PSI - Issue 30

Anna Zykova et al. / Structural Integrity Procedia 00 (2020) 000–000

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Anna Zykova et al. / Procedia Structural Integrity 30 (2020) 216–223

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Fig. 4. Actual content of the main alloying elements of the initial AISI 304 wire and the walls formed by electron-beam technology in modes 1-8.

Alloying elements that determine the grade of material, such as Cr, Ni and Ti in the walls of the samples by the modes 4-6 correspond to the initial chemical composition of the wire (Fig. 4). At the same time the content of Mg, as the chemical element most sensitive to increased temperatures in the process of remelting, decreased by 2 times in comparison with the initial material (1.163 wt.%) for mode 5, and by 6.5 times – for mode 6. In other words, increased linear energy values cause excessive evaporation of heat-sensitive elements. Micropores, shrinkage pores, and other defects in the transition layer between the first layers of the experimental samples and the substrate are also absent (Fig. 5). The first layers of the experimental samples from austenitic steel AISI 304 are characterized by a fine-cell dendritic structure with carbide particles along the boundaries of dendrites (Fig. 5). The structure of the samples consists of solid solutions of γ -Fe (austenite) and residual  -Fe or δ -Fe (ferrite). The size and shape of dendritic cells changes with increasing of the wall layers (Fig. 5). When studying the microstructure of the samples according to modes 1, 2, 4-6, there were no defects revealed, such as pores and cracks, which indicates complete deposition of the layers. The samples obtained from AISI 304 austenitic steel wire have high mechanical properties that are at the level of rolled sheets of AISI 304 steel in a heat-treated state (quenching 1030-1080 °C in water or air), which are characterized by a tensile strength of 530 MPa, flow strength 216 MPa and relative elongation of 38%. Figure 6 shows the values of mechanical properties during tensile testing of samples in various modes. The characteristic features of stress changes are typical for all experimental samples of austenitic steel AISI 304 obtained by the additive manufacturing method in tensile tests in modes 1, 2, 4-6 (Fig. 6). The highest values of the mechanical characteristics are achieved for the samples obtained at the modes 1 and 5. It should be noted that the difference in the values of the mechanical properties obtained in different modes lies in a narrow range.