Role of Aging Precipitates on Mechanical Properties of HNS with Different Nitrogen Content

Abstract

This paper illutrates the role of aging precipitates and the effects of nitrogen content on mechanical properties of 18Cr-18Mn-2Mo-0.77N (HNS-77), 18Cr-18Mn-2Mo-0.96N (HNS-B) and 18Cr-16Mn-2Mo-1.1N (HNS-110) through Vickers hardness, Charpy impact (CVN) and uniform tensile methods. The results show that intergranular, cellular Cr2N and χ phase precipitate gradually in three HNSs aged at the nose temperature for different time. Based on transmission electron microscopy (TEM) analysis, intergranular and cellular Cr2N precipitation has a hexagonal structure and intermetallic χ phase has a B.C.C structure. Compared to the solution treated specimens, Vickers hardness of HNS-77, HNS-96 and HNS-110 aged at nose temperature with increasing the aging time firstly decreases then increases; impact absorbed energy, ultimate tensile strength (UTS) and elongation (El) decrease monotonously. Yield strength (YS) of HNS-77 and HNS-96 firstly increases then decreases except HNS-110 with a monotonously decreased trendency. Vickers hardness of HNS-77, HNS-96 and HNS-110 arrives at the maximum value at nose temperature. Meanwhile, impact absorbed energy arrives at the minimum value. Impact absorbed energy of aged HNSs decreases with the formation and increment of intergranular, cellular Cr2N and intermetallic χ phases. With increasing the nitrogen content, aging behavior of HNS presents more obvious susceptibility. The rate of increased amount and size of intergranular, cellular Cr2N and relative minor χ phase grows and affects the mechanical properties of aged HNS remarkably.