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Hardness Test

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DETERMINE STEEL STRENGTH THROUGH DEFORMATION

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Concerning metals, hardness testing determines a material’s strength by measuring its resistance to penetration. Hardness is a characteristic of a material, not a fundamental physical property. It is defined as the resistance to indentation, which is determined by measuring the permanent depth of the indentation.

Hardness affects many physical characteristics, such as how much the metal will wear, scratch, or withstand stress. Foundries, fabricators, manufacturers, metal stockholders, importers and welding inspectors need the reassurance that metal or alloy will be suitable for a product’s intended use or meets industry specifications. The application possibilities are far-ranging – this refers to both large and smaller components, especially at positions which are difficult to access. Mobile hardness testing is in advance: in these times of cost pressure and higher quality requirements, it represents not only a quick but, most of all, an economical supplement to stationary hardness testing in the modern production process.

At Professional Testing Services, we provide both portable and bench types of hardness.

Mobile Hardness Testing

Our team of Hardness test experts will press a specifically dimensioned and loaded object (indenter) into the surface of the material you are testing. The hardness determines resistance to penetration (hardness) of a specimen and is occasionally employed to obtain a quick approximation of tensile strength

The UCI method is recommended for fine-grained testing material having almost any shape and size. It is primarily used where material properties are to be determined within narrow tolerances, e.g. for determination of the strain-hardening process on drop forgings.

Rebound hardness testing is mainly carried out on large, coarse-grained materials, forgings, and all types of cast materials because the spherical tungsten carbide tip of the impact device produces a larger indentation than the Vickers diamond. Therefore reveals the characteristics of the cast structure better.

Many UCI probes and rebound impact devices with different test loads or indenter diameters enable an application-oriented selection of a suitable method and a suitable probe/impact device. On the other hand, UCI probes’ relatively small test indentations allow hardness testing on welds, especially in the critical area of the heat-affected zone (HAZ).

Hardness affects a wide range of physical characteristics, such as how much the metal will wear, scratch, or withstand stress.

Foundries, fabricators, manufacturers, metal stockholders, importers and welding inspectors need the reassurance that a metal or alloy will be suitable for a product’s intended use or meets industry specifications.

Our portable hardness tests

1) Ultrasonic Contact Impedance (UCI)

With the UCI method, the size of the hardness test indentation is not measured optically. Still, the indentation area is detected electronically by determining the shift of ultrasonic frequency under load. With ”soft” materials, the Vickers diamond penetrates deeper into the material, leaving a relatively large indentation area, leading to a high-frequency shift.

One of the benefits of UCI hardness testing: the frequency shift is proportional to the indentation size produced by the Vickers diamond in the material. UCI instruments can be easily calibrated to different test materials.

Typical applications:

  • Heat-treated or case-hardened mechanical parts (e.g. camshafts),
  • Weld testing (HAZ),
  • Finished precision parts, gears, turbine blades, thin layers

 

*Common Test Methods (To be written by the testing team)

ASTM A1038

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Fig. 1 Vickers hardness test. (a) Schematic of the square-based diamond pyramidal indenter used for the Vickers test and an example of the indentation it produces. (b) Vickers indents made in ferrite in a ferritic-martensitic high-carbon version of 430 stainless steel using (left to right) 500, 300, 100, 50, and 10 gf test forces (differential interference contrast illumination, aqueous 60% nitric acid, 1.5 V dc). 250×

2) Rebound Method

With the rebound method, an impact body is accelerated at a defined speed against the test object’s surface. Due to the plastic deformation of the surface produced at the moment of impact, the impact body loses some of its original energy/velocity.

The velocities before and after the impact are measured in non-contact mode. A permanent magnet in the impact body generates an induction voltage when passing through the coil, which is proportional to the velocity. The rebound velocity, on the other hand, is a measure of the hardness of the test material. With soft material, the test indentation produced by the impact body is relatively large, i.e. the impact body loses most of its original energy and rebounds at a correspondingly lower velocity. In addition to this, the equipment PTS uses can be easily calibrated to other test materials.

Typical applications:

  • Significant, coarse-grained components with the surface as rolled, motor units,
  • Mechanical parts of finished products

 

*Common Test Methods (To be written by the testing team)

ASTM A956

3) Rockwell Hardness Test

The Rockwell Hardness Test measures the depth of penetration of an indenter under a large load compared to the penetration made by a preload. The permanent deformation caused by the more significant load offers information on the material’s hardness.

The penetrator may be either a steel ball or a diamond cone. The hardness number is related to the depth of the indentation, and the higher the number, the harder the material.

  • Generally used for larger sample geometries.
  • Quick (short test cycle) and cost-effective process
  • No specimen preparation is required (separation, grinding, embedding)

 

*Common Test Methods (To be written by the testing team)

  • ASTM E18
  • ASTM E110
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Fig. 2 Knoop hardness test. (a) Schematic of the rhombohedral-shaped diamond indenter used for the Knoop test and an example of the indentation it produces. (b) Knoop indents made in ferrite in a ferritic martensitic high-carbon version of 430 stainless steel using (left to right) 500, 300, 100, 50, and 10 gf test forces (differential interference contrast illumination, aqueous 60% nitric acid, 1.5 V dc). 300×

4) The Brinell hardness test (King Tester)

The Brinell hardness test is used to test materials with a structure that is too coarse, or that has a surface that is too rough to be tested using another test method, e.g., castings and forgings.

The hardness of a metal is determined by measuring the permanent indentation size produced by an indenter. Harder materials will generate shallow indentations, while softer materials will create deeper indentations. In this test method, a predetermined force (F) is applied to a tungsten carbide ball of fixed diameter (D), held for a predetermined period, and then removed. The spherical indenter creates an impression (permanent deformation) on the test metal piece.

  • Used for materials with a rough or inhomogeneous grain structure
  • Used for larger samples
  • Suitable for forgings and castings where the structural elements are large

 

*Common Test Methods (To be written by the testing team)

  • ASTM E10
  • ASTM E110

Talk to us today

Professional Testing Services can advise you on the most suitable method for your hardness testing project needs. Our experience testing team will provide you with the necessary information to help you ensure your products safe and reliable operation. Contact us today for more information about how we perform testing or request a quote.

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