Mechanism Of Ferrite Grain Refinement Of Hot Rolled Cu-P-Cr-Ni-Mo Dual-phase Weathering Steel

Dual-phase weathering steel have great predominance for the applications ofbuildings, automobiles, electric towers, railways and bridges due to their highweatherability and excellent comprehensive mechanical properties. At present, the ferritegrain sizes of Cu-P-Cr-Ni-Mo weathering steel were about30-40μm, so ferrite refinementwas a potential way to promote the strength of materials. Effects of deformation behaviorcharacteristic and microstructure evolution on ferrite grain refinement of Cu-P-Cr-Ni-Moweathering steel during different temperature regions were investigated, as well as ferritegrain refinement mechanism.The stress-strain curves and microstructure evolution of the experiment steel wereanalyzed by Gleeble-3500thermal simulator though different processes in the criticaltemperature region. Making sure that the deformation induced ferrite transformation wasresponsible for the ferrite refinement at875℃; and with the strain and strain rateincreasing, the fraction of deformation induced ferrite increased and grain sizes decreased;but when the strain and the strain rate reached an certain value, amount of deformationinduced ferrite transformation tended to saturation, meanwhile, the ferrite grain sizedecreased slowly.Ferrite grain refinement mechanism were studied by optical microscope and electronback scattering diffraction technology in the (γ+α) region. The results showed thatcontinuous dynamic recrystallization was responsible for the ferrite grain refinement in the(γ+α) region; when the strain was over0.69, the transformation fraction of ferriteincreased not obviously, but the fraction of equiaxed ferrite grains surrounded by highangle boundaries increased quickly; With the temperature decreasing, the amount oftransformation fraction of ferrite increased, ferrite grain size decreased, and the number ofsub-grains surrounded by low angle boundaries increased, which concluded that the abilityof continuous dynamic recrystallization of ferrite was enhanced.Different deformation process parameters were performed by using Gleeble-3500simulator to study the influence on the ferrite refinement. The results showed that with the strain rate increasing, the type of curve changed from peak stress to the work hardeningtype; peak stress increased with the deformation temperature increasing, and the peakstrain corresponding to the peak stress also increased. Deformation induced ferrite grainswere formed in recrystallization and unrecrystallization zone; and the number of smallerequiaxed ferrite grains increased, grain sizes decrease.