The effects of carbon and nitrogen addition on the athermal α′-martensitic transformation in metastable 18%Cr-8%Ni austenite are investigated. The thermal stability of austenite in nitrogen-added steel is higher than that in carbon-added steel, and the difference between the effects of carbon and nitrogen addition becomes remarkable as the amount of both elements increases. As the two-step transformation (γ → ε → α′) always occurs in metastable 18%Cr-8%Ni austenite, the suppression of ε-martensite results in the thermal stabilization of austenite. Nitrogen is more effective than carbon for increasing the stacking fault energy, leading to a higher thermal stability of the nitrogen-bearing 18%Cr-8%Ni steels.
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