SIST EN ISO 18203:2026

SLOVENSKI STANDARD
01-april-2026
Jekla - Določanje debeline površinsko utrjenih plasti (ISO 18203:2026)
Steel - Determination of the thickness of surface-hardened layers (ISO 18203:2026)
Stahl - Bestimmung der Dicke gehärteter Randschichten (ISO 18203:2026)
Acier - Détermination de l'épaisseur des couches durcies superficielles (ISO
18203:2026)
Ta slovenski standard je istoveten z: EN ISO 18203:2026
ICS:
77.040.99 Druge metode za Other methods of testing of
preskušanje kovin metals
77.080.20 Jekla Steels
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EN ISO 18203
EUROPEAN STANDARD
NORME EUROPÉENNE
February 2026
EUROPÄISCHE NORM
ICS 77.040.99 Supersedes EN ISO 18203:2022
English Version
Steel - Determination of the thickness of surface-hardened
layers (ISO 18203:2026)
Acier - Détermination de l'épaisseur des couches Stahl - Bestimmung der Dicke gehärteter
durcies superficielles (ISO 18203:2026) Randschichten (ISO 18203:2026)
This European Standard was approved by CEN on 12 January 2026.

CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this
European Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references
concerning such national standards may be obtained on application to the CEN-CENELEC Management Centre or to any CEN
member.
This European Standard exists in three official versions (English, French, German). A version in any other language made by
translation under the responsibility of a CEN member into its own language and notified to the CEN-CENELEC Management
Centre has the same status as the official versions.

CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,
Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway,
Poland, Portugal, Republic of North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Türkiye and
United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION

EUROPÄISCHES KOMITEE FÜR NORMUNG

CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels
© 2026 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 18203:2026 E
worldwide for CEN national Members.

Contents Page
European foreword . 3

European foreword
This document (EN ISO 18203:2026) has been prepared by Technical Committee ISO/TC 17 "Steel" in
collaboration with Technical Committee CEN/TC 459/SC 1 “Test methods for steel (other than chemical
analysis)” the secretariat of which is held by AFNOR.
This European Standard shall be given the status of a national standard, either by publication of an
identical text or by endorsement, at the latest by August 2026, and conflicting national standards shall
be withdrawn at the latest by August 2026.
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CEN shall not be held responsible for identifying any or all such patent rights.
This document supersedes EN ISO 18203:2022.
Any feedback and questions on this document should be directed to the users’ national standards
body/national committee. A complete listing of these bodies can be found on the CEN website.
According to the CEN-CENELEC Internal Regulations, the national standards organizations of the
following countries are bound to implement this European Standard: Austria, Belgium, Bulgaria,
Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland,
Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Republic of
North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Türkiye and the
United Kingdom.
Endorsement notice
The text of ISO 18203:2026 has been approved by CEN as EN ISO 18203:2026 without any modification.

International
Standard
ISO 18203
Second edition
Steel — Determination of the
2026-01
thickness of surface-hardened
layers
Acier — Détermination de l'épaisseur des couches durcies
superficielles
Reference number
ISO 18203:2026(en) © ISO 2026
ISO 18203:2026(en)
© ISO 2026
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
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii
ISO 18203:2026(en)
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Symbols, abbreviated terms and designations . 3
5 Principle . 4
6 Apparatus . 4
7 Test specimen . 4
7.1 General .4
7.2 Measurement capability . .4
7.3 Preparation of the surface to be examined .5
8 Method of measurement . 6
8.1 CHD, SHD and NHD by hardness measurement .6
8.2 THD by hardness measurement .7
8.3 THD by microscopic measurement .7
9 Evaluation of the results . 8
9.1 Case hardening depth (CHD), surface hardening depth (SHD) and nitriding hardness
depth (NHD) .8
9.2 Total thickness of surface hardening depth (THD) .9
10 Test report . 9
Annex A (normative) Interpolation method for determining the case hardening depth (CHD) –
surface hardening depth (SHD) – nitriding hardness depth (NHD) .11
Bibliography .13

iii
ISO 18203:2026(en)
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).
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, Subcommittee SC 7, Methods of
testing (other than mechanical tests and chemical analysis), in collaboration with the European Committee
for Standardization (CEN) Technical Committee CEN/TC 459/SC 1, Test methods for steel (other than chemical
analysis), in accordance with the Agreement on technical cooperation between ISO and CEN (Vienna
Agreement).
This second edition cancels and replaces the first edition (ISO 18203:2016), which has been technically
revised.
The main changes are as follows:
— removal of the reference to shot peening;
— removal of the compound layer thickness (CLT);
— introduction of standard test loads for the determination of hardness depths, and the procedure for
measurements in the event of arbitration;
— extension of Table 1 by Rockwell test methods;
— extension of Table 2 by further abbreviations;
— precise definition of how the core hardness shall be tested;
— determination of the edge distance of the first hardness impression from the edge;
— explanation of how to determine the total thickness of surface hardening depth THD.
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 18203:2026(en)
Introduction
There are several ways of creating a surface-hardened layer in steel, but the measurement of its thickness
follows the same principle, regardless of the chemical composition or heat treatment of the sample. This
document presents the basic principle of determining the thickness of surface-hardened layers as well as the
differences particular to the different methods of creating the surface-hardened layer.
No method of estimating uncertainty is presented in this document. As real applications of this procedure
accrue, the need may arise to address this topic in future revisions.

