ISO 23825:2020

Method for evaluating the nodularity of spheroidal carbides — Steels for cold heading and cold extruding

This document specifies a micrographic method based on comparison charts for determining the degree of spheroidisation of carbides after annealing of wire rod, wire or bars made of non-alloy and low alloy steels intended for cold heading and cold extrusion. The range of carbon content is up to 1,20 % C. In addition, Annex A includes a method based on machine vision for routine measurements.

Titre manque

General Information

• Status: Published
• Publication Date: 22-Dec-2020
• ICS: 77.140.10 - Heat-treatable steels
• Technical Committee: ISO/TC 17/SC 4 - Heat treatable and alloy steels
• Drafting Committee: ISO/TC 17/SC 4 - Heat treatable and alloy steels
• Current Stage: 6060 - International Standard published
• Start Date: 23-Dec-2020
• Due Date: 22-Jan-2022
• Completion Date: 23-Dec-2020

Standards Content (Sample)

INTERNATIONAL ISO
STANDARD 23825
First edition
2020-12
Method for evaluating the nodularity
of spheroidal carbides — Steels for
cold heading and cold extruding
Reference number
ISO 23825:2020(E)
©
ISO 2020

---------------------- Page: 1 ----------------------
ISO 23825:2020(E)

COPYRIGHT PROTECTED DOCUMENT
© ISO 2020
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
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: [phone]
Email: [e-mail]
Website: www.iso.org
Published in Switzerland
ii © ISO 2020 – All rights reserved

---------------------- Page: 2 ----------------------
ISO 23825:2020(E)

Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Sampling and sample preparation . 4
5 Evaluation . 4
5.1 General . 4
5.2 Evaluation methods . 4
6 Characterization of carbide particles by means of microscopic examination .5
6.1 Groups of steel grades and levels of spheroidisation . 5
6.2 Series of diagrams . 5
6.3 Procedure for carbide classification . 8
6.3.1 General. 8
6.3.2 Procedure . 8
7 Test report . 8
Annex A (informative) Automatised image processing for determining the level of carbide
spheroidisation .10
Bibliography .22
© ISO 2020 – All rights reserved iii

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ISO 23825:2020(E)

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
through ISO technical committees. Each member body interested in a subject for which a technical
committee has been established has the right to be represented on that committee. International
organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.
ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
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
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www .iso .org/ patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to the
World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT), see www .iso .org/
iso/ foreword .html.
This document was prepared by Technical Committee ISO/TC 17, Steel, Subcommittee SC 4, Heat
treatable and alloy steels.
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 © ISO 2020 – All rights reserved

---------------------- Page: 4 ----------------------
ISO 23825:2020(E)

Introduction
The nodularity of spheroidal carbide is an important characteristic of steel for cold heading or cold
extruding. However, the degree of spheroidization is assessed with reference to an agreed series of
standard images, which does not exist up-to-now as subject of an International standard. Thus, there
has been a continuing debate between supply and demand for the determination of the degree of
spheroidization.
This document specifies a test method for evaluating the degree of spheroidal carbide in CHQ wire
(Cold Heading Quality wire).
© ISO 2020 – All rights reserved v

---------------------- Page: 5 ----------------------
INTERNATIONAL STANDARD ISO 23825:2020(E)
Method for evaluating the nodularity of spheroidal
carbides — Steels for cold heading and cold extruding
1 Scope
This document specifies a micrographic method based on comparison charts for determining the degree
of spheroidisation of carbides after annealing of wire rod, wire or bars made of non-alloy and low alloy
steels intended for cold heading and cold extrusion. The range of carbon content is up to 1,20 % C.
In addition, Annex A includes a method based on machine vision for routine measurements.
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 (including any amendments) applies.
ISO 4954, Steels for cold heading and cold extruding
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at http:// www .electropedia .org/
3.1
maximum Féret diameter
maximum length of an object whatever its orientation, as shown in Figure 1
3.2
roundness
area of the carbide particle divided by the area of the circle whose diameter is the maximum Féret
diameter of the same carbide particle, calculated according to Formula (1):
2
Roundness = A/A = 4A/π⋅l (1)
m m
© ISO 2020 – All rights reserved 1

