Metallic materials - Vickers hardness test - Part 2: Verification and calibration of testing machines (ISO 6507-2:2018)

This document specifies a method of verification and calibration of testing machines and diagonal
measuring system for determining Vickers hardness in accordance with ISO 6507-1.
A direct method of verification and calibration is specified for the testing machine, indenter and the
diagonal length measuring system. An indirect verification method using reference blocks is specified
for the overall checking of the machine.
If a testing machine is also to be used for other methods of hardness testing, it shall be verified
independently for each method.
This document is also applicable to portable hardness testing machines but not applicable to hardness
testing machines based on different measurement principles, e.g. ultrasonic impedance method.

Metallische Werkstoffe - Härteprüfung nach Vickers - Teil 2: Überprüfung und Kalibrierung der Prüfmaschinen (ISO 6507-2:2018)

Dieses Dokument legt ein Verfahren für die Überprüfung und Kalibrierung von Härteprüfmaschinen und Diagonalmesssystemen zur Bestimmung der Vickers-Härte nach ISO 6507 1 fest.
Für die Überprüfung und Kalibrierung der Prüfmaschine, des Eindringkörpers und des Diagonalmesssystems wird ein direktes Verfahren festgelegt. Für die allgemeine Überprüfung der Maschine wird ein indirektes Überprüfungsverfahren unter Verwendung von Härtevergleichsplatten festgelegt.
Wird eine Prüfmaschine auch für andere Härteprüfverfahren verwendet, muss sie unabhängig für jedes Verfahren überprüft werden.
Dieses Dokument ist auch auf tragbare Härteprüfgeräte anwendbar, jedoch nicht auf Härteprüfmaschinen auf Grundlage von verschiedenen Messgrundsätzen, z. B. Ultraschall-Impedanzverfahren.

Matériaux métalliques - Essai de dureté Vickers - Partie 2: Vérification et étalonnage des machines d'essai (ISO 6507-2:2018)

L'ISO 6507-2:2018 spécifie une méthode de vérification des machines d'essai et des systèmes de mesure de diagonale utilisées pour la détermination de la dureté Vickers conformément à l'ISO 6507‑1.
Une méthode directe de vérification et d'étalonnage est spécifiée pour la machine d'essais, le pénétrateur et le système de mesure de la longueur de la diagonale. Une méthode de vérification indirecte à l'aide de blocs de référence est spécifiée pour la vérification globale de la machine.
Si une machine d'essai est également utilisée pour d'autres méthodes d'essai de dureté, elle doit être vérifiée indépendamment pour chaque méthode.
L'ISO 6507-2:2018 est également applicable aux machines d'essai de dureté portables mais n'est pas applicable aux machines d'essai de dureté basées sur des principes de mesure différents, par exemple une méthode d'impédance ultrasonore.

Kovinski materiali - Preskus trdote po Vickersu - 2. del: Preverjanje in umerjanje naprav za preskušanje (ISO 6507-2:2018)

Ta dokument določa metodo za preverjanje in umerjanje preskuševalnih naprav in sistema za merjenje diagonale za določanje trdote po Vickersu v skladu s standardom ISO 6507-1.
Določa neposredno metodo za preverjanje in umerjanje naprave za preskušanje, preskusne konice in sistema za merjenje dolžine diagonale. Za splošno pregledovanje naprave določa posredno metodo preverjanja z uporabo primerjalnih ploščic.
Če se naprava za preskušanje uporablja tudi za druge metode preskusa trdote, jo je treba preveriti posebej za vsako metodo.
Ta dokument se uporablja tudi za prenosne naprave za preskušanje trdote, vendar pa se ne uporablja za naprave za preskušanje trdote, ki temeljijo na drugih načelih merjenja, npr. na metodi ultrazvočne impedance.

General Information

Status
Published
Public Enquiry End Date
03-Oct-2016
Publication Date
07-May-2018
Current Stage
6060 - National Implementation/Publication (Adopted Project)
Start Date
15-Mar-2018
Due Date
20-May-2018
Completion Date
08-May-2018

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SLOVENSKI STANDARD
SIST EN ISO 6507-2:2018
01-julij-2018
1DGRPHãþD
SIST EN ISO 6507-2:2006

Kovinski materiali - Preskus trdote po Vickersu - 2. del: Preverjanje in umerjanje

naprav za preskušanje (ISO 6507-2:2018)

Metallic materials - Vickers hardness test - Part 2: Verification and calibration of testing

machines (ISO 6507-2:2018)
Metallische Werkstoffe - Härteprüfung nach Vickers - Teil 2: Überprüfung und
Kalibrierung der Prüfmaschinen (ISO 6507-2:2018)

