prEN ISO 6508-3

Metallic materials - Rockwell hardness test - Part 3: Calibration of reference blocks (ISO/DIS 6508-3:2022)

ISO 6508-3:2015 specifies a method for the calibration of reference blocks to be used for the indirect and daily verification of Rockwell hardness testing machines, as specified in ISO 6508‑2:2015.
Attention is drawn to the fact that the use of hard metal for ball indenters is considered to be the standard type of Rockwell indenter ball. Steel indenter balls can be used only when complying with ISO 6508‑1:2015, Annex A.

Metallische Werkstoffe - Härteprüfung nach Rockwell - Teil 3: Kalibrierung von Härtevergleichsplatten (ISO/DIS 6508-3:2022)

Dieser Teil der ISO 6508 legt ein Verfahren für die Kalibrierung von Härtevergleichsplatten fest, die bei der indirekten Überprüfung und der täglichen Überprüfung von Härteprüfmaschinen nach Rockwell und Eindringkörpern nach ISO 6508 2 zu verwenden sind. Dieser Teil legt darüber hinaus Anforderungen an Härteprüfmaschinen nach Rockwell und Eindringkörper, die für die Kalibrierung von Härtevergleichsplatten verwendet werden, sowie Verfahren für deren Kalibrierung und Überprüfung fest.
Es ist zu beachten, dass als Normeindringkugeln für die Härteprüfung nach Rockwell nur solche aus Hartmetall gelten. Stahleindringkugeln dürfen nur dann noch verwendet werden, wenn sie dem Anhang der ISO 6508 1 entsprechen, der die „Spezielle HR30TSm  und HR15TSm Prüfung für dünne Erzeugnisse“ festlegt.

Matériaux métalliques - Essai de dureté Rockwell - Partie 3: Étalonnage des blocs de référence (ISO/DIS 6508-3:2022)

L'ISO 6508-3:2015 spécifie une méthode pour l'étalonnage des blocs de référence à utiliser pour la vérification indirecte et la vérification quotidienne des machines d'essai de dureté Rockwell, comme spécifié dans l'ISO 6508‑2:2015.
L'attention est attirée sur le fait que l'utilisation de métaux durs pour les pénétrateurs à billes est considérée être le type courant de bille de pénétrateur Rockwell. Des billes de pénétrateur en acier peuvent continuer d'être utilisées seulement en conformité avec l'Annexe A de l'ISO 6508‑1:2015.

Kovinski materiali - Preskus trdote po Rockwellu - 3. del: Umerjanje primerjalnih ploščic (ISO/DIS 6508-3:2022)

General Information

• Status: Not Published
• Publication Date: 27-Nov-2024
• ICS: 77.040.10 - Mechanical testing of metals
• Technical Committee: ECISS/TC 101 - Test methods for steel (other than chemical analysis)
• Drafting Committee: ECISS/TC 101 - Test methods for steel (other than chemical analysis)
• Current Stage: 4599 - Dispatch of FV draft to CMC - Finalization for Vote
• Start Date: 05-Jun-2023
• Completion Date: 05-Jun-2023
• Ref Project: oSIST prEN ISO 6508-3:2023 - Metallic materials - Rockwell hardness test - Part 3: Calibration of reference blocks (ISO/DIS 6508-3:2022)

Relations

• Revises: EN ISO 6508-3:2015 - Metallic materials - Rockwell hardness test - Part 3: Calibration of reference blocks (ISO 6508-3:2015)
• Effective Date: 18-Jan-2023

Standards Content (Sample)

SLOVENSKI STANDARD
oSIST prEN ISO 6508-3:2023
01-januar-2023

Kovinski materiali - Preskus trdote po Rockwellu - 3. del: Umerjanje primerjalnih

ploščic (ISO/DIS 6508-3:2022)

Metallic materials - Rockwell hardness test - Part 3: Calibration of reference blocks

(ISO/DIS 6508-3:2022)
Metallische Werkstoffe - Härteprüfung nach Rockwell - Teil 3: Kalibrierung von
Härtevergleichsplatten (ISO/DIS 6508-3:2022)

