EN ISO 6508-3:2023

SLOVENSKI STANDARD
01-april-2024
Kovinski materiali - Preskus trdote po Rockwellu - 3. del: Umerjanje primerjalnih
ploščic (ISO 6508-3:2023)
Metallic materials - Rockwell hardness test - Part 3: Calibration of reference blocks (ISO
6508-3:2023)
Metallische Werkstoffe - Härteprüfung nach Rockwell - Teil 3: Kalibrierung von
Härtevergleichsplatten (ISO 6508-3:2023)
Matériaux métalliques - Essai de dureté Rockwell - Partie 3: Étalonnage des blocs de
référence (ISO 6508-3:2023)
Ta slovenski standard je istoveten z: EN ISO 6508-3:2023
ICS:
77.040.10 Mehansko preskušanje kovin Mechanical testing of metals
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EN ISO 6508-3
EUROPEAN STANDARD
NORME EUROPÉENNE
December 2023
EUROPÄISCHE NORM
ICS 77.040.10 Supersedes EN ISO 6508-3:2015
English Version
Metallic materials - Rockwell hardness test - Part 3:
Calibration of reference blocks (ISO 6508-3:2023)
Matériaux métalliques - Essai de dureté Rockwell - Metallische Werkstoffe - Härteprüfung nach Rockwell -
Partie 3: Étalonnage des blocs de référence (ISO 6508- Teil 3: Kalibrierung von Härtevergleichsplatten (ISO
3:2023) 6508-3:2023)
This European Standard was approved by CEN on 13 November 2023.

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
© 2023 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 6508-3:2023 E
worldwide for CEN national Members.

Contents Page
European foreword . 3

European foreword
This document (EN ISO 6508-3:2023) has been prepared by Technical Committee ISO/TC 164
"Mechanical testing of metals" 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 June 2024, and conflicting national standards shall be
withdrawn at the latest by June 2024.
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 6508-3:2015.
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 6508-3:2023 has been approved by CEN as EN ISO 6508-3:2023 without any
modification.
INTERNATIONAL ISO
STANDARD 6508-3
Fourth edition
2023-12
Metallic materials — Rockwell
hardness test —
Part 3:
Calibration of reference blocks
Matériaux métalliques — Essai de dureté Rockwell —
Partie 3: Étalonnage des blocs de référence
Reference number
ISO 6508-3:2023(E)
ISO 6508-3:2023(E)
© ISO 2023
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 6508-3:2023(E)
Contents Page
Foreword .iv
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Manufacture of reference blocks . 1
5 Calibration machine and calibration indenter . 2
5.1 General . 2
5.2 Direct verification of the calibration machine . 2
5.3 Calibration diamond indenter . 3
5.4 Calibration ball indenter . 4
5.5 Performance verification of the calibration machine and indenter . 5
6 Reference block calibration procedure . 6
7 Number of indentations . 7
8 Uniformity of hardness . 7
9 Marking . . 8
10 Calibration certificate .8
11 Validity . 8
Annex A (informative) Uniformity of reference blocks . 9
Annex B (informative) Uncertainty of the mean hardness value of hardness-reference
blocks .11
Annex C (normative) Requirements for reference diamond indenters .16
Annex D (normative) Control verification of the calibration machine .17
Bibliography .18
iii
ISO 6508-3:2023(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 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 164, Mechanical testing of metals,
Subcommittee SC 3, Hardness testing, in collaboration with the European Committee for Standardization
(CEN) Technical Committee CEN/TC 459, ECISS - European Committee for Iron and Steel Standardization,
in accordance with the Agreement on technical cooperation between ISO and CEN (Vienna Agreement).
This fourth edition cancels and replaces the third edition (ISO 6508-3:2015), which has been technically
revised.
The main changes are as follows:
— removed all statements of requirements, permissions, and recommendations from the Scope of the
document (Clause 1);
— addition of Clause 3, Terms and definitions;
— modification of the requirements for the calibration and verification of the machine and indenter
(Clause 5);
— added a performance verification for the calibration machine and indenter (Clause 5);
— added a requirement to conduct a control verification prior to the calibration of reference blocks
(Clause 6);
— added a normative Annex D for the control verification of the calibration machine (Annex D).
A list of all parts in the ISO 6508 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
INTERNATIONAL STANDARD ISO 6508-3:2023(E)
Metallic materials — Rockwell hardness test —
Part 3:
Calibration of reference blocks
1 Scope
This document specifies a method for the calibration of reference blocks to be used for the indirect
and daily verification of Rockwell hardness testing machines and indenters, as specified in ISO 6508-2.
This document also specifies requirements for Rockwell machines and indenters used for calibrating
reference blocks and specifies methods for their calibration and verification.
