Effect of manganese on microstructure of an isothermally transformed Fe–Nb–C alloy

AbstractAbstractThe effect of manganese on the microstructure developed by isothermal transformation of an Fe-Nb-C alloy was examined over a wide range of temperatures. A well defined discontinuity was found at about 750°C in the time-temperature-transformation curve of an Fe–0·033Nb–0·07C–1·07Mn (wt-%) alloy. The discontinuity appears close to the temperature at which the interphase precipitation of NbC begins to occur, this temperature being about 50 K lower than that for a corresponding Fe–Nb–C alloy. Carbide-free ferrite is principally formed between 850 and 780°C in the Mn-containing alloy, a wider temperature range than that for the alloy without manganese. The amount of NbC dispersed in ferrite is decreased by the addition of manganese. The changes that develop in the microstructure after the addition of manganese are explained in terms of the reduction of ferrite growth rate and the decrease in supersaturation of NbC in ferrite.MST/45