1、Designation: A956/A956M 17A956/A956M 17aStandard Test Method forLeeb Hardness Testing of Steel Products1This standard is issued under the fixed designation A956/A956M; the number immediately following the designation indicates the yearof original adoption or, in the case of revision, the year of las
2、t revision. A number in parentheses indicates the year of last reapproval.A superscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope*1.1 This test method covers the determination of the Leeb hardness of steel, cast steel, and cast iron (Part A), including t
3、hemethods 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 inch
4、-pound units are to be regarded separately as standard. The values stated in eachsystem may not be exact equivalents; therefore, each system shall be used independently of the other. Combining values from thetwo systems may result in non-conformance with the standard.1.3 This standard does not purpo
5、rt 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, health, and environmental practices and determine the applicability ofregulatory limitations prior to use.1.4 This international standard w
6、as developed in accordance with internationally recognized principles on standardizationestablished in the Decision on Principles for the Development of International Standards, Guides and Recommendations issuedby the World Trade Organization Technical Barriers to Trade (TBT) Committee.2. Referenced
7、 Documents2.1 ASTM Standards:2E140 Hardness Conversion Tables for Metals Relationship Among Brinell Hardness, Vickers Hardness, Rockwell Hardness,Superficial Hardness, Knoop Hardness, Scleroscope Hardness, and Leeb HardnessE177 Practice for Use of the Terms Precision and Bias in ASTM Test MethodsE69
8、1 Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method3. Terminology3.1 Definitions:3.1.1 calibrationdetermination of the values of the significant operating parameters of the instrument by comparison withvalues indicated by a reference instrument or by a set
9、of reference standards.3.1.2 Leeb hardness numbera number equal to the ratio of the rebound velocity to the impact velocity of a 0.118 in. 3 mmor 0.197 in. 5 mm (based on the type of impact device) diameter spherically shaped tungsten carbide, silicon nitride, or diamondtipped impact body, multiplie
10、d by 1000.L 5Rebound VelocityImpact Velocity 31000The Leeb hardness number is followed by the symbol HL with one or 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 shapedtungs
11、ten carbide, silicon nitride, or diamond tipped body with a fixed velocity (generated by a spring force) onto a surface 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
12、under the jurisdiction of ASTM Committee A01 on Steel, Stainless Steel and Related Alloys and is the direct responsibility of Subcommittee A01.06on Steel Forgings and Billets.Current edition approved Sept. 1, 2017Nov. 1, 2017. Published September 2017December 2017. Originally approved in 1996. Last
13、previous edition approved in 20122017as A956 12.A956/A956M 17.Leeb and Equotip are registered trademarks used with permission of Proceq SA. DOI: 10.1520/A0956_A0956M-17.10.1520/A0956_A0956M-17A.2 For referencedASTM standards, visit theASTM website, www.astm.org, or contactASTM Customer Service at se
14、rviceastm.org. For Annual Book of ASTM Standardsvolume information, refer to the standards Document Summary pageon 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.
