Effects of silicon, molybdenum, and nitrogen on elevated temperature properties of low carbon austenitic stainless steels

To improve the high temperature mechanical properties of low carbon medium nitrogen type 316 stainless steels (316FR) the effect of Si addition on high temperature properties was investigated in relation to Mo and N which are the strengthening elements of 316FR. Tensile and creep rupture tests at 550 degrees C and aging tests at 550, 600, and 650 degrees C were conducted. The microstructures of ruptured specimens and aged ones were examined with an electron microscope and extracted residues analysis. The addition of 3 mass% Si, 2% Mo, and 0.08% N increased both tensile strength and elongation. Creep rupture strength was slightly increased by the addition of Si with or without Mo and N, while the addition of Mo or N remarkably increased rupture strength. Although rupture elongation increased by the addition of Si to a base alloy and a Mo containing one, it did not changed with Si in case of a Mo and N containing alloy. The addition of Si to base alloy caused precipitation of G phase on grain boundaries, while in case of a Mo containing alloys Si remarkably accelerated precipitation of G phase on grain boundaries and Laves phase in matrix.