Attention is drawn to the fact that the use of hard metal for ball indenters is considered to be the
standard type of Rockwell indenter ball.
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 376, Metallic materials — Calibration of force-proving instruments used for the verification of uniaxial
testing machines
ISO 6508-1:2023, Metallic materials — Rockwell hardness test — Part 1: Test method
ISO 6508-2:2023, Metallic materials — Rockwell hardness test — Part 2: Verification and calibration of
testing machines and indenters
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 Manufacture of reference blocks
4.1 The block shall be specially manufactured for use as a hardness-reference block.
NOTE Attention is drawn to the need to use a manufacturing process, which will give the necessary
homogeneity, stability of structure, and uniformity of surface hardness.
4.2 Each hardness reference block shall be of a thickness not less than 6 mm. To minimize the effect
of hardness change with increasing number of indents, thicker blocks should be used.
4.3 The reference blocks shall be free of magnetism. It is recommended that the manufacturer
ensures that the blocks, if made of steel, have been demagnetized at the end of the manufacturing
process (before calibration).
ISO 6508-3:2023(E)
4.4 The deviation from surface flatness of the top and bottom surfaces shall be ≤0,01 mm. The bottom
of the blocks shall not be convex. The deviation from parallelism of the top and bottom surfaces shall
be ≤0,02 mm per 50 mm.
4.5 The test surface and bottom surface shall be free from damage, such as notches, scratches, oxide
layers, etc., which can interfere with the measurement of the indentations. The surface roughness,
Ra, shall not exceed 0,3 µm for the test surface and 0,8 µm for the bottom surface. Sampling length is
l = 0,8 mm (see ISO 4287:1997, 3.1.9).
4.6 To verify that no material is subsequently removed from the reference block, the thickness at the
time of calibration shall be marked on it, to the nearest 0,1 mm, or an identifying mark shall be made on
the test surface [see 9.1 e)].
5 Calibration machine and calibration indenter
5.1 General
5.1.1 Calibrations and verifications of Rockwell calibration machines and calibration indenters shall
be carried out at a temperature of (23 ± 5) °C.
5.1.2 The instruments used for calibration and verification shall be traceable to national standards.
5.2 Direct verification of the calibration machine
5.2.1 In addition to fulfilling the conditions in ISO 6508-2:2023, Clause 4, the calibration machine
shall also meet the requirements given in 5.2.2, 5.2.3, 5.2.4, 5.2.5, 5.2.6 and 5.2.7 determined by the
procedures specified in ISO 6508-2:2023, Clause 5.
5.2.2 The machine shall be directly verified annually, not to exceed 13 months. Direct verification
involves calibration and verification of the following:
a) test force;
b) measuring system;
c) testing cycle; if this is not possible, at least the force versus time behaviour.
d) machine hysteresis test.
5.2.3 The test force shall be measured by means of an elastic proving device (according to ISO 376)
class 0,5 or better and calibrated for reversibility, or by another method having the same or better
accuracy.
Evidence should be available to demonstrate that the output of the force-proving device does not vary
by more than 0,1 % in a period of 1 s to 30 s, following a stepped change in force.
5.2.4 Each test force shall be measured and shall agree with the nominal preliminary test force, F , to
within ±0,2 % and the nominal total test force, F, to within ±0,1 %.
5.2.5 The measuring system shall have a resolution of ±0,000 1 mm and a maximum expanded
uncertainty of 0,000 2 mm, when calculated with a confidence level of 95 % over its working range.
5.2.6 The testing cycle shall be timed with an uncertainty less than ±0,5 s and shall conform to the
testing cycle of Clause 6.
ISO 6508-3:2023(E)
5.2.7 The average of the last three tests when evaluating the hysteresis of the calibration machine
shall indicate a hardness number of (130 ± 0,5) Rockwell units when the regular Rockwell ball scales B,
E, F, G, H, and K are used, or within (100 ± 0,5) Rockwell units when any other Rockwell scale is used.
5.3 Calibration diamond indenter
5.3.1 The geometric shape and performance of calibration diamond indenters shall be calibrated as
specified below. Direct verification of the geometric shape shall be made before first use. The condition
of the diamond shall be checked at frequent intervals using appropriate optical devices (microscope,
magnifying glass, etc.) as specified in ISO 6508-1:2023, Annex F.
Verification of the indenter performance, as specified in 5.3.3, shall be made before first use and
annually, not to exceed 13 months.