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ISO 23825:2020(E)

Figure 1 — Illustration of maximum Féret diameter of a carbide particle
where
l is the maximum Féret diameter of the carbide particle;
m
A is the area of the circle diameter lm;
m
A is the area of the carbide particle
3.3
area ratio
accepted/all objects area ratio and describes the relative amount of round objects on the image,
calculated according to Formula (2):
A
accepted
A%= (2)
AA+
()
accepted rejected
Note 1 to entry: Round (spheroidized) objects on real images are shown in Figure 2 in green colour (bright)
whereas rejected (non-round) objects are drawn in red colour (dark). From class 70 to class 90 the area ratio is
increased, so 90 class images contain relatively more round particles.
2 © ISO 2020 – All rights reserved

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ISO 23825:2020(E)

a) b)
Figure 2 — The ratio of accepted objects to rejected objects on (a) is less than on (b).
3.4
area mean and area standard deviation
objects mean area (A) with its standard deviation (σ ) describe the particle distribution (see Figure 3)
A
and when considering the particle size from class 70 % to class 90 %, the frequency of inclusions of
large particles increases
3.5
spheroidite
characteristic soft microstructure consisting of sphere-like globular cementite particles within a
ferrite matrix
Note 1 to entry: see ISO 4885, 3.190.
Note 2 to entry: Carbide particles classified as globular carbide with roundness ≥0,75 to 1,00.
3.6
spheroidizing
annealing just below the A1 temperature of steels with long soaking time to bring the carbides in the
form of spheroids
Note 1 to entry: see ISO 4885, 3.191
3.7
nodularity
assessment of the proportion of spheroidal carbide particles in a CHQ Wire (Cold Heading Quality wire)
sample, generally expressed as a percentage
© ISO 2020 – All rights reserved 3

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ISO 23825:2020(E)

a) b)
Figure 3 — Round objects area distribution for two different classes
4 Sampling and sample preparation
Sampling and sample preparation are conducted according to ISO 4954. Sampling shall be carried out in
such a way that the samples are characteristic of the respective delivery.
2
The microsection per test piece to be examined shall have a size of 100 mm , if possible and practicable.
Its position in the cross or longitudinal microsection can differ depending on requirements and should
be left to the discretion of the manufacturer.
The test pieces shall be ground and polished. They should be etched in a suitable way, normally with a
2 % Picric acid solution (2 % C H N O in C H OH).
6 3 3 7 2 5
Attention should be paid to a good metallographic preparation to ensure that the microstructure is not
altered.
5 Evaluation
5.1 General
To characterize the carbide particles observed, information is generally necessary on the nodularity,
the roundness and the distribution of the carbide particles.
5.2 Evaluation methods
This document characterises carbide particles by series of standard images. For routine measurements
other methods can be preferred, especially examination by automatized image processing. An example
for the automatized image processing is given in Annex A.
In case of dispute, however, the reference method for the characterisation of carbide particles is done
by a comparision of images of a test piece under a microscop with a series of standard images.
4 © ISO 2020 – All rights reserved

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ISO 23825:2020(E)

6 Characterization of carbide particles by means of microscopic examination
6.1 Groups of steel grades and levels of spheroidisation
The volume of carbides depends principally on the carbon content. Other alloying elements of cold
heading steel grades have minor influence. The steel grades are classified as presented in Table 1.
Table 1 — Groups of steel grades
Groups of steel grades Carbon content
1 ≤0,10
2 >0,10 ≤0,25
3 >0,25 ≤0,40
4 >0,40 ≤0,80
5 >0,80 ≤1,20
The spheroidisation is characterised as percentage. Partial spheroidisation is for instance ≥70 % and
optimal spheroidisation is for instance between 90 % and 100 %. For the spheroidisation four different
levels are defined as shown in Table 2.
Table 2 — Different levels of spheroidisation
Abbreviation for Level of Microstructure level
Characteristic
the level Spheroidisation (Example of heat treatement)
0 S around 0 % initial structure not soft annealed/not annealed
on spheroidized carbides
70 70 %
...

