Microstructure evolution during deformation of undercooled austenite at 760℃ was investigated in Nb-microalloyed steel by using SEM （scanning electron microscope）, TEM （transmission electron microscope）, and EBSD...Microstructure evolution during deformation of undercooled austenite at 760℃ was investigated in Nb-microalloyed steel by using SEM （scanning electron microscope）, TEM （transmission electron microscope）, and EBSD （electron backscattered diffraction）. It is indicated that during deformation-enhanced ferrite transformation （DEFT） in Nb-microalloyed steel, the incubation period is prolonged, and the higher strain is needed to accomplish ferrite transformation. Therefore, the transformation kinetics curves move to high strain parallelly; and the transformation kinetics curves of Nb-microalloyed steel can be divided into three stages. At the fast stage, the solute drag effect of Nb and the consumption of strain energy for the dynamic precipitation of Nb（CN） led to a long incubation period, and at the second stage, ferrite transformation was accelerated significantly and fine Nb（CN） precipitates restrict the grain growth of ferrite effectively. The results also showed that DEFT in Nb-microalloyed steel is still a nucleation dominated process, and during the microstructure evolution the interchange of 〈001〉 and 〈111〉 texture was obtained.展开更多
Effects of C and Mn contents on the deformation-enhanced ferrite transformation （DEFT） in low carbon （Mn） steels have been investigated by hot compression. The microstructures of 2-4μm ultra-fine equiaxed ferrite...Effects of C and Mn contents on the deformation-enhanced ferrite transformation （DEFT） in low carbon （Mn） steels have been investigated by hot compression. The microstructures of 2-4μm ultra-fine equiaxed ferrite grains with minors distributed homogeneously can be obtained by DEFT in all the tested steels. The more pronounced refinement is achieved as the C or Mn content increasing because of the higher-density nucleating sites and lower growth rate. The effectiveness of C on the level of refinement is more obvious than that of Mn.展开更多
The hot compression tests using Gleeble 1500 were performed by varying the true strain up to 1.6 （80% reduction） in Nbfree and Nb-microalloyed steels. The effect of Nb addition on the transformation kinetics during ...The hot compression tests using Gleeble 1500 were performed by varying the true strain up to 1.6 （80% reduction） in Nbfree and Nb-microalloyed steels. The effect of Nb addition on the transformation kinetics during deformation of undercooled austenite was investigated. It was found that as compared with Nb-free steel, the transformation incubation period of Nb-bearing steel was prolonged and the transformation kinetics curves parallelly moved to higher strain because of the solute Nb drag effect. Studies on kinetics also showed that the deformation-enhanced ferrite transformation （DEFT） of the two steels were composed of three stages, which can be expressed by the J-M-A equations individually. However, the parameter n related to the mode of nucleation and growth is somewhat different in the first and second stages of the two steels, and the same in the third stage for both the steels corresponding to the nucleation Of retained austenite.展开更多
A low carbon steel was used to determine the critical strain εc for completion of deformation enhanced ferrite transformation （DEFT） through a series of hot compression tests. In addition, the influence of prior au...A low carbon steel was used to determine the critical strain εc for completion of deformation enhanced ferrite transformation （DEFT） through a series of hot compression tests. In addition, the influence of prior austenite grain size （PAGS） on the critical strain was systematically investigated. Experimental results showed that the critical strain is affected by PAGS. When γ→α transformation completes, the smaller the PAGS is, the smaller the critical strain is. The ferrite grains obtained through DEFT can be refined to about 3 μm when the DEFT is completed.展开更多
The precipitation behavior of V（C, N） in steels microalloyed with vanadium was researched using a thermal simulator during single-pass deformation at 800-750 ℃. The V（C, N） precipitates and its nucleation effect ...The precipitation behavior of V（C, N） in steels microalloyed with vanadium was researched using a thermal simulator during single-pass deformation at 800-750 ℃. The V（C, N） precipitates and its nucleation effect on ferrite were investigated by TEM and EDS. The experimental results show that there are two remarkable heterogeneous nucleation effects of V（C, N） particles precipitated before γ →/ α phase change： primary reason is that high coherency between V（C, N） and ferrite promotes V（C, N） to become a nucleating center of intragranular ferrite; secondary reason is that the coarsening of V（C, N） causes locally solute-poor region in austenite, thus expedites the nucleation of intragranular ferrites further. Furthermore, the relationship between the size and shape of V（C, N） was studied, and identification method was provided for distinguishing interphase precipitation and general precipitation to avoid erroneous judgment and misguide.展开更多
基金This work was financially supported by the National High-Tech Research and Development Program of China ("863" Program)(No.2001AA332020).
