstählen beschreibt. Der Anwendungsbereich dieser Norm konzentriert sich speziell auf die Prüfung der Nicht-Sensibilisierung von austenitischen Edelstählen durch den Einsatz von Oxalsäure-Etch-Methoden. Ein wesentlicher Stärke dieser Norm ist die detaillierte Vorgehensweise zur Durchführung des Tests, die es Fachleuten ermöglicht, die Struktur der geätzten Oberfläche mithilfe eines Mikroskops genau zu beobachten. Durch den beschriebenen elektrolytischen Ätzprozess in einer Oxalsäurelösung können potenzielle Schwächen in der Korrosionsbeständigkeit dieser Werkstoffe effektiv identifiziert werden. Die Relevanz der ISO 4212:2023 kann nicht hoch genug eingeschätzt werden, insbesondere in Branchen, in denen austenitische Edelstähle häufig eingesetzt werden, wie im Bauwesen, in der chemischen Verarbeitung und in der Lebensmittelindustrie. Durch die Bereitstellung eines klaren Standards zur Bewertung der intergranularen Korrosion stellt dieses Dokument sicher, dass Unternehmen und Ingenieure effektive Maßnahmen zur Gewährleistung der Materialintegrität ergreifen können. Dies ist entscheidend, um sicherzustellen, dass Produkte langlebig und sicher sind. Zusammenfassend lässt sich sagen, dass die ISO 4212:2023 eine wichtige Ressource für die Prüfung der interkristallinen Korrosion von austenitischen Edelstählen darstellt. Ihre umfassenden Richtlinien und die Fokussierung auf die Testmethodik gewährleisten, dass hochwertigste Materialien verwendet werden, die den Herausforderungen moderner Anwendungen gewachsen sind.
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