The Effect of Volume Fraction of Δ-Ferrite on Hydrogen Embrittlement in High-Nitrogen Austenitic Steel

The effect of volume fraction of δ-ferrite and the density of interphase (austenite/δ-ferrite) and grain (austenite/austenite) boundaries on the mechanical properties and fracture mechanisms of a high-nitrogen austenitic steel before and after hydrogen electrolytic charging for 100 h was investigated. An increase in the density of interphase and grain boundaries and decrease in fraction of δ-ferrite increase the resistance of steel against hydrogen embrittlement.Было исследовано влияние объемной доли δ-феррита и плотности межфазных (аустенит/δ-феррит) и межзеренных границ (аустенит/аустенит) на механические свойства и механизмы разрушения высокоазотистой аустенитной стали до и после электролитического наводороживания. Увеличение плотности межфазных и межзеренных границ и уменьшение доли феррита приводит к повышению устойчивости стали и водородному охрупчиванию.Работа выполнена при финансовой поддержке Российского научного фонда (грант № 17–19–01197)

Microstructure, phase composition, and microhardness of the NiCr/Al gradient material produced by wire-feed electron-beam additive manufacturing

Metal additive manufacturing is one of the new industrial technologies for fast prototyping of the metalcomponents with a complex internal architecture, gradient composition, or functionally gradient properties. Intermetallic alloys are hard-to-work materials, their conventional production and post-production processing are very complex and expensive routine. New production methods, such as an additive manufacturing, are promising for fast and relatively simple fabrication of the intermetallic billets with the desired phase composition and architecture. Multiple-wire electron-beam additive manufacturing is among them. In this work, we fabricated a bimetallic material (plain wall) using the industrial NiCr and Al wires. For the as-built state, we provided the elemental and phase analyses of the NiCr lower part and Al upper part of the billet with the focus on the intermediate gradient layers between two materials. During the additive manufacturing of the NiCr part of the billet, the Ni-based fcc solid solution forms. Scanning electron microscopical analysis, X-ray diffraction analysis, and energy dispersive spectroscopy confirm the formation of NiAl and Ni3Al intermetallic phases in the transition zone under electron beam additive manufacturing of the bimetallic material. This intermetallic zone has high microhardness (up to 10 GPa). The Al3Ni intermetallic phase has been found in the Al-based part of the billet, but the microhardness of the composite material (Al + Al3Ni) is just a bit higher than that in the upper Al-based part of the billet