Matériaux métalliques - Essai de dureté Vickers - Partie 2: Vérification et étalonnage des

machines d'essai (ISO 6507-2:2018)
Ta slovenski standard je istoveten z: EN ISO 6507-2:2018
ICS:
77.040.10 Mehansko preskušanje kovin Mechanical testing of metals
SIST EN ISO 6507-2:2018 en,fr,de

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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SIST EN ISO 6507-2:2018
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SIST EN ISO 6507-2:2018
EN ISO 6507-2
EUROPEAN STANDARD
NORME EUROPÉENNE
March 2018
EUROPÄISCHE NORM
ICS 77.040.10 Supersedes EN ISO 6507-2:2005
English Version
Metallic materials - Vickers hardness test - Part 2:
Verification and calibration of testing machines (ISO 6507-
2:2018)

Matériaux métalliques - Essai de dureté Vickers - Partie Metallische Werkstoffe - Härteprüfung nach Vickers -

2: Vérification et étalonnage des machines d'essai (ISO Teil 2: Überprüfung und Kalibrierung der

6507-2:2018) Prüfmaschinen (ISO 6507-2:2018)
This European Standard was approved by CEN on 18 January 2018.

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, Former Yugoslav Republic of Macedonia, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania,

Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland,

Turkey 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

© 2018 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 6507-2:2018 E

worldwide for CEN national Members.
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SIST EN ISO 6507-2:2018
EN ISO 6507-2:2018 (E)
Contents Page

European foreword ....................................................................................................................................................... 3

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SIST EN ISO 6507-2:2018
EN ISO 6507-2:2018 (E)
European foreword

This document (EN ISO 6507-2:2018) has been prepared by Technical Committee ISO/TC 164

“Mechanical testing of metals” in collaboration with Technical Committee ECISS/TC 101 “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 September 2018, and conflicting national standards

shall be withdrawn at the latest by September 2018.

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 6507-2:2005.

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, Former Yugoslav Republic of Macedonia,

France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta,

Netherlands, Norway, Poland, Portugal, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland,

Turkey and the United Kingdom.
Endorsement notice

The text of ISO 6507-2:2018 has been approved by CEN as EN ISO 6507-2:2018 without any

modification.
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SIST EN ISO 6507-2:2018
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SIST EN ISO 6507-2:2018
INTERNATIONAL ISO
STANDARD 6507-2
Fourth edition
2018-01
Metallic materials — Vickers
hardness test —
Part 2:
Verification and calibration of testing
machines
Matériaux métalliques — Essai de dureté Vickers —
Partie 2: Vérification et étalonnage des machines d'essai
Reference number
ISO 6507-2:2018(E)
ISO 2018
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SIST EN ISO 6507-2:2018
ISO 6507-2:2018(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2018

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, Switzerland
Tel. +41 22 749 01 11
Fax +41 22 749 09 47
copyright@iso.org
www.iso.org
Published in Switzerland
ii © ISO 2018 – All rights reserved
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SIST EN ISO 6507-2:2018
ISO 6507-2:2018(E)
Contents Page

Foreword ........................................................................................................................................................................................................................................iv

1 Scope ................................................................................................................................................................................................................................. 1

2 Normative references ...................................................................................................................................................................................... 1

3 Terms and definitions ..................................................................................................................................................................................... 1

4 General conditions ............................................................................................................................................................................................. 1

5 Direct verification ............................................................................................................................................................................................... 2

5.1 General ........................................................................................................................................................................................................... 2

5.2 Calibration of the test force .......................................................................................................................................................... 2

5.3 Verification of the indenter .......................................................................................................................................................... 3

5.4 Calibration and verification of the diagonal measuring system ................................................................... 4

5.5 Verification of the testing cycle ................................................................................................................................................. 5

5.6 Uncertainty of calibration/verification ............................................................................................................................. 5

6 Indirect verification .......................................................................................................................................................................................... 5

6.1 General ........................................................................................................................................................................................................... 5

6.2 Test force and hardness levels ................................................................................................................................................... 5

6.3 Measurement of reference indentation ............................................................................................................................. 6

6.4 Number of indentations .................................................................................................................................................................. 6

6.5 Verification result ................................................................................................................................................................................. 6

6.6 Repeatability ............................................................................................................................................................................................. 6

6.7 Bias .................................................................................................................................................................................................................... 6

6.8 Uncertainty of calibration/verification ............................................................................................................................. 7

7 Intervals between verifications ............................................................................................................................................................ 7

8 Verification report/calibration certificate ................................................................................................................................ 7

8.1 Vickers testing machine .................................................................................................................................................................. 7

8.2 Vickers indenter ..................................................................................................................................................................................... 8

Annex A (informative) Uncertainty of the calibration results of the hardness testing system ................9

Bibliography .............................................................................................................................................................................................................................18

© ISO 2018 – All rights reserved iii
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SIST EN ISO 6507-2:2018
ISO 6507-2:2018(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 on 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 the following

URL: 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.

