The X8CrNi25-21 grade steel is austenitic heat-resisting steel used in power engineering. This steel owes its heat resistance to the high contents of alloy additions of nickel and chromium, whereby compact Cr2O3 chromium oxide films form on the steel surface at elevated temperature [1, 2]. Heat-resisting steels are also used for applying protective coatings, especially on elements less resistant to the high temperature. Due to their multicomponent nature, the most suitable method of applying coatings of heat-resisting steels is the plasma-assisted physical vapour deposition (PVD) method [3÷5]. The microand nanocrystalline structure of the coatings promotes the diffusion of chrome [6]. An additional increase in the heat-resisting properties of both the steel and the coating can be achieved by enriching their chemical composition with additions of silicon and aluminium [7÷9]. As a metallic alloy, steel is an electric current conductor, thus offering the possibility of being resistance heated, e.g. for heat treatment or heat resistance assessment purposes. Resistance heating also finds an application for joining steel sheets by welding [10]. In any case current thermal power P is used for heating up steel, which is the Joule-Lenz effect, being proportional to the square current intensity I and the resistance R of steel, according to the following relationship (1) [11].
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