文摘Microstructure evolution during deformation of undercooled austenite at 760℃ was investigated in Nb-microalloyed steel by using SEM （scanning electron microscope）, TEM （transmission electron microscope）, and EBSD （electron backscattered diffraction）. It is indicated that during deformation-enhanced ferrite transformation （DEFT） in Nb-microalloyed steel, the incubation period is prolonged, and the higher strain is needed to accomplish ferrite transformation. Therefore, the transformation kinetics curves move to high strain parallelly; and the transformation kinetics curves of Nb-microalloyed steel can be divided into three stages. At the fast stage, the solute drag effect of Nb and the consumption of strain energy for the dynamic precipitation of Nb（CN） led to a long incubation period, and at the second stage, ferrite transformation was accelerated significantly and fine Nb（CN） precipitates restrict the grain growth of ferrite effectively. The results also showed that DEFT in Nb-microalloyed steel is still a nucleation dominated process, and during the microstructure evolution the interchange of 〈001〉 and 〈111〉 texture was obtained.
基金This work was financially supported by the National High-Tech Research and Development Program of China (No.2001AA3 32020).
文摘Effects of C and Mn contents on the deformation-enhanced ferrite transformation （DEFT） in low carbon （Mn） steels have been investigated by hot compression. The microstructures of 2-4μm ultra-fine equiaxed ferrite grains with minors distributed homogeneously can be obtained by DEFT in all the tested steels. The more pronounced refinement is achieved as the C or Mn content increasing because of the higher-density nucleating sites and lower growth rate. The effectiveness of C on the level of refinement is more obvious than that of Mn.
基金This work was financially supported by the National High-Tech Research and Development Program of China (No.2001AA332020).
文摘The hot compression tests using Gleeble 1500 were performed by varying the true strain up to 1.6 （80% reduction） in Nbfree and Nb-microalloyed steels. The effect of Nb addition on the transformation kinetics during deformation of undercooled austenite was investigated. It was found that as compared with Nb-free steel, the transformation incubation period of Nb-bearing steel was prolonged and the transformation kinetics curves parallelly moved to higher strain because of the solute Nb drag effect. Studies on kinetics also showed that the deformation-enhanced ferrite transformation （DEFT） of the two steels were composed of three stages, which can be expressed by the J-M-A equations individually. However, the parameter n related to the mode of nucleation and growth is somewhat different in the first and second stages of the two steels, and the same in the third stage for both the steels corresponding to the nucleation Of retained austenite.
基金This work was financially supported by the National Science and Technology Ministry to the research project ‘Advanced industriali-zation technique of manufacture for carbon steel of 500 MPa grade’ (No.2001AA332020).
文摘A low carbon steel was used to determine the critical strain εc for completion of deformation enhanced ferrite transformation （DEFT） through a series of hot compression tests. In addition, the influence of prior austenite grain size （PAGS） on the critical strain was systematically investigated. Experimental results showed that the critical strain is affected by PAGS. When γ→α transformation completes, the smaller the PAGS is, the smaller the critical strain is. The ferrite grains obtained through DEFT can be refined to about 3 μm when the DEFT is completed.
基金Funded by the National Natural Science Foundation of China (50775102)the Universities Natural Science Fund Key Project of Jiangsu Province (04KJA430021)
文摘The precipitation behavior of V（C, N） in steels microalloyed with vanadium was researched using a thermal simulator during single-pass deformation at 800-750 ℃. The V（C, N） precipitates and its nucleation effect on ferrite were investigated by TEM and EDS. The experimental results show that there are two remarkable heterogeneous nucleation effects of V（C, N） particles precipitated before γ →/ α phase change： primary reason is that high coherency between V（C, N） and ferrite promotes V（C, N） to become a nucleating center of intragranular ferrite; secondary reason is that the coarsening of V（C, N） causes locally solute-poor region in austenite, thus expedites the nucleation of intragranular ferrites further. Furthermore, the relationship between the size and shape of V（C, N） was studied, and identification method was provided for distinguishing interphase precipitation and general precipitation to avoid erroneous judgment and misguide.
