ASTM_A_956-06.pdf

Designation:A 956-06NTERNATIONALStandard Test Method forLeeb Hardness Testing of Steel Products1This standard is issued under the fixed designation A 956;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 parentheses indicates the year of last reapproval.Asuperscript epsilon(e)indicates an editorial change since the last revision or reapproval.1.Scope*Rebound VelocityL=10001.1 This test method covers the determination of the LeebImpact Velocityhardness of steel,cast steel,and cast iron(Part A),includingthe methods for the verification of Leeb hardness testingThe Leeb hardness number is followed by the symbol HLinstruments(Part B).and the calibration of standardized testwith one or more suffix characters representing the type ofblocks(Part C).impact device.3.1.3 Leeb hardness test-a dynamic hardness test methodNorE 1-The original title of this standard was Standard Test Methodusing a calibrated instrument that impacts a spherically shapedfor Equotip Hardness Testing of Steel Products.carbide ball or diamond tipped body with a fixed velocity1.2 The values stated in inch-pound units are to be regarded(generated by a spring force)onto a surface of the materialas standard.The values given in parentheses are mathematicalunder test.The ratio of the rebound velocity to the impactconversions to SI units that are provided for information onlyvelocity of the impact body is a measure of the hardness of theand are not considered standard.material under test.1.3 This standard does not purport to address all of the3.1.4 surface finish-all references to surface finish in thissafety concerns,if any,associated with its use.It is thetest method are defined as surface roughness(that is,Raresponsibility of the user of this standard to establish appro-average roughness value,AA arithmetic average).priate safery and health practices and determine the applica-3.1.5 verification-checking or testing the instrument tobility of regulatory limitations prior to use.ensure conformance with this test method.2.Referenced Documents4.Significance and Use2.1 ASTM Standards:24.1 Hardness of a material is a poorly defined term that mayE 691 Practice for Conducting an Interlaboratory Study tohave many meanings depending on the type of test performedDetermine the Precision of a Test Methodand the expectations of the person involved.The Leeb hardness3.Terminologytest is of the dynamic or rebound type,which primarilydepends both on the plastic and on the elastic properties of the3.1 Definitions:material being tested.The results obtained are indicative of the3.1.1 calibration-determination of the values of the sig-strength and dependent on the heat treatment of the materialnificant operating parameters of the instrument by comparisontested.with values indicated by a reference instrument or by a set of4.2 The Leeb hardness test is a superficial determinationreference standards.only measuring the condition of the surface contacted.The3.1.2 Leeb hardness number-a number equal to the ratio ofresults generated at that location do not represent the part atthe rebound velocity to the impact velocity of a 3-mm or 5-mmany other surface location and yield no information about the(based on the type of impact device)diameter tungsten carbidematerial at subsurface locations.ball or diamond tipped impact body,multiplied by 1000.A.GENERAL DESCRIPTION OF INSTRUMENTSAND TEST PROCEDURE FOR LEEB HARDNESSThis test method is under the jurisdiction of ASTM Committee A0l on Steel.TESTStainless Steel and Related Alloys and is the direct responsibility of SubcommitteeA01.06 on Steel Forgings and Billets.Current edition approved Sept.1,2006.Published September 2006.Originally5.Apparatusapproved in 1996.Last previous edition approved in 2002 as A 956-02.5.1 The instrument used for Leeb hardness testing consistsLeeb and Equotip are registered trademarks used with permission of Proceq SA.of()an impact device that is equipped with a tungsten carbide2 For referenced ASTM standards,visit the ASTM website,www.astm.org.orcontact ASTM Customer Service at serviceastm.org.For Annual Book of ASTMball or synthetic diamond tipped impact body,an induction coilStandards volume information.refer to the standards Document Summary page onthe ASTM website.*A Summary of Changes section appears at the end of this standard.Copyright ASTM Intemational,100 Barr Harbor Drive.PO Box C700,West Conshohocken,PA 19428-2959.United States.4A956-06velocity measuring assembly,and a support ring,and(2)anelectronic digital display hardness indicating device.D,DC,D+15,E63 uin.(2 um)2005.2 Impact Devices-There are six types of impact devices250in.(7m)6516in.