This fourth edition cancels and replaces the third edition (ISO 6507-2:2005), which has been technically

revised.
The main changes compared to the previous edition are as follows:
— all references of indentation diagonals, <0,020 mm, have been removed;

— requirements for the calibration and verification of the measuring system have been revised;

— requirements for the maximum permissible error in measuring a reference indentation have been

revised;

— recommendations for inspection and monitoring of the indenter have been moved to ISO 6507-1;

— requirements have been added to the test report for reporting the hardness values of reference

blocks used;
— Annex A has been revised.
A list of all parts in the ISO 6507 series can be found on the ISO website.
iv © ISO 2018 – All rights reserved
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SIST EN ISO 6507-2:2018
INTERNATIONAL STANDARD ISO 6507-2:2018(E)
Metallic materials — Vickers hardness test —
Part 2:
Verification and calibration of testing machines
1 Scope

This document specifies a method of verification and calibration of testing machines and diagonal

measuring system for determining Vickers hardness in accordance with ISO 6507-1.

A direct method of verification and calibration is specified for the testing machine, indenter and the

diagonal length measuring system. An indirect verification method using reference blocks is specified

for the overall checking of the machine.

If a testing machine is also to be used for other methods of hardness testing, it shall be verified

independently for each method.

This document is also applicable to portable hardness testing machines but not applicable to hardness

testing machines based on different measurement principles, e.g. ultrasonic impedance method.

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 6507-3, Metallic materials — Vickers 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 terminological databases for use in standardization at the following addresses:

— IEC Electropedia: available at http://www.electropedia.org/
— ISO Online browsing platform: available at https://www.iso.org/obp
4 General conditions

Before a Vickers hardness testing machine is verified, the machine shall be checked to ensure that it is

properly set up in accordance with the manufacturer's instructions.
Especially, it should be checked that:

a) the plunger holding the indenter is capable of sliding in its guide without any friction or excessive

side play;
b) the indenter-holder is firmly mounted in the plunger;
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SIST EN ISO 6507-2:2018
ISO 6507-2:2018(E)

c) the test force can be applied and removed without shock, vibration or overshoot and in such a

manner that the readings are not influenced;
d) the diagonal measuring system:

1) if integral with the machine, the change from removing the test force to measuring mode does

not influence the readings;

2) the illumination device of the measuring microscope produces uniform lighting of the whole

observed field with enough contrast between the indentation and the surrounding surface to

determine the boundary clearly;

3) the centre of the indentation is in the centre of the field of view, if necessary.

NOTE The criteria specified in this document for the performance of the testing machine have been

developed and refined over a significant period of time. When determining a specific tolerance that the machine

needs to meet, the uncertainty associated with the use of measuring equipment and/or reference standards has

been incorporated within this tolerance and it would therefore be inappropriate to make any further allowance

for this uncertainty by, for example, reducing the tolerance by the measurement uncertainty. This applies to all

measurements made when performing a direct or indirect verification of the machine.

5 Direct verification
5.1 General

5.1.1 Direct verification shall be conducted in accordance with the schedule given in Clause 7.

5.1.2 Direct verification involves:
a) calibration of the test force;
b) verification of the indenter;
c) calibration and verification of the diagonal measuring system;
d) verification of the testing cycle.

5.1.3 Direct verification should be carried out at a temperature of (23 ± 5) °C. If the verification is

made outside this temperature range, this shall be stated in the verification report.

5.1.4 The instruments used for verification and calibration shall be traceable to national standards.

5.2 Calibration of the test force

5.2.1 Each test force used within the working range of the testing machine shall be measured. Whenever

the indenter position affects the applied force, this shall be done at not less than three positions of the

plunger uniformly spaced throughout its range of movement during testing.

For testing machines whose test force is shown not to be influenced by the position of the plunger, e.g.

closed-loop controlled loading system, the test force can be calibrated in one position.

