🔩 Classification of the graphite microstructure in cast irons by comparative visual analysis under the microscope — graphite form designated by Roman numerals I–VI, distribution by letters A–E (grey cast iron only, form I), size by numbers 1–8 (size 1: ≥ 1 mm, 2: 0,5 to < 1 mm, 3: 0,25 to < 0,5 mm, 4: 0,12 to < 0,25 mm at ×100 magnification), reference images in a 120 mm circle, PN-EN ISO 945-1

Materials and NDT PN-EN ISO 945-1

Overview

WHAT THE STANDARD COVERS. Scope from the PKN catalogue card of PN-EN ISO 945-1:2019-09 (English version), in full (our translation of the Polish card text): “This document specifies a method of classifying the microstructure of graphite in cast irons by comparative visual analysis. The purpose of this document is to give information on a method of classifying graphite. It is not intended to give information on the suitability of types and grades of cast iron for any particular application. The individual material grades are specified mainly by mechanical properties and, in the case of austenitic and abrasion-resistant cast irons, by their chemical composition. The interpretation of the form and size of graphite does not permit a statistically valid statement of conformity with the requirements of the relevant material standard.” We read the text of the standard in the sample extract of ISO 945-1:2019 from the cover to Figure 3 d) (reference image of graphite size 4, page 7); we do not have the rest — the reference images for sizes 5–8, Figures 4 and 5, Table 1, the clauses on samples, preparation of the section and performing the assessment, or Annexes A and B.

ACCORDING TO THE TEXT OF ISO 945-1:2019 (foreword, introduction, Clauses 1–4.4 up to Figure 3 d). The third edition replaced the second (ISO 945-1:2017) as a minor revision: Figures 3 and 4 were corrected to a diameter of 120 mm to allow direct comparison with the microscope screen, and so that the largest graphite dimensions agree with Table 1. Introduction: designation of the microstructure makes it possible to classify the form, distribution and size of graphite in cast iron; visual classification is a recognized method in foundries for quickly determining the general graphite microstructure in a casting. Scope (Clause 1): as on the card — a method of classification by comparative visual analysis, without information on the suitability of grades; interpretation of graphite form and size does not allow a statistically valid statement of conformity with the requirements of a material standard. The standard has no normative references and no definitions. Designation system (4.1): when cast iron is examined under the microscope according to this standard, graphite is classified by a) form — Roman numerals I–VI (Figure 1 and Annex A); b) distribution — capital letters A–E (Figure 2 and Annex B), designated only for grey cast iron (form I); c) size — numbers 1–8 (Figures 3, 4 and 5 and Table 1); note: Figures 1–5 show only outlines, not the structure of graphite. Form (4.2): Figure 1 — reference images of the principal graphite forms in cast iron, ×100 magnification. Distribution (4.3): Figure 2 — reference images of graphite distribution (form I), ×100 magnification. Size (4.4): reference images at ×100 magnification for form I — a) size 1: ≥ 1 mm; b) size 2: from 0,5 mm to < 1 mm; c) size 3: from 0,25 mm to < 0,5 mm; d) size 4: from 0,12 mm to < 0,25 mm; this is where the extract we read ends.

STATUS (cards as of 02.10.2026). The card of PN-EN ISO 945-1:2019-09 (English version) has no “Withdrawn” header — the standard is CURRENT: published 20-09-2019, 46 pages, price group T, Metallurgy Sector, KT 301 Foundry, ICS 77.080.10, “Introduces: EN ISO 945-1:2019 [IDT], ISO 945-1:2019 [IDT]”, “Replaces: PN-EN ISO 945-1:2018-04 – English version”. The last Polish version, PN-EN ISO 945-1:2009 (introduced ISO 945-1:2008, with corrigendum AC:2010), was withdrawn on 12-04-2018 and replaced by PN-EN ISO 945-1:2018-04 (English version; introduced ISO 945-1:2017), withdrawn on 20-09-2019 in favour of the 2019-09 edition. The Polish standard PN-H-04661:1975 “Grey, spheroidal graphite and malleable cast iron — Metallographic examination — Determination of microstructure”, cited in the scopes next to PN-EN ISO 945-1, has been WITHDRAWN since 29-11-2010 and replaced by PN-EN ISO 945:1999, which itself was withdrawn on 05-03-2009 in favour of PN-EN ISO 945-1:2009 — today PN-EN ISO 945-1:2019-09 (cards, read 02.10.2026; the successor's withdrawal date is earlier than the predecessor's — as given by the PKN cards). The PKN search for “PN-EN ISO 945-1” (02.10.2026) shows the cards 2009 (Polish and English), 2018-04 and 2019-09. There is no Polish version of the 2019 edition.

