OBRABOTKAMETALLOV technology Vol. 25 No. 4 2023 Manufacturing the specimens using electron-beam surfacing In this work, 5 experimental specimens were printed using the electron-beam 3D wire printing technology. As a result of the preliminary work, the optimal value of the beam current was determined to be 30 mA (fig. 3). Fig. 3. A specimen obtained by electron-beam surfacing with a 0.4 C-13 Cr steel wire The first printed layer has the fastest cooling rate. If the beam current is too high, this leads to the meltthrough of not only the wire, but also of the substrate material. As a result, a hole appears at the border of the printed specimen. Printing the next layer will not be possible. As the beam current decreases, the print path length increases. As the number of the printed layers increases, the cooling rate decreases and the overall temperature of the specimen increases. Based on this, when printing the specimens, the optimal printing modes were determined under which it was possible to form the workpiece layer by layer. This is a beam current of 30 mA and a wire feed of 700 mm/min [28]. Study of the microstructure of the printed specimens Traditional methods of forming blanks (forging, casting) ensure a completely martensitic structure for the stainless steel 0.4 % C-13 % Cr. When using additive technologies, austenite and δ-ferrite can form in such steel. In the course of our work, we studied the microstructure of steels. As shown in fig. 4, the printed specimens have a dense structure. There are no cracks at the interlayer boundaries and there is no boundary of the molten pool. The microstructure of the manufactured specimens is similar to the microstructure of the steel 0.4 % C-13 % Cr after quenching and low tempering [29–33]. Martensite has a needle-like structure. This behavior is attributed to the high cooling rate during solidification in electron-beam additive manufacturing, which facilitates the phase transformation of austenite to martensite. These randomly oriented martensitic needles are much smaller than the martensitic needles formed during the casting and quenching of stainless steel 0.4 % C-13 % Cr [26, 27]. When additively printing a specimen, the heat coming from the applied new layer affects the previously printed ones. The underlying layers below the printed layer are heated above the austenitizing temperature. The previously formed martensite transforms into austenite and, after cooling, retained austenite and martensite form again. However, if the temperature is insufficient and below the austenitization temperature, then the process of martensite tempering occurs, the retained austenite again turns into martensite.
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