PSI - Issue 65

A.V. Byzov et al. / Procedia Structural Integrity 65 (2024) 48–55 A.V. Byzov, A.E. Konygin, D.G. Ksenofontov, O.N. Vasilenko / Structural Integrity Procedia 00 (2024) 000–000

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and improve the mechanical properties of the surface, while significantly increasing its lifetime. Klyuev et al. (2008) state that one of the most popular and widely used methods in industry is the surface quenching method. In such treatment, it is very important to test the hardening depth. As noted by Skobelev (2017), destructive testing methods are inefficient in this case since they are time-consuming. The main disadvantage of such methods is that, as a result of such testing, the integrity of the product is upset and that, therefore, there is no possibility of its realization. This, in turn, leads to an increase in the cost of finished products, and it is also impossible to check the entire batch of manufactured products. For these purposes, non-destructive methods are used today, which allow the required parameters to be quickly and effectively determined without breaking or damaging the object of testing. Nowadays the eddy current method is actively used for non-destructive testing of conductive materials. It is highly sensitive to the chemical composition, microstructure, and mechanical properties of the object. It can be used to detect any changes in the electromagnetic properties of the material and to determine its mechanical properties. Also, it is important that eddy current sensors are insensitive to dirt, dust, humidity, oil, i.e. everything that can be present in production, and that they have a wide range of operating temperatures. Nomenclature A c3 temperature point of the end of ferrite dissolution in hypoeutectoid steels or cementite in hypereutectoid steels ε electromotive force d hardened layer depth, mm z penetration depth of eddy currents, m f excitation current frequency, Hz µ relative permeability of the hardened layer, arb. unit µ 0 permeability of vacuum, H/m µ in initial relative permeability, arb. unit σ electric conductivity of the hardened layer, S/m U 0 modulus of ε across the secondary coil in the open-circuit operation mode, V U refl  reflected ε across the secondary coil when it is located at the object to be tested, V  modulus of relative reflected ε across the secondary coil when it is located at the object to be, arb. unit Δφ 0 phase difference between the current across the primary coil and ε across the secondary coil of the eddy current probe in the no-load mode, deg. Δφ k phase difference between the current across the primary coil and the ε across the secondary coil of the eddy current probe when it is located at the tested object, deg. HRC Rockwell hardness ECP eddy current probe TO tested object 0 U refl rel U e 

1.1. Surface hardening

Maisuradze et al. (2021) argue that some parts in operation require high hardness and wear resistance of the surface, combined with good toughness in the core. This applies to parts operating under conditions of wear with the simultaneous action of dynamic loads (gears, pins, connecting links of caterpillar tracks). In such cases, not the whole part is hardened, but only a thin (a few millimeters) surface layer. Surface hardening is heating to hardening temperatures of only the surface layer of the workpiece followed by rapid cooling and the formation of a martensitic structure only in this layer.