Hardness testing

Portable hardness testing devices were developed because bringing a stationary Brinell, Rockwell or Vickers tester to the field was impractical . In addition, it is not always practical to cut samples from a component to have hardness testing performed under controlled laboratory conditions.

At Zengary, hardness testing is performed by only experienced technicians who are qualified to Zengary procedures, industry standards, and client specifications to obtain reliable, precise measurements. There are several variables that affect the accuracy and repeatability of hardness testing performed in the field including:

• The operator
• Surface condition
• Material geometry
• Material thickness
• Metallurgy

Each of these variables must be considered when selecting the appropriate test method, and the Zengary team has the knowledge and experience to get the job done right.

Determination of hardness of metallic materials by the Ultrasonic Contact Impedance (UCI) method, as specified in ASTM A1038, is done using the MicroDur series of hardness testers. The UCI method uses a Vickers diamond indenter, allowing for precise placement of the indent and resulting in a highly localized hardness test. But unlike in conventional Vickers testing, the reading is not derived through optical measurement of the test indentation. Instead, the indentation area is detected by electronically measuring the shift in an ultrasonic frequency that occurs when the load is applied. Because of the small footprint of the Vickers diamond, it is quite effective at measuring the hardness in a heat-affected zone, and up to the toe of a weld. Other portable testers have a larger footprint and this limits their ability to measure in this area. It is also an excellent tool for looking at the hardness of gear teeth due to the small impression. This method requires the most surface preparation as compared to other methods.

Zengary performs both Shear Pin and Telebrinell methods of testing for determining the macrohardness of metallic samples. Telebrinell tests are covered by ASTM A833, however, the Shear Pin test method is not covered under an ASTM standard at this time. The Shear Pin and Telebrinell tests utilize a three-pound hammer to supply the load required for creating a round impression on the workpiece. The diameter of the indentation is then measured optically, and this value is then converted to a Brinell hardness number using a formula or chart. This method requires less surface preparation than microhardness testing, although it cannot be used to measure the hardness in smaller areas such as the hardness in a narrow heat affected zone of a weld.