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 Knoop Hardness > 500 gf load
Symbol:  HK

The Knoop Hardness Test, using an elongated pyramidal indenter, is a micro-indentation method suitable for thin plastic sheets, thin metal sheets, brittle materials, or materials where the applied load must never exceed 3.6 kgf.

In the Knoop Hardness Test, a load (typically in the range of 25 ~ 3600 gf) is applied to the surface of the test specimen via a pyramidal diamond indenting tool. The resulting indentation is shaped like the diamond tool, with a long-to-short axis ratio of 7:1, and point angles of 130º and 172º respectively. Knoop indentations are about 2.8 times longer and shallower than the Vickers indentations made at the same load. Optical microscope resolution may limit the application of the Knoop hardness test due to the resulting shallow indentions.

The Knoop hardness number is the ratio of the applied load to the area of the indentation, in accordance with the formula:

 Convert   HK        (suggested range: 97 ~ 920)
 HK   508   approximately* = Hardness Symbol Amount Name SuggestedRange HB (3000) 455 Brinell 10 mm Standard 3000 kgf 80~445 HB (500) >> Brinell 10 mm Standard 500 kgf 89~189 HB (Tungsten 3000) 456 Brinell 10 mm Tungsten 3000 kgf 80~620 HB (Indentation) 2.89 mm Brinell Indentation 6~2 HM 4.5 Mohs 1~10 HRA 75 Rockwell A-Scale 59~86 HRB >> Rockwell B-Scale 41~100 HRC 48 Rockwell C-Scale 19~69 HRD 62 Rockwell D-Scale 39~77 HRF >> Rockwell F-Scale 88~100 HR-15N 85 Rockwell Superficial 15N 69~94 HR-15T >> Rockwell Superficial 15T 77~93 HR-30N 67 Rockwell Superficial 30N 41~85 HR-30T >> Rockwell Superficial 30T 53~82 HR-45N 53 Rockwell Superficial 45N 19~76 HR-45T >> Rockwell Superficial 45T 28~71 HS 64 Shore Scleroscope 17~97 Approx. TS 1631 MPa Tensile Strength (Approx.) 390~2450 HV 485 Vickers 20~1800

 Legend << The hardness value is below the acceptable range of the particular hardness scale. >> The hardness value is above the acceptable range of the particular hardness scale. ### The hardness value is near the limit (within 15%) of the acceptable range of the particular hardness scale. * The many hardness tests listed here measure hardness under different experimental conditions (e.g. indenters made in different sizes, shapes, and materials, and applied with different loads) and reduce their data using different formulae. As a result, there is NO direct analytic conversion between hardness measures. Instead, one must correlate test results across the multiple hardness tests. This calculator is based on hardness data compiled from ASM Metals Reference Book 3rd ed, published by ASM International, and Machinery's Handbook 25th ed, published by Industrial Press. The calculator curve-fits multiple hardness data onto a common polynomial basis and then performs an analytic conversion. The accuracy of the conversion depends on the accuracy of the provided data and the resulting curve-fits, and on the valid ranges spanned by the different hardness tests. Converted hardness values should be used for comparative purposes only.