1、Designation: A956 12Standard Test Method forLeeb Hardness Testing of Steel Products1This standard is issued under the fixed designation A956; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revision. A number in pa
2、rentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method covers the determination of the Leebhardness of steel, cast steel, and cast iron (Part A), includingthe methods for the verificati
3、on of Leeb hardness testinginstruments (Part B), and the calibration of standardized testblocks (Part C).NOTE 1The original title of this standard was “Standard Test Methodfor Equotip Hardness Testing of Steel Products.”11.2 The values stated in inch-pound units are to be regardedas standard. The va
4、lues given in parentheses are mathematicalconversions to SI units that are provided for information onlyand are not considered standard.1.3 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to es
5、tablish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2E691 Practice for Conducting an Interlaboratory Study toDetermine the Precision of a Test Method3. Terminology3.1 Definitions:3.1.1 cali
6、brationdetermination of the values of the sig-nificant operating parameters of the instrument by comparisonwith values indicated by a reference instrument or by a set ofreference standards.3.1.2 Leeb hardness numbera number equal to the ratio ofthe rebound velocity to the impact velocity of a 3-mm o
7、r 5-mm(based on the type of impact device) diameter sphericallyshaped tungsten carbide, silicon nitride, or diamond tippedimpact body, multiplied by 1000.L 5Rebound VelocityImpact Velocity31000The Leeb hardness number is followed by the symbol HLwith one or more suffix characters representing the ty
8、pe ofimpact device.3.1.3 Leeb hardness testa dynamic hardness test methodusing a calibrated instrument that impacts a spherically shapedtungsten carbide, silicon nitride, or diamond tipped body witha fixed velocity (generated by a spring force) onto a surface ofthe material under test. The ratio of
9、the rebound velocity to theimpact velocity of the impact body is a measure of the hardnessof the material under test.3.1.4 surface finishall references to surface finish in thistest method are defined as surface roughness (that is, Ra =average roughness value, AA = arithmetic average).3.1.5 verifica
10、tionchecking or testing the instrument toensure conformance with this test method.4. Summary of Test Method4.1 During a hardness test, an impact body with a spheri-cally shaped tungsten carbide, silicon nitride, or diamond tipimpacts under spring force, the test surface from which itrebounds. The im
11、pact and rebound velocities are measuredwhen the impact body is approximately 1 mm from the testsurface. This is accomplished by means of a permanent magnetmounted in the impact body which, during the test, movesthrough a coil in the impact device and induces an electricvoltage on both the impact an
12、d rebound movements. Theseinduced voltages are proportional to the respective impact andrebound velocities. The quotient of these measured voltagevalues derived from the impact and rebound velocities, multi-plied by the factor 1000 produces a number which constitutesthe Leeb hardness value.5. Signif
13、icance and Use5.1 Hardness of a material is a poorly defined term that mayhave many meanings depending on the type of test performedand the expectations of the person involved. The Leeb hardnesstest is of the dynamic or rebound type, which primarilydepends both on the plastic and on the elastic prop
14、erties of the1This test method is under the jurisdiction of ASTM Committee A01 on Steel,Stainless Steel and Related Alloys and is the direct responsibility of SubcommitteeA01.06 on Steel Forgings and Billets.Current edition approved Nov. 15, 2012. Published December 2012. Originallyapproved in 1996.