Matériaux métalliques - Essai de dureté Rockwell - Partie 3: Étalonnage des blocs de

référence (ISO/DIS 6508-3:2022)
Ta slovenski standard je istoveten z: prEN ISO 6508-3
ICS:
77.040.10 Mehansko preskušanje kovin Mechanical testing of metals
oSIST prEN ISO 6508-3:2023 en,fr,de

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

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oSIST prEN ISO 6508-3:2023
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oSIST prEN ISO 6508-3:2023
DRAFT INTERNATIONAL STANDARD
ISO/DIS 6508-3
ISO/TC 164/SC 3 Secretariat: DIN
Voting begins on: Voting terminates on:
2022-11-04 2023-01-27
Metallic materials — Rockwell hardness test —
Part 3:
Calibration of reference blocks
Matériaux métalliques — Essai de dureté Rockwell —
Partie 3: Étalonnage des blocs de référence
ICS: 77.040.10
This document is circulated as received from the committee secretariat.
THIS DOCUMENT IS A DRAFT CIRCULATED
FOR COMMENT AND APPROVAL. IT IS
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WHICH REFERENCE MAY BE MADE IN
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NATIONAL REGULATIONS.
ISO/DIS 6508-3:2022(E)
RECIPIENTS OF THIS DRAFT ARE INVITED
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NOTIFICATION OF ANY RELEVANT PATENT
RIGHTS OF WHICH THEY ARE AWARE AND TO
PROVIDE SUPPORTING DOCUMENTATION. © ISO 2022
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oSIST prEN ISO 6508-3:2023
ISO/DIS 6508-3:2022(E)
DRAFT INTERNATIONAL STANDARD
ISO/DIS 6508-3
ISO/TC 164/SC 3 Secretariat: DIN
Voting begins on: Voting terminates on:
Metallic materials — Rockwell hardness test —
Part 3:
Calibration of reference blocks
Matériaux métalliques — Essai de dureté Rockwell —
Partie 3: Étalonnage des blocs de référence
ICS: 77.040.10
This document is circulated as received from the committee secretariat.
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NATIONAL REGULATIONS.
Website: www.iso.org ISO/DIS 6508-3:2022(E)
RECIPIENTS OF THIS DRAFT ARE INVITED
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NOTIFICATION OF ANY RELEVANT PATENT
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PROVIDE SUPPORTING DOCUMENTATION. © ISO 2022
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oSIST prEN ISO 6508-3:2023
ISO/DIS 6508-3:2022(E)
Contents Page

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

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

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

3 Manufacture of reference blocks ........................................................................................................................................................ 1

4 Calibration machine and calibration indenter .................................................................................................................... 2

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

4.2 Direct verification of the calibration machine ........................................................................................................... 2

4.3 Calibration diamond indenter ................................................................................................................................................... 3

4.4 Calibration ball indenter ................................................................................................................................................................ 4

4.5 Performance verification of the calibration machine and indenter ........................................................ 5

5 Reference block calibration procedure ....................................................................................................................................... 6

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

7 Uniformity of hardness ................................................................................................................................................................................. 7

8 Marking ........................................................................................................................................... ............................................................................... 8

9 Calibration certificate ....................................................................................................................................................................................8

10 Validity ........................................................................................................................................................................................................................... 8

Annex A (normative) Uniformity of reference blocks ....................................................................................................................... 9

Annex B (informative) Uncertainty of the mean hardness value of hardness-reference

blocks ............................................................................................................................................................................................................................11

Annex C (normative) Requirements for reference diamond indenters .......................................................................17

Annex D (normative) Control verification of the calibration machine ........................................................................18

Bibliography .............................................................................................................................................................................................................................19

iii
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oSIST prEN ISO 6508-3:2023
ISO/DIS 6508-3:2022(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 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/TC 164, Mechanical testing of metals, Subcommittee

SC 3, Hardness testing.

This third edition cancels and replaces the second edition (ISO 6508-3:2005), 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 6508-3:2023
DRAFT INTERNATIONAL STANDARD ISO/DIS 6508-3:2022(E)
Metallic materials — Rockwell hardness test —
Part 3:
Calibration of reference blocks
1 Scope

This part of ISO 6508 specifies a method for the calibration of reference blocks to be used for the

indirect and daily verification of Rockwell hardness testing machines and indenters, as specified

in ISO 6508-2. This part also specifies requirements for Rockwell machines and indenters used for

calibrating reference blocks and specifies methods for their calibration and verification.