HOW MANY LABORATORIES AND IN WHAT FORM (copy of the accreditation scope database, data up to 17.09.2026, read 02.10.2026). The number 945-1 appears in 14 records at 8 laboratories: AB 053 (7 — the same position at several locations), AB 001, AB 099, AB 128, AB 197, AB 369, AB 490, AB 699 (1 each). In the current scopes on the PCA website (read 02.10.2026, issues from 17.12.2025 to 06.08.2026) the number appears at all 8: with the year “2019-09” at AB 001, AB 053, AB 099, AB 197, AB 490 and AB 699, without a year at AB 128 and AB 369. At AB 053 the entry reads “PN-EN ISO 945-1:2019-09 z wyłączeniem p. 8.5” (excluding point 8.5). At AB 197 part of the scope is suspended at the request of the body (from 15.06.2026 to 12.12.2026), but the row with the number 945-1 is not set in bold italics. The “Laboratories” tab searches entries BEGINNING WITH “PN-EN ISO 945-1” and shows all 8 laboratories and 14 positions — checked with the tab query on the labcoda.pl production server on 02.10.2026.

WHAT THE LABORATORIES TEST (positions in PCA). Castings of grey, spheroidal graphite, malleable and alloyed cast iron — graphite precipitates and metal matrix (AB 197, AB 490), castings (AB 099), metallic structural products and materials (AB 369, next to PN-EN 13674-1), metals, alloys, products (AB 699, next to procedure PB-01), materials in the raw, as-cast, annealed condition (AB 128, next to procedure BOSMAL/I-7-44); method: optical microscopy. Almost everywhere it stands next to PN-75/H-04661 (Polish standard on the microstructure of cast iron, withdrawn 29-11-2010 — we do not describe its content) and PN-66/H-04505 or PN-63/H-04504 (whose status we did not check).

WHERE A SEEMINGLY CORRECT RESULT IS EASY TO GET. In magnification: the reference images are for ×100 magnification — size read at another magnification without conversion gives another class. In comparison with the screen: since the 2019 edition the size figures have a diameter of 120 mm, matched to the microscope screen — reference images from earlier editions do not have this scale. In distribution: letters A–E apply ONLY to grey cast iron of form I — a letter for spheroidal graphite cast iron has no meaning in this standard. In the conclusion: graphite classification does NOT decide conformity with a material standard — the grade is defined by mechanical properties or chemical composition. In the citation: the scope “excluding point 8.5” (AB 053) excludes a point we have not read; PN-75/H-04661 standing next to it in the scopes has been withdrawn since 2010 — classification according to it is not classification according to PN-EN ISO 945-1.

WHAT WE DO NOT GIVE. We do not have the reference images for sizes 5–8, Figures 4 and 5, Table 1 (dimensions for all classes), the rules for sampling and preparation of the section, the assessment procedure and notation of the result, or Annexes A and B (descriptions of forms and distributions) — we therefore do not give the limits of sizes 5–8, descriptions of forms I–VI or the test procedure.

Method principle

On a polished section of cast iron the graphite precipitates are examined under an optical microscope and compared with reference images at ×100 magnification: form (I–VI), distribution (A–E, only grey cast iron of form I) and size (1–8, size 1 ≥ 1 mm … size 4 from 0,12 to < 0,25 mm); the result is a designation composed of these three elements.

Applications

• Castings of grey, spheroidal graphite, malleable and alloyed cast iron — graphite form, distribution and size (8 laboratories, optical microscopy)
• Quick assessment of the general graphite microstructure in foundries — without deciding conformity with a material standard
• Examination of the microstructure of metals next to laboratories’ own procedures and PN-75/H-04661

Key parameters

Standard

Standard number

PN-EN ISO 945-1:2019-09 (wersja angielska; EN ISO 945-1:2019 IDT, ISO 945-1:2019 IDT)

Title (PL)

Mikrostruktura żeliwa — Część 1: Klasyfikacja wydzieleń grafitu na podstawie analizy wizualnej

Title (EN)

Microstructure of cast irons — Part 1: Graphite classification by visual analysis

Step-by-step procedure

1. Sample and section

   Taking a sample from the casting and preparing the section — details NOT GIVEN. PN-EN ISO 945-1:2019-09 current (cards as of 02.10.2026).

2. Graphite form

   Comparison with Figure 1 at ×100 and assignment of form I–VI.

3. Distribution

   Only for grey cast iron (form I): comparison with Figure 2 and assignment of a letter A–E.

4. Size

   Comparison with Figures 3–5 (120 mm circle, ×100) and assignment of class 1–8; for form I sizes 1–4: ≥ 1 mm, 0,5–1 mm, 0,25–0,5 mm, 0,12–0,25 mm.

5. Result

   Designation of form, distribution and size; without a conclusion on conformity with a material standard — the notation from the further part of the standard NOT GIVEN.

Required equipment and apparatus

Health and safety (OHS)

• Microscopic examination; when preparing sections — grinders, polishers and etching reagents according to laboratory procedures; the extract of the standard we read contains no safety warnings
• TECHNICAL NOTE: the reference images apply to ×100 magnification, and the distribution letters only to grey cast iron of form I; graphite classification is not proof of conformity with the requirements of a cast iron grade standard

Frequently asked questions