Understandings of the effect of hot deformation parameters close to the practical production line on grain refinement are crucial for enhancing both the strength and toughness of future rail steels.In this work,the au...Understandings of the effect of hot deformation parameters close to the practical production line on grain refinement are crucial for enhancing both the strength and toughness of future rail steels.In this work,the austenite dynamic recrystallization(DRX)behaviors of a eutectoid pearlite rail steel were studied using a thermo-mechanical simulator with hot deformation parameters frequently employed in rail production lines.The single-pass hot deformation results reveal that the prior austenite grain sizes(PAGSs)for samples with different deformation reductions decrease initially with an increase in deformation temperature.However,once the deformation temperature is beyond a certain threshold,the PAGSs start to increase.It can be attributed to the rise in DRX volume fraction and the increase of DRX grain with deformation temperature,respectively.Three-pass hot deformation results show that the accumulated strain generated in the first and second deformation passes can increase the extent of DRX.In the case of complete DRX,PAGS is predominantly determined by the deformation temperature of the final pass.It suggests a strategic approach during industrial production where part of the deformation reduction in low temperature range can be shifted to the medium temperature range to release rolling mill loads.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
For the great significance of the prediction of control parameters selected for hot-rolling and the evaluation of hot-rolling quality for the analysis of prod uction problems and production management, the selection o...For the great significance of the prediction of control parameters selected for hot-rolling and the evaluation of hot-rolling quality for the analysis of prod uction problems and production management, the selection of hot-rolling control parameters was studied for microalloy steel by following the neural network principle. An experimental scheme was first worked out for acquisition of sample data, in which a gleeble-1500 thermal simolator was used to obtain rolling temperature, strain, stain rate, and stress-strain curves. And consequently the aust enite grain sizes was obtained through microscopic observation. The experimental data was then processed through regression. By using the training network of BP algorithm, the mapping relationship between the hotrooling control parameters (rolling temperature, stain, and strain rate) and the microstructural paramete rs (austenite grain in size and flow stress) of microalloy steel was function appro ached for the establishment of a neural network-based model of the austeuite grain size and flow stress of microalloy steel. From the results of estimation made with the neural network based model, the hot-rolling control parameters can be effectively predicted.展开更多
On the basis of transformation thermodynamics and kinetics theories,an algorithm for predicting ferrite grain size after continuous cooling transformation from deformed austenite to ferrite is suggested.The calculated...On the basis of transformation thermodynamics and kinetics theories,an algorithm for predicting ferrite grain size after continuous cooling transformation from deformed austenite to ferrite is suggested.The calculated results of computer simulation with the algorithm are in so good agreement with the measured ones in controlled rolling and controlled cooling experiments that the theoretical algorithm is feasible.展开更多
18 Mn18 Cr0.5 N steel with an initial grain size of 28–177 μm was processed by 2.5%–20% cold rolling and annealing at 1000°C for 24 h,and the grain boundary character distribution was examined via electron bac...18 Mn18 Cr0.5 N steel with an initial grain size of 28–177 μm was processed by 2.5%–20% cold rolling and annealing at 1000°C for 24 h,and the grain boundary character distribution was examined via electron backscatter diffraction.Low strain(2.5%) favored the formation of low-Σ boundaries.At this strain,the fraction of low-Σ boundaries was insensitive to the initial grain size.However,specimens with fine initial grains showed decreasing grain size after grain boundary engineering processing.The fraction of low-Σ boundaries and the(Σ9 + Σ27)/Σ3 value decreased with increasing strain; furthermore,the specimens with fine initial grain size were sensitive to the strain.Finally,the effects of the initial grain size and strain on the grain boundary engineering were discussed in detail.展开更多
The austenite grain growth behavior of Q1030 steel was studied under different heating conditions. The austenite grain size increases with the heating temperature and holding time increasing. Austenite grains grow in ...The austenite grain growth behavior of Q1030 steel was studied under different heating conditions. The austenite grain size increases with the heating temperature and holding time increasing. Austenite grains grow in an exponential manner with rising heating tem- perature and in a parabolic manner with prolonging holding time. A mathematical model for describing the austenite grain growth behavior of Q 1030 steel was obtained on the basis of experimental results using regression analysis. When the heating temperatures lie between 1000 and 1100℃ at a certain holding time, abnormal grain growth appears, which causes mixed grains in Q1030 steel.展开更多
The changes in austenite grain size of the specimens with coarse ferrite grains under different heat treatment process were investigated.The focus was on studying the effect of annealing on refining coarse ferrite gra...The changes in austenite grain size of the specimens with coarse ferrite grains under different heat treatment process were investigated.The focus was on studying the effect of annealing on refining coarse ferrite grains,as well as the influence of the ferrite grain size on the main technical indicators of gas carburizing.The results show that coarse ferrite grains may not necessarily cause the coarse austenite grains,but may result in mixed austenite grains.After annealing treatment,the coarse ferrite grains can be significantly refined and homogenized.Moreover,the coarse ferrite grains have no significant effects on hardnessand intergranular oxidationof gas carburizing.展开更多
