MECHANICAL PROPERTIES AND STRUCTURE OF THE WELDED SEAM OF THE IP-718 (INCONEL 718) ALLOY OBTAINED BY ELECTRON BEAM WELDING

Welded joints of heat-resistant nickel alloys are produced by various methods, the most promising are those using concentrated energy flows, including laser and electron beam welding. In this paper, electron beam welding of chromium-nickel precipitation hardening heat-resistant alloy EP718 (CrNi45WMoTiAlBP-ID) is considered. In the work, welds were obtained in welding modes with a constant beam travel speed over the sample surface and different beam currents while ensuring complete sample penetration. Before the study, the samples were heat treated (quenching + aging). Their microstructure, mechanical properties (tensile strength, yield strength, relative elongation and contraction, impact toughness) were studied; the effect of thickened grain boundaries in the heat-affected zone of welds on the durability of a permanent joint was studied. In welding modes with linear energy of 2.25 and 2.33 kJ/mm, the presence of thickened grain boundaries was revealed in the microstructure of all samples; with linear energy of 2.44 kJ/mm, samples were obtained both with thickened grain boundaries and without them. The thickened grain boundaries in the HAZ have a width of 3 ‒ 7 μm. During endurance testing of the samples, their destruction in both cases occurred both along the weld and along the HAZ. An assumption has been made about the mechanism of occurrence of grain boundary thickenings in the HAZ. Based on the test results, it has been revealed that grain boundary thickenings up to 4 μm wide do not affect the fatigue strength of welded joints. The presence of grain boundary thickenings more than 5 μm wide reduces the strength of the weld of the heat-resistant precipitation-hardening alloy EP718; they are stress concentrators and can lead to further cracking under real loading conditions.

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