ICS 71.060.10
Prüfung von Kohlenstoffmaterialien – Härteprüfung nach Rockwell – Verfahren mit Kugel; Feststoffe
In keeping with current practice in standards published by the International Organization for Standardization (ISO), a comma has been used throughout as the decimal marker.
Ref.No.DIN 51917:2002-12
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DEUTSCHE NORM December 2002
51917
{
©No part of this translation may be reproduced without the prior permission of
DIN Deutsches Institut für Normung e.V., Berlin. Beuth Verlag GmbH , 10772Berlin, Germany,
has the exclusive right of sale for German Standards (DIN-Normen).Translation by DIN-Sprachendienst.
In case of doubt, the German-language original should be consulted as the authoritative text.
Rockwell hardness testing of carbonaceous materials by the steel ball indentation method
Continued on pages 2 to 5.
Foreword
The December 1997 edition of this standard has been revised by Technical Committee Prüfverfahren für Kohlenstoff und Graphit  of the Normenausschuss Materialprüfung  (Materials Testing Standards Committee)taking into account DIN EN ISO 6508-1 (which has superseded DIN EN 10109-1) on which it was based.Amendments
This standard differs from the December 1997 edition in that the steel ball has been replaced by a hard-metal ball, details relating to the test pieces have been changed, the text has been editorially revised and refer-ences have been updated.Previous editions
DIN 51917:1987-10, 1997-12.
1Scope
This standard specifies a method of determining the Rockwell hardness of carbon/graphite materials, which can also be used to determine the hardness of metal/graphite materials such as those of carbon brushes for use in electrical machinery.
NOTE:In this standard, the ball indentation method specified in DIN EN ISO 6508-1 has been modified to be suitable for carbonaceous materials.
2Normative references
This standard incorporates, by dated or undated reference, provisions from other publications. These normative references are cited at the appropriate place in the text and the titles of the publications are listed below. For dated references, subsequent amendments to or revisions of any of these publications apply to this standard only when incorporated into it by amendment or revision. For undated references, the latest edition of the publication referred to applies.DIN 1333Presentation of numerical data
DIN 51200
Design and application of test piece holding devices in hardness testing machines
Supersedes
December1997 edition.
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DIN 51917:2002-12DIN EN ISO 6506-2Metallic materials – Brinell hardness – Part 2:Verification and calibration of testing machines (ISO 6506-2:1999)
DIN EN ISO 6508-1Metallic materials – Rockwell hardness test – Part 1: Test method (scales A, B, C, D, E,F, G, H, K, N, T) (ISO 6508-1:1999)
DIN EN ISO 6508-2Metallic materials – Rockwell hardness test – Part 2: Verification and calibration of
testing machines (scales A, B, C, D, E, F, G, H, K, N, T) (ISO 6508-2:1999)
IEC 413
Test procedures for determining the physical properties of brush materials for electrical machines
ISO 5725-1:1994Accuracy (trueness and precision) of measurement methods and results – Part 1: General principles and definitions
ISO 5725-2:1994
Accuracy (trueness and precision) of measurement methods and results – Part 2: Basic method for the determination of repeatability and reproducibility of a standard measure-ment method
3Principle
A hard-metal ball indenter is forced into a test piece in two stages under the conditions specified in clause 9,and the permanent depth of the indentation , h , produced by the initial test force is measured after removing the additional test force. The Rockwell hardness number, HR , is then determined using the following equation (cf. table 1):
h Rockwell hardness, HR  =N –                                                S
4Quantities, symbols and units
See tables 1 and 2 and figure 1.
Table 1:Quantities, symbols and units
Symbol
Quantity
Unit F 0Initial test force N F 1Additional test force N F Total test force N S Scale unit
mm N Hardness number specific to the scale –h Permanent indentation depth at F 0mm
after removing additional test force e
Permanent indentation depth, expressed in multiples of  S , i.e. 0,002 mm or 0,001 mm.HR 10/20, HR 5/20HR 10/40, HR 5/40
heditorially
HR 10/60, HR 5/60Rockwell hardness HR  =130–
HR 10/100, HR 5/100                                                  0,002
HR 10/150, HR 5/150
h
HR 5/7, HR 2,5/7
Rockwell hardness HR  =100–
0,001
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DIN 51917:2002-12
Table 2:Test forces
5Designation
Designation of a Rockwell hardness test 1) (HR) in accordance with this standard, determined with an indenter of diameter (10t 0,005) mm (10) and a total test force of 60 daN (60):
Test DIN 51917 – HR 10/60
6
Apparatus
6.1Te sting machine , capable of applying the test forces specified in table 2 and conforming to
DIN EN ISO 6508-2.