5.3.2 The diamond indenter shall be measured on at least eight unique axial section planes equidistant
from each other (e.g. the eight cross-sections will be spaced approximately 22,5° apart at 0°, 22,5°, 45°,
67,5°, 90°, 112,5°, 135°, 157,5°), and shall meet the following requirements.
a) The cone angle shall be measured adjacent to the blend. The diamond cone shall have a mean
included angle of (120 ± 0,1)°. In each measured axial section, the included angle shall be
(120 ± 0,17)°.
b) The mean deviation from straightness of the generatrix of the diamond cone adjacent to the blend
shall not exceed 0,000 5 mm over a minimum length of 0,4 mm. In each measured section, the
deviation shall not exceed 0,000 7 mm.
c) The radius of the spherical tip of the diamond shall be measured adjacent to the blend. The tip shall
have a mean radius of (0,200 ± 0,005) mm. In each measured section, the radius shall be within
(0,200 ± 0,007) mm and local deviations from a true radius shall not exceed 0,002 mm.
NOTE The tip of the diamond indenter is usually not truly spherical, but often varies in radius across
its surface. Depending on the crystallographic orientation of the diamond stone with respect to the indenter
axis, diamond tends to preferentially polish away more easily or with more difficulty at the tip, producing
an increasingly flat or sharp surface in the central indenter axis region. The sphericity of the diamond tip
can be better evaluated by measuring multiple measurement windows of varying width. The measurement
window would be bounded by widths measured along a line normal to the indenter axis. For example, the
following window sizes can be evaluated:
— between ±80 µm from the indenter axis;
— between ±60 µm from the indenter axis;
— between ±40 µm from the indenter axis.
d) The surfaces of the cone and the spherical tip shall blend in a smooth tangential manner. The
location where the spherical tip and the cone of the diamond blend together will vary depending on
the values of the tip radius and cone angle. Ideally for a perfect indenter geometry, the blend point
is located at 100 µm from the indenter axis measured along a line normal to the indenter axis. To
avoid including the blend area in the measurement of the tip radius and cone angle, the portion of
the diamond surface between 90 µm and 110 µm should be ignored.
e) The inclination of the axis of the diamond cone to the axis of the indenter holder (normal to the
seating surface) shall be within 0,3°.
5.3.3 Calibration diamond indenters shall be performance verified by performing comparison tests
with reference diamond indenter(s) that meet the requirements of Annex C. Calibration diamond
indenters can be verified for use on either regular or superficial Rockwell diamond scales or both. The
test blocks used for the comparison testing shall meet the requirements of Clause 4 and be calibrated at
the hardness levels given in Table 1, Table 2, Table 3, or Table 4, depending on the scales for which the
indenter is verified. The testing shall be carried out in accordance with ISO 6508-1.
ISO 6508-3:2023(E)
NOTE The alternate hardness levels given in Table 2 are provided to accommodate indenters calibrated to
other International Standards. It is believed that calibrations conducted to Table 1 or Table 2 will yield equivalent
results.
For each block, the mean hardness value of three indentations made using the calibration diamond
indenter to be verified shall not differ from the mean hardness value of three indentations obtained
with a reference diamond indenter by more than ±0,4 Rockwell units. The indentations made with
the calibration diamond indenter to be verified and with the reference diamond indenter should be
adjacent.
Table 1 — Hardness levels for indenters to be used for calibrating Rockwell regular and
superficial scale test blocks (A, C, D, and N)
Nominal hard-
Scale Ranges
ness
HRC 23 20 to 26
HRC 55 52 to 58
HR45N 43 40 to 46
HR15N 91 88 to 94
Table 2 — Alternate hardness levels for indenters to be used for calibrating Rockwell regular
and superficial scale test blocks (A, C, D, and N)
Nominal hard-
Scale Ranges
ness
HRC 25 22 to 28
HRC 63 60 to 65
HR30N 64 60 to 69
HR15N 91 88 to 94
Table 3 — Hardness levels for indenters to be used for calibrating Rockwell regular scale test
blocks only (A, C, and D)
Nominal hard-
Scale Ranges
ness
HRC 25 22 to 28
HRC 45 42 to 50
HRC 63 60 to 65
HRA 81 78 to 84
Table 4 — Hardness levels for indenters to be used for calibrating Rockwell superficial scale
test blocks only (N)
Nominal hard-
Scale Ranges
ness
HR15N 91 88 to 94
HR30N 64 60 to 69
HR30N 46 42 to 50
HR45N 25 22 to 29
5.4 Calibration ball indenter
5.4.1 The calibration tungsten carbide composite ball shall be replaced at a frequency no greater
than 13 months.
ISO 6508-3:2023(E)
5.4.2 Calibration tungsten carbide composite balls shall meet the requirements of ISO 6508-2, with
the exception of the following tolerances for the ball diameter:
— ±0,002 mm for the ball of diameter 1,587 5 mm;
— ±0,003 mm for the ball of diameter 3,175 mm.
5.5 Performance verification of the calibration machine and ind
...