EN ISO 6508-2:2023
(Main)Metallic materials - Rockwell hardness test - Part 2: Verification and calibration of testing machines and indenters (ISO 6508-2:2023)
Metallic materials - Rockwell hardness test - Part 2: Verification and calibration of testing machines and indenters (ISO 6508-2:2023)
This document specifies two separate methods of verification of testing machines (direct and indirect) for determining Rockwell hardness in accordance with ISO 6508-1, together with a method for verifying Rockwell hardness indenters.
The direct verification method is used to determine whether the main parameters associated with the machine function, such as applied force, depth measurement, and testing cycle timing, fall within specified tolerances. The indirect verification method uses a number of calibrated reference hardness blocks to determine how well the machine can measure a material of known hardness.
This document is applicable to stationary and portable hardness testing machines.
Attention is drawn to the fact that the use of tungsten carbide composite for ball indenters is considered to be the standard type of Rockwell indenter ball.
Metallische Werkstoffe - Härteprüfung nach Rockwell - Teil 2: Überprüfung und Kalibrierung der Prüfmaschinen und Eindringkörper (ISO 6508-2:2023)
Dieses Dokument legt zwei unterschiedliche Verfahren für die Überprüfung von Härteprüfmaschinen (direkt und indirekt) zur Bestimmung der Rockwellhärte nach ISO 6508 1 in Verbindung mit einem Verfahren für die Überprüfung von Rockwell-Härteeindringkörpern fest.
Die direkte Überprüfung wird angewendet, um festzustellen, ob die Hauptparameter der Maschinenfunktion, wie z. B. die aufgebrachte Kraft, die Eindringtiefenmessung und die zeitliche Steuerung der Prüfzyklen, die festgelegten Grenzabweichungen einhalten. Bei der indirekten Überprüfung wird eine Reihe von kalibrierten Härtevergleichsplatten verwendet, um festzustellen, wie gut die Prüfmaschine, einen Werkstoff bekannter Härte messen kann.
Dieses Dokument ist auf ortsfeste und tragbare Härteprüfmaschinen anwendbar.
Es ist zu beachten, dass als Normeindringkugel für die Rockwell-Prüfung nur solche aus Wolframcarbidgemisch gelten.
Matériaux métalliques - Essai de dureté Rockwell - Partie 2: Vérification et étalonnage des machines d'essai et des pénétrateurs (ISO 6508-2:2023)
Le présent document spécifie deux méthodes séparées de vérification des machines d'essai (directe et indirecte) pour la détermination de la dureté Rockwell selon l’ISO 6508-1, de même qu’une méthode de vérification des pénétrateurs de dureté Rockwell.
La méthode de vérification directe est utilisée pour déterminer si les principaux paramètres associés aux fonctions de la machine, telles que la force appliquée, le mesurage de l’enfoncement et le phasage du cycle d’essai, se situent dans les tolérances spécifiées. La méthode de vérification indirecte utilise un certain nombre de blocs de dureté de référence étalonnés pour déterminer avec quelle exactitude la machine peut mesurer un matériau de dureté connue.
Le présent document est applicable aux machines d'essai de dureté fixes et portables.
L’attention est attirée sur le fait que l’utilisation d’un composite en carbure de tungstène pour les pénétrateurs à bille est considérée être le type courant de bille de pénétrateur Rockwell.
Kovinski materiali - Preskus trdote po Rockwellu - 2. del: Preverjanje in umerjanje naprav za preskušanje (ISO 6508-2:2023)
Ta dokument določa dve ločeni metodi za preverjanje naprav za preskušanje (neposredna in posredna)
za določanje trdote po Rockwellu v skladu s standardom ISO 6508-1 skupaj z metodo za preverjanje
vtisnih teles za preskušanje trdote po Rockwellu.
