Abstract:
Electrolytic extraction followed by XRD analysis of precipitates after isothermal annealing of an AISI 441
ferritic stainless steel between 600 and 850 ◦C produced the time–temperature–precipitation (TTP) diagram
for the Fe2Nb-Laves phase. The TTP diagram shows two classical C noses, the first one between 750
and 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 Fe2Nb 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 0.435 J m−2 and an initial particle center-to-center separation
distance on grain boundaries of about 0.2 m.