Attention is drawn to the fact that the use of hard metal for ball indenters is considered to be the

standard type of Rockwell indenter ball. Steel indenter balls can be used only when complying with the

Annex of ISO 6508-1 that specifies the “Special HR30TSm and HR15TSm test for thin products.”

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 6508-1:2015, Metallic materials — Rockwell hardness test — Part 1: Test method

ISO 6508-2:2015, Metallic materials — Rockwell hardness test — Part 2: Verification and calibration of

testing machines and indenters
3 Manufacture of reference blocks

3.1 The block shall be specially manufactured for use as a hardness-reference block.

NOTE Attention is drawn to the need to use a manufacturing process, which will give the necessary

homogeneity, stability of structure, and uniformity of surface hardness.

3.2 Each hardness reference block shall be of a thickness not less than 6 mm. To minimize the effect

of hardness change with increasing number of indents, thicker blocks should be used.

3.3 The reference blocks shall be free of magnetism. It is recommended that the manufacturer ensure

that the blocks, if made of steel, have been demagnetized at the end of the manufacturing process

(before calibration).

3.4 The deviation from surface flatness of the top and bottom surfaces shall be ≤0,01 mm. The bottom

of the blocks shall not be convex. The deviation from parallelism of the top and bottom surfaces shall

be ≤0,02 mm per 50 mm.

3.5 The test surface and bottom surface shall be free from damage, such as notches, scratches, oxide

layers, etc., which can interfere with the measurement of the indentations. The surface roughness,

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oSIST prEN ISO 6508-3:2023
ISO/DIS 6508-3:2022(E)

Ra, shall not exceed 0,3 µm for the test surface and 0,8 µm for the bottom surface. Sampling length is

l = 0,8 mm (see ISO 4287:1997, 3.1.9).

3.6 To verify that no material is subsequently removed from the reference block, the thickness at the

time of calibration shall be marked on it, to the nearest 0,1 mm, or an identifying mark shall be made on

the test surface [see 8.1 e)].
4 Calibration machine and calibration indenter
4.1 General

4.1.1 Calibrations and verifications of Rockwell calibration machines and calibration indenters shall

be carried out at a temperature of (23 ± 5) °C.

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

4.2 Direct verification of the calibration machine

4.2.1 In addition to fulfilling the ”General conditions” clause specified in ISO 6508-2, the calibration

machine shall also meet the requirements given in 4.2.2, 4.2.3, 4.2.4, 4.2.5, 4.2.6 and 4.2.7 determined

by the procedures specified in the “Direct verification of the testing machine” clause of ISO 6508-2.

4.2.2 The machine shall be directly verified annually, not to exceed 13 months. Direct verification

involves calibration and verification of the following:
a) test force;
b) measuring system;

c) testing cycle; if this is not possible, at least the force versus time behaviour.

d) machine hysteresis test.

4.2.3 The test force shall be measured by means of an elastic proving device (according to ISO 376)

class 0,5 or better and calibrated for reversibility, or by another method having the same or better

accuracy.

Evidence should be available to demonstrate that the output of the force-proving device does not vary

by more than 0,1 % in a period of 1 s to 30 s, following a stepped change in force.

4.2.4 Each test force shall be measured and shall agree with the nominal preliminary test force, F , to

within ±0,2 % and the nominal total test force, F, to within ±0,1 %.

4.2.5 The measuring system shall have a resolution of ±0,000 1 mm and a maximum expanded

uncertainty of 0,000 2 mm, when calculated with a confidence level of 95 % over its working range.

4.2.6 The testing cycle shall be timed with an uncertainty less than ±0,5 s and shall conform to the

testing cycle of Clause 5.

4.2.7 The average of the last three tests when evaluating the hysteresis of the calibration machine

shall indicate a hardness number of (130 ± 0,5) Rockwell units when the regular Rockwell ball scales B,

E, F, G, H, and K are used, or within (100 ± 0,5) Rockwell units when any other Rockwell scale is used.

