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Applications & Tips

All you need to know.

Here you will find general practical tips on hardness testing as well as useful information on the most common hardness testing applications such as progression measurements (CHD, NHT, RHT), hardness mapping, weld sample testing and other applications such as the Jominy test.

General Tips

Validity period of the hardness reference block calibration

Validity period of the hardness reference block calibration

The validity period for the calibration of a given hardness reference block is specified in part 3 of the ISO standard published for the respective hardness testing process.

The validity for steel hardness reference blocks should be limited to five years, whereas the validity period can be reduced to two to three years for aluminium and copper alloys.

According to the standard, no subsequent rework may be carried out on the hardness reference blocks.

However, hardness reference blocks do not lose their certified properties on the very day that the calibration certificate expires, recalibration of the respective hardness reference block by an appropriately certified respectively accredited company is possible.
 

Hardness reference block file retrieval measurement uncertainty

Embedded specimens

Rockwell method, minimum specimen thickness

Brinell method, minimum specimen thickness

Vickers method, minimum specimen thickness

Minimum distance between test points and to the specimen edge

Period of exposure to test force in the Brinell method

Period of exposure to test force in the Vickers method

How large a difference may there be between the diagonals in the Vickers test?

Rockwell correction value for testing cylindrical specimens

What standardised conversion tables are currently available?

What is the minimum content for a test report according to the Vickers standard ISO 6507?

hat is the minimum content for a test report according to the Brinell standard ISO 6506?

What is the minimum content for a test report according to the Rockwell standard ISO 6508?

Hardness Mapping

What is meant by hardness mapping?

Hardness mapping refers to the creation of a comprehensive hardness curve for a specimen or a specific area.

The hardness curve can be determined through the equal distribution of test points across the entire specimen. The result – the hardness map – can either be shown as a 2D colour image or a 3D diagram.

In a similar way to the FEM method, this quality of information and representation allows detailed statements to be made pertaining, for example, to specimen homogeneity or any imperfections in the specimen.

Welding Sample Test

Standardized weld sample testing

Standardized weld sample testing

Testing of weld samples is defined in standards ISO 9015 and ISO 22826.

ISO 9015 Part 1 describes hardness testing of arc-welded joints. Part 2 deals with micro hardness testing of welded joints.

ISO 22826 explains hardness testing of narrow joints welded by laser and electron beam.

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Curve Measurements

CHD - Case Hardness Depth

CHD - Case Hardness Depth

Case-hardened components are heat-treated steel workpieces. Here the workpiece is carburised, hardened, then tempered. This produces a hard, wear-resistant surface, while the core remains relatively soft and tough.

Case hardening is used on non-hardenable steels. Carburising with a carburising medium (e.g. gas or packing into carbon granulate) at a temperature of 850°-950°C, enriches the surface layer with carbon atoms.

NHD - Nitriding Hardness Depth

SHD - Surface Hardness Depth

Further Applications

Jominy test (End-quench test)

The Jominy test, also known as the End-quench test, is a standardised method for determining the hardenability of steel in accordance with ISO 642 and ASTM A255.
The hardenability describes the ability of the steel to increase the hardness at the surface or throughout the workpiece by forming martensite or bainite. 

The test procedure in compliance with DIN EN ISO 642 can be divided into four steps:

1. Creation of the shape and preparation of the specimen;
2. Heating of the specimen to a defined temperature in the austenitic range for a defined period;
3. Quenching of the specimen by spraying a controlled flow of water onto one end;
4. Testing of the hardness at defined points along the length of the partially ground specimen test surface.
 

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