15、 Becauseit may not be technically possible to adequately depict all changes accurately, ASTM recommends that users 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
16、appears at the end of this standardCopyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, 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 = a
17、rithmetic average).3.1.5 verificationchecking or testing the instrument to ensure conformance with this test method.4. Summary of Test Method4.1 During a hardness test, an impact body with a spherically shaped tungsten carbide, silicon nitride, or diamond tip impacts,after being propelled to the spe
18、cified velocity, the test surface from which it rebounds. The impact and rebound velocities aremeasured when the impact body is approximately 0.039 in. 1 mm from the test surface. This is accomplished by means of apermanent magnet mounted in the impact body which, during the test, moves through a co
19、il in the impact device and induces anelectric voltage on both the impact and rebound movements. These induced voltages are proportional to the respective impact andrebound velocities. The quotient of these measured voltage values derived from the impact and rebound velocities, multiplied bythe fact
20、or 1000 produces a number which constitutes the Leeb hardness value.5. Significance 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 r
21、ebound type, which primarily depends bothon the plastic and on the elastic 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 t
22、he condition of the surface contacted. The resultsgenerated at that location 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 i
23、nstrument used for Leeb hardness testing consists of (1) an impact device 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 hard
24、ness indicating device.6.2 Impact DevicesThere are eight types of impact devices 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 specifi
25、cations for the Leeb scales according to impact device type.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 weight of the tes
26、t piece shall be considered when selecting the impact device tobe employed. 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 minimu
27、m thicknessrequire rigid support and coupling to a thick, heavier non-yielding 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 DevicesProp
28、erty Symbol Unit D/DC S E D+15 DL C GImpact velocityA VA ft/s m/s 6.73 2.05 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 0.05
29、0.705 0.00220.00 0.05Indenter, radius R in. mm 0.059 1.5 0.059 1.5 0.059 1.5 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
30、 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 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
31、/A956M 17a2ImpactDeviceMinimum MasswithoutRigid SupportMinimum MasswithRigid SupportMinimumThickness(Uncoupled)MinimumThickness(Coupled)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 33.1 lb 15 kg 11.0 lb 5 kg 2.756 in.70 mm 0.394 in.10 mmC 3.3 lb 1.5 kg 0.3 lb 0.5 kg 0.394
32、 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 less than 1.969 in. 50 mm for the Gimpact device or 1.181 in. 30 m
33、m 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 paint, scale, pits, or other surface coatings shall becompletely removed.The surfaces
34、 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 machined or groundand polished to the following finishes. (The grinding wheel grit size s
35、hown for each finish is offered for guidance in achieving thefinish noted.)Impact Device Surface FinishRa(max) Grit Size(Approx.)D, DC, D+15, DL,S, E 78.7 in. 2 m 200G 275.6 in. 7 m 65C 15.7 in. 0.4 m 5007.5 Magnetic FieldsPerformance of the Leeb hardness test on parts with a residual magnetic field
36、 may affect the results. Itis recommended that any residual magnetic field be less than 4 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 tes
37、t piece may affect the results of the test. In addition, this effect may be differentfor different materials. Testing to this procedure shall be performed with the temperature of the test piece between 39 F 4 Cand 100 F 38 C. At temperatures outside this range, the user shall develop a temperature c
38、orrection for the specific materialbeing tested.8. Verification of 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 requir
39、ements of Part B shall notbe employed for the acceptance testing 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 us
40、ing a single standard test blockmay indicate acceptable results, 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, onecal
41、ibration block of a hardness equal to or lower than the minimum expected 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
42、.9. Procedure9.1 To perform a hardness test, the impact device is connected to the user interface device and powered on.9.1.1 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 me
43、chanism that propels the impact body at the prescribed velocity. The impact device, while not in contact withthe test piece, 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
44、 slowly return to its resting position.9.1.1.2 Otherwise Charged DeviceDevices that are not charged mechanically may use gravity or other force applicationmethod to propel the impact body at the prescribed velocity. Charging of these devices should be conducted according tomanufacturers instructions
45、.9.1.2 After placing the readied (loaded) impact device on the test surface, trigger the impact by actuating the release mechanismaccording 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
46、device may take the form of a computer or PLC that does not display the hardness value directly to the user. Such a userA956/A956M 17a3interface 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 fr
47、om 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 direction (perpendicular to a horizontalsurface). For other impact directions such as 45
48、 from the horizontal plane or from underneath, the measured hardness values willrequire adjustment (see 10.2). Some newer models automatically compensate for test direction.9.4 Spacing IndentationsThe distance between any two impact points shall not be less than two diameters edge-to-edge. Thedistan
49、ce between the impact point and a specimen edge shall not be less than three diameters edge-to-edge. No point shall beimpacted more than once.9.5 Reading the Leeb InstrumentHardness values in Leeb units are read directly on the electronic display of the indicatordevice. The indicated value is automatically replaced with the next test impact result.9.6 Number of ImpactsFive impacts in an a
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