M-11MHardness Testing MachinesQuick Guide to Precision Measuring InstrumentsMethods of Hardness Measurement(1) VickersVickers hardness is a test method that has the widest application range, allowing hardness inspection with an arbitrary test force. This test has an extremely large number of application elds particularly for hardness tests conducted with a test force less than 9.807 N (1 kgf). As shown in the following formula, Vickers hardness is a value determined by dividing test force F (N) by contact area S (mm2) between a specimen and an indenter, which is calculated from diagonal length d (mm, mean of two directional lengths) of an indentation formed by the indenter (a square pyramidal diamond , opposing face angle θ=136˚) in the specimen using a test force F (N). k is a constant (1/g=1/9.80665).HV=kFS=0.102FS=0.1022Fsin d2q2=0.1891Fd2F: Nd: mmThe error in the calculated Vickers hardness is given by the following formula. Here, Dd1, Dd2, and ‘a’ represent the measurement error that is due to the microscope, an error in reading an indentation, and the length of an edge line generated by opposing faces of an indenter tip, respectively. The unit of Dq is degrees.DFF- 2-a2d2DHVHVDd1d- 2Dd2d3.5×10-3Dq(2) KnoopAs shown in the following formula, Knoop hardness is a value obtained by dividing test force by the projected area A (mm2) of an indentation, which is calculated from the longer diagonal length d (mm) of the indentation formed by pressing a rhomboidal diamond indenter (oppo-sing edge angles of 172˚30' and 130˚) into a specimen with test force F applied. Knoop hardness can also be measured by replacing the Vickers indenter of a microhardness testing machine with a Knoop indenter.HK=kFA=0.102FA=0.102Fcd2=1.451Fd2F: Nd: mmc: Constant(3) Rockwell and Rockwell SupercialTo measure Rockwell or Rockwell Supercial hardness, rst apply a preload force and then the test force to a specimen and return to the preload force using a diamond indenter (tip cone angle: 120˚, tip radius: 0.2 mm) or a sphere indenter (steel ball or carbide ball). This hardness value is obtained from the hardness formula expressed by the difference in indentation depth h (µm) between the preload and test forces. Rockwell uses a preload force of 98.07 N, and Rockwell Supercial 29.42 N. A specic symbol provided in combination with a type of indenter, test force, and hardness formula is known as a scale. Japanese Industrial Standards (JIS) dene various scales of related hardness.Relationship between Vickers Hardness and the Minimum Allowable Thickness of a SpecimenHV=0.1891t>1.5dh≒d/7t: Thickness of specimen (mm)d: Diagonal length (mm)h: Depth of indentation (mm)[Example]Specimen thickness t: 0.15 mmSpecimen hardness: 185 HV1Test force F: 9.807 N (1 kgf)Diagonal length d: 0.1 mmFd2Vickers hardnessHV200010005003002001005030200.0010.0020.0030.0050.010.020.030.050.10.20.30.51230.0010.0020.0030.0050.010.020.030.050.10.20.30.512t: mm d: mm0.0010.0020.0030.0050.010.020.030.050.10.20.30.51235102030504.903×10-3Test forceHardness symbolF: NHV0.0005Minimum thickness of specimenDiagonal length of indentation9.807×10-319.61×10-329.42×10-349.03×10-398.07×10-30.19610.29420.49030.98071.9612.9424.9039.80719.6129.4249.0398.07196.1294.2490.3dthScaleIndenterTest force ApplicationADiamond588.4 NCarbide, sheet steelCase-hardened steelSteel (100 HRB or more to 70 HRC or less) D980.7 NC1471 NFSphere of1.5875 mmdiameter588.4 NBearing metal, annealed copperBrassHard aluminum alloy, beryllium copper, phosphor bronzeB980.7 NG1471 NHSphere of3.175 mmdiameter588.4 NBearing metal, grinding wheelBearing metalBearing metal E980.7 NK1471 NLSphere of6.35 mmdiameter588.4 NPlastic, leadM980.7 NP1471 NRSphere of12.7 mmdiameter588.4 NPlasticS980.7 NV1471 NRockwell Hardness ScalesRockwell Supercial Hardness ScalesScaleIndenterTest force Application15-NDiamond147.1 NThin surface-hardened layer on steel suchas carburized or nitrided30-N294.2 N45-N441.3 N15-TSphere of1.5875 mmdiameter147.1 NSheet of mild steel, brass, bronze, etc.30-T294.2 N45-T 441.3 N15-WSphere of3.175 mmdiameter147.1 NPlastic, zinc, bearing alloy30-W294.2 N45-W441.3 N15-XSphere of6.35 mmdiameter147.1 NPlastic, zinc, bearing alloy30-X294.2 N45-X441.3 N15-YSphere of12.7 mmdiameter147.1 NPlastic, zinc, bearing alloy30-Y294.2 N45-Y441.3 NRelationship between Rockwell/Rockwell Supercial Hardness and the Minimum Thickness of a SpecimenRockwell hardnessRockwell Supercial hardnessRockwell hardnessMinimum thickness of specimen (mm)Minimum thickness of specimen (mm)Minimum thickness of specimen (mm)1.81.71.61.51.41.31.21.11.00.90.80.70.60.50.40.30.20.1 10 20 30 40 50 60 70 80 90 100 10 20 30 40 50 60 70 80 90 100 20 30 40 50 60 70 80 90 1001.41.21.00.80.60.40.203.33.1532.852.72.552.42.252.11.951.81.651.51.351.21.050.90.75
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