The effect of subsequent heating treatment on the microstructure and mechanical properties of additive manufactured Hastelloy X alloy

In general, the components prepared by selective laser melting (SLM) possess high strength but low ductility. It is of great significance to obtain the SLMed samples with the excellent combination of the strength and ductility for the wide application. In this work, we regulate the subsequent heating treatment to optimize the microstructure of the SLMed Hastelloy X samples and improve their mechanical properties. The results show that when the original SLMed Hastelloy X sample is heated at 1050 °C for 1 h (denoted as HT1), its internal dislocations are partially eliminated while the subgrains remain their original shape. Besides, numerous M 23 C 6 carbides are precipitated within the grains during this heating treatment process. Compared with the original SLMed sample, the strength of HT1 sample is reduced slightly but the elongation is increased to 43.2 ± 2.6%. On the other hand, when the original SLMed Hastelloy X sample is heated at 1150 °C for 1 h (denoted as HT2), the complete recrystallization occurs and its internal dislocations are greatly reduced, and even some annealing twins appear. Although the strength of HT2 sample is decreased due to the reduction of dislocation density, its elongation is significantly increased to 69.9 ± 4.1% due to the appearance of annealing twins and the effect of slip mechanism. Our work indicates that the SLMed Hastelloy X alloys with ideal matching relationship of strength and ductility can be obtained by employing a suitable subsequent heat treatment system according to the specific industrial service environment. • Hastelloy X alloy fabricated via selective laser melting was heat treated and characterized. • SLMed Hastelloy X with ideal mechanical properties can be obtained by suitable heat treatment. • The microstructural evolution of SLMed Hastelloy X was systematically studied. • The toughening and strengthening mechanisms were discussed in detail.