ISO/FDIS 4948-1

ISO/DISFDIS 4948-1
ISO/TC 17
Secretariat: JISC
Date: 2026-06-2908-12
Steels — Classification —
Part 1:
Classification of steels based on chemical composition
Acier — Classification —
Partie 1: Classification des aciers en fonction de leur composition chimique
DISFDIS stage
VVVVVVototototototiiiiiinnnnnngggggg b b b b b beeeeeeggggggiiiiiinnnnnnssssss on on on on on on::::::   222222000000222222555555------111111222222------000000888888
VVVVVVooooootintintintintintingggggg te te te te te termrmrmrmrmrmiiiiiinnnnnnaaaaaatetetetetetessssss o o o o o onnnnnn:::::: 2 2 2 2 2 2000000222222666666------000000333333------000000222222

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: + 41 22 749 01 11
E-mail: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii
Contents
Foreword . iv
Introduction . v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Classification by chemical composition . 3
4.1 General. 3
4.2 Non-alloy steel . 3
4.3 Low-alloy steel . 5
4.4 High-alloy steel . 8
Bibliography . 9

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 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 document 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).
ISO draws attention to the possibility that the implementation of this document may involve the use of (a)
patent(s). ISO takes no position concerning the evidence, validity or applicability of any claimed patent rights
in respect thereof. As of the date of publication of this document, ISO had not received notice of (a) patent(s)
which may be required to implement this document. However, implementers are cautioned that this may not
represent the latest information, which may be obtained from the patent database available at
www.iso.org/patents.ISO shall not be held responsible for identifying any or all such patent rights.
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.
This second edition cancels and replaces the first edition (ISO 4948-1:1982), which has been technically
revised.
The main changes are as follows:
— the main classes of steels based on chemical compositions arehave been identified as: a) non-alloy steels,
b) low-alloy steels and c) high-alloy steels;
— micro-alloy steels have been included in this document.
A list of all parts in the ISO 4948 series can be found on the ISO website.
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
Introduction
There are around 70,000 types of steel grades worldwide. Steel consumers deal with this diversity differently
than steel manufacturers. Consumers may wonder how to select the right material for their purposes and what
properties it must have. Manufacturers want to sell their products and be identifiable.
The development of steel technology—from production to various applications—has made enormous
progress over the past 50 years. Micro-alloy steels are now the largest group worldwide. Many groups, such
as high-strength low-alloy steels, bake-hardening steels, maraging steels, and TRIP steels, have been
developed. Better properties of steel products, such as strength, toughness, and formability, enable lighter and
more sustainable solutions.
The classification of steel grades has a long history. First Europeans began doing so in the 1940s, and the
International Standard ISO 4849 was published in 1982. The need for an updated classification standard is
obvious especially due to the ambiguity of the word alloy steels. According to the definition of alloy steels in
ISO 4948-1:1982, stainless steels are also alloy steels, buthowever many standards instead use the term alloy
steel in the meaning of alloy steel but not a stainless or high alloy steel.
This standarddocument can be used not only by the steel industry, but also by a large group of steel users,
designers, students, researchers, and authorities.
v
Steels — Classification —
Part 1:
Classification of steels based on chemical composition
1 Scope
This document specifies the definition and classification of steels. It classifies the steel grades as main criteria
by the chemical composition into non-alloy, low-alloy and high-alloy steels.
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 4885, Ferrous materials — Heat treatments — Vocabulary
ISO 6306, Chemical analysis of steel — Order of listing elements in steel standards
ISO 6929, Steel products — Vocabulary
ISO 15510:2014, Stainless steels — Chemical composition
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 4885, ISO 6929, ISO 15510:2014 as
well as the following apply.
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/
3.1
steel
material which contains by mass more iron than any other single element, having a carbon content generally
less than 2 % and containing other elements
Note 1 to entry: The presence of large quantities of carbide-forming elements can modify the upper limit of the carbon
content, but 2 % is the usual dividing line between steel and cast iron, e.g. a limited number of chromium steels may
contain more than 2% of carbon.
[1]
Note 2 to entry: This definition is similar to the definition in ISO 4885 .
Note 3 to entry: Other elements and substances may be existing or added into steel for different reasons: a) to improve
the steel making process such as de-oxidation, castability and rolling; b) to remove detrimental elements resulting from
raw materials such as phosphorus and sulphur; c) to improve the properties of steel products such as strength, toughness,
hardenability, formability, weldability, corrosion and wear resistance.
Note 4 to entry: If producing steel based on recycled raw materials, some residual elements are practically impossible to
remove such as: Cu, Ni, Co.
Note 5 to entry: If the amount of alloying elements exceeds the iron content, the material is defined as Ni-based alloy or
Co-based alloy.
3.2
non-alloy steel
steels where no alloying elements are intentionally added
Note 1 to entry: The use of additions aimed to deoxidation or to guarantee the castability or to guarantee other steel
making processes and performances is allowed.
Note 2 to entry: Residual elements from raw material and/or process equipment can exist in non-alloy steels.
3.3
alloy steel
steels where alloying elements are intentionally added
Note 1 to entry: Alloy steels are low-alloy and high-alloy steels.
Note 2 to entry: In daily practice and in standards the term alloy steel is mostly used for low-alloy steels.
3.4
low-alloy steel
steels where alloying elements are intentionally added, but with a content of any alloying element less than
5,0 % and with a total content of alloying elements of less than 8,0 %
Note 1 to entry: Additions for deoxidation, castability and/or for other steel making processes and performances shall
not be considered for alloying.
3.4.1
micro-alloy steel
steels in which at least one of the following elements is specified niobium, vanadium, titanium, zirconium,
boron and lanthanides and in which alloying elements are not exceeding certain levels
Note 1 to entry: These elements are used to refine the grain microstructure and/or to facilitate precipitation and/or
increase hardenability in quench hardening.
Note 2 to entry: Micro-alloying technology is used in a variety of applications and some applications are relatively new.
Microalloying technology is not restricted to any class of steel.
Note 3 to entry: Micro-alloy steel for construction purposes is introduced in this document as part and subgroup of low-
alloy steel
3.5
high-alloy steel
steels with a content of any alloying element equal to or greater than 5,0 % or with a total content of alloying
elements of equal to or greater 8,0 % and for the upper limit the amount of one alloying element shall not
exceed the iron content, otherwise the material is defined according to the main element, i.e. nickel or cobalt
base alloy
Note 1 to entry: High-alloy steels include, for example, stainless steels, other corrosion and heat resistant steels and
partly also tool and bearing steels.
3.5.1
stainless steel
high-alloy steels with at least 10,5 % (mass fraction) Cr and maximum 1,2 % (mass fraction) C
[2]
[SOURCE: ISO 15510:2014 ISO 15510:2014,, 3.1]
4 Classification by chemical composition
4.1 General
4.1.1 Steels are divided into non-alloy, low-alloy and high-alloy steels, see Figure 1. Classification is based
on the cast analysis specified in the product standard or specification.
NOTE For this document, all the % values for the chemical composition are % by mass.

Figure 1 — Classification of steels according to chemical composition
4.1.2 Classification is determined by the minimum value specified for each element. If the content for an
alloying element i
...