v
International Standard ISO 18203:2026(en)
Steel — Determination of the thickness of surface-hardened
layers
1 Scope
This document specifies a method of measuring the case hardening depth, surface hardening depth,
nitriding hardness depth and total thickness of surface hardening depth obtained using, e.g. thermal
(flame and induction hardening, electron beam hardening, laser beam hardening, etc.) or thermochemical
(carbonitriding, carburizing and hardening, hardening and nitriding, etc.) treatment.
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 4545-2, Metallic materials — Knoop hardness test — Part 2: Verification and calibration of testing machines
ISO 6507-1, Metallic materials — Vickers hardness test — Part 1: Test method
ISO 6507-2, Metallic materials — Vickers hardness test — Part 2: Verification and calibration of testing machines
3 Terms and definitions
For the purposes of this document, the following terms and definitions 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
case hardening depth
CHD
perpendicular distance between the surface and the layer having a hardness of 550 HV or equivalent Knoop
hardness of 550 HK
Note 1 to entry: For steels which present a hardness higher than 450 HV at a distance three times of the case hardening
depth (determined with a limiting hardness value of 550 HV in accordance with ISO 6507-1 or equivalent Knoop
hardness of 550 HK in accordance with ISO 4545-1) from the surface, a limiting hardness value higher than 550 HV, in
steps of 25 units, can be selected for the determination of the case hardening depth by agreement between interested
parties.
Note 2 to entry: To measure the core hardness, five individual hardness measurements should be made, and the
average value of these measurements should be taken. To determine the depth for the core hardness measurement,
use three times the upper value of the case depth tolerance.
04,
EXAMPLE CHD 10, = depth for core hardness 4,2 mm. If this is not geometrically possible (e.g. in case the
0
workpiece is too thin), separate agreements can be made to specify the core hardness check position. The core
hardness is only determined once for several hardness curves and is taken for all hardness curves measured on the
sample.
ISO 18203:2026(en)
Note 3 to entry: In general, case hardening consists of carburizing or carbonitriding followed by quench hardening
(see ISO 4885).
Note 4 to entry: A distinction shall be made between the case hardening hardness depth CHD in the case-hardened
condition only and the CHD in the case-hardened and tempered condition. This shall be noted in the report. If the
surface hardness after tempering is so tolerated that the rule of the distance of 100 HV between core hardness and
limit hardness cannot be complied, separate agreements shall be made for this.
3.2
surface hardening depth
SHD
distance between the surface and the layer where HV is equal to the value specified by the term “hardness
limit”
Note 1 to entry: Recommended hardness limit values are listed in Table 1.
Table 1 — Recommended hardness limit values of SHD
Minimum surface hardness in HV, HRC, HRA or HRN
Hardness limit
HV
HV HRC HRA HR15N HR30N HR45N
250 300 to 330 30 to 33 65 to 67 75, 76 51 to 53 32 to 35
275 335 to 355 34 to 36 68 77, 78 54, 55 36 to 38
300 360 to 385 37 to 39 69, 70 79 56 to 58 39 to 41
325 390 to 420 40 to 42 71 80, 81 58 to 62 42 to 46
350 425 to 455 43 to 45 72, 73 82, 83 63, 64 47 to 49
375 460 to 480 46, 47 74 84 65, 66 50 to 52
400 485 to 515 48 to 50 75 85 67, 68 53, 54
425 520 to 545 51, 52 76 86 69, 70 55 to 57
450 550 to 575 53 77 87 71 58, 59
475 580 to 605 54, 55 78 89 72, 73 60, 61
500 610 to 635 56, 57 79 - 74 62, 63
525 640 to 665 58 80 90 75, 76 64, 65
550 670 to 705 59, 60 81 - 77 66, 67
575 710 to 730 61 82 91 78 68
600 735 to 765 62 - - 79 69
625 770 to 795 63 83 92 80 70
650 800 to 835 64, 65 - - 81 71, 72
675 840 to 865 66 84 - 82 73
This table shall not be used as a table of comparison of hardness values.
In ISO 15787 it is noted that Vickers hardness values are ending with 5 or 0, and Rockwell values with a full number. See ISO
15787:2016, Figures 2 to 39.
Note 2 to entry: Hardness limit is a function of the minimum surface hardness required for the part, given by the
following Formula (1):
H = A × H (1)
L msh
where
H is the hardness limit;
L
A is a coefficient (usually 0,8);
H is the minimum surface hardness (lowest value of the tolerance).
msh
ISO 18203:2026(en)
If the required minimum surface hardness is not specified, the parties involved shall agree on the limit hardness to be
used.
Note 3 to entry: 0,80 is usually used for A. Other values can be applied.
Note 4 to
...