INTERNATIONAL ISO
STANDARD 23825
First edition
Method for evaluating the nodularity
of spheroidal carbides — Steels for
cold heading and cold extruding
PROOF/ÉPREUVE
Reference number
ISO 23825:2020(E)
©
ISO 2020

---------------------- Page: 1 ----------------------
ISO 23825:2020(E)

COPYRIGHT PROTECTED DOCUMENT
© ISO 2020
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
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: [phone]
Email: [e-mail]
Website: www.iso.org
Published in Switzerland
ii PROOF/ÉPREUVE © ISO 2020 – All rights reserved

---------------------- Page: 2 ----------------------
ISO 23825:2020(E)

Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Sampling and sample preparation . 4
5 Evaluation . 4
5.1 General . 4
5.2 Evaluation methods . 4
6 Characterization of carbide particles by means of microscopic examination .5
6.1 Groups of steel grades and levels of spheroidisation . 5
6.2 Series of diagrams . 5
6.3 Procedure for carbide classification . 8
6.3.1 General. 8
6.3.2 Procedure . 8
7 Test report . 8
Annex A (informative) Automatised image processing for determining the level of carbide
spheroidisation .10
Bibliography .22
© ISO 2020 – All rights reserved PROOF/ÉPREUVE iii

---------------------- Page: 3 ----------------------
ISO 23825:2020(E)

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
through ISO technical committees. Each member body interested in a subject for which a technical
committee has been established has the right to be represented on that committee. International
organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.
ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
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
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www .iso .org/ patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to the
World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT), see www .iso .org/
iso/ foreword .html.
This document was prepared by Technical Committee ISO/TC 17, Steel, Subcommittee SC 4, Heat
treatable and alloy steels.
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 PROOF/ÉPREUVE © ISO 2020 – All rights reserved

---------------------- Page: 4 ----------------------
ISO 23825:2020(E)

Introduction
The nodularity of spheroidal carbide is an important characteristic of steel for cold heading or cold
extruding. However, the degree of spheroidization should be assessed with reference to an agreed
series of standard images, which does not exist up-to-now as subject of an International standard. Thus,
there has been a continuing debate between supply and demand for the determination of the degree of
spheroidization.
This document specifies a test method for evaluating the degree of spheroidal carbide in CHQ wire
(Cold Heading Quality wire).
© ISO 2020 – All rights reserved PROOF/ÉPREUVE v

---------------------- Page: 5 ----------------------
INTERNATIONAL STANDARD ISO 23825:2020(E)
Method for evaluating the nodularity of spheroidal
carbides — Steels for cold heading and cold extruding
1 Scope
This document specifies a micrographic method based on comparison charts for determining the degree
of spheroidisation of carbides after annealing of wire rod, wire or bars made of non-alloy and low alloy
steels intended for cold heading and cold extrusion. The range of carbon content is up to 1,20 % C.
In addition, Annex A includes a method based on machine vision for routine measurements.
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 (including any amendments) applies.
ISO 4954, Steels for cold heading and cold extruding
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at http:// www .electropedia .org/
3.1
maximum Féret diameter
maximum length of an object whatever its orientation, as shown in Figure 1
3.2
roundness
area of the carbide particle divided by the area of the circle whose diameter is the maximum Féret
diameter of the same carbide particle, calculated according to Formula (1):
2
Roundness = A/A = 4A/π⋅l (1)
m m
© ISO 2020 – All rights reserved PROOF/ÉPREUVE 1

---------------------- Page: 6 ----------------------
ISO 23825:2020(E)