Metoda neposrednega preverjanja se uporablja za določanje, ali so glavni parametri, povezani z
delovanjem stroja, npr. uporabljena sila, merjenje globine in čas preskusnega cikla, znotraj
dovoljenih toleranc. Pri posredni metodi preverjanja se uporabi določeno število
umerjenih ploščic referenčne trdote, s katerimi se preveri, kako natančno lahko naprava izmeri material z znano trdoto.
Ta dokument se uporablja za nepremične in premične naprave za preskušanje trdote.
Opozoriti je treba, da se za standardno vrsto vtisne krogle po Rockwellu šteje kroglično vtisno telo
iz kompozita volframovega karbida.
General Information
Relations
Standards Content (Sample)
SLOVENSKI STANDARD
01-marec-2024
Kovinski materiali - Preskus trdote po Rockwellu - 2. del: Preverjanje in umerjanje
naprav za preskušanje (ISO 6508-2:2023)
Metallic materials - Rockwell hardness test - Part 2: Verification and calibration of testing
machines and indenters (ISO 6508-2:2023)
Metallische Werkstoffe - Härteprüfung nach Rockwell - Teil 2: Überprüfung und
Kalibrierung der Prüfmaschinen und Eindringkörper (ISO 6508-2:2023)
Matériaux métalliques - Essai de dureté Rockwell - Partie 2: Vérification et étalonnage
des machines d'essai et des pénétrateurs (ISO 6508-2:2023)
Ta slovenski standard je istoveten z: EN ISO 6508-2:2023
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 6508-2
EUROPEAN STANDARD
NORME EUROPÉENNE
December 2023
EUROPÄISCHE NORM
ICS 77.040.10 Supersedes EN ISO 6508-2:2015
English Version
Metallic materials - Rockwell hardness test - Part 2:
Verification and calibration of testing machines and
indenters (ISO 6508-2:2023)
Matériaux métalliques - Essai de dureté Rockwell - Metallische Werkstoffe - Härteprüfung nach Rockwell -
Partie 2: Vérification et étalonnage des machines Teil 2: Überprüfung und Kalibrierung der
d'essai et des pénétrateurs (ISO 6508-2:2023) Prüfmaschinen und Eindringkörper (ISO 6508-2:2023)
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 6508-2:2023 E
worldwide for CEN national Members.
Contents Page
European foreword . 3
European foreword
This document (EN ISO 6508-2:2023) 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 6508-2:2015.
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 6508-2:2023 has been approved by CEN as EN ISO 6508-2:2023 without any
modification.
INTERNATIONAL ISO
STANDARD 6508-2
Fourth edition
2023-12
Metallic materials — Rockwell
hardness test —
Part 2:
Verification and calibration of testing
machines and indenters
Matériaux métalliques — Essai de dureté Rockwell —
Partie 2: Vérification et étalonnage des machines d'essai et des
pénétrateurs
Reference number
ISO 6508-2:2023(E)
ISO 6508-2:2023(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 6508-2:2023(E)
Contents Page
Foreword .iv
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 General conditions .1
5 Direct verification of the testing machine . 2
5.1 General . 2
5.2 Calibration and verification of the test force . 2
5.3 Calibration and verification of the depth-measuring system . 3
5.4 Calibration and verification of the testing cycle . 4
5.5 Calibration and verification of the machine hysteresis . 4
6 Indirect verification of the testing machine . 4
6.1 General . 4
6.2 Procedure . 4
6.3 Repeatability . 5
6.4 Bias . 7
6.5 Uncertainty of measurement . 7
7 Calibration and verification of Rockwell hardness indenters . 7
7.1 General . 7
7.2 Diamond indenter . 7
7.2.1 General . 7
7.2.2 Direct calibration and verification of the diamond indenter . 7
7.2.3 Indirect verification of diamond indenters . 8
7.3 Ball indenter . 9
7.3.1 Direct calibration and verification of the ball indenter . 10
7.3.2 Indirect verification of the ball holder assembly . . 10
7.4 Marking . 11
8 Intervals between direct and indirect calibrations and verifications .11
9 Verification report .12
Annex A (normative) Repeatability of testing machines .13
Annex B (informative) Uncertainty of measurement of the calibration results of the
hardness testing machine .15
Bibliography .23
iii
ISO 6508-2:2023(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 6508-2:2015), 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 force and depth
measuring systems (Clause 4);
— added a requirement for the hardness of the indenter ball holder (Clause 6);
— changed the layout of Table 8 (Clause 6);
— modified the requirements for direct and indirect calibration and verification (Clause 7);
— modified the information related to the determination of uncertainty of measurement (Annex B).
