Structure Formation in Vanadium-Alloyed Chromium-Manganese Steel with a High Concentration of Interstitial Atoms C + N = 1.9 wt % during Electron-Beam Additive Manufacturing
Е. Г. Астафурова, С. В. Астафуров, K. A. Reunova, E. Melnikov, Valentina Moskvina, M. Yu. Panchenko, Galina G. Maier, В. Е. Рубцов, Е. А. Колубаев
Abstract
In the present paper, the method of electron-beam additive manufacturing is used to produce specimens of vanadium-alloyed chromium-manganese steel with a high concentration of interstitial atoms (C + N = 1.9 wt %). Microstructure and mechanical properties of the specimens are analyzed against the specimens obtained by conventional metallurgy and thermal-mechanical treatments. It is experimentally shown that additive manufacturing and subsequent heat treatment do not affect the concentration of interstitial atoms in the steel specimens, do not change the mechanism of steel crystallization, and do not provide high-temperature ferrite formation. Regardless of the production method, specimens of vanadium-alloyed chromium-manganese steel with a high concentration of interstitial atoms have a heterophase structure composed of austenite and dispersed phases. In addition to vanadium and chromium carbonitrides, which are characteristic of the conventionally fabricated steel and do not dissolve during thermal-mechanical treatment, repeated heating and cooling during additive manufacturing cause the formation of plates of chromium and manganese carbonitrides within austenitic grains and globular intermetallides (Fe, Cr, Mn, and V) along grain boundaries. The high concentration of interstitial atoms promotes high solid-solution and precipitation hardening of additively manufactured specimens, resulting in a higher yield stress (σ0.2 = 880 MPa) as compared to conventionally fabricated specimens (σ0.2 = 840 MPa). At the same time, the presence of dispersed phases leads to premature fracture of the specimens, so that the additively manufactured steel, even after heat treatment, has low plasticity.