1、Designation: A956 12A956/A956M 17Standard Test Method forLeeb Hardness Testing of Steel Products1This standard is issued under the fixed designationA956;A956/A956M; the number immediately following the designation indicates theyear of original adoption or, in the case of revision, the year of last r
2、evision. A number in parentheses indicates the year of lastreapproval. A superscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope Scope*1.1 This test method covers the determination of the Leeb hardness of steel, cast steel, and cast iron (Part A), includin
3、g themethods for the verification of Leeb hardness testing instruments (Part B), and the calibration of standardized test blocks (Part C).NOTE 1The original title of this standard was “Standard Test Method for Equotip Hardness Testing of Steel Products.”11.2 The values stated in either SI units or i
4、nch-pound units are to be regarded separately as standard. The values given inparentheses are mathematical conversions to SI units that are provided for information only and are not considered stated in eachsystem may not be exact equivalents; therefore, each system shall be used independently of th
5、e other. Combining values from thetwo systems may result in non-conformance with the standard.1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibilityof the user of this standard to establish appropriate safety safety, health
6、, and healthenvironmental practices and determine theapplicability of regulatory limitations prior to use.1.4 This international standard was developed in accordance with internationally recognized principles on standardizationestablished in the Decision on Principles for the Development of Internat
7、ional Standards, Guides and Recommendations issuedby the World Trade Organization Technical Barriers to Trade (TBT) Committee.2. Referenced Documents2.1 ASTM Standards:2E691 Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method3. Terminology3.1 Definitions:3.1.
8、1 calibrationdetermination of the values of the significant operating parameters of the instrument by comparison withvalues indicated by a reference instrument or by a set of reference standards.3.1.2 Leeb hardness numbera number equal to the ratio of the rebound velocity to the impact velocity of a
9、 3-mm or 5-mm0.118 in. 3 mm or 0.197 in. 5 mm (based on the type of impact device) diameter spherically shaped tungsten carbide, siliconnitride, or diamond tipped impact body, multiplied by 1000.L 5Rebound VelocityImpact Velocity 31000The Leeb hardness number is followed by the symbol HL with one or
10、 more suffix characters representing the type of impactdevice.3.1.3 Leeb hardness testa dynamic hardness test method using a calibrated instrument that impacts a spherically shapedtungsten carbide, silicon nitride, or diamond tipped body with a fixed velocity (generated by a spring force) onto a sur
11、face of thematerial under test. The ratio of the rebound velocity to the impact velocity of the impact body is a measure of the hardness ofthe material under test.1 This test method is under the jurisdiction of ASTM Committee A01 on Steel, Stainless Steel and Related Alloys and is the direct respons
12、ibility of Subcommittee A01.06on Steel Forgings and Billets.Current edition approved Nov. 15, 2012Sept. 1, 2017. Published December 2012September 2017. Originally approved in 1996. Last previous edition approved in 20062012as A956 06.A956 12.Leeb and Equotip are registered trademarks used with permi
13、ssion of Proceq SA. DOI: 10.1520/A0956-12.10.1520/A0956_A0956M-17.2 For referencedASTM standards, visit theASTM website, www.astm.org, or contactASTM Customer Service at serviceastm.org. For Annual Book of ASTM Standardsvolume information, refer to the standardsstandards Document Summary page on pag
14、eon the ASTM website.This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Becauseit may not be technically possible to adequately depict all changes accurately, ASTM recommends that us
15、ers consult prior editions as appropriate. In all cases only the current versionof the standard as published by ASTM is to be considered the official document.*A Summary of Changes section appears at the end of this standardCopyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Consh
16、ohocken, PA 19428-2959. United States13.1.4 surface finishall references to surface finish in this test method are defined as surface roughness (that is, Ra = averageroughness value, AA = arithmetic average).3.1.5 verificationchecking or testing the instrument to ensure conformance with this test me
17、thod.4. Summary of Test Method4.1 During a hardness test, an impact body with a spherically shaped tungsten carbide, silicon nitride, or diamond tip impactsunder spring force, the impacts, after being propelled to the specified velocity, the test surface from which it rebounds. The impactand rebound