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 6508-2:2023(E)
Metallic materials — Rockwell hardness test —
Part 2:
Verification and calibration of testing machines and
indenters
1 Scope
This document specifies two separate methods of verification of testing machines (direct and indirect)
for determining Rockwell hardness in accordance with ISO 6508-1, together with a method for verifying
Rockwell hardness indenters.
The direct verification method is used to determine whether the main parameters associated with
the machine function, such as applied force, depth measurement, and testing cycle timing, fall within
specified tolerances. The indirect verification method uses a number of calibrated reference hardness
blocks to determine how well the machine can measure a material of known hardness.
This document is applicable to stationary and portable hardness testing machines.
Attention is drawn to the fact that the use of tungsten carbide composite 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 6507-1, Metallic materials — Vickers hardness test — Part 1: Test method
ISO 6508-1, Metallic materials — Rockwell hardness test — Part 1: Test method
ISO 6508-3, Metallic materials — Rockwell hardness test — Part 3: Calibration of reference blocks
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 conditions
Before a Rockwell hardness testing machine is verified, the machine shall be checked to ensure that it is
properly set up and operating in accordance with the manufacturer's instructions.
ISO 6508-2:2023(E)
Especially, it should be checked that the test force can be applied and removed without shock, vibration,
or overload and in such a manner that the readings are not influenced.
5 Direct verification of the testing machine
5.1 General
5.1.1 Direct verification involves calibration and verification of the following:
a) test forces;
b) depth-measuring system;
c) testing cycle;
d) machine hysteresis test.
5.1.2 Direct verification should be carried out at a temperature of (23 ± 5) °C. If the verification is
made outside of this temperature range, this shall be reported in the verification report.
5.1.3 The instruments used for calibration shall be traceable to national standards.
5.1.4 An indirect verification according to Clause 6 shall be performed following a successful direct
verification.
5.2 Calibration and verification of the test force
5.2.1 Each preliminary test force, F , (see 5.2.4) and each total test force, F, used (see 5.2.5) shall be
measured, and, whenever applicable, this shall be done at not less than three positions of the plunger
spaced throughout its range of movement during testing. For testing machine designs where the force
is not influenced by the position of the plunger, e.g. controlled loading systems with closed-loop control,
the test force can be calibrated in one position. The preliminary test force shall be held for at least 2 s.
5.2.2 Three readings shall be taken for each force at each position of the plunger. Immediately before
each reading is taken, the plunger shall be moved in the same direction as during testing.
5.2.3 The forces shall be measured by one of the following two methods:
— by means of a force-proving device according to ISO 376 class 1 or better and calibrated for
reversibility;
— by balancing against a force, accurate to ±0,2 %, applied by means of calibrated masses or by another
method having the same accuracy.
Evidence should be available to demonstrate that the output of the force-proving device does not vary
by more than 0,2 % in the period 1 s to 30 s following a stepped change in force.
5.2.4 A relative error value, expressed as a percentage, shall be calculated for each measured force by
the general Formula (1):
FF−
ij, RS
ΔF =×100 (1)
rel,,ij
F
RS
where ΔF is the relative error of each force measurement value, F , (whether it is a preliminary
rel,ij, i,j
force value, F , or the total force value, F) with respect to the reference force value, F , to be measured.
0 RS
ISO 6508-2:2023(E)
The indices i and j of the force measurement value, F indicate the j-th force measurement at the i-th
i,j
plunger height position.