The aim of the current study was to investigate the microstructural evolution during dynamic recrystallization in coarse Nb microalloyed austenite in thin slab direct rolling (TSDR) processing. A model was developed...The aim of the current study was to investigate the microstructural evolution during dynamic recrystallization in coarse Nb microalloyed austenite in thin slab direct rolling (TSDR) processing. A model was developed to predict the change of the austenite grain size during the dynamic recrystallization, by using the law of mixtures. The equations initially developed for partial static recrystallization were used for partial dynamic recrystallization, by adjusting the value of the constant. The results show that the change of the austenite grain size can be reasonably described by using the equations developed according to the law of mixtures.展开更多
The initial solidification process of microalloyed steels was simulated using a confocal scanning laser microscope,and the growth behavior of austenite grain was observed in situ.The method for measuring the initial a...The initial solidification process of microalloyed steels was simulated using a confocal scanning laser microscope,and the growth behavior of austenite grain was observed in situ.The method for measuring the initial austenite grain size was studied,and the M_(0)^(*)(the parameter to describe the grain boundary migration)values at different cooling rates were then calculated using the initial austenite grain size and the final grain size.Next,a newly modified model for predicting the austenite grain size was established by introducing the relationship between M_(0)^(*)and the cooling rate,and the value calculated from the modified model closely corresponds to the measured value,with average relative error being less than 5%.Further,the relationship between T^(γ)(the starting temperature for austenite grain growth)and equivalent carbon content C_(P)(C_(P)>0.18%)was obtained by in situ observation,and it was introduced into the modified model,which expanded the application scope of the model.Taking the continuous casting slab produced by a steel plant as the experimental object,the modified austenite grain size prediction model was used to predict the austenite grain size at different depths of oscillation mark on the surface of slab,and the predicted value was in good agreement with the actual measured value.展开更多
The transformation behaviors and microstructures of a low carbon multi-phase steel were investigated by the simulation of deformation-relaxation-accelerated cooling processing,using a Gleeble 3500 thermal-mechanical s...The transformation behaviors and microstructures of a low carbon multi-phase steel were investigated by the simulation of deformation-relaxation-accelerated cooling processing,using a Gleeble 3500 thermal-mechanical simulator.A pre-treatment of solid solution at 1200°C was implemented to minimize the influence on transformation from solid solution/precipitation qualities of 0.08%Nb in this steel.On this basis,the effect of austenite grain size and accelerated cooling start temperature were studied individually.The results indicated that the transformation of ferrite in multi-phase steel could be significantly promoted by the refinement of austenite grains and the increase of relaxation time,while the hard phase,such as lath bainite or martensite,could still be obtained with the following accelerated cooling.In contrast,more uniform lower temperature transformed microstructure could form from coarse grain austenite.The potential benefit of austenite grain size on adjusting the proportion of phases in multiphase steel was also discussed.展开更多
基金financially supported by the National Natural Science Foundation of China(Nos.52293395 and 52293393)the Xiongan Science and Technology Innovation Talent Project of MOST,China(No.2022XACX0500)。
文摘Understandings of the effect of hot deformation parameters close to the practical production line on grain refinement are crucial for enhancing both the strength and toughness of future rail steels.In this work,the austenite dynamic recrystallization(DRX)behaviors of a eutectoid pearlite rail steel were studied using a thermo-mechanical simulator with hot deformation parameters frequently employed in rail production lines.The single-pass hot deformation results reveal that the prior austenite grain sizes(PAGSs)for samples with different deformation reductions decrease initially with an increase in deformation temperature.However,once the deformation temperature is beyond a certain threshold,the PAGSs start to increase.It can be attributed to the rise in DRX volume fraction and the increase of DRX grain with deformation temperature,respectively.Three-pass hot deformation results show that the accumulated strain generated in the first and second deformation passes can increase the extent of DRX.In the case of complete DRX,PAGS is predominantly determined by the deformation temperature of the final pass.It suggests a strategic approach during industrial production where part of the deformation reduction in low temperature range can be shifted to the medium temperature range to release rolling mill loads.
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.
文摘For the great significance of the prediction of control parameters selected for hot-rolling and the evaluation of hot-rolling quality for the analysis of prod uction problems and production management, the selection of hot-rolling control parameters was studied for microalloy steel by following the neural network principle. An experimental scheme was first worked out for acquisition of sample data, in which a gleeble-1500 thermal simolator was used to obtain rolling temperature, strain, stain rate, and stress-strain curves. And consequently the aust enite grain sizes was obtained through microscopic observation. The experimental data was then processed through regression. By using the training network of BP algorithm, the mapping relationship between the hotrooling control parameters (rolling temperature, stain, and strain rate) and the microstructural paramete rs (austenite grain in size and flow stress) of microalloy steel was function appro ached for the establishment of a neural network-based model of the austeuite grain size and flow stress of microalloy steel. From the results of estimation made with the neural network based model, the hot-rolling control parameters can be effectively predicted.
