摘要
Some observations are reported on the simulation of two thermomechanical routes to produce ultrafine ferrite grainsize in steels. One C-Mn grade and Nb, Nb-Ti and Nb-high Ti bearing steels were used in the tests performed ona Gleeble simulator and a laboratory rolling mill. The routes included severe hot deformation of prior grain-refinedaustenite at the temperature close to Ar3 (DIF) and static recrystallization of fine-grained cold-rolled martensite(SRM). It was observed that the hot deformation induces the formation of ferrite above the Ar3 temperature of thesteel, but severe reductions are required for the complete transformation. Strain of 1.2 can result in about 70% offerrite with the grain size of about 1.4～2μm in all the studied steels. Similarly, in short annealing of cold-workedmartensite, the static recrystallization can also lead to a grain size of about 1.5 μm. The distribution of carbonvaries in the microstructures, carbon being in the second phase in the DIF route and in carbide particles in the SRMroute, which may have a significant influence on the mechanical properties and the thermal stability of ultrafine grainstructure.