5.2.5 The maximum permissible relative error on each measurement of the preliminary test force, F ,
(before application and after removal of the additional test force, F ) as calculated by Formula (1) shall
be ±2,0 %. The range of all force measurements (highest value minus lowest value) at each measurement
position shall be ≤ 1,5 % of F .
5.2.6 The maximum permissible relative error on each measurement of the total test force, F, as
calculated by Formula (1), shall be ±1,0 %. The range of the force measurements (highest value minus
lowest value) shall be ≤ 0,75 % of F.
5.3 Calibration and verification of the depth-measuring system
5.3.1 The depth-measuring system shall be calibrated by making known incremental movements of
the indenter or the indenter holder.
5.3.2 The instrument or gauge blocks used to verify the depth-measuring system shall have a
maximum expanded uncertainty of 0,000 3 mm when calculated with a 95 % confidence level.
NOTE The use of gauge blocks to verify the depth measuring system may not be appropriate for all types of
Rockwell hardness machines.
5.3.3 Calibrate the testing machine’s depth measurement system at not less than four evenly spaced
intervals covering the full range of the normal working depth for the required scales to be calibrated in
the testing machine. Three cycles of depth readings shall be taken over the evenly spaced intervals of
the depth measuring system.
NOTE The maximum depth required for each scale is different, ranging from 0,25 mm for Rockwell regular
scale B to 0,04 mm for Rockwell superficial scale 15N.
5.3.4 Some testing machines have a long-stroke depth measuring system where the location of the
working range of the depth measuring system varies to suit the sample. This type of testing machine
shall be able to electronically verify that the depth measuring device is continuous over the full range.
These types of testers shall be verified using the following steps:
a) at the approximate top, midpoint and bottom of the total stroke of the measuring device, verify the
depth measurement system at no less than four evenly spaced intervals of approximately 0,05 mm
at each of the three locations;
b) operate the actuator over its full range of travel to monitor whether the displacement measurement
is continuous. The displacement indication shall be continuously indicated over the full range.
5.3.5 Calculate the difference, ΔL , between each depth measurement value, L and the reference
i,j i,j
value of the calibration device, L , in accordance with the general Formula (2):
RS
ΔLL=−L (2)
ij,,ij RS
The indices i and j of the depth measurement value, L indicate the j-th depth measurement at the i-th
i,j
interval of the depth measuring system.
The depth-measuring system shall correctly indicate within ±0,001 mm for the scales A to K and
within ±0,000 5 mm for scales N and T, i.e. within ±0,5 of a scale unit, over each range.
ISO 6508-2:2023(E)
5.4 Calibration and verification of the testing cycle
5.4.1 The testing cycle is to be calibrated by the testing machine manufacturer at the time of
manufacture and when the testing machine undergoes repair which may have affected the testing
cycle. Calibration of the complete testing cycle is not required as part of the direct verification at other
times, see Table 10.
5.4.2 The testing cycle shall conform to the testing cycle specified in ISO 6508-1.
5.4.3 For testing machines that automatically control the testing cycle, the measurement uncertainty
(k = 2) of the timing instrument used to verify the testing cycle shall not exceed 0,2 s. It is recommended
that the measured times for the testing cycle, plus or minus the measurement uncertainty (k = 2) of the
calibration measurements, not exceed the timing limits specified in ISO 6508-1.
5.4.4 For testing machines that require the user to manually control the testing cycle, the testing
machine shall be verified to be capable of achieving the specified testing cycle.
5.5 Calibration and verification of the machine hysteresis
5.5.1 The machine shall be checked to ensure that the readings are not affected by a hysteresial
flexure of testing machine components (e.g. frame, specimen holder, etc.) during a test. The influence
of any hysteresis behaviour shall be checked by making repeated hardness tests using a spherical
indenter of at least 10 mm diameter, bearing directly against the specimen holder or through a spacer
such that no permanent deformation occurs. A parallel block placed between the indenter holder and
the specimen holder may be used instead of a blunt indenter. The material of the blunt indenter and of
the spacer or parallel block shall have a hardness of at least 60 HRC.