(0.4m500used in Leeb hardness testing.These are the D,DC,D+15,G.C,and the E impact units.Brief descriptions of the types of6.5 Magnetic Fields-Performance of the Leeb hardnessdevices and their common applications are given in Appendixtest on parts with a residual magnetic field may affect theX1.results.It is recommended that any residual magnetic field be5.3 Summary of Test Method-During a hardness test,anless than 4 G.impact body with a spherically shaped tungsten carbide or6.6 Vibration-Vibration of the test specimen may affect thediamond tip impacts under spring force,the test surface fromresults of the Leeb hardness test.It is recommended that thiswhich it rebounds.The impact and rebound velocities aretest be performed with the test piece at rest.measured when the impact body is approximately 1 mm from6.7 Temperature-The temperature of the test piece maythe test surface.This is accomplished by means of a permanentaffect the results of the test.In addition,this effect may bemagnet mounted in the impact body which,during the test,different for different materials.Testing to this procedure shallmoves through a coil in the impact device and induces anbe performed with the temperature of the test piece betweenelectric voltage on both the impact and rebound movements.40F(4C)and 100F(38C).At temperatures outside thisThese induced voltages are proportional to the respectiverange,the user shall develop a temperature correction for theimpact and rebound velocities.The quotient of these measuredspecific material being tested.voltage values derived from the impact and rebound velocities,multiplied by the factor 1000 produces a number which7.Verification of Apparatusconstitutes the Leeb hardness value.7.1 Verification Method-Prior to each shift,work period,5.4 See 7.1.1 when using replacement machine components.or use,and following a period of extended continuous use(1000 impacts).the instrument shall be verified as specified in6.Test PiecePart B.Any instrument not meeting the requirements of Part B6.1 Form-The Leeb hardness test is acceptable for steel,shall not be employed for the acceptance testing of product.cast steel,and cast iron with varying shapes and sizes.7.1.1 Cautionary note:When replacement parts are used ina Leeb hardness tester it is important that they be fully6.2 Thickness and Weight-The thickness and weight of thecompatible with the original equipment,otherwise incorrecttest piece shall be considered when selecting the impact deviceto be employed.The following guidelines are offered ashardness readings may be obtained.Calibration using a singlestandard test block may indicate acceptable results,but addi-minimum weights and sizes of test pieces for selecting theproper test equipment.Test pieces of weights less than thetional calibration tests using blocks of differing hardness mayyield unacceptable results.If replacement,non-original equip-minimum or pieces of any weight with sections less than theminimum thickness require rigid support and coupling to ament parts are used,multiple block calibration verification isstrongly advised.Specifically,one calibration block of athick,heavier non-yielding surface to resist the impact of thedevice.Failure to provide adequate support and coupling willhardness equal to or lower than the minimum expectedhardness of the material being tested,one calibration block ofproduce test results lower than the true hardness value.a hardness equal to or greater than the maximum expectedImpact DeviceWeight(min)orThickness(min)hardness of the material being tested,and one calibration blockD,DC,D+15,E15b(5kg)in.(3 mm)near the middle of the range should be used.40b(15kg%in.(10 mm)4b(1.5kg】2in.(1mm)8.Procedure6.3 Curvature-Test pieces with curved surfaces may be8.1 Test Method-To perform a hardness test,the impacttested on either the convex or concave surfaces providing thatdevice is connected to the indicator device and the instrumentthis radius of curvature of the specimens is matched to the sizeis turned on.The impact device,while not in contact with theof the support ring and is not less than 2 in.(50 mm)for the Gtest piece,is held firmly with one hand and the charging tubeimpact device or 136 in.(30 mm)for other impact devices.is depressed with the other hand until contact is felt.The6.4 Surface Finish/Preparation-The test surface shall becharging tube is allowed to slowly return to the startingcarefully prepared to avoid any alterations in hardness causedposition.The impact body is now in its loaded or lockedby heating during grinding or by work hardening duringposition.After placing the impact device on the test surface,machining.Any paint,scale,pits,or other surface coatingstrigger the impact body by exerting a light pressure on theshall be completely removed.The surfaces to be tested shall berelease button.The Leeb hardness value is read on the indicatorsmooth.Failure to provide adequate surface finish will producedevice.questionable test results.Coarse finishes will tend to lower the8.2 Alignment-To prevent errors resulting from misalign-measured value.It is recommended that the test surface bement,the base support ring of the impact device shall be heldmachined or ground and polished to the following finishes.snugly and perpendicular to the surface of the test piece.