Hardness is a characteristic that applies to a range of materials—metals and nonmetals alike— and is defined as the resistance of the material to deformation. Element experts measure hardness according to the requirements of the material and its applications with equipment calibrated to hardness scales, including
- Mohs Hardness: Devised in 1812 and based on relative resistance to scratching, this test is now used mainly to identify minerals in the field.
- Brinell Hardness: The oldest method still in common use, this instrument employs an indentor ball. Brinell hardness testing is frequently used to measure hardness of castings and forgings.
- Rockwell Hardness: Using a ball or cone shaped indentor, Rockwell hardness machines simplify hardness measurement by providing a hardness number visible immediately after removing the load.
- Vickers and Knoop Hardness: Vickers microhardness testing measures film coatings or surface hardness of case-hardened parts with a diamond-pyramid-shaped indentor; with Knoop the indentor is rhombic-pyramid-shaped for longer but shallower indentations.
- Durometer Hardness: Commonly used for soft polymers or elastomers, a durometer tester uses a calibrated spring for a cone-shaped or sphere shaped indentor foot.
- Barcol Hardness: This is a penetration test using a sharp steel point under a spring load and is usually used on rigid plastics and resins.
Hot hardness testing for metals and coatings
Hot hardness testing is the measurement of material hardness while at elevated temperature. Hot hardness can be valuable for assessing and comparing materials, such as tool steels and wear resistant coatings, which are used in high temperature applications such as valve seats and dies.
Solving high temperature hardness issues
Because room temperature hardness changes relatively little after high temperature exposure, it cannot be used to assess high-temperature properties. However, hardness-at-temperature changes significantly and reflects high temperature properties and problems such as tempering, abrasive wear, erosion and "hot erosion," stress and creep rupture, aging, sliding wear, softening, creep deformation, and workability issues. It can also cause galling, which is the adhesive wear and transfer of material between metallic surfaces during sheet metal forming and other industrial applications. Galling often occurs with aluminium compounds and is a common cause of tool breakdown.
Benefits of hot hardness testing
Hot hardness can characterize a material more quickly and inexpensively than hot tensile, prototype, or service testing because multiple temperatures and exposure times can be tested in a single hot hardness test run. This makes hot hardness testing an excellent way to compare multiple materials at elevated temperature.
How Element experts conduct hot hardness testing
Element in Wixom, Michigan, is one of the very few commercial laboratories with hot hardness testing capabilities. Element conducts hot hardness testing similarly to normal Vickers hardness testing, except that the test is conducted inside a vacuum chamber at an elevated temperature.
| Element experts provide hot hardness testing for these materials . . . | | . . . and products: |
- stainless steel hardness testing
- tool steel hardness testing
- carbon steel hardness testing
- aluminum hardness testing
- copper hardness testing
- titanium hardness testing
- die steel hardness testing
- other metal hardness testing
| | - die hardness testing
- valve hardness testing
- valve stem hardness testing
- valve seat hardness testing
- cylinder hardness testing
- tool hardness testing
- weld hardness testing
- many more
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