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oSIST prEN ISO 6508-3:2023
ISO/DIS 6508-3:2022(E)
4.3 Calibration diamond indenter

4.3.1 The geometric shape and performance of calibration diamond indenters shall be calibrated as

defined below. Direct verification of the geometric shape shall be made before first use. The condition

of the diamond shall be checked at frequent intervals using appropriate optical devices (microscope,

magnifying glass, etc.) as specified in the “Inspection of diamond indenters” Annex of ISO 6508-1.

Verification of the indenter performance, as specified in 4.3.3, shall be made before first use and

annually, not to exceed 13 months.

4.3.2 The diamond indenter shall be measured on at least eight unique axial section planes equidistant

from each other (e.g. the eight cross-sections will be spaced approximately 22,5° apart at 0°, 22,5°, 45°,

67,5°, 90°, 112,5°, 135°, 157,5°), and shall meet the following requirements:

a) The cone angle shall be measured adjacent to the blend. The diamond cone shall have a mean

included angle of (120 ± 0,1)°. In each measured axial section, the included angle shall be

(120 ± 0,17)°.

b) The mean deviation from straightness of the generatrix of the diamond cone adjacent to the blend

shall not exceed 0,000 5 mm over a minimum length of 0,4 mm. In each measured section, the

deviation shall not exceed 0,000 7 mm.

c) The radius of the spherical tip of the diamond shall be measured adjacent to the blend. The tip shall

have a mean radius of (0,200 ± 0,005) mm. In each measured section, the radius shall be within

(0,200 ± 0,007) mm and local deviations from a true radius shall not exceed 0,002 mm.

NOTE The tip of the diamond indenter is usually not truly spherical, but often varies in radius across

its surface. Depending on the crystallographic orientation of the diamond stone with respect to the indenter

axis, diamond tends to preferentially polish away more easily or with more difficulty at the tip, producing

an increasingly flat or sharp surface in the central indenter axis region. The sphericity of the diamond tip

can be better evaluated by measuring multiple measurement windows of varying width. The measurement

window would be bounded by widths measured along a line normal to the indenter axis. For example, the

following window sizes can be evaluated:
— between ±80 µm from the indenter axis;
— between ±60 µm from the indenter axis;
— between ±40 µm from the indenter axis.

d) The surfaces of the cone and the spherical tip shall blend in a smooth tangential manner. The

location where the spherical tip and the cone of the diamond blend together will vary depending on

the values of the tip radius and cone angle. Ideally for a perfect indenter geometry, the blend point

is located at 100 µm from the indenter axis measured along a line normal to the indenter axis. To

avoid including the blend area in the measurement of the tip radius and cone angle, the portion of

the diamond surface between 90 µm and 110 µm should be ignored.

e) The inclination of the axis of the diamond cone to the axis of the indenter holder (normal to the

seating surface) shall be within 0,3°.

4.3.3 Calibration diamond indenters shall be performance verified by performing comparison tests

with reference diamond indenter(s) that meet the requirements of Annex C. Calibration diamond

indenters can be verified for use on either regular or superficial Rockwell diamond scales or both. The

test blocks used for the comparison testing shall meet the requirements of Clause 3 and be calibrated at

the hardness levels given in Table 1, Table 2, Table 3, or Table 4, depending on the scales for which the

indenter is verified. The testing shall be carried out in accordance with ISO 6508-1.

NOTE The alternate hardness levels given in Table 2 are provided to accommodate indenters calibrated to

other International Standards. It is believed that calibrations conducted to Table 1 or Table 2 will yield equivalent

results.
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oSIST prEN ISO 6508-3:2023
ISO/DIS 6508-3:2022(E)

For each block, the mean hardness value of three indentations made using the calibration diamond

indenter to be verified shall not differ from the mean hardness value of three indentations obtained

with a reference diamond indenter by more than ±0,4 Rockwell units. The indentations made with

the calibration diamond indenter to be verified and with the reference diamond indenter should be

adjacent.