5.5.2 Perform repeated Rockwell tests using the setup specified in 5.5.1. The tests shall be conducted
using the Rockwell scale with the highest test force that is used during normal testing. Repeat the
hysteresis verification procedure for a maximum of 10 measurements and average the last three tests.
5.5.3 The average of the last three tests shall indicate a hardness number of (130 ± 1,0) Rockwell
units when the regular Rockwell ball scales B, E, F, G, H, and K are used, or within (100 ± 1,0) Rockwell
units when any other Rockwell scale is used.
6 Indirect verification of the testing machine
6.1 General
6.1.1 Indirect verification involves the calibration and verification of the testing machine by
performing tests on reference blocks.
6.1.2 Indirect verification should be carried out at a temperature of (23 ± 5) °C by means of reference
blocks calibrated in accordance with ISO 6508-3. If the verification is made outside of this temperature
range, this shall be reported in the verification report.
6.2 Procedure
6.2.1 For the indirect verification of a testing machine, the following procedures shall be applied.
The testing machine shall be verified for each scale for which it will be used. For each scale to be
verified, reference blocks from each of the hardness ranges given in Table 1 shall be used. The hardness
ISO 6508-2:2023(E)
values of the blocks shall be chosen to approximate the limits of the intended use. It is recommended to
perform the same test cycle used when the reference blocks were calibrated.
Only the calibrated surfaces of the test blocks are to be used for testing.
6.2.2 On each reference block, a minimum of five indentations, made in accordance with ISO 6508-1,
shall be uniformly distributed over the test surface and each hardness number observed to a resolution
of no greater than 0,2 HR of a scale unit. Before making these indentations, at least two preliminary
indentations shall be made to ensure that the machine is working freely and that the reference block, the
indenter, and the specimen holder are seating correctly. The results of these preliminary indentations
shall be ignored.
Table 1 — Hardness ranges for different scales
Rockwell hardness Hardness range of reference Rockwell hardness Hardness range of reference
scale block scale block
A 20 to 40 HRA K 40 to 60 HRKW
45 to 75 HRA 65 to 80 HRKW
80 to 95 HRA 85 to 100 HRKW
B 10 to 50 HRBW 15N 70 to 77 HR15N
60 to 80 HRBW 78 to 88 HR15N
85 to 100 HRBW 89 to 94 HR15N
C 10 to 30 HRC 30N 42 to 54 HR30N
35 to 55 HRC 55 to 73 HR30N
60 to 70 HRC 74 to 86 HR30N
D 40 to 47 HRD 45N 20 to 31 HR45N
55 to 63 HRD 32 to 61 HR45N
70 to 77 HRD 63 to 77 HR45N
E 70 to 77 HREW 15T 67 to 80 HR15TW
84 to 90 HREW 81 to 87 HR15TW
93 to 100 HREW 88 to 93 HR15TW
F 60 to 75 HRFW 30T 29 to 56 HR30TW
80 to 90 HRFW 57 to 69 HR30TW
94 to 100 HRFW 70 to 82 HR30TW
G 30 to 50 HRGW 45T 10 to 33 HR45TW
55 to 75 HRGW 34 to 54 HR45TW
80 to 94 HRGW 55 to 72 HR45TW
H 80 to 94 HRHW
96 to 100 HRHW
6.3 Repeatability
6.3.1 For each reference block, let H , H , H , H ,….H be the values of the measured hardness
1 2 3 4 n
arranged in increasing order of magnitude.
The repeatability range, r, of the testing machine in Rockwell units, under the particular verification
conditions, is determined by Formula (3):
rH=−H (3)
n 1
ISO 6508-2:2023(E)
The mean hardness value of all indentations H is defined according to Formula (4):
HH++HH++.+H
12 34 n
H= (4)
n
where
H , H , H , H ,…. H are the hardness values corresponding to all the indentations;
1 2 3 4 n
n is the total number of indentations.
