Effect of Carbon Content on Bainite Transformation Start Temperature on Fe–9Ni–C Alloys

Abstract

Upper bainite in steels has many common features with lath martensite in steels. But there are some studies that indicate that bainite transformation start temperature (B_s) is greater than T₀ on steels containing high carbon content. We measured B_s on Fe–9 mass% Ni alloys containing 0.003–0.89 mass% C. In low carbon alloys, B_s is below T₀, and the increasing of carbon content decreases B_s standing in a line that is parallel to T₀. On the other hand, in high carbon alloys, carbon content does not affect B_s which stands around 753 K. The border between these two tendencies and B_s in high carbon alloys seem to correspond to the intersection point between the line of B_s on low carbon alloys and the calculated γ/(γ + θ) phase boundary.