15、 Last previous edition approved in 2006 as A956 06.Leeb and Equotip are registered trademarks used with permission of Proceq SA.DOI: 10.1520/A0956-12.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStand
16、ards volume information, refer to the standards Document Summary page onthe ASTM website.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States1material being tested. The results obtained are indicative of thestrength and dependent on the he
17、at treatment of the materialtested.5.2 The Leeb hardness test is a superficial determinationonly measuring the condition of the surface contacted. Theresults generated at that location do not represent the part atany other surface location and yield no information about thematerial at subsurface loc
18、ations.A. GENERAL DESCRIPTION OF INSTRUMENTSAND TEST PROCEDURE FOR LEEB HARDNESSTEST6. Apparatus6.1 The instrument used for Leeb hardness testing consistsof (1) an impact device that is equipped with a sphericallyshaped tungsten carbide, silicon nitride, or synthetic diamondtipped impact body, an in
19、duction coil velocity measuringassembly, and a support ring, and (2) an electronic digitaldisplay hardness indicating device.6.2 Impact DevicesThere are eight types of impact de-vices used in Leeb hardness testing. These are the D, DC,D+15, DL, G, C, S, and the E impact units. Brief descriptionsof t
20、he types of devices and their common applications aregiven in Appendix X1.6.3 See 8.1.1 when using replacement machine components.7. Test Piece7.1 FormThe Leeb hardness test is acceptable for steel,cast steel, and cast iron with varying shapes and sizes.7.2 Thickness and WeightThe thickness and weig
21、ht of thetest piece shall be considered when selecting the impact deviceto be employed. The following guidelines are offered asminimum weights and sizes of test pieces for selecting theproper test equipment. Test pieces of weights less than theminimum or pieces of any weight with sections less than
22、theminimum thickness require rigid support and coupling to athick, heavier non-yielding surface to resist the impact of thedevice. Failure to provide adequate support and coupling willproduce test results lower than the true hardness value.Impact Device Weight (min) or Thickness (min)D, DC, D+15,DL,
23、 S, E15 lb (5 kg)18 in. (3 mm)G 40 lb (15 kg)38 in. (10 mm)C 4lb(1.5kg)132 in. (1 mm)7.3 CurvatureTest pieces with curved surfaces may betested on either the convex or concave surfaces providing thatthis radius of curvature of the specimens is matched to the sizeof the support ring and is not less t
24、han 2 in. (50 mm) for the Gimpact device or 1316 in. (30 mm) for other impact devices.7.4 Surface Finish/PreparationThe test surface shall becarefully prepared to avoid any alterations in hardness causedby heating during grinding or by work hardening duringmachining. Any paint, scale, pits, or other
25、 surface coatingsshall be completely removed. The surfaces to be tested shall besmooth. Failure to provide adequate surface finish will producequestionable test results. Coarse finishes will tend to lower themeasured value. It is recommended that the test surface bemachined or ground and polished to
26、 the following finishes.(The grinding wheel grit size shown for each finish is offeredfor guidance in achieving the finish noted.)Impact Device Surface FinishRa(max)Grit Size (Approx.)D, DC, D+15,DL, S, E63 in. (2 m) 200G 250 in. (7 m) 65C 16 in. (0.4 m) 5007.5 Magnetic FieldsPerformance of the Leeb
27、 hardnesstest on parts with a residual magnetic field may affect theresults. It is recommended that any residual magnetic field beless than 4 G.7.6 VibrationVibration of the test specimen may affect theresults of the Leeb hardness test. It is recommended that thistest be performed with the test piec
28、e at rest.7.7 TemperatureThe temperature of the test piece mayaffect the results of the test. In addition, this effect may bedifferent for different materials. Testing to this procedure shallbe performed with the temperature of the test piece between40F (4C) and 100F (38C). At temperatures outside t
29、hisrange, the user shall develop a temperature correction for thespecific material being tested.8. Verification of Apparatus8.1 Verification MethodPrior to each shift, work period, oruse, and following a period of extended continuous use (1000impacts), the instrument shall be verified as specified i
30、n Part B.Any instrument not meeting the requirements of Part B shallnot be employed for the acceptance testing of product.8.1.1 Cautionary note: When replacement parts are used ina Leeb hardness tester it is important that they be fullycompatible with the original equipment, otherwise incorrecthardn
31、ess readings may be obtained. Calibration using a singlestandard test block may indicate acceptable results, but addi-tional calibration tests using blocks of differing hardness mayyield unacceptable results. If replacement, non-original equip-ment parts are used, multiple block calibration verifica
32、tion isstrongly advised. Specifically, one calibration block of ahardness equal to or lower than the minimum expectedhardness of the material being tested, one calibration block ofa hardness equal to or greater than the maximum expectedhardness of the material being tested, and one calibration block