Table 1 — Hardness levels for indenters to be used for calibrating Rockwell regular and

superficial scale test blocks (A, C, D, and N)
Scale Nominal hardness Ranges
HRC 23 20 to 26
HRC 55 52 to 58
HR45N 43 40 to 46
HR15N 91 88 to 94

Table 2 — Alternate hardness levels for indenters to be used for calibrating Rockwell regular

and superficial scale test blocks (A, C, D, and N)
Scale Nominal hardness Ranges
HRC 25 22 to 28
HRC 63 60 to 65
HR30N 64 60 to 69
HR15N 91 88 to 94

Table 3 — Hardness levels for indenters to be used for calibrating Rockwell regular scale test

blocks only (A, C, and D)
Scale Nominal hardness Ranges
HRC 25 22 to 28
HRC 45 42 to 50
HRC 63 60 to 65
HRA 81 78 to 84

Table 4 — Hardness levels for indenters to be used for calibrating Rockwell superficial scale

test blocks only (N)
Scale Nominal hardness Ranges
HR15N 91 88 to 94
HR30N 64 60 to 69
HR30N 46 42 to 50
HR45N 25 22 to 29
4.4 Calibration ball indenter

4.4.1 The calibration tungsten carbide composite ball shall be replaced at a frequency no greater

than 12 months.

4.4.2 Calibration tungsten carbide composite balls shall meet the requirements of ISO 6508-2, with

the exception of the following tolerances for the ball diameter:
— ±0,002 mm for the ball of diameter 1,587 5 mm;
— ±0,003 mm for the ball of diameter 3,175 mm.
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oSIST prEN ISO 6508-3:2023
ISO/DIS 6508-3:2022(E)
4.5 Performance verification of the calibration machine and indenter

4.5.1 Performance verification involves verification of the calibration machine with the calibration

indenter by performing comparisons with laboratories having measurement capabilities with lower

uncertainties. The comparisons shall be made by one or more of the following procedures:

— tests on primary reference blocks calibrated by National Metrology Institutes
— intercomparisons with National Metrology Institutes

— intercomparisons with other Rockwell calibration laboratories having lower or equivalent stated

measurement uncertainties, such as part of a Proficiency Testing (PT) program.

4.5.2 The calibration laboratory shall schedule the performance verification comparisons such

that, at a minimum, the following number of Rockwell scales are compared during each performance

verification interval depending on the reference blocks calibrated by the laboratory. Comparisons are

only required for the scales that blocks will be calibrated in the future.
— One (1) regular Rockwell diamond scale (A, C, D)
— One (1) superficial Rockwell diamond scale (15N, 30N, 45N)
— One (1) 1,587 5 mm ball scale (B, F, G)
— One (1) 3,175 mm ball scale (E, H, K)

4.5.3 For each Rockwell scale to be compared, comparison tests shall be made at hardness levels

within each of the hardness ranges specified by the table titled “Hardness ranges for different scales” in

ISO 6508-2 (i.e., three hardness levels for each Rockwell scale except two hardness levels for the HRHW

scale).

4.5.4 For each subsequent performance verification interval, the Rockwell scales chosen to be

compared shall be different scales than compared previously for each category listed in 4.5.2 until all

applicable scales are compared. Additional comparisons of previously compared scales can also be

included in addition to the required comparisons.

4.5.5 Performance verification of the calibration machine with the calibration indenter shall be

performed at least once annually, not to exceed 13 months. The verification measurements shall be

carried out at a temperature of (23 ± 5) °C.

4.5.6 The results of each comparison shall be evaluated by appropriate statistical techniques,

including calculating the Normalized Error, E . according to Formula (1) as
HH−
LabRef
E = (1)
UU+
LabRef
where
is the measurement result of the calibration laboratory
Lab
is the measurement result of the reference laboratory
Ref
is the Expanded Uncertainty of the calibration laboratory’s measurement result
Lab
is the Expanded Uncertainty of the reference laboratory’s measurement result.
Ref
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oSIST prEN ISO 6508-3:2023
ISO/DIS 6508-3:2022(E)

4.5.7 The comparison results are considered satisfactory when the value of E ≤ 1 (i.e. between -1

and +1),
5 Reference block calibration procedure

5.1 The calibration machine shall undergo control verifications as defined in Annex D and be

determined to be in-control prior to calibrating reference blocks.

5.2 The reference blocks shall be calibrated in a calibration machine as described in Clause 4, at a

temperature of (23 ± 5) °C, using the general procedure described in ISO 6508-1.
During calibration, the thermal drift should not exceed 1 °C.

