TESTING THE HARDNESS OF METALS
Comparison of Hardness Scales
Comparison of Hardness Scales - All such tables are based on the assumption that the metal - All such tables are based on the assumption that the metal tested is homogeneous to a depth se
tested is homogeneous to a depth several times that of the indentation. To the extent that the metalveral times that of the indentation. To the extent that the metal being tested is not homogeneous, errors are intro
being tested is not homogeneous, errors are introduced because different loads and different shapesduced because different loads and different shapes of penetrators meet the resistance of metal of varying hardness, depending on the depth of of penetrators meet the resistance of metal of varying hardness, depending on the depth of indentation. Another source of error is introduced in comparing the hardness of different materials indentation. Another source of error is introduced in comparing the hardness of different materials as measured on different hardness scales. This error arises from the fact that in any hardness test, as measured on different hardness scales. This error arises from the fact that in any hardness test, metal that is severely coldworked actually supports the penetrator, and different metals, different metal that is severely coldworked actually supports the penetrator, and different metals, different alloys, and different analyses of the same type of alloy have different cold-working properties. In alloys, and different analyses of the same type of alloy have different cold-working properties. In spite of the possible inaccuracies introduced by such factors, it is of considerable value to be able to spite of the possible inaccuracies introduced by such factors, it is of considerable value to be able to compare hardness value
compare hardness values in a general way.s in a general way.
The data shown is based on extensive tests on carbon and alloy steels mostly in the heat-treated The data shown is based on extensive tests on carbon and alloy steels mostly in the heat-treated condition, but have been found to be reliable on con
condition, but have been found to be reliable on constructional alloy steels and tool steels in the as-structional alloy steels and tool steels in the as-forged, annealed, normalized, quenched, and tempered conditions, providing they are
forged, annealed, normalized, quenched, and tempered conditions, providing they are homogeneous.homogeneous.
These hardness comparisons are not as accurate for special alloys such as high manganese steel, 18–8 These hardness comparisons are not as accurate for special alloys such as high manganese steel, 18–8 stainless steel and other austenitic steels, base alloys, constructional alloy steels, and stainless steel and other austenitic steels, base alloys, constructional alloy steels, and nickel-base alloys in the coldworked condition.
base alloys in the coldworked condition.
The data shown is for hardness measurements of unhardened steel, steel of soft temper, grey and The data shown is for hardness measurements of unhardened steel, steel of soft temper, grey and malleable cast iron, and most nonferrous metals. Again these hard
malleable cast iron, and most nonferrous metals. Again these hardness comparisons are not as accurateness comparisons are not as accurate for annealed metals of high Rockwell B hardness such as austenitic stainless steel, nickel and high for annealed metals of high Rockwell B hardness such as austenitic stainless steel, nickel and high nickel alloys, and coldworked metals of low B-scale hardne
nickel alloys, and coldworked metals of low B-scale hardness such as aluminum and the softer alloys.ss such as aluminum and the softer alloys.
HRA
Cemented carbides, thin steel and shallow case hardened steel Cemented carbides, thin steel and shallow case hardened steel
Copper alloys, soft steels, aluminum alloys, malleable iron Copper alloys, soft steels, aluminum alloys, malleable iron
Steel, hard cast irons, pearlitic malleable iron, titanium, deep case hardened Steel, hard cast irons, pearlitic malleable iron, titanium, deep case hardened
steel and other materials harder than B100 steel and other materials harder than B100
Thin steel and medium case hardened steel and pearlitic malleable iron Thin steel and medium case hardened steel and pearlitic malleable iron
Cast iron, aluminum and magnesium alloys, bearing metals Cast iron, aluminum and magnesium alloys, bearing metals
Annealed copper alloys, thin soft sheet metals Annealed copper alloys, thin soft sheet metals Phosphor bronze, beryllium copper
Phosphor bronze, beryllium copper, malleable irons. , malleable irons. Upper limit G92 toUpper limit G92 to avoid possible flattening of ball
avoid possible flattening of ball Aluminum, zinc, lead Aluminum, zinc, lead
Bearing metals and other very
Bearing metals and other very soft or thin soft or thin materials, including plastics. materials, including plastics. UseUse the smallest ball and heaviest load that do not give anvil effect.
the smallest ball and heaviest load that do not give anvil effect.
Brale
The Rockwell Hardness Scales The various Rockwell scales and their applications are shown The various Rockwell scales and their applications are shown in thein the following table.
following table.
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Relation Between Ha
Relation Between Hardness and Tensile Strengthrdness and Tensile Strength The approximate relationship between theThe approximate relationship between the hardness and tensile strength is shown by the following formula:
hardness and tensile strength is shown by the following formula:
Tensile strength =
Tensile strength = BhnBhn x 515 (for Brinell numbers up to 175).x 515 (for Brinell numbers up to 175).
Tensile strength =
Tensile strength = BhnBhn x 490 (for Brinell numbers larger than 175).x 490 (for Brinell numbers larger than 175).
The above formulas give the tensile stren
The above formulas give the tensile strength in pounds per square inch for steels. These apgth in pounds per square inch for steels. These approximateproximate relationships between hardness and tensile strength do not apply to nonferrous metals with the relationships between hardness and tensile strength do not apply to nonferrous metals with the possible exception of certain aluminum alloys.
possible exception of certain aluminum alloys.
Durometer
Durometer TTestsests The durometer is a portable The durometer is a portable hardness tester for measuring hardness of rubberhardness tester for measuring hardness of rubber,, plastics, and some soft metals. The instrument is designed to apply pressure to the specimen and plastics, and some soft metals. The instrument is designed to apply pressure to the specimen and the hardness is read from a scale while the pressure is maintained. Various scales can be used by the hardness is read from a scale while the pressure is maintained. Various scales can be used by changing the indentor and the load applied.
changing the indentor and the load applied.