Austenitic stainless steel 316L is widely used in various industries including oil and gas, chemical and automotive due to its high toughness, excellent resistance to corrosion and fatigue, biocompatibility, availability and reasonable price. In recent years, extensive research has been done in the field of additive manufacturing of this steel, including selective laser melting (SLM), and parts with very complex and precise geometric shapes have been made. One of the structural aspects of the parts resulting from the selective laser melting process is the epitaxial growth conditions and the formation of columnar grains, which may be unfavorable in some cases. Studies have shown that the modification and control of the variables of the selective laser melting process have a good role in controlling the microstructure. One of the methods of controlling the microstructure and grain refinment in the selective laser melting process is the use of inoculant materials in-situ or ex-situ. In the current research, used 2% weight of ceramic nanopowder titanium nitride (TiN) as inoculant particles in 316L powder. The purpose of the current research is to determine the optimal manufacturing conditions using a new composite powder and to investigate the resulting microstructure and tensile properties. In this research, different values of laser energy density along with two different scanning strategies (Meander 67 and Island) have been used for construction. The results showed that with the increase of the energy density from 53 to 101.9 J/mm3, the density of the parts made with 316L+TiN powder and the meander scanning strategy from 95.5% to 99.7% and also in the island scanning strategy, from 90.8% increases to 99.7%. The use of inoculant materials caused the longitudinal size of columnar beads to be significantly smaller. In addition to the effect of inoculant particles, changing the screening strategy also caused a change in the size of the beads. Changing the screening strategy also changed the morphology of the molten pool so that the largest width of the molten pool was obtained in the 316L steel piece made by the island method and the largest depth of the pools was obtained in the 316L+TiN piece made with the island screening strategy. The eva‎luation of the tensile properties of the samples at room temperature showed that with the addition of inoculant materials and the fineness of the grain structure, the yield strength and ultimate tensile strength increase by 74 and 87 MPa in the Meander scanning strategy and 61 and 65 MPa in the island scanning strategy. On the other hand, the increase in length of 316L+TiN samples compared to the non-inoculant sample was reduced by 14% and 12%, respectively, for the meander and island strategies. In general, it seems that if the appropriate manufacturing variables are selected, the addition of titanium nitride improves the microstructure and tensile properties of 316L steel.

احمد كرمانپور

احمد رضائيان , مسعود عطاپور