Quick Guide to Precision Measuring Instruments

PG64Hardness Test Methods and Guidelines for Selection of a Hardness Testing MachineTest MethodMicrohardness (Micro-Vickers)Micro surface material characteristicsVickersRockwellRockwell SupercialBrinellShoreFor sponge, rubber, and plasticRebound type portableMaterialIC wafer●●Carbide, ceramics (cutting tool)▲●●Steel (heat-treated material, raw material)●▲●●●●●Non-ferrous metal●▲●●●●Plastic▲●●Grinding stone●Casting●Sponge, rubber●FormThin metal sheet (safety razor, metal foil)●●●●Thin lm, plating, painting, surface layer (nitrided layer)●●small parts, acicular parts (clock hand, sewing-machine needle)●▲Large specimen (structure)●●●Metallic material conguration (hardness for each phase of multilayer alloy)●●Plastic plate▲▲●●Sponge, rubber plate●ApplicationStrength or physical property of materials●●●●●●●●▲Heat treatment process●●●●▲▲Carburized case depth●●Decarburized layer depth●●●Flame or high-frequency hardening layer depth●●●Hardenability test●●Maximum hardness of a welded spot ●Weld hardness●●High-temperature hardness (high-temperature characteristics, hot-workability)●Fracture toughness (ceramics)●●Key:●●●Well-suited ▲▲▲Reasonably suitedMethods 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 9.807N (1kgf). 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-2Dd2d3.5x10-3Dq(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 (opposing 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 Superficial hardness, first 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: 0.2mm) 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 98.07N, and Rockwell Superficial 29.42N. A specific 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.Hardness Testing Machines

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