Abstract
Structural diagrams and tensile properties of the 18%Cr-Fe-Ni-N system alloys were examined in the range of compositions from 0 to 20% nickel and up to 0.4% nitrogen. The results are summarized as follows: (1) The phase reaction in this system was considered from the isothermal structural diagrams at various temperatures between 1300° and 500°C. The austenite-promoting effect of nitrogen is about 25 times that of nickel. Also the solubility of nitrogen in austenite decreases in the proportion of about 4×10−3%N/%Ni with increasing nickel content. (2) The vertical section diagrams were obtained for 2, 5, and 8% nickel contents and for 0.1 and 0.2% nitrogen contents. The solubility of nitrogen in austenite of 18%Cr-8%Ni-Fe alloy may be expressed by the equation, log(%N)=−1080⁄T+0.284. (3) The quench-hardening introduces in vicinity of γ⁄α+γ boundary, especially the maximum value in the composition range of about 2% nickel and 0.3∼0.4% nitrogen. The metastable austenitic alloys as the 18%Cr-8%Ni-Fe system possess the characteristic tensile property that both the strength and ductility increase due to the martensite formation during deformation. In the stable austenitic alloys containing about 10% nickel or more, both the tensile and yield strengths increase at a ratio of about 7 kg/mm2 per 0.1% nitrogen.
