Correlation between heat treatment process parameters, phase composition, texture, and mechanical properties of 12H18N10T stainless steel processed by selective laser melting

Abstract

The phase composition, texturing degree, oriented stresses and strains of the crystal lattice, the physical and mechanical properties of austenitic steel 12H18N10T (AISI 321) manufactured by selective laser melting (SLM) before and after heat treatment with various temperatures and protective gas composition have been investigated. SLM stainless steel has better mechanical properties, given that the phase volume content is as follows: γ-Fe ∼ 65%, α-Fe ∼20%, NiTi ∼ 5%; the texturing degree equals to T111∼0.70 and the dominant crystal-lattice orientation is (111). Such a phase composition is formed in the steel after annealing at 620 °C in argon. As the temperature rises during the stabilizing annealing process up to 825 °C, the phase transformation γ→α takes place in SLM steel with a change in the phase concentration γ-Fe and α-Fe in the range from 40 to 50%. In the high-temperature intermetallic phase NiTi, dissolution at 825 °C and a multiple rise of the FeO concentration lead to a change in the crystal lattice parameter of the γ-Fe and α-Fe phases and a decrease in the mechanical properties of SLM steel. This study showed that the improvement of mechanical properties was due to the separation of high-temperature intermetallic phase from austenite and an increase in the concentration of iron carbide Fe3C in SLM steel.