6.2Hard-metal ball indenter , having a diameter of (10t 0,005)mm, (5t 0,004)mm or (2,5t 0,003)mm and
meeting the requirements specified in DIN EN ISO 6506-2.
6.3Depth-measuring device , conforming to DIN EN ISO 6508-2.
7Sampling
Sampling shall be subject to agreement.
8Test pieces
Test pieces of any size may be used, provided that they meet the following requirements.
a)The thickness is such that no deformation is visible on the back of the test piece after testing. (The minimum thickness will depend on the material of the test piece and may need to be determined by experi-ment.
b)The surfaces of test pieces are flat and the arithmetical mean deviation of the profile, Ra , is no greater than 5 µm.
1)
Cf. section 303.2 of IEC 413.
Hardness symbol
Diameter of ball indenter,in mm
Hardness number, N
Scale unit,
S ,in mm
Initial test force, F 0,in N
Additional test
force,F 1,in N
Total test force,
F ,in N
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DIN 51917:2002-12
9Procedure
Testing shall be carried out at an ambient temperature of between 10°C and 35°C.
Place the test piece on a supporting surface or in a holder so that the surface to be indented is normal to the direction of the indenting force.
Since any permanent change in the position of the test piece caused by the applied test force affects the measured indentation depth, the contact surfaces of the test piece and support or holder shall be free of foreign matter, such as grease or dust. If its shape allows, the test piece shall be clamped in the machine (cf. DIN 51200).Press the test piece against the steel ball indenter until the initial force, F 0, is reached and then set the datum position of the measuring device at the hardness number, N .
Avoiding shock and vibration as far as possible, slowly apply the additional force, F 1, for five to eight s
econds until the total force, F , is reached. Maintain this force until the reading is steady (which normally takes ten to twenty seconds).
Now remove the additional force, avoiding shock and vibration as far as possible. The Rockwell hardness can usually be read directly from the measuring device, but if necessary, determine it from the permanent inden-tation depth, h  (see figure 1).
1Initial test force
2Surface of test piece 3Datum line
a Indentation depth due to initial test force, F 0
b Indentation depth due to additional test force, F 1
c Recovery after removal of additional test force
d Permanent indentation depth, h
Figure 1:Principle of Rockwell hardness test
The distance between the centres of two adjacent indentations and that from the centre of each indentation to the edge of the test piece shall be at least equal to the ball diameter or 2,5 times the diameter of the indentation,unless otherwise agreed.
If the mean value obtained is greater than 110 or less than 30, repeat the measurement after selecting a more suitable indenter diameter and test forces from table 2.
10Evaluation
Most testing machines give a direct reading of the Rockwell hardness; where this is not the case, calculate the Rockwell hardness, HR ../.. (ball diameter/total test force), using the following equations:      h e =      S
HR  ../..=N –e
Rounding of results shall be in accordance with DIN 1333.
11Test report
The test report shall refer to this standard and include the following information:a)type, position, orientation and identification of test pieces;b)number of test pieces;
c)ball diameter and total test force;
a
b
d
c
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DIN51917:2002-12
d)Rockwell hardness obtained and the mean of all results, both rounded to the nearest integer;
e)any agreed deviations from this standard;
f)date of testing.
12Precision
(cf. ISO5725-1 and ISO5725-2)
The following characteristics shall be used to assess the reliability of results.
Repeatability limit
(same observer, same equipment)
If two results are obtained under repeatability conditions, both results shall be considered acceptable and in
conformity with this standard if they differ by no more than the value shown in table 3.
Reproducibility limit
(different observers, different equipment)
If two laboratories each obtain a result under reproducibility conditions, both results shall be considered
acceptable and in conformity with this standard if they differ by no more than the value shown in table 3.
Table3:Repeatability and reproducibility
Carbon/graphite materials Metal/graphite materials
HR 10/40HR 5/40HR 10/40HR 5/40
Repeatability limit3547
Reproducibility limit4869
Other relevant standard
ASTM C 748-83Test method for Rockwell hardness of fine-grained graphite materials (1993 revision)2)
2)Obtainable from Beuth Verlag GmbH, 10772 Berlin, Germany.
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