18、 velocities are measured when the impact body is approximately 1 mm 0.039 in. 1 mm from the test surface. Thisis accomplished by means of a permanent magnet mounted in the impact body which, during the test, moves through a coil in theimpact device and induces an electric voltage on both the impact
19、and rebound movements. These induced voltages are proportionalto the respective impact and rebound velocities. The quotient of these measured voltage values derived from the impact andrebound velocities, multiplied by the factor 1000 produces a number which constitutes the Leeb hardness value.5. Sig
20、nificance and Use5.1 Hardness of a material is a poorly defined term that may have many meanings depending on the type of test performed andthe expectations of the person involved. The Leeb hardness test is of the dynamic or rebound type, which primarily depends bothon the plastic and on the elastic
21、 properties of the material being tested. The results obtained are indicative of the strength anddependent on the heat treatment of the material tested.5.2 The Leeb hardness test is a superficial determination only measuring the condition of the surface contacted. The resultsgenerated at that locati
22、on do not represent the part at any other surface location and yield no information about the material atsubsurface locations.A. GENERAL DESCRIPTION OF INSTRUMENTS AND TEST PROCEDURE FOR LEEB HARDNESS TEST6. Apparatus6.1 The instrument used for Leeb hardness testing consists of (1) an impact device
23、that is equipped with a spherically shapedtungsten carbide, silicon nitride, or synthetic diamond tipped impact body, an induction coil velocity measuring assembly, and asupport ring, and (2) an electronic digital display hardness indicating device.6.2 Impact DevicesThere are eight types of impact d
24、evices used in Leeb hardness testing. These are the D, DC, D+15, DL,G,C, S, and the E impact units. Brief descriptions of the types of devices and their common applications are given in Appendix X1.Table 1 provides the specifications for the Leeb scales according to impact device type.6.3 See 8.1.1
25、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 weight of the test piece shall be considered when selecting the impact device tobe employed
26、. The following guidelines are offered as minimum weights and sizes of test pieces for selecting the proper testequipment. Test pieces of weights less than the minimum or pieces of any weight with sections less than the minimum thicknessrequire rigid support and coupling to a thick, heavier non-yiel
27、ding surface to resist the impact of the device. Failure to provideadequate support and coupling will produce test results lower than the true hardness value.TABLE 1 Specifications of Standard Leeb Hardness Testing DevicesProperty Symbol Unit D/DC S E D+15 DL C GImpact velocityA VA ft/s m/s 6.73 2.0
28、5 5 %6.73 2.05 5 %6.73 2.05 5 %5.58 1.7 5 %5.97 1.82 5 %4.56 1.39 5 %9.78 2.98 5 %Impact body, mass M oz g 0.192 0.0025.45 0.050.190 0.0025.40 0.050.192 0.0025.45 0.050.273 0.0027.75 0.050.256 0.0027.25 0.050.109 0.0023.1 0.050.705 0.00220.00 0.05Indenter, radius R in. mm 0.059 1.5 0.059 1.5 0.059 1
29、.5 0.059 1.5 0.055 1.39 0.059 1.5 0.098 2.5material TCB Si3N4 PCDC TC TC TC TChardness h HV2 1600 100 1600 100 $4500D 1600 100 1600 100 1600 100 1600 100Maximum distance ofball indenter from thetest piece surface whenmeasuring velocityH in. mm 0.079 2.0 0.079 2.0 0.079 2.0 0.079 2.0 0.079 2.0 0.079
30、2.0 0.118 3.0A Impact direction: vertical down, in the direction of gravity.B TC = tungsten carbide.C PCD = polycrystaline diamond.D The hardness of the impact body E indenter is informational, not required to be verified.A956/A956M 172ImpactDeviceWeight (min)orThickness(min)ImpactDeviceMinimum Mass
31、withoutRigid SupportMinimum MasswithRigid SupportMinimumThickness(Uncoupled)MinimumThickness(Coupled)D, DC, D+15,DL,S, E15 lb (5kg)18 in.(3 mm)D, DC, D+15,DL,S, E 11.0 lb 5 kg 4.4 lb 2 kg0.984 in.25 mm0.118 in.3 mmG 40 lb (15kg) 38 in.(10 mm)G 33.1 lb 15 kg 11.0 lb 5 kg 2.756 in.70 mm 0.394 in.10 mm
32、C 4 lb (1.5kg) 132 in.(1 mm)C 3.3 lb 1.5 kg 0.3 lb 0.5 kg 0.394 in.10 mm 0.039 in.1 mm7.3 CurvatureTest pieces with curved surfaces may be tested on either the convex or concave surfaces providing that thisradius of curvature of the specimens is matched to the size of the support ring and is not les
33、s than 21.969 in. (50 mm)50 mmfor the G impact device or 11.181316 in. (30 mm)30 mm for other impact devices.7.4 Surface Finish/PreparationThe test surface shall be carefully prepared to avoid any alterations in hardness caused byheating during grinding or by work hardening during machining. Any pai
