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− Work hardening - can be formed in the surface layer after turning and milling,
as well as rough grinding.
− Hardening - the presence of such layers (the presence, in some cases, can be
determined using a hardness tester) has a much greater impact on the readings
of the hardness tester than the readings of static instruments.
The thickness of such layers usually does not exceed 0.2 mm / 0.4". To ensure the
accuracy of the measurements, if any, they must be removed from the measuring area using
a grinder.
1.13 Hardness measurement of the reinforced surface layers
Depending on the type of probe used and the hardness of the product, the indenter
creates prints of different depths (see section 1.5 "Probes of the hardness tester", table 1.4).
Plastic deformation of the metal is formed at much greater depths.
As a rule, the hardness of the surface reinforced layers differs sharply from the hardness
of the base metal of the product (for example, HDTV hardening). It is recommended to
measure hardness in such cases when the thickness of the layer is not less than 1.5 mm.
It is possible to clarify the value of this parameter and evaluate the possibility of
measuring the hardness of the layer on a specific type of product by comparing the readings
of the hardness tester with the readings of the static device.
To measure the hardness of reinforced surface layers, it is recommended to use only
probes of types D and E, or specialized probes made to order.
When measuring hardness, it is necessary to additionally take into account paragraph
1.8 "Working with products that differ in properties from carbon structural steels".
The device corresponds to: ASTM A956 “Standard Test Method for Leeb Hardness
Testing of Steel Products”; ASTM A 1038 “Standard Test Method for Portable Hardness
Testing by the Ultrasonic Contact Impedance Method”.
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