ISO 4968:2022

Steel - Macrographic examination by sulphur print (Baumann method)

This document specifies a method (Baumann) for the macrographic examination of steel by means of contact printing using silver salts and acid. The method is applicable to steels of which the sulphur content is less than 0,40 %. This method can also be applied to cast irons.

Acier — Examen macrographique par empreinte au soufre (méthode Baumann)

General Information

• Status: Published
• Publication Date: 03-Apr-2022
• ICS: 77.040.99 - Other methods of testing of metals
• Technical Committee: ISO/TC 17/SC 7 - Methods of testing (other than mechanical tests and chemical analysis)
• Drafting Committee: ISO/TC 17/SC 7 - Methods of testing (other than mechanical tests and chemical analysis)
• Current Stage: 6060 - International Standard published
• Start Date: 04-Apr-2022
• Due Date: 02-Nov-2021
• Completion Date: 31-Mar-2022

Relations

• Consolidated By: ISO/TS 5798:2022 - In vitro diagnostic test systems - Requirements and recommendations for detection of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) by nucleic acid amplification methods
• Effective Date: 06-Jun-2022
• Revises: ISO 4968:1979 - Steel - Macrographic examination by sulfur print (Baumann method)
• Effective Date: 05-Aug-2017

Overview

ISO 4968:2022 - "Steel - Macrographic examination by sulphur print (Baumann method)" specifies a contact-printing procedure to reveal sulphur-bearing inclusions and segregation in steels and cast irons. The method uses photographic paper (or flat film) impregnated with an acid reagent to convert metal sulphides into hydrogen sulphide, which darkens the silver-sensitive emulsion. ISO 4968:2022 applies to steels with sulphur content up to 0.40 wt % and provides updated guidance on reagents, surface preparation, printing procedure and result classification.

Key Topics

• Scope & limitations: Qualitative macrographic test; not a direct measure of sulphur concentration. Applicable to steels with S ≤ 0.40% and to cast irons.
• Principle: Local release of H2S from sulphides darkens silver halide emulsion forming a visible print of inclusion distribution.
• Test materials:
  • Photographic paper or flat film (thin matt, gelatin-bromide enlarging papers recommended).
  • Reagents: sulphuric, acetic or citric acid solutions with concentrations selected by steel sulphur content (see Table 1 in the standard).
  • Fixing solution: commercial fixer or 15–20% sodium thiosulphate solution.
• Surface preparation & machining:
  • Clean, minimally cold-worked, ground surface (recommended surface roughness Rz/Ra guidance).
  • Avoid mirror finishes (paper slippage) and contamination (clean with alcohol/acetone).
• Procedure parameters:
  • Soak photographic paper in reagent (≈5 min), apply damp paper to test surface, remove bubbles, maintain firm contact.
  • Contact time typically 30 s to 10 min, depending on reagent and sulphur content.
  • Wash, fix, rinse and dry the print; usually only one usable print per ground surface unless regrinding.
• Result reporting: Include steel grade, cast number, surface position, reagent types/concentrations, and test result.
• Classification of prints: Positive, negative, central, dispersed and linear segregation patterns (informative Annex A).
• Caveats: Print darkness can be affected by steel chemistry (e.g., Ti > 0.1% can mask sulphides), surface condition and paper sensitivity.

Applications

• Quality control in steel mills and foundries to map sulphide inclusions and chemical segregation.
• Incoming inspection for bars, billets and forgings to identify regions for further testing or sampling.
• Forensic metallography to reveal porosity, cracks or segregation-related defects.
• Process optimization (melting, casting, rolling) by monitoring inclusion distribution. Users include metallurgists, QC engineers, inspection laboratories, foundries and steel fabricators seeking a low-cost, visual method to assess macro-inhomogeneities.

Related Standards (if applicable)

• ISO 4968:2022 contains no normative references; interpretation and acceptance criteria are normally defined in product standards or by special agreement between parties. For implementation, coordinate test parameters and acceptance criteria with applicable product or contractual standards.

Standards Content (Sample)

INTERNATIONAL ISO
STANDARD 4968
Second edition
2022-03
Steel — Macrographic examination by
sulphur print (Baumann method)
Reference number
© ISO 2022
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on
the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below
or ISO’s member body in the country of the requester.
ISO copyright office
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Phone: [phone]
Email: [e-mail]
Website: www.iso.org
Published in Switzerland
ii
Contents Page
Foreword .iv
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 General . 1
5 Principle and aim of the test .1
6 Test paper and reagents . 2
6.1 Photographic paper . 2
6.2 Reagents . 2
7 Fixing solution .2
8 Test piece . 3
9 Sampling . 3
10 Machining . 3
11 Procedure . 3
12 Test report . 4
Annex A (informative) Classification of sulphur print test results . 5
iii
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
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electrotechnical standardization.
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described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
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Any trade name used in this document is information given for the convenience of users and does not
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www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 17, Steel, Subcommittee SC 7, Methods of
testing (other than mechanical tests and chemical analysis).
This second edition cancels and replaces the first edition (ISO 4968:1979), which has been technically
revised.
The main changes are as follows:
— in the Scope, the applicable steels for this method are specified as from 0,005 % to 0,40 %, and this
method may also be applied to cast irons;
— type and concentration of recommended reagents have been explicitly specified for steels with
different sulphur content, respectively, to improve test effect and efficiency;
— method to remove extra acid solution and bubbles, and method to drain have been added in detail;
— classification of test results as positive segregation, negative segregation and central segregation,
with examples in Annex, has been added.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.
iv
INTERNATIONAL STANDARD ISO 4968:2022(E)
Steel — Macrographic examination by sulphur print
(Baumann method)
1 Scope
This document specifies a method (Baumann) for the macrographic examination of steel by means of
contact printing using silver salts and acid.
The method is applicable to steels of which the sulphur content is less than 0,40 %. This method can
also be applied to cast irons.
2 Normative references
There are no normative references in this document.
3 Terms and definitions
No terms and definitions are listed in this document.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
4 General
4.1 The sulphur print test is essentially a qualitative test. It is inadvisable to evaluate the sulphur
content of a given steel merely on the basis of its sulphur print.
4.2 Experience shows that the degree of darkening of the photo-sensitive emulsion is not always
in proportion to the quantity of sulphides present in the metal. Certain factors may influence the
macrographic attack to a greater or lesser extent; as examples, the following may be quoted:
— the chemical composition of the steel: the presence of certain elements modifies the type and shape
of the sulphides and consequently the appearance of the image obtained, for example concentrations
of titanium greater than 0,1 % give prints which do not reveal sulphides;
— the surface condition of the sample: the presence of surface cold working may alter the image
obtained;
— the sensitivity of the photographic paper.
4.3 The use of the test, and the conditions for interpreting the results observed, depend on the
particular case: details are laid down in product standards or shall be subject to special agreement.
5 Principle and aim of the test
5.1 The aim of macrographic examination by sulphur printing is to detect, by printing on photo-
sensitive papers previously soaked in acid, the position of areas containing sulphur inclusions found
in the metal in various chemical forms and with
...