The hot deformation behavior of Fe-26Mn-6.2A1-0.05C steel was studied by experimental hot compression tests in the temperature range of 800-1050℃ and strain rate range of 0.01-30 s-1 on a Gleeble-3500 thermal simulat...The hot deformation behavior of Fe-26Mn-6.2A1-0.05C steel was studied by experimental hot compression tests in the temperature range of 800-1050℃ and strain rate range of 0.01-30 s-1 on a Gleeble-3500 thermal simulation machine.The microstructural evolution during the corresponding thermal process was observed in situ by confocal laser scanning microscopy.Electron backscattered diffraction and transmission electron microscopy analyses were carried out to observe the microstructural morphology before and after the hot deformation.Furthermore,interrupted compression tests were conducted to correlate the microstructural characteristics and softening mechanisms at different deformation stages.The results showed that hot compression tests of this steel were all carried out on a duplex matrix composed of austenite and fi-ferrite.As the deformation temperature increased from 800 to 1050℃,the volume fraction of austenite decreased from 70.9% to 44.0%,while that of 6-ferrite increased from 29.1% to 56.0%.Due to the different stress exponents(n)and apparent activation energies(Q),the generated strain was mostly accommodated by δ-ferrite at the commencement of deformation,and then both dynamic recovery and dynamic recrystallization occurred earlier in δ-ferrite than in austenite.This interaction of strain partitioning and unsynchronized softening behavior caused an abnormal hot deformation behavior profile in the Fe-Mn-A1 duplex steel,such as yield-like behavior,peculiar work-hardening behavior,and dynamic softening behavior,which are influenced by not only temperature and strain rate but also by microstructural evolution.展开更多
The intercritical annealing treatment at 650 and 700 ℃ results in two ultrafine-grained (UFG) dual-phase ferrite-austenitesteels. The two steels exhibit different and special discontinuous yielding and pronounced L...The intercritical annealing treatment at 650 and 700 ℃ results in two ultrafine-grained (UFG) dual-phase ferrite-austenitesteels. The two steels exhibit different and special discontinuous yielding and pronounced Lüders-like strain phenomenawith large yielding strain which are related to their retained γ-austenite (RA) volume fractions and RA stabilities. The steelannealed at 650 ℃ shows an absent or very small strain hardening, while the steel annealed at 700 ℃ shows an obviousstrain hardening upward curvature with increasing strain. The results show that before and during straining, the steel annealedat 650 ℃ exhibits a mixture of equiaxed and elongated UFG α-ferrite and austenite phases;however, the steel annealed at700 ℃ exhibits only elongated UFG α and γ phases. It was found that most of the γ-austenite to α′-martensite transformationoccurred at the initial deformation stage and very small or almost no transformation occurred afterward. This demonstratesthat the strain-induced martensite (SIM) transformation (γ-α′) or transformation-induced plasticity (TRIP) effect dominatesonly at the initial deformation stage. RA remained stable, and no TRIP effect was observed at the final deformation stage. Theload-unload-reload test was performed to evaluate the back stress (σb) hardening effect. It is believed that the pronouncedstrain hardening behavior at the later deformation stage is mainly associated with σb enhancement induced by the strainpartitioning between the soft and hard phases due to SIM transformation during tensile deformation.展开更多
基金financially supported by the National Natural Science Foundation of China(No.51474031)
文摘The hot deformation behavior of Fe-26Mn-6.2A1-0.05C steel was studied by experimental hot compression tests in the temperature range of 800-1050℃ and strain rate range of 0.01-30 s-1 on a Gleeble-3500 thermal simulation machine.The microstructural evolution during the corresponding thermal process was observed in situ by confocal laser scanning microscopy.Electron backscattered diffraction and transmission electron microscopy analyses were carried out to observe the microstructural morphology before and after the hot deformation.Furthermore,interrupted compression tests were conducted to correlate the microstructural characteristics and softening mechanisms at different deformation stages.The results showed that hot compression tests of this steel were all carried out on a duplex matrix composed of austenite and fi-ferrite.As the deformation temperature increased from 800 to 1050℃,the volume fraction of austenite decreased from 70.9% to 44.0%,while that of 6-ferrite increased from 29.1% to 56.0%.Due to the different stress exponents(n)and apparent activation energies(Q),the generated strain was mostly accommodated by δ-ferrite at the commencement of deformation,and then both dynamic recovery and dynamic recrystallization occurred earlier in δ-ferrite than in austenite.This interaction of strain partitioning and unsynchronized softening behavior caused an abnormal hot deformation behavior profile in the Fe-Mn-A1 duplex steel,such as yield-like behavior,peculiar work-hardening behavior,and dynamic softening behavior,which are influenced by not only temperature and strain rate but also by microstructural evolution.
基金supported by the Joint Research Center for Future Iron and Steel,SJTU&BaosteelThe author(L.M.Fu)is grateful to the financial support from Startup Fund for Youngman Research at SJTU(SFYR at SJTU,No.18X100040023).
文摘The intercritical annealing treatment at 650 and 700 ℃ results in two ultrafine-grained (UFG) dual-phase ferrite-austenitesteels. The two steels exhibit different and special discontinuous yielding and pronounced Lüders-like strain phenomenawith large yielding strain which are related to their retained γ-austenite (RA) volume fractions and RA stabilities. The steelannealed at 650 ℃ shows an absent or very small strain hardening, while the steel annealed at 700 ℃ shows an obviousstrain hardening upward curvature with increasing strain. The results show that before and during straining, the steel annealedat 650 ℃ exhibits a mixture of equiaxed and elongated UFG α-ferrite and austenite phases;however, the steel annealed at700 ℃ exhibits only elongated UFG α and γ phases. It was found that most of the γ-austenite to α′-martensite transformationoccurred at the initial deformation stage and very small or almost no transformation occurred afterward. This demonstratesthat the strain-induced martensite (SIM) transformation (γ-α′) or transformation-induced plasticity (TRIP) effect dominatesonly at the initial deformation stage. RA remained stable, and no TRIP effect was observed at the final deformation stage. Theload-unload-reload test was performed to evaluate the back stress (σb) hardening effect. It is believed that the pronouncedstrain hardening behavior at the later deformation stage is mainly associated with σb enhancement induced by the strainpartitioning between the soft and hard phases due to SIM transformation during tensile deformation.