No abstract

Electrolytic extraction followed by XRD analysis of precipitates after isothermal annealing of an AISI 441 ferritic stainless steel between 600-850°C, produced the time-temperature-precipitation (TTP) diagram for the Fe 2 Nb-Laves phase. The TTP diagram shows two classical C noses, the first one between 750 to 825 C and the second one, estimated to be close to 650-675 C. TEM analyses show two independent nucleation mechanisms, i.e. at about 600 °C nucleation takes place on dislocations but above 750 °C, grain boundary nucleation is dominant. The measured solvus temperature of 875 C for Fe 2 Nb in this steel is 50C higher than predicted by Thermo-Calc®. Kinetic modelling at 800 C agreed well with the experimental results for a surface energy of 0.435Jm-2 and an initial particle center-to-center separation distance on grain boundaries of about 0.2m.