5.2 The velocity of the indenter, when it comes into contact with the surface, shall not exceed

1 mm/s.

The velocity of the indenter, when it comes into contact with the surface, should not exceed 0,3 mm/s

for undamped systems.

5.3 Bring the indenter into contact with the test surface and apply the preliminary test force, F ,

without shock or vibration and without oscillation or overload of the test force. The application time, T ,

of the preliminary test force, F , shall not exceed 2 s.

The duration, T , of the preliminary test force, F , shall be equal to (3 ± 1) s, as shown in Formula (2):

p 0
TT=+23T =±1 s (2)
pa pm
where
T is the preliminary test force time;
T is the application time of preliminary test force;

T is the duration time of preliminary test force prior to measuring the initial indentation depth.

For testing machines that apply the preliminary test force in less than 1 s (T ), T can be calculated as

a p
being equal to T .

5.4 Bring the measuring system to its datum position, and without shock, vibration, oscillation, or

overload, apply the additional test force, F .

For the regular Rockwell scale tests, apply the additional test force, F , in 7 s. For all HRN and HRTW

1 −6

Rockwell superficial test scales, apply the additional test force, F , in less than or equal to 4 s. During

the final stage of the indentation process (approximately in the range of 0,8 F to 0,99 F), the indentation

speed should be in the range of 0,015 mm/s to 0,04 mm/s.

5.5 The duration of the application of the total force, F, shall be equal to (5 ± 1) s.

5.6 The final reading shall be made (4 ± 1) s after removing the additional test force, F, and returning

to the preliminary test force, F .
6 Number of indentations

On each reference block, at least five indentations shall be made, uniformly distributed over the test

surface. The arithmetic mean of the hardness values characterizes the hardness value of the block.

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oSIST prEN ISO 6508-3:2023
ISO/DIS 6508-3:2022(E)

To reduce the measurement uncertainty, more than five indentations should be made.

7 Uniformity of hardness

7.1 For each reference block, let H , H , H , H , … H be the values of the measured hardness, arranged

1 2 3 4 n
in increasing order of magnitude.

The mean hardness value of all the indentations is defined according to Formula (3):

HH++HH++...+H
12 34 n
H= (3)
where

H , H , H , H , H are the hardness values corresponding to all the indentations arranged in

1 2 3 4 … n
increasing order of magnitude;
n is the total number of indentations.

The non-uniformity, R, of the block in Rockwell units, under the particular conditions of calibration, is

characterized by Formula (4):
RH=−H (4)
n 1

7.2 The maximum permissible value of non-uniformity, R, of a reference block in Rockwell units is

given in Table 5 and is graphically presented in Figure A.1 and Figure A.2.
Table 5 — Maximum permissible value of non-uniformity
Rockwell hardness scale Maximum permissible value of
non-uniformity, R
0,015 (100 - H ) or 0,4 HRA Rockwell units
0,020 (130 - H ) or 1,0 HRBW Rockwell units
0,010 (100 - H ) or 0,4 HRC Rockwell units
0,010 (100 - H ) or 0,4 HRD Rockwell units
0,020 (130 - H ) or 1,0 HREW Rockwell units
0,020 (130 - H ) or 1,0 HRFW Rockwell units
0,020 (130 - H ) or 1,0 HRGW Rockwell units
0,020 (130 - H ) or 1,0 HRHW Rockwell units
0,020 (130 - H ) or 1,0 HRKW Rockwell units
15N, 30N, 45N
0,020 (100 - H ) or 0,6 HR-N Rockwell units
15T, 30T, 45T
0,030 (100 - H ) or 1,2 HR-TW Rockwell units
The greater of the two values shall apply.

7.3 The uncertainty of measurement of the hardness reference blocks shall be calculated. An example

method is given in Annex B.
© ISO 2022 – All rights reserved
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oSIST prEN ISO 6508-3:2023
ISO/DIS 6508-3:2022(E)
8 Marking
8.1 Each reference block shall be marked with the following:

a) arithmetic mean of the hardness values found in the calibration test. For example, 66,3 HRC;

b) name or mark of the supplier or manufacturer;
c) serial number;
d) name or mark of the calibration agency;
e) thickness o
...