6.3.2 The repeatability range of the testing machine being verified shall be considered satisfactory if
it satisfies the conditions given in Table 2. Permissible repeatability is presented graphically in Annex A,
Figures A.1 and A.2.
Table 2 — Permissible repeatability range and bias of the testing machine
Permissible bias Permissible repeatability
Rockwell hardness Hardness range of
a
Rockwell units range of the testing machine
scale the reference block
b r
A 20 to 75 HRA ±2 HRA
≤ 0,02 (100 − H ) or
> 75 to 95 HRA ±1,5 HRA b
0,8 HRA Rockwell units
B 10 to 45 HRBW ±4 HRBW
≤ 0,04 (130 − H )
> 45 to 80 HRBW ±3 HRBW
HRBW Rockwell units
> 80 to 100 HRBW ±2 HRBW
C 10 to 70 HRC ±1,5 HRC
≤ 0,02 (100 − H ) or
b
0,8 HRC Rockwell units
D 40 to 70 HRD ±2 HRD
≤ 0,02 (100 − H ) or
> 70 to 77 HRD ±1,5 HRD b
0,8 HRD Rockwell units
E 70 to 90 HREW ±2,5 HREW
≤ 0,04 (130 − H )
> 90 to 100 HREW ±2 HREW
HREW Rockwell units
F 60 to 90 HRFW ±3 HRFW
≤ 0,04 (130 − H )
> 90 to 100 HRFW ±2 HRFW
HRFW Rockwell units
G 30 to 50 HRGW ±6 HRGW
≤ 0,04 (130 − H )
> 50 to 75 HRGW ±4,5 HRGW
HRGW Rockwell units
> 75 to 94 HRGW ±3 HRGW
H 80 to 100 HRHW ±2 HRHW
≤ 0,04 (130 − H )
HRHW Rockwell units
K 40 to 60 HRKW ±4 HRKW
≤ 0,04 (130 − H )
> 60 to 80 HRKW ±3 HRKW
HRKW Rockwell units
> 80 to 100 HRKW ±2 HRKW
15N, 30N, 45N All ranges ±2 HRN
≤ 0,04 (100 − H ) or
b
1,2 HRN Rockwell units
15T, 30T, 45T All ranges ±3 HRTW
≤ 0,06 (100 − H ) or
b
2,4 HRTW Rockwell units
a
H is the mean hardness value.
b
The one with a greater value becomes the permissible repeatability range of the testing machine.
NOTE The requirements for permissible repeatability range, r, and/or permissible bias, b, might be different in
ASTM E 18.
ISO 6508-2:2023(E)
6.4 Bias
6.4.1 The bias, b, of the testing machine in Rockwell units, under the particular calibration conditions,
is expressed by the following Formula (5):
bH=−H (5)
CRM
where
is the mean hardness value, from Formula (4);
H
H is the certified hardness of the reference block used.
CRM
6.4.2 The bias of the testing machine shall not exceed the values given in Table 2.
6.5 Uncertainty of measurement
A method to determine the uncertainty of measurement of the calibration results of the hardness
testing machines is given in Annex B.
7 Calibration and verification of Rockwell hardness indenters
7.1 General
7.1.1 Indenter calibrations and verifications should be carried out at a temperature of (23 ± 5) °C.
If the verification is made outside of this temperature range, this shall be reported in the verification
report.
7.1.2 The instruments used for calibration and verifications shall be traceable to national standards.
7.2 Diamond indenter
7.2.1 General
To verify the reliable performance of the spheroconical diamond indenter in conformance with this
document, a direct and an indirect calibration and verification shall be carried out on each indenter.
7.2.2 Direct calibration and verification of the diamond indenter
7.2.2.1 The surfaces of the diamond cone and spherical tip shall be polished for a penetration depth of
0,3 mm and s
...
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