Metallic materials - Rockwell hardness test - Part 2: Verification and calibration of testing machines and indenters (ISO/DIS 6508-2:2022)

ISO 6508-2:2015 specifies two separate methods of verification of testing machines (direct and indirect) for determining Rockwell hardness in accordance with ISO 6508‑1:2015, 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.
The indirect method may be used on its own for periodic routine checking of the machine in service.
If a testing machine is also to be used for other methods of hardness testing, it shall be verified independently for each method.
ISO 6508-2:2015 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. Steel indenter balls may continue to be used only when complying with ISO 6508‑1:2015, Annex A.

Metallische Werkstoffe - Härteprüfung nach Rockwell - Teil 2: Überprüfung und Kalibrierung der Prüfmaschinen und Eindringkörper (ISO/DIS 6508-2:2022)

In diesem Teil von ISO 6508 sind 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 festgelegt.
Die direkte Überprüfung wird angewendet, um festzustellen, ob die Hauptparameter der Maschinenfunktion, wie z. B. die aufgebrachte Kraft, Eindringtiefenmessung und 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 in der Lage ist einen Werkstoff bekannter Härte zu messen..
Das indirekte Verfahren kann für sich allein zur regelmäßigen Routineüberprüfung der Maschine beim Anwender angewendet werden.
Soll eine Härteprüfmaschine auch für andere Härteprüfverfahren verwendet werden, so muss sie unabhängig für jedes dieser Verfahren überprüft werden.
Dieser Teil von ISO 6508 ist auf ortsfeste und tragbare Härteprüfmaschinen anwendbar.
Es ist zu beachten, dass als Normeindringkugel für die Rockwell-Prüfung nur solche aus Wolframcarbid-Hart-metall gelten. Stahleindringkugeln dürfen nur dann noch verwendet werden, wenn sie ISO 6508 1: , Anhang A entsprechen.

Matériaux métalliques - Essai de dureté Rockwell - Partie 2: Vérification et étalonnage des machines d'essai et des pénétrateurs (ISO/DIS 6508-2:2022)

L'ISO 6508-2:2015 spécifie deux méthodes séparées de vérification des machines d'essai (directe et indirecte) pour la détermination de la dureté Rockwell conformément à l'ISO 6508‑1:2015, 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.
La méthode indirecte peut être utilisée seule pour une vérification périodique de routine de la machine en service.
Si une machine d'essai est également à utiliser pour d'autres méthodes d'essai de dureté, elle doit être vérifiée indépendamment pour chaque méthode.
L'ISO 6508-2:2015 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. Des billes de pénétrateur en acier peuvent continuer d'être utilisées seulement lorsqu'elles sont conformes à l'Annexe A de l'ISO 6508‑1:2015.

Kovinski materiali - Preskus trdote po Rockwellu - 2. del: Preverjanje in umerjanje naprav za preskušanje (ISO/DIS 6508-2:2022)

General Information

Status
Not Published
Public Enquiry End Date
22-Jan-2023
Current Stage
4020 - Public enquire (PE) (Adopted Project)
Start Date
21-Nov-2022
Due Date
10-Apr-2023

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SLOVENSKI STANDARD
oSIST prEN ISO 6508-2:2023
01-januar-2023

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

naprav za preskušanje (ISO/DIS 6508-2:2022)

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

machines and indenters (ISO/DIS 6508-2:2022)
Metallische Werkstoffe - Härteprüfung nach Rockwell - Teil 2: Überprüfung und
Kalibrierung der Prüfmaschinen und Eindringkörper (ISO/DIS 6508-2:2022)

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

des machines d'essai et des pénétrateurs (ISO/DIS 6508-2:2022)
Ta slovenski standard je istoveten z: prEN ISO 6508-2
ICS:
77.040.10 Mehansko preskušanje kovin Mechanical testing of metals
oSIST prEN ISO 6508-2:2023 en,fr,de

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

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oSIST prEN ISO 6508-2:2023
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oSIST prEN ISO 6508-2:2023
DRAFT INTERNATIONAL STANDARD
ISO/DIS 6508-2
ISO/TC 164/SC 3 Secretariat: DIN
Voting begins on: Voting terminates on:
2022-11-03 2023-01-26
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
ICS: 77.040.10
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oSIST prEN ISO 6508-2:2023
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DRAFT INTERNATIONAL STANDARD
ISO/DIS 6508-2
ISO/TC 164/SC 3 Secretariat: DIN
Voting begins on: Voting terminates on:
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
ICS: 77.040.10
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oSIST prEN ISO 6508-2:2023
ISO/DIS 6508-2:2022(E)
Contents Page

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

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

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

3 General conditions .............................................................................................................................................................................................1

4 Direct verification of the testing machine ................................................................................................................................ 2

4.1 General ........................................................................................................................................................................................................... 2

4.2 Calibration and verification of the test force ............................................................................................................... 2

4.3 Calibration and verification of the depth-measuring system ....................................................................... 3

4.4 Calibration and verification of the testing cycle ....................................................................................................... 3

4.5 Calibration and verification of the machine hysteresis ..................................................................................... 4

5 Indirect verification of the testing machine .......................................................................................................................... 4

5.1 General ........................................................................................................................................................................................................... 4

5.2 Procedure .................................................................................................................................................................................................... 4

5.3 Repeatability ............................................................................................................................................................................................ 5

5.4 Bias .................................................................................................................................................................................................................... 7

5.5 Uncertainty of measurement ..................................................................................................................................................... 7

6 Calibration and verification of Rockwell hardness indenters ............................................................................ 7

6.1 General ........................................................................................................................................................................................................... 7

