Structural and mechanical properties of stainless steel formed under conditions of layer-by-layer fusion of a wire by an electron beam

OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 23 No. 4 2021 Fig. 9 . Isothermal section at 900 °C of the Fe - Cr - Ni triple system [25] on γ -( Fe , Ni , Cr ) phasewithdifferent chemical composition in different local sections of the specimens under study. Therefore, the results of XRD analysis of the specimens allows drawing a conclusion that nonequilibrium processes during layer-by-layer formation of a blank by electron-beam deposition welding promote the formation of two solid solutions based on γ - Fe -phase having close lattice parameters and that can be conditionally identi fi ed as γ 1 -( Fe , Ni , Cr ) and γ 2 -( Fe , Ni , Cr ) phases. For solid solution γ 1 -( Fe , Ni , Cr ), the lattice parameter а = 0.3592  0.0002 nm; while for γ 2 -( Fe , Ni , Cr ) phase, а = 0.3582  0.0002 nm. The microhardness tests of different phases of obtained specimens in longitudinal and transverse sections have shown that the indentation in the region with higher content of  - Fe phase leaves smaller indent. This testi fi es to higher hardness (122 HV) in these regions, as compared to the regions with austenitic matrix (100 HV) (Figs. 10 and 11). The received data demonstrate that the  - Fe phase is harder than the  - Fe -based austenitic phase. When manufacturing parts and structures with higher strength, the presence of  - Fe will negatively affect the durability under long static loads causing higher concentration of stresses that promote cracking. To increase the durability of parts, the negative effect of  - Fe can be reduced by preliminary thermomechanical treatment or consequent hardening thermal treatment. The diagram, depicted in Fig. 11 shows no evident alteration of hardness along the height from the substrate to the upper deposited layer in both longitudinal and transverse sections. The average hardness in longitudinal section ( XOZ ) was 187±7 HV; that of transverse section ( YOZ ) was 200±9 HV. According to the results of nanoindentation, the average value of elastic aftereffect amounted to 7.24±0.63%. Conclusions It was established that the AISI 308LSi stainless steel specimens manufactured using the electron-beam 3D-printing setup contain no macro-defects in the bulk of the specimens. There are small micro-defects in the form of residual gas pores occurred during growing of the blank. The diameter of the gas pores is less than 5.2 μ m. The microstructure of the specimens is close to that of large-grain cast austenitic steels. a b Fig. 10. Microhardness in the zone of  - Fe (a) and the zone of (  +  ) Fe (b)