5.2.2 The test force shall be measured by one of the following methods:

— by means of an elastic proving device in accordance with ISO 376, class 1 or better;

— by balancing against a force, accurate to ±0,2 %, applied by means of calibrated masses or another

method with the same accuracy.
2 © ISO 2018 – All rights reserved
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SIST EN ISO 6507-2:2018
ISO 6507-2:2018(E)

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 of 1 s to 30 s following a stepped change in force.

5.2.3 Three readings shall be taken for each test force, F, at each position of the plunger. Immediately

before each reading is taken, the indenter shall be moved in the same direction as during testing. All

readings shall be within the maximum permissible percent relative error, ∆F , defined in Table 1.

rel

The percent relative error, ∆F , of each measurement of the force, F, is calculated according to

rel
Formula (1):
FF−
ΔF =×100 (1)
rel
where
F is the measured test force;
F is the nominal test force.
Table 1 — Test force tolerances
Maximum permissible relative
Ranges of the nominal test force, F
error, ΔF
rel
N %F
0,009 807 ≤ F < 0,098 07 ±2,0
0,098 07 ≤ F < 1,961 ±1,5
F ≥ 1,961 ±1,0
5.3 Verification of the indenter

5.3.1 The four faces of the square-based diamond pyramid shall be polished and free from surface

defects.

5.3.2 The verification of the shape of the indenter can be made by direct measurement or optical

measurement. The device used for the verification shall have a maximum expanded uncertainty of 0,07°.

5.3.3 The measured angles between the opposite faces at the vertex of the diamond pyramid shall be

within the range 136° ± 0,5° (see Figure 1).

The angles between the opposite faces may also be verified by measuring the angle between the opposite

edges. To meet the requirements, the angles between the opposite edges shall be 148,11° ± 0,76°.

5.3.4 The angle between the axis of the diamond pyramid and the axis of the indenter-holder (normal

to the seating surface) shall be less than 0,5°.

5.3.5 The four faces should ideally meet at a common point, however, there is usually a line of junction,

a, between opposite faces as shown in Figure 2. The length of the line of junction shall be determined by

directly measuring the indenter tip or by measuring the tip impression in an indentation. The maximum

permissible length of the line of junction between opposite faces is given in Table 2.

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SIST EN ISO 6507-2:2018
ISO 6507-2:2018(E)

5.3.6 A valid calibration certificate shall exist which confirms the geometrical deviations of the

indenter (see 8.2).
Figure 1 — Angle of the diamond pyramid
Key
a length of line of junction
Figure 2 — Line of junction on the top of the indenter (schematic)
Table 2 — Line of junction tolerance
Ranges of test force, F Maximum permissible length of the line of junction, a
N mm
0,009 807 ≤ F < 1,961 0,000 5
1,961 ≤ F < 49,03 0,001
F ≥ 49,03 0,002
5.4 Calibration and verification of the diagonal measuring system

5.4.1 The system for measuring the diagonal of the indentation shall be verified at each magnification

and for each incorporated line scale to be used. When an individual scale is used in two perpendicular

axes, it shall be calibrated in both orientations. Measurements shall be performed using a calibrated

stage micrometer. The maximum expanded uncertainty of the distances between the line intervals on the

stage micrometer shall be as indicated in Table 3.

5.4.2 Measurements shall be made at a minimum of four evenly spaced intervals, arranged centrally in

the field of view, covering each working range. Three measurements shall be made at each of the evenly

4 © ISO 2018 – All rights reserved
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SIST EN ISO 6507-2:2018
ISO 6507-2:2018(E)

spaced intervals. The maximum permissible error of each of the three measurements at each interval

shall be as indicated in Table 3.
Table 3 — Calibration and verification requirements of the measuring system
Measurement parameters Calibration and verification requirements
Maximum expanded uncertainty of the distances between the Greater of 0,000 4 mm
line intervals on the stage micrometer (see 5.4.1) or 0,2 %
Maximum permissible error of the measurements of the stage Greater of 0,000 8 mm
micrometer intervals (see 5.4.2) or 1,0 % of the length measured
5.5 Verification of the testing cycle

The testing cycle shall be timed with equipment having a maximum expanded uncertainty of 1 s. The

timing values obtained shall fall within the limits set for the testing cycle in ISO 6507-1.

5.6 Uncertainty of calibration/verification

Uncertainty of the calibration/verification results shall be determined. An example is given in Annex A.

6 Indirect verification
6.1 General

6.1.1 Indirect verification shall be conducted in accordance with the schedule given in Clause 7.

6.1.2 Indirect verification involves verification of the overall performance of the testing machine by

means of reference blocks calibrated in accordance with ISO 6507-3.