6.2 Diamond indenter ................................................................................................................................................................................ 7

6.2.1 General ........................................................................................................................................................................................ 7

6.2.2 Direct calibration and verification of the diamond indenter ...................................................... 7

6.2.3 Indirect verification of diamond indenters ................................................................................................ 8

6.3 Ball indenter ............................................................................................................................................................................................. 9

6.3.1 Direct calibration and verification of the ball indenter ................................................................ 10

6.3.2 Indirect verification of the ball holder assembly ................................... ............................................. 11

6.4 Marking ...................................................................................................................................................................................................... 11

7 Intervals between direct and indirect calibrations and verifications ....................................................11

8 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
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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 meaning of ISO specific terms and expressions related to conformity

assessment, as well as information about ISO's adherence to the WTO principles in the Technical

Barriers to Trade (TBT) see the following URL: Foreword - Supplementary information

The committee responsible for this document is ISO ISO/TC 164, Mechanical testing of metals,

Subcommittee SC 3, Hardness testing.

This third edition cancels and replaces the first edition (ISO 6508-2:2005), which has been technically

revised.

ISO 6508 consists of the following parts, under the general title Metallic materials — Rockwell hardness

test:
— Part 1: Test method
— Part 2: Verification and calibration of testing machines and Indenters
— Part 3: Calibration of reference blocks
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oSIST prEN ISO 6508-2:2023
DRAFT INTERNATIONAL STANDARD ISO/DIS 6508-2:2022(E)
Metallic materials — Rockwell hardness test —
Part 2:
Verification and calibration of testing machines and
indenters
1 Scope

This part of ISO 6508 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.

The indirect method may be used on its own for periodic routine checking of the machine in service.

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

independently for each method.

This part of ISO 6508 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. Steel indenter balls may continue to be used only

when complying with the Special HR30TSm and HR15TSm test for thin products of ISO 6508-1, .

2 Normative references

The following documents, in whole or in part, are normatively referenced in this document and are

indispensable for its application. 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 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.

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.
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oSIST prEN ISO 6508-2:2023
ISO/DIS 6508-2:2022(E)
4 Direct verification of the testing machine
4.1 General

4.1.1 Direct verification involves calibration and verification of the following:

a) test forces;
b) depth-measuring system;
c) testing cycle;
d) machine hysteresis test.

4.1.2 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.

4.1.3 The instruments used for calibration shall be traceable to national standards.

4.1.4 An indirect verification according to Clause 5 shall be performed following a successful direct

verification.
4.2 Calibration and verification of the test force

4.2.1 Each preliminary test force, F , (see 4.2.4) and each total test force, F, used (see 4.2.5) 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.

4.2.2 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.

4.2.3 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.

4.2.4 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

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

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.
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oSIST prEN ISO 6508-2:2023
ISO/DIS 6508-2:2022(E)

4.2.5 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) shall be ≤ 1,5 % of

F .

4.2.6 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.
4.3 Calibration and verification of the depth-measuring system

4.3.1 The depth-measuring system shall be calibrated by making known incremental movements of

the indenter or the indenter holder.

4.3.2 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.

4.3.3 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.

4.3.4 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.

4.3.5 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):
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.

4.4 Calibration and verification of the testing cycle

4.4.1 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

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oSIST prEN ISO 6508-2:2023
ISO/DIS 6508-2:2022(E)

cycle. Calibration of the complete testing cycle is not required as part of the direct verification at other

times, see Table 10.

4.4.2 The testing cycle shall conform to the testing cycle defined in ISO 6508-1.

4.4.3 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.

4.4.4 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 defined testing cycle.
4.5 Calibration and verification of the machine hysteresis

4.5.1 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.

4.5.2 Perform repeated Rockwell tests using the setup defined in 4.5.1. 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.

4.5.3 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.
5 Indirect verification of the testing machine
5.1 General

5.1.1 Indirect verification involves the calibration and verification of the testing machine by

performing tests on reference blocks.

5.1.2 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.
5.2 Procedure

5.2.1 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

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.
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oSIST prEN ISO 6508-2:2023
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5.2.2 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 within

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
5.3 Repeatability

5.3.1 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

The mean hardness value of all indentations H is defined according to Formula (4):

HH++HH++...+H
12 34 n
H= (4)
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ISO/DIS 6508-2:2022(E)
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.

5.3.2 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

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
0,8 HRC Rockwell units
D 40 to 70 HRD ±2 HRD
≤ 0,02 (100 − H ) or
> 70 to 77 HRD ±1,5 HRD
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 HR-N
≤ 0,04 (100 − H ) or
1,2 HR-N Rockwell units
15T, 30T, 45T All ranges ±3 HR-TW
≤ 0,06 (100 − H ) or
2,4 HR-TW Rockwell units
H is the mean hardness value.

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 2022 – All rights reserved
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oSIST prEN ISO 6508-2:2023
ISO/DIS 6508-2:2022(E)
5.4 Bias

5.4.1 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 is the certified hardness of the reference block used.
CRM

5.4.2 The bias of the testing machine shall not exceed the values given in Table 2.

5.5 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.
6 Calibration and verification of Rockwell hardness indenters
6.1 General

6.1.1 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.

6.1.2 The instruments used for calibration and verifications shall be traceable to national standards.

6.2 Diamond indenter
6.2.1 General

To verify the reliable performance of the spheroconical diamond indenter in conformance with this part

of ISO 6508, a direct and an indirect calibration and verification shall be carried out on each indenter.

6.2.2 Direct calibration and verification of the diamond indenter

6.2.2.1 The surfaces of the diamond cone and spherical tip shall be polished for a penetration depth of

0,3 mm and shall blend in a s
...

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