-
-
The identification of materials during goods receipt and dispatch is of great importance. Appropriate testing methods, such as hardness testing, are successfully used for this purpose. However, there are exceptions where the risk of confusion through hardness testing significantly increases. The risk of material confusion during goods receipt and dispatch increases with the number of quite
similar alloys. For example, it is not possible to distinguish between a cold-worked steel and a heat
treated steel with the same tensile strength (see tab.1) using classical hardness testing. In this case,
the same hardness is measured. This significantly increases the risk of confusion in operations.
The risk of material confusion is minimized in practice by assigning unique identifiers at goods dispatch.
These identifiers (such as color markings, QR codes, etc.) provide a remedy. If errors occur in the identification,
the wrong materials are unintentionally processed further. Additionally, hardness testing is also
often used to identify materials. In table 1, the hardness values, tensile strength, and the yield strength
of two steels are shown.
_
heat treated steel cold-worked steel hardness HRC 24-26 24-26 comparative tensile strength RIm [MPa] 581 580 comparative yield strength RIp0,2 [MPa] 348 522 _
The values according to Rockwell C in accordance with DIN EN ISO 6508 show the same hardness and do not indicate any difference in strength. Imprint Testing as a problem solver for the identification of materials and strength levels: To circumvent this danger and significantly minimize the risk of confusion, the Imprint Test according to DIN SPEC 4864 is used. It provides plastic stress-strain (see Fig.1) curves and comparative values for yield strength and tensile strength. This indentation method is additionally based on highly accurate 3D measurements and finite element simulations. The pile-up of an indent appears as a new signal and reflects the plastic deformation behavior of the tested material and leads to the mechanical properties within under one minute. According to measured plastic stress-strain curves, the strength level of UTS is nearly the same. Furthermore, the yield strength shows a significant difference and the materials can be identified correctly.