Figure 1 — Illustration of maximum Féret diameter of a carbide particle
where
l is the maximum Féret diameter of the carbide particle;
m
A is the area of the circle diameter lm;
m
A is the area of the carbide particle
3.3
Area ratio
accepted/all objects area ratio and describes the relative amount of round objects on the image,
calculated according to Formula (2):
A
accepted
A%= (2)
AA+
()
accepted rejected
Note 1 to entry: Round (spheroidized) objects on real images are shown in Figure 2 in green colour (bright)
whereas rejected (non-round) objects are drawn in red colour (dark). From class 70 to class 90 the area ratio is
increased, so 90 class images contain relatively more round particles.
2 PROOF/ÉPREUVE © ISO 2020 – All rights reserved

---------------------- Page: 7 ----------------------
ISO 23825:2020(E)

a) b)
Figure 2 — The ratio of accepted objects to rejected objects on (a) is less than on (b).
3.4
area mean and area standard deviation
objects mean area (A) with its standard deviation (σ ) describe the particle distribution (see Figure 3)
A
and when considering the particle size from class 70 % to class 90 %, the frequency of inclusions of
large particles increases
3.5
spheroidite
characteristic soft microstructure consisting of sphere-like globular cementite particles within a
ferrite matrix
Note 1 to entry: see ISO 4885, 3.190.
Note 2 to entry: Carbide particles classified as globular carbide with roundness ≥0,75 to 1,00.
3.6
spheroidizing
annealing just below the A1 temperature of steels with long soaking time to bring the carbides in the
form of spheroids
Note 1 to entry: see ISO 4885, 3.191
3.7
nodularity
assessment of the proportion of spheroidal carbide particles in a CHQ Wire (Cold Heading Quality wire)
sample, generally expressed as a percentage
© ISO 2020 – All rights reserved PROOF/ÉPREUVE 3

---------------------- Page: 8 ----------------------
ISO 23825:2020(E)

a) b)
Figure 3 — Round objects area distribution for two different classes
4 Sampling and sample preparation
Sampling and sample preparation are conducted according to ISO 4954. Sampling shall be carried out in
such a way that the samples are characteristic of the respective delivery.
2
The microsection per test piece to be examined shall have a size of 100 mm , if possible and practicable.
Its position in the cross or longitudinal microsection can differ depending on requirements and should
be left to the discretion of the manufacturer.
The test pieces shall be ground and polished. They should be etched in a suitable way, normally with a
2 % Picric acid solution (2 % C H N O in C H OH).
6 3 3 7 2 5
Attention should be paid to a good metallographic preparation to ensure that the microstructure is not
altered.
5 Evaluation
5.1 General
To characterize the carbide particles observed, information is generally necessary on the nodularity,
the roundness and the distribution of the carbide particles.
5.2 Evaluation methods
This standard characterises carbide particles by series of standard images. For routine measurements
other methods can be preferred, especially examination by automatized image processing. An example
for the automatized image processing is given in Annex A.
In case of dispute, however, the reference method for the characterisation of carbide particles is done
by a comparision of images of a test piece under a microscop with a series of standard images.
4 PROOF/ÉPREUVE © ISO 2020 – All rights reserved

---------------------- Page: 9 ----------------------
ISO 23825:2020(E)

6 Characterization of carbide particles by means of microscopic examination
6.1 Groups of steel grades and levels of spheroidisation
The volume of carbides depends principally on the carbon content. Other alloying elements of cold
heading steel grades have minor influence. The steel grades are classified as presented in Table 1.
Table 1 — Groups of steel grades
Groups of steel grades Carbon content
1 ≤0,10
2 >0,10 ≤0,25
3 >0,25 ≤0,40
4 >0,40 ≤0,80
5 >0,80 ≤1,20
The spheroidisation is characterised as percentage. Partial spheroidisation is for instance ≥70 % and
optimal spheroidisation is for instance between 90 % and 100 %. For the spheroidisation four different
levels are defined as shown in Table 2.
Table 2 — Different levels of spheroidisation
Abbreviation for Level of Microstructure level
Characteristic
the level Spheroidisation (Example of heat treatement)
0 S around 0 % initial structure not soft annealed/not annealed
on spheroidized carbides
70 70 % ≤ S < 80 % partial globularisation Spheroidisation of more than
...