6.1.3 Indirect verification should be carried out at a temperature of (23 ± 5) °C. If the verification is

made outside this temperature range, this shall be reported in the verification report.

6.1.4 The instruments used for verification and calibration shall be traceable to national standards.

6.2 Test force and hardness levels

The testing machine shall be verified by testing reference blocks that have been calibrated in accordance

with ISO 6507-3. The blocks shall have been calibrated using the same test forces that the machine will

use for future testing. When verifying more than one test force, at least two reference blocks shall be

selected from the hardness ranges specified below for each test force that the machine will be verified.

The set of blocks needed for verifying the machine for all the test forces shall be chosen so that at least

one reference block from each hardness range is used for the verifications. When verifying testing

machines using only one test force, three reference blocks shall be used, one from each of the three

hardness ranges specified below. The hardness ranges should be chosen, when possible, to replicate the

hardness levels most commonly tested when using the specific test forces.
— <250 HV
— 400 HV to 600 HV
— >700 HV
© ISO 2018 – All rights reserved 5
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SIST EN ISO 6507-2:2018
ISO 6507-2:2018(E)
6.3 Measurement of reference indentation

One of the reference indentations from the current calibration period on each reference block shall be

measured. For each indentation, the difference between the mean measured value and the certified

mean diagonal length shall not exceed greater than 0,001 mm or 1,25 % of the reference indentation

length. If preferred, this check may instead be made on a similarly-sized indentation in a different

reference block with similar hardness.
6.4 Number of indentations

On each reference block, five indentations shall be made and measured. The test shall be carried out in

accordance with ISO 6507-1. Only the calibrated surfaces of the test blocks are to be used for testing.

6.5 Verification result

For each reference block, let H , H , H , H , H be the measured hardness arranged in increasing order

1 2 3 4 5

of magnitude corresponding to the measured diagonals, d , d , d , d , d , in decreasing order of

1 2 3 4 5

magnitude. The mean hardness value, H , is calculated according to Formula (2) and the mean diagonal

length, d , is calculated according to Formula (3):
HH++ HH++ H
12 34 5
H= (2)
dd++ dd++ d
12 34 5
d= (3)
6.6 Repeatability

The relative repeatability of the testing machine, r , expressed as a percentage of H is calculated

rel
according to Formula (4):
HH−
r =×100 (4)
rel

The repeatability of the testing machine is satisfactory if (d – d ) ≤ 0,001 mm. If (d – d ) > 0,001 mm,

1 5 1 5

the testing machine is satisfactory if r is less than or equal to the percentages indicated in Table 4.

rel
Table 4 — Maximum permissible relative repeatability
Maximum permissible relative HV repeatability of the testing machine, r
rel
Vickers hardness of
%HV
the reference block
HV 5 to HV 100 HV 0,2 to < HV 5 < HV 0,2
HV ≤250 6,0 12,0 18,0
HV >250 4,0 8,0 12,0

NOTE Lower hardness materials often exhibit higher values of repeatability than those for higher hardness materials.

6.7 Bias

The bias, b, of the testing machine under the particular verification conditions is calculated according

to Formula (5):
bH=−H (5)
CRM
where H is the certified hardness of the reference block used.
CRM
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SIST EN ISO 6507-2:2018
ISO 6507-2:2018(E)
The percent bias, b , is calculated according to Formula (6):
rel
HH−
CRM
b =×100 (6)
rel
CRM

The maximum positive or negative bias of the testing machine, expressed as a percentage of the

specified hardness of the reference block, shall not exceed the values given in Table 5.

Table 5 — Maximum permissible percent HV bias
Mean diagonal length,
Maximum permissible percent HV bias, b ,
rel
of the testing machine
± %HV
0,02 ≤ d < 0,14 0,21/ d + 1,5
0,14 ≤ d ≤ 1,4
6.8 Uncertainty of calibration/verification

Uncertainty of the calibration results shall be determined. An example is given in Annex A.

7 Intervals between verifications

Direct verifications shall be performed according to the schedule given in Table 6. It is recommended

that direct verifications be performed every 12 months.

Indirect verification shall be performed at least once every 12 months and after a direct verification

has been performed.
Table 6 — Direct verifications of hardness testing machines
Diagonal
Requirements of verification Force measuring Test cycle Indenter
system
Before setting to work first time x x x x
After dismantling and reassembling,
if force, diagonal measuring system or test x x x
cycle are affected.
Failure of indirect verification x x x
Indirect verification > 13 months ago x x x

In addition, it is recommended that the indenter be directly verified after 2 years of use.

Direct verification of these parameters may be carried out sequenti
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Questions, Comments and Discussion

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