33、near the middle of the range should be used.9. Procedure9.1 Test MethodTo perform a hardness test, the impactdevice is connected to the indicator device and the instrumentis turned on. The impact device, while not in contact with thetest piece, is held firmly with one hand and the charging tubeis de
34、pressed with the other hand until contact is felt. Thecharging tube is allowed to slowly return to the startingposition. The impact body is now in its loaded or lockedposition. After placing the impact device on the test surface,trigger the impact body by exerting a light pressure on therelease butt
35、on. The Leeb hardness value is read on the indicatordevice.A956 1229.2 AlignmentTo prevent errors resulting frommisalignment, the base support ring of the impact device shallbe held snugly and perpendicular to the surface of the testpiece.9.3 Impact DirectionThe impact device is calibrated forthe do
36、wn vertical impact direction (perpendicular to a horizon-tal surface). For other impact directions such as 45 from thehorizontal plane or from underneath, the measured hardnessvalues will require adjustment (see 10.2). Some newer modelsautomatically compensate for test direction.9.4 Spacing Indentat
37、ionsThe distance between any twoimpact points shall not be less than two diameters edge-to-edge. The distance between the impact point and a specimenedge shall not be less than three diameters edge-to-edge. Nopoint shall be impacted more than once.9.5 Reading the Leeb InstrumentHardness values in Le
38、ebunits are read directly on the electronic display of the indicatordevice. The indicated value is automatically replaced with thenext test impact result.9.6 Number of ImpactsFive impacts in an area of approxi-mately 1 in.2(645 mm2) shall constitute a test. If the materialbeing tested is considered
39、to be nonhomogeneous (forexample, cast iron) ten impacts in an area shall be made toconstitute a test.10. Calculation of Hardness Result10.1 The hardness test result shall be the arithmetic averageof the five individual impact readings in the measuring area.10.2 Compensation for Test DirectionWhen u
40、sing anLeeb instrument without automatic compensation for testdirection, the compensation value for direction of test impact isto be subtracted from the average value determined for themeasuring area. This compensation value can be determined inaccordance with Tables 1-8.11. Conversion to Other Hard
41、ness Scales or TensileStrength Values11.1 There is no direct correlation between the Leeb hard-ness test principle and other hardness methods or a tensilestrength test. All such conversions are, at best, approximationsand therefore conversions should be avoided except for specialcases where a reliab
42、le basis for the approximate conversion andthe accuracy of the conversion has been obtained by compari-son testing. No conversions shall be employed without specificagreement between the party specifying this test method andthe party performing the hardness test.12. Report12.1 Report the following i
43、nformation:12.1.1 The average Leeb hardness number for each test areawith the impact device indicated (for example, xxx HLD or xxxHLD+15).12.1.2 When hardness values converted from the Leebnumber are reported, the instrument used shall be reported inparentheses, for example, HB ( HLG).13. Precision
44、and Bias13.1 Precision:13.1.1 Interlaboratory Test ProgramAn interlaboratorytest program was conducted in accordance with to developinformation regarding the precision of the Leeb hardnessTABLE 1 Compensation Values for Other Impact Directions:Device DLD300-6 -12 -20 -29350-6 -12 -19 -27400-5 -11 -1
45、8 -25450-5 -10 -17 -24500-5 -10 -16 -22550-4 -9 -15 -20600-4 -8 -14 -19650-4 -8 -13 -18700-3 -7 -12 -17750-3 -6 -11 -16800-3 -6 -10 -15850-2 -5 -9 -14900TABLE 2 Compensation Values for Other Impact Directions:DeviceD+15LD+15300-7 -14 -26 -38350-7 -13 -25 -36400-6 -12 -23 -34450-6 -12 -22 -32500-6 -1
46、1 -21 -30550-6 -11 -20 -28600-5 -10 -19 -27650-5 -10 -18 -25700-5 -9 -17 -24750-4 -9 -16 -22800-4 -8 -15 -21850-4 -8 -14 -20900A956 123measurements. Eight laboratories tested five certified testblocks. Each laboratory measured the hardness of each block25 times.13.1.2 Test ResultThe precision inform
47、ation given belowis the average of the five certified test blocks, each of a differenthardness.13.1.3 Repeatability and Reproducibility:95 % Repeatability Limit (within laboratory) = 4.4 %95 % Reproducibility Limit (between laboratories) = 8.8 %13.1.3.1 The terms in 13.1.3 (repeatability limit and r
48、epro-ducibility limit) are used as specified in Practice E691. Therespective standard deviations among test results, related to theabove numbers by the factor 2.8, are:Repeatability Standard Deviation = 1.6 %Reproducibility Standard Deviation = 3.2 %13.2 BiasSince hardness is not an intrinsic proper
49、ty of amaterial, there is no basis on which to determine or assign anaccepted reference value. Consequently, there is no basis fordefining the bias of this test method.B. VERIFICATION OF LEEB HARDNESSINSTRUMENTS14. Scope14.1 Part B covers the procedure for verification of Leebhardness instruments by a standardized block method.TABLE 3 Compensation Values for Other Impact Directions:Device ELE300-5 -9 -18 -26350-4 -9 -17 -24400-4 -9 -16 -22450-4 -8 -15 -21500-4 -8 -14 -20550-4 -8 -13 -18600-3 -7 -12 -17650-3 -7 -12 -16700-3 -6 -11 -15750-3 -