34、nt, scale, pits, or other surface coatings shall becompletely removed.The surfaces to be tested shall be smooth. Failure to provide adequate surface finish will produce questionabletest results. Coarse finishes will tend to lower the measured value. It is recommended that the test surface be machine
35、d or groundand polished to the following finishes. (The grinding wheel grit size shown for each finish is offered for guidance in achieving thefinish noted.)Impact Device Surface FinishRa(max) Grit Size(Approx.)Impact Device Surface FinishRa(max) Grit Size(Approx.)D, DC, D+15, DL,S, E 63 in. (2 m) 2
36、00D, DC, D+15, DL,S, E 78.7 in. 2 m 200G 250 in. (7 m) 65G 275.6 in. 7 m 65C 16 in. (0.4 m) 500C 15.7 in. 0.4 m 5007.5 Magnetic FieldsPerformance of the Leeb hardness test on parts with a residual magnetic field may affect the results. Itis recommended that any residual magnetic field be less than 4
37、 G.7.6 VibrationVibration of the test specimen may affect the results of the Leeb hardness test. It is recommended that this testbe performed with the test piece at rest.7.7 TemperatureThe temperature of the test piece may affect the results of the test. In addition, this effect may be differentfor
38、different materials. Testing to this procedure shall be performed with the temperature of the test piece between 40F (4C) and100F (38C).39 F 4 C and 100 F 38 C. At temperatures outside this range, the user shall develop a temperature correctionfor the specific material being tested.8. Verification o
39、f Apparatus8.1 Verification MethodPrior to each shift, work period, or use, and following a period of extended continuous use (1000impacts), the instrument shall be verified as specified in Part B. Any instrument not meeting the requirements of Part B shall notbe employed for the acceptance testing
40、of product.8.1.1 Cautionary note: When replacement parts are used in a Leeb hardness tester it is important that they be fully compatiblewith the original equipment, otherwise incorrect hardness readings may be obtained. Calibration using a single standard test blockmay indicate acceptable results,
41、but additional calibration tests using blocks of differing hardness may yield unacceptable results.If replacement, non-original equipment parts are used, multiple block calibration verification is strongly advised. Specifically, onecalibration block of a hardness equal to or lower than the minimum e
42、xpected hardness of the material being tested, one calibrationblock of a hardness equal to or greater than the maximum expected hardness of the material being tested, and one calibration blocknear the middle of the range should be used.9. Procedure9.1 Test MethodTo perform a hardness test, the impac
43、t device is connected to the indicator user interface device and theinstrument is turned on. The impact device, while not in contact with the test piece, is held firmly with one hand and the chargingtube is depressed with the other hand until contact is felt. The charging tube is allowed to slowly r
44、eturn to the starting position.A956/A956M 173The impact body is now in its loaded or locked position. After placing the impact device on the test surface, trigger the impactbody by exerting a light pressure on the release button. The Leeb hardness value is read on the indicator device.powered on.9.1
45、.1 The impact device is readied for impact.9.1.1.1 Mechanically Charged DeviceSome impact devices are charged mechanically by pulling the impact body against aspring or other mechanism that propels the impact body at the prescribed velocity. The impact device, while not in contact withthe test piece
46、, is held firmly with one hand while the charging mechanism is activated with the other hand. Once the impact bodyis in the charged position the charging mechanism is allowed to slowly return to its resting position.9.1.1.2 Otherwise Charged DeviceDevices that are not charged mechanically may use gr
47、avity or other force applicationmethod to propel the impact body at the prescribed velocity. Charging of these devices should be conducted according tomanufacturers instructions.9.1.2 After placing the readied (loaded) impact device on the test surface, trigger the impact by actuating the release me
48、chanismaccording to manufacturers instructions.9.1.3 The Leeb hardness value is displayed or otherwise used by a user interface device after the impact.NOTE 2The user interface device may take the form of a computer or PLC that does not display the hardness value directly to the user. Such a userint
49、erface device may use the hardness value to operate an automatic sorting machine or simply log the value in a database.9.2 AlignmentTo prevent errors resulting from misalignment, the base support ring of the impact device shall be held snuglyand perpendicular to the surface of the test piece.9.3 Impact DirectionThe impact device is calibrated for the down vertical impact dire
