Effect of Ti addition on the microstructure and strengthening behavior in press hardening steels(PHS)was analyzed by optical metallography(OM),scanning electron microscopy(SEM),transmission electron microscopy(TEM)and...Effect of Ti addition on the microstructure and strengthening behavior in press hardening steels(PHS)was analyzed by optical metallography(OM),scanning electron microscopy(SEM),transmission electron microscopy(TEM)and X-ray diffraction(XRD).The results show that the microstructure of PHS is martensite,and two sizes of particles disperse in the martensite matrix during the forming and quenching process.The size of the bigger particles is between 100 and 200 nm,and the small particles are nanometer-sized.The quantity of the particles has a positive relation with the Ti content.More importantly,the microstructure and strengthening mechanism are affected by the precipitating behavior of the particles.Besides the prior austenite grain,martensite packet,block and lath are refined by Ti addition.The steels are strengthened by the fine grains,martensite substructure and precipitates.The uniformly distributed dislocation in the martensite lath,the density of which is between 3.0?10^(14) cm^(–2) and 5.0?10^(14) cm^(–2),strengthens the steels through associating with fine carbide particles.展开更多
304 austenitic stainless steel was cold rolled in the range of 20%-80%reductions and then annealed at 700-900°C for 60 sto obtain nano/ultrafine-grained（NG/UFG）structure.Transmission electron microscopy,electro...304 austenitic stainless steel was cold rolled in the range of 20%-80%reductions and then annealed at 700-900°C for 60 sto obtain nano/ultrafine-grained（NG/UFG）structure.Transmission electron microscopy,electron backscatter diffraction and X-ray diffraction were used to characterize the resulting microstructures.The results showed that with the increase of cold reduction,the content of martensite was increased.The steel performed work hardening during cold-working owing to the occurrence of strain induced martensite which nucleated in single shear bands.Further rolling broke up the lath-type martensite into dislocation-cell type martensite because of the formation of slip bands.Samples annealed at 800-960°C for 60 swere of NG/UFG structure with different percentage of nanocrystalline（60-100 nm）and ultrafine（100-500 nm）grains,submicron size（500-1000 nm）grains and micron size（〉1000 nm）grains.The value of the Gibbs free energy exhibited that the reversion mechanism of the reversion process was shear controlled by the annealing temperature.For a certain annealing time during the reversion process,austenite nucleated first on dislocation-cell type martensite and the grains grew up subsequently and eventually to be micrometer/submicrometer grains,while the nucleation of austenite on lath-type martensite occurred later resulting in nanocrystalline/ultrafine grains.The existence of the NG/UFG structure led to a higher strength and toughness during tensile test.展开更多
基金Project(U1460101)supported by the National Natural Science Foundation of ChinaProject(20120006120002)supported by Specialized Research Fund for the Doctoral Program of Higher Education,China
文摘Effect of Ti addition on the microstructure and strengthening behavior in press hardening steels(PHS)was analyzed by optical metallography(OM),scanning electron microscopy(SEM),transmission electron microscopy(TEM)and X-ray diffraction(XRD).The results show that the microstructure of PHS is martensite,and two sizes of particles disperse in the martensite matrix during the forming and quenching process.The size of the bigger particles is between 100 and 200 nm,and the small particles are nanometer-sized.The quantity of the particles has a positive relation with the Ti content.More importantly,the microstructure and strengthening mechanism are affected by the precipitating behavior of the particles.Besides the prior austenite grain,martensite packet,block and lath are refined by Ti addition.The steels are strengthened by the fine grains,martensite substructure and precipitates.The uniformly distributed dislocation in the martensite lath,the density of which is between 3.0?10^(14) cm^(–2) and 5.0?10^(14) cm^(–2),strengthens the steels through associating with fine carbide particles.
基金supported by the National Natural Science Foundation of China(Grant No.51474031)
文摘304 austenitic stainless steel was cold rolled in the range of 20%-80%reductions and then annealed at 700-900°C for 60 sto obtain nano/ultrafine-grained（NG/UFG）structure.Transmission electron microscopy,electron backscatter diffraction and X-ray diffraction were used to characterize the resulting microstructures.The results showed that with the increase of cold reduction,the content of martensite was increased.The steel performed work hardening during cold-working owing to the occurrence of strain induced martensite which nucleated in single shear bands.Further rolling broke up the lath-type martensite into dislocation-cell type martensite because of the formation of slip bands.Samples annealed at 800-960°C for 60 swere of NG/UFG structure with different percentage of nanocrystalline（60-100 nm）and ultrafine（100-500 nm）grains,submicron size（500-1000 nm）grains and micron size（〉1000 nm）grains.The value of the Gibbs free energy exhibited that the reversion mechanism of the reversion process was shear controlled by the annealing temperature.For a certain annealing time during the reversion process,austenite nucleated first on dislocation-cell type martensite and the grains grew up subsequently and eventually to be micrometer/submicrometer grains,while the nucleation of austenite on lath-type martensite occurred later resulting in nanocrystalline/ultrafine grains.The existence of the NG/UFG structure led to a higher strength and toughness during tensile test.