文摘On the basis of transformation thermodynamics and kinetics theories,an algorithm for predicting ferrite grain size after continuous cooling transformation from deformed austenite to ferrite is suggested.The calculated results of computer simulation with the algorithm are in so good agreement with the measured ones in controlled rolling and controlled cooling experiments that the theoretical algorithm is feasible.
基金financially supported by the National Natural Science Foundation of China (No.51505416)the Natural Science Foundation-Steel and Iron Foundation of Hebei Province,China (No.E2017203041)+1 种基金the Natural Science Foundation of Hebei Province,China (No.E2016203436)the Post-Doctoral Research Project of Hebei Province,China (No.B2016003029)
文摘18 Mn18 Cr0.5 N steel with an initial grain size of 28–177 μm was processed by 2.5%–20% cold rolling and annealing at 1000°C for 24 h,and the grain boundary character distribution was examined via electron backscatter diffraction.Low strain(2.5%) favored the formation of low-Σ boundaries.At this strain,the fraction of low-Σ boundaries was insensitive to the initial grain size.However,specimens with fine initial grains showed decreasing grain size after grain boundary engineering processing.The fraction of low-Σ boundaries and the(Σ9 + Σ27)/Σ3 value decreased with increasing strain; furthermore,the specimens with fine initial grain size were sensitive to the strain.Finally,the effects of the initial grain size and strain on the grain boundary engineering were discussed in detail.
文摘The austenite grain growth behavior of Q1030 steel was studied under different heating conditions. The austenite grain size increases with the heating temperature and holding time increasing. Austenite grains grow in an exponential manner with rising heating tem- perature and in a parabolic manner with prolonging holding time. A mathematical model for describing the austenite grain growth behavior of Q 1030 steel was obtained on the basis of experimental results using regression analysis. When the heating temperatures lie between 1000 and 1100℃ at a certain holding time, abnormal grain growth appears, which causes mixed grains in Q1030 steel.
基金the Shaanxi Innovation Talent Promotion Plan-Youth Science and Technology New Star Project(Talent).Project No.:2023KJXX-121。
文摘The changes in austenite grain size of the specimens with coarse ferrite grains under different heat treatment process were investigated.The focus was on studying the effect of annealing on refining coarse ferrite grains,as well as the influence of the ferrite grain size on the main technical indicators of gas carburizing.The results show that coarse ferrite grains may not necessarily cause the coarse austenite grains,but may result in mixed austenite grains.After annealing treatment,the coarse ferrite grains can be significantly refined and homogenized.Moreover,the coarse ferrite grains have no significant effects on hardnessand intergranular oxidationof gas carburizing.
基金This work was financially supported by the Major State Basic Research Development of China ("973" Program, No.2004CB619102)CITIC Metal Co. Ltd.
文摘The aim of the current study was to investigate the microstructural evolution during dynamic recrystallization in coarse Nb microalloyed austenite in thin slab direct rolling (TSDR) processing. A model was developed to predict the change of the austenite grain size during the dynamic recrystallization, by using the law of mixtures. The equations initially developed for partial static recrystallization were used for partial dynamic recrystallization, by adjusting the value of the constant. The results show that the change of the austenite grain size can be reasonably described by using the equations developed according to the law of mixtures.
基金supported by the National Natural Science Foundations of China (No.50734008)the Fundamental Research Funds for the Central Universities (No.FRF-AS-11-003A)
基金the Joint Fund of Iron and Steel Research of the National Natural Science Foundation of China and Baowu Group Corporation(Grant No.U1760103).
文摘The initial solidification process of microalloyed steels was simulated using a confocal scanning laser microscope,and the growth behavior of austenite grain was observed in situ.The method for measuring the initial austenite grain size was studied,and the M_(0)^(*)(the parameter to describe the grain boundary migration)values at different cooling rates were then calculated using the initial austenite grain size and the final grain size.Next,a newly modified model for predicting the austenite grain size was established by introducing the relationship between M_(0)^(*)and the cooling rate,and the value calculated from the modified model closely corresponds to the measured value,with average relative error being less than 5%.Further,the relationship between T^(γ)(the starting temperature for austenite grain growth)and equivalent carbon content C_(P)(C_(P)>0.18%)was obtained by in situ observation,and it was introduced into the modified model,which expanded the application scope of the model.Taking the continuous casting slab produced by a steel plant as the experimental object,the modified austenite grain size prediction model was used to predict the austenite grain size at different depths of oscillation mark on the surface of slab,and the predicted value was in good agreement with the actual measured value.
基金supported by the National Basic Research Program of China ("973" Program) (Grant No. 2010CB630801)
文摘The transformation behaviors and microstructures of a low carbon multi-phase steel were investigated by the simