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ISO INTERNATIONAL STANDARD. Metallic materials Vickers hardness test Part 2: Verification and calibration of testing machines - PDF
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1 INTERNATIONAL STANDARD ISO Third edition 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 :2005(E) ISO 2005
3 Contents Page Foreword... iv 1 Scope Normative references General conditions Direct verification Indirect verification Intervals between verifications Verification report/calibration certificate... 8 Annex A (informative) Notes on diamond indenters... 9 Annex B (informative) Uncertainty of measurement of the calibration results of the hardness testing machine Bibliography ISO 2005 All rights reserved iii
4 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. International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2. The main task of technical committees is to prepare International Standards. Draft International Standards adopted by the technical committees are circulated to the member bodies for voting. Publication as an International Standard requires approval by at least 75 % of the member bodies casting a vote. 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. ISO was prepared by Technical Committee ISO/TC 164, Mechanical testing of metals, Subcommittee SC 3, Hardness testing. This third edition cancels and replaces the second edition (ISO :1997), which has been technically revised. ISO 6507 consists of the following parts, under the general title Metallic materials Vickers hardness test: Part 1: Test method Part 2: Verification and calibration of testing machines Part 3: Calibration of reference blocks Part 4: Tables of hardness values iv ISO 2005 All rights reserved
5 INTERNATIONAL STANDARD ISO :2005(E) Metallic materials Vickers hardness test Part 2: Verification and calibration of testing machines 1 Scope This part of ISO 6507 specifies a method of verification of testing machines for determining Vickers hardness in accordance with ISO It specifies a direct verification method for checking the main functions of the machine operation, and an indirect method suitable for the overall checking of the machine. 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 6507 is also applicable to portable hardness testing machines. 2 Normative references The following referenced documents are indispensable for the application 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 3878, Hardmetals Vickers hardness test ISO :2005, Metallic materials Vickers hardness test Part 1: Test method ISO , Metallic materials Vickers hardness test Part 3: Calibration of reference blocks 3 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; b) the indenter-holder is firmly mounted in the plunger; c) the test force can be applied and removed without shock or vibration and in such a manner that the readings are not influenced; ISO 2005 All rights reserved 1
6 d) if the measuring system is integral with the machine the change from removing the test force to measuring mode does not influence the readings, illumination does not affect the readings, the centre of the indentation is in the centre of the field of view, if necessary. The illumination device of the measuring microscope shall produce uniform lighting of the whole observed field and maximum contrast between the indentation and the surrounding surface. 4 Direct verification 4.1 General 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 reported in the verification report The instruments used for verification and calibration shall be traceable to national standards Direct verification involves: a) calibration of the test force; b) verification of the indenter; c) calibration of the measuring system; d) verification of the testing cycle. 4.2 Calibration of the test force Each test force used within the working range of the testing machine shall be measured. Whenever applicable, this shall be done at not less than three positions of the plunger uniformly spaced throughout its range of movement during testing Three readings shall be taken for each test force at each position of the plunger. Immediately before each reading is taken, the plunger shall have been moved in the same direction as during testing The test force shall be measured by one of the following two methods: by means of an elastic proving device in accordance with ISO 376:2004, class 1, or by balancing against a force, accurate to ± 0,2 %, applied by means of calibrated masses or another method with the same accuracy Each measurement of the force shall be within the tolerances of the nominal value of the test force, as given in Table 1. 2 ISO 2005 All rights reserved
7 Table 1 Ranges of the test force, F N Tolerances % F W 1,961 ± 1,0 0, u F < 1,961 ± 1,5 4.3 Verification of the indenter The four faces of the square-based diamond pyramid shall be polished and free from surface defects The verification of the shape of the indenter can be made by direct measurement or by measurement of its projection on a screen The angle between the opposite faces at the vertex of the diamond pyramid shall be 136 ± 0,5 (see Figure 1). NOTE The angle between the opposite faces may also be determined by the angle between the opposite edges; this value is 148,11 ± 0, 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 0,50. The four faces shall meet at a point; the maximum permissible length of the line of conjunction between opposite faces is given in Table 2 (see also Figure 2). Figure 1 Angle of the diamond pyramid Key a = length of line of conjunction Figure 2 Line of conjunction on the top of the indenter (schematic) ISO 2005 All rights reserved 3
8 Table 2 Ranges of test force, F N Maximum permissible length of the line of conjunction, a mm F W 49,03 0,002 1,961 u F < 49,03 0,001 0, u F < 1,961 0, Calibration of the measuring system The resolution required of the measuring system depends on the size of the smallest indentation to be measured. The scale of the measuring system shall be graduated to permit estimation of the diagonals of the indentation in accordance with Table 3. Diagonal length, d mm Table 3 Resolution of the measuring system Maximum permissible error d u 0,040 0,000 2 mm 0,000 4 mm 0,040 < d u 0,200 0,5 % of d 1,0 % of d d > 0,200 0,001 mm 0,002 mm NOTE The diagonal length of the indentation determines the necessary magnification V of the measuring system according to the following condition: V d W 14 mm For indentation diagonals d < 0,035 mm this condition may not be fulfilled, but the magnification should be at least 400. The resolution of the measuring system for Vickers hardness testing of hardmetals is specified in ISO The measuring system shall be verified by measurements made on an object micrometer at a minimum of five intervals over each working range. The maximum permissible error shall not exceed the values given in Table Verification of the testing cycle The testing cycle shall be timed with an uncertainty of ± 1,0 s and shall conform to the testing cycle of ISO Indirect verification 5.1 Indirect verification should be carried out at a temperature of (23 ± 5) C by means of reference blocks calibrated in accordance with ISO If the verification is made outside this temperature range, this shall be reported in the verification report. 4 ISO 2005 All rights reserved
9 5.2 On each reference block, the reference indentation shall be measured. For each block, the difference between the mean measured value and the certified mean diagonal shall not exceed the maximum permissible errors given in Table The machine shall be verified at each test force which is used. For each test force, two reference blocks shall be selected from the hardness ranges specified below. The blocks shall be chosen so that at least one reference block in each hardness range is used for the verification. u 225 HV 400 HV to 600 HV > 700 HV 5.4 When verifying testing machines using only one test force, three reference blocks shall be used, one in each of the ranges specified in On each reference block, five indentations shall be made and measured. The test shall be carried out in accordance with ISO For special purposes, a hardness testing machine may be verified at one hardness value only, corresponding approximately to that of the tests to be made. 5.7 For each reference block, let d 1, d 2, d 3, d 4, d 5 be the arithmetic mean values of the measured lengths of the two diagonals of the indentations, arranged in increasing order of magnitude, and d1+ d2 + d3 + d4 + d 5 d = (1) The repeatability of the testing machine, under the particular verification conditions, is determined by the difference r = d5 d1 (2) The repeatability, expressed as a percentage of d, is calculated as: r rel 100 d d d 5 1 = (3) The repeatability of the testing machine verified is not considered satisfactory unless it satisfies the conditions given in Table 4. ISO 2005 All rights reserved 5
10 Table 4 Hardness of the reference block HV 5 to HV 100 r rel, % HV 0,2 to < HV 5 < HV 0,2 Repeatability of the testing machine max r HV b HV 5 to HV 100 HV 0,2 to < HV 5 Hardness of the reference block HV Hardness of the reference block HV u 225 HV 3,0 a 6,0 a 9,0 a > 225 HV 2,0 a 4,0 a 5,0 a a b or 0,001 mm, whichever is greater. HV: Vickers hardness. 5.9 The error, E, of the testing machine under the particular verification conditions is characterized by the difference: where where E = H H c (4) H1+ H2 + H3 + H4 + H5 H = (5) 5 H 1, H 2, H 3, H 4, H 5 are the hardness values corresponding to d 1, d 2, d 3, d 4, d 5 ; H c is the specified hardness of the reference block used. The percent error, E rel, is calculated by the following equation: E H H c rel = 100 (6) H c The maximum error 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. 6 ISO 2005 All rights reserved
11 Table 5 Hardness symbol Maximum permissible percentage error E rel, of the hardness testing machine Hardness, HV HV 0,01 HV 0, HV 0,02 8 HV 0, HV 0, HV 0, HV 0, HV 0, HV 0, HV HV HV HV HV HV HV HV HV NOTE 1 Values are not given when the length of the indentation diagonal is less than 0,020 mm. NOTE 2 For intermediate values, the maximum permissible error may be obtained by interpolation. NOTE 3 The values for microhardness testing machines are based on a maximum permissible error of 0,001 mm or 2 % of the mean diagonal length of indentation, whichever is the greater The determination of the uncertainty of measurement of the calibration results of the hardness testing machine is given in Annex B. 6 Intervals between verifications The specifications for the direct verifications of hardness testing machines are given in Table 6. Indirect verification shall be performed at least once every 12 months and after a direct verification has been performed. ISO 2005 All rights reserved 7
12 Table 6 Requirements of verification Force Measuring device Test cycle Indenter a Before setting to work first time x x x x After dismantling and reassembling, if force, measuring system or test cycle are affected x x x a Failure of indirect verification b x x x Indirect verification > 14 months ago x x x In addition, it is recommended that the indenter be directly verified after 2 years of use. b Direct verification of these parameters may be carried out sequentially (until the machine passes indirect verification) and is not required if it can be demonstrated (e.g. by tests with a reference indenter) that the indenter was the cause of the failure. 7 Verification report/calibration certificate The verification report/calibration certificate shall include the following information: a) a reference to this part of ISO 6507; b) method of verification (direct and/or indirect); c) identification data of the hardness testing machine; d) means of verification (reference blocks, elastic proving devices, etc); e) test forces verified; f) verification temperature; g) the result obtained; h) date of verification and reference to the verification institution; i) uncertainty of the verification result. 8 ISO 2005 All rights reserved
13 Annex A (informative) Notes on diamond indenters Experience has shown that a number of initially satisfactory indenters can become defective after use for a comparatively short time. This is due to small cracks, pits or other flaws in the surface. lf such faults are detected in time, many indenters may be reclaimed by regrinding. If not, any small defects on the surface rapidly worsen and make the indenter useless. Therefore, the condition of indenters should be monitored by visually checking the aspect of the indentation on a reference block, each day the testing machine is used; the verification of the indenter is no longer valid when the indenter shows defects; reground or otherwise repaired indenters shall be reverified. ISO 2005 All rights reserved 9
14 Annex B (informative) Uncertainty of measurement of the calibration results of the hardness testing machine The metrological chain necessary to define and disseminate hardness scales is shown in Figure D.1 in ISO :2005. B.1 Direct calibration of the hardness testing machine B.1.1 Calibration of the test force The combined relative standard uncertainty of the test force calibration is calculated according to the following equation: where 2 2 F = FRS + FHTM (B.1) u u u u FRS is the relative uncertainty of measurement of the force transducer (from calibration certificate); u FHTM is the relative standard uncertainty of the test force generated by the hardness testing machine. The uncertainty of measurement of the reference instrument, force transducer, is indicated in the corresponding calibration certificate. The influence quantities, like temperature dependence, long-term stability, and interpolation deviation, should be considered for critical applications. Depending on the design of the force transducer, the rotational position of the transducer related to the indenter axis of the hardness testing machine should be considered. EXAMPLE Uncertainty of measurement of the force transducer (from calibration certificate): U FRS = 0,12 % (k = 2) Calibration value of the force transducer F RS = 294,2 N 10 ISO 2005 All rights reserved
15 Table B.1 Results of the test force calibration Number of height position for test force calibration Series 1 F 1, N Series 2 F 2, N Series 3 F 3, N Mean value F, N Relative deviation F rel, % Relative standard measurement uncertainty u FHTM, % 1 294,7 294,9 294,5 294,7 0,17 0, ,9 294,5 294,6 294,3 0,03 0, ,1 294,0 293,7 293,6 0,20 0,09 where Frel FRS F F = (B.2) u s 1 Fi FHTM =, (n = 3) (B.3) F n s Fi is the standard deviation of the test-force indication values in the i-th height position. In Table B.2, the maximum value of u FHTM from Table B.1 is used. Table B.2 Calculation of the uncertainty of measurement of the test force Quantity X i Estimated value x i Relative limit values a i Distribution type Relative standard measurement uncertainty u(x i ) Sensitivity coefficient c i Relative uncertainty contribution u i (H) u FRS 294,2 N Normal 6, , u FHTM 0,06 N Normal 9, , Relative combined standard uncertainty u(f) Relative expanded uncertainty of measurement U(F) (k = 2) 1, , Table B.3 Calculation of the maximum relative deviation of the test force including the uncertainty of measurement of the reference instrument Relative deviation of test force F rel Expanded relative measurement uncertainty of test force U F Max. relative deviation of test force including measurement uncertainty of reference instrument F max % % % 0,20 0,22 0,42 where F max = I F rel I + U F (B.4) The result of the example means that the deviation of the test force, including the uncertainty of measurement of the reference instrument specified in 4.2 amounting to ± 1,0 % is complied with. ISO 2005 All rights reserved 11
16 B.1.2 Calibration of the optical measuring system The combined relative standard uncertainty of the reference instrument for the measuring system is calculated as follows: where L = LRS + ms + LHTM (B.5) u u u u u LRS u ms is the relative uncertainty of measurement of the object micrometer (reference standard) from the calibration certificate for k = 1; is the relative uncertainty of measurement due to the resolution of the measuring system; u LHTM is the relative standard uncertainty of measurement of the hardness testing machine. The uncertainty of measurement of the reference instrument for the optical measuring system, the object micrometer, is indicated in the corresponding calibration certificate. The influence quantities, for example, temperature dependence, long-term stability, and interpolation deviation, do not exert an essential influence on the uncertainty of measurement of the object micrometer. EXAMPLE Uncertainty of measurement of the object micrometer: U LRS = 0,000 5 mm (k = 2) Resolution of the measuring system δ ms = 0,1 µm Table B.4 Results of the calibration of the measuring system Indication value of the object micrometer L RS mm Series 1 L 1 mm Series 2 L 2 mm Series 3 L 3 mm Mean value L mm Relative deviation L rel % Relative standard measurement uncertainty u LHTM % 0,05 0, , , , ,07 0,07 0,10 0, , , , ,10 0,06 0,20 0, , , , ,02 0,03 0,30 0, , , , ,01 0,04 0,40 0, , , , ,05 0,01 where ulhtm Lrel sli L 1 =, (n = 3) (B.6) n L LRS LRS = (B.7) 12 ISO 2005 All rights reserved
17 s Li is the standard deviation of the length indication values for the i-th indication value of the object micrometer. Table B.5 Calculation of the uncertainty of measurement of the measuring system Quantity X i Estimated value x i Limit value a i Distribution type Relative standard measurement uncertainty u(x i ) Sensitivity coefficient c i Relative uncertainty contribution u i (H) u LRS 0,40 mm 0,5 µm Normal 1, , u ms 0 mm 0,1 µm Rectangular 0, , u LHTM 0 Normal 6, , Relative combined uncertainty of measurement u L, % (related to L RS = 0,4 mm) 0,07 Relative expanded uncertainty of measurement U L (k = 2), % 0,14 Table B.6 Calculation of the maximum relative deviation of the measuring system including the uncertainty of measurement of the length reference instrument Test length L RS Relative deviation of the measuring system L rel Expanded relative uncertainty of measurement U L Max. relative deviation of measuring system incl. measurement uncertainty of length reference instrument L max % % % 0,40 mm 0,10 0,14 0,24 where L max = I L rel I + U L (B.8) The result of the example means that the deviation of the measuring system, including the uncertainty of measurement of the length reference instrument specified in 4.4 amounting to ± 0,5 % is complied with. B.1.3 Verification of the indenter The indenter, consisting of indenter tip and holder, cannot be verified, respectively calibrated, in-site. A valid calibration certificate of an accredited calibration laboratory shall exist which confirms the geometrical deviations of the indenter (see 4.3). B.1.4 Verification of the test cycle In 4.5, the permissible deviation for every section of the test cycle is stipulated as ± 0,5 s. While measuring with a usual time measuring system (stopwatch), the uncertainty of measurement can be indicated as 0,1 s. Therefore, an estimation of the uncertainty of measurement is not necessary. ISO 2005 All rights reserved 13
18 B.2 Indirect verification of the hardness testing machine By indirect verification with hardness reference blocks, the overall function of the hardness testing machine is checked and the repeatability, as well as the deviation of the hardness testing machine from the real hardness value, are determined. The uncertainty of measurement of the indirect verification of the hardness testing machine follows from the equation: where HTM = CRM + CRM D + H + ms (B.9) u u u u u u CRM is the calibration uncertainty of the hardness reference block according to the calibration certificate for k = 1; u CRM-D is the hardness change of the hardness reference block since its last calibration due to drift (negligible for use of the hardness reference block complying with the standard); u H u ms is the standard uncertainty of hardness testing machine when measuring CRM; is the uncertainty due to the resolution of the hardness testing machine. EXAMPLE Hardness of the hardness reference block H CRM = (400,0 ± 5,0) HV30 Uncertainty of measurement of the hardness reference block U CRM = ± 5,0 HV30 Resolution of the hardness testing machine δ ms = 0,1 µm No. Table B.7 Results of the indirect verification Measured indentation diagonal d, mm Calculated hardness value H, HV a 1 0,371 6 min 402,9 max 2 0, ,1 3 0,372 8 max 400,3 min 4 0, ,2 5 0, ,5 Mean value H 0, ,6 Standard deviation s H 0,99 a HV: Vickers hardness. b = H HCRM b = 401,6 400,0 = 1,6 HV (B.10) uh t sh n = (B.11) For t = 1,15, n = 5 and s H = 0,99 HV follows: u H = 0,51 HV 14 ISO 2005 All rights reserved
19 B.3 Budget of uncertainty of measurement Table B.8 Budget of uncertainty of measurement Quantity X i Estimated value x i Standard uncertainty of measurement u(x i ) Distribution type Sensitivity coefficient c i Uncertainty contribution u i (H) u CRM 400 HV b 2,50 HV Normal 1,0 2,50 HV u H 0 HV 0,51 HV Normal 1,0 0,51 HV u ms 0 HV 0, mm Rectangular 2 145,1 a 0,06 HV u CMR-D 0 HV 0 HV Triangular 1,0 0 HV Combined uncertainty of measurement u HTM Expanded uncertainty of measurement U HTM (k = 2) 2,55 HV 5,1 HV a b c = H/ d = 2(H/d) for H = 400 HV30 and d = 0,372 9 mm. HV: Vickers hardness. Table B.9 Maximum deviation of the hardness testing machine including the uncertainty of measurement Measured hardness on the hardness testing machine H Expanded uncertainty of measurement U HTM Deviation of the testing machine when calibrating with the reference block b Maximum deviation of the testing machine including uncertainty of measurement H HTMmax HV HV HV HV 401,6 HV30 5,1 1,6 6,7 HV: Vickers hardness. where b = H H CRM (B.12) H HTMmax = U HTM + b = 5,1 + 1,6 = 6,7 HV The result of the example above means that the permissible limit deviation of the testing machine, including the uncertainty of measurement of the testing machine specified in Clause 5 amounting to ± 2 % ( H HTMmax /H = 1,7 %), is complied with. ISO 2005 All rights reserved 15
20 Bibliography [1] SAWLA A. Uncertainty of measurement in the verification and calibration of the force measuring systems of testing machines, Proceedings of the Asia-Pacific symposium on measurement of force, mass and torque (APMF), Tsukuba, Japan, Novembre 2000 [2] WEHRSTEDT A., PATKOVSZKY I. News in the field of standardization about verification and calibration of materials testing machines, May 2001, EMPA Academy 2001 [3] GABAUER W. Manual codes of practice for the determination of uncertainties in mechanical tests on metallic materials, The estimation of uncertainties in hardness measurements, Project No. SMT4-CT , UNCERT COP 14:2000 [4] POLZIN, T., SCHWENK D. Method for Uncertainty Determination of Hardness Testing; PC File for Determination, Materialprüfung 44 (2002) 3, pp ISO 2005 All rights reserved
22 ICS Price based on 16 pages ISO 2005 All rights reserved