(The grinding wheel grit size shown for each finish is offered8.3 Impact Direction-The impact device is calibrated forfor guidance in achieving the finish noted.)the down vertical impact direction(perpendicular to a horizon-Impact DeviceSurface Finish-RaGrit Size(Approx.)tal surface).For other impact directions such as 45 from the(max)horizontal plane or from underneath,the measured hardness24A956-06values will require adjustment(see 9.2).Some newer modelsTABLE 2 Correction Values for Other Impact Directions:automatically compensate for test direction.Device D+158.4 Spacing Indentations-The distance between any two0+15入Timpact 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.No300point shall be impacted more than once.-1426-383508.5 Reading the Leeb Instrument-Hardness values in Leeb-1325-36units are read directly on the electronic display of the indicator400device.The indicated value is automatically replaced with the-1223-34450next test impact result.-1222328.6 Number of Impacts-Five impacts in an area of approxi-500mately I in.2(645 mm2)shall constitute a test.If the material-6112130550being tested is considered to be nonhomogeneous(for ex-112028ample,cast iron)ten impacts in an area shall be made to600constitute a test.1019冯650-5-10-18-259.Calculation of Hardness Result7009.1 The hardness test result shall be the arithmetic average5边1724750of the five individual impact readings in the measuring area.4-916-229.2 Correction for Test Direction-When using an Leeb800-8-15-21instrument without automatic compensation for test direction850the correction value for direction of test impact is to be4-1420subtracted from the average value determined for the measur-900ing area.This correction value can be determined in accor-dance with Tables 1-6.TABLE 3 Correction Values for Other Impact Directions:10.Conversion to Other Hardness Scales or TensileDevice EStrength Values10.1 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,approximations30091826and therefore conversions should be avoided except for special350-1724400TABLE 1 Correction Values for Other Impact Directions:-9-16-22Device D4508-1521T5001420550-133009海600-6-12-20-293503-7-12-176-1927650400-12-16700-5-11-1825450361115750-5-10-17246500-10-14-10-162280055039-13-9-15208506002-12900.48-14.19650-4-8-13-18700cases where a reliable basis for the approximate conversion and3-7-12-17the accuracy of the conversion has been obtained by compari-7506-11-16son testing.No conversions shall be employed without specific800agreement between the party specifying this test method and6-10-15850the party performing the hardness test.2-9-1490011.Report11.1 Report the following information:34-A956-0615.2 The Leeb hardness instrument shall be consideredmark or the thickness to an accuracy of=0.001 in.verified if the individual readings fall within+6 HL units of(0.025 mm)at the time of calibration shall be marked on thethe reference value.Any instrument not verified shall not betest surface.used for testing without repair and re-verification.18.Standardizing ProcedureC.CALIBRATION OF STANDARDIZED HARDNESSTEST BLOCKS FOR LEEB HARDNESS18.1 The standardizing hardness test blocks shall be cali-INSTRUMENTSbrated with an Leeb instrument for which the operationalcharacteristics have been certified by the manufacturer and16.Scopewhich has been verified in accordance with the requirements of16.1 Part C covers the calibration of standardized hardnessPart B.test blocks used for the verification of Leeb hardness instru-18.2 Make ten randomly distributed hardness impacts on thements.test surface of the test block.18.3 Take the arithmetic mean of all of the readings as the17.Manufacturemean hardness of the test block.17.1 Each test block shall be made of steel with dimensionsnot less than 3 in.(90 mm)in diameter by 2%in.(54 mm)19.Uniformity of Hardnessthick for impact devices D,DC.D+15.C.and E and 4%4 in.19.1 Unless the difference between the largest and the(120 mm)in diameter by 234 in.(70 mm)thick for impactsmallest of the ten readings is less than 13 Leeb units,the blockdevice G.The two opposite end plane surfaces shall be parallel.cannot be regarded as sufficiently uniform for standardization17.2 Each block shall be specifically prepared and heatpurposes.treated to give a specific hardness and the necessary homoge-neity and stability of structure.20.Marking17.3 Each steel block shall be demagnetized by the manu-facturer and maintained demagnetized by the user.20.1 Each block shall be marked with:17.4 A non-test surface of the test block shall have a fine20.1.1 Arithmetic mean of the hardness values found in theground finish of 250 uin.(7 um)maximum.standardization test suffixed by the scale designation letter(for17.5 The test surface shall be polished or fine ground andexample.HLD).free of scratches and other discontinuities which would influ-20.1.2 The name or mark of the supplier.ence the rebound characteristics of the test block.20.1.3 The thickness of the test block.17.6 The surface finish of the test surface shall not exceed16 uin.(0.4 um)maximum.21.Keywords17.7 To ensure that no material is subsequently removed21.1 dynamic hardness test;Equotip;Equotip hardness test;from the test surface of the standardized test block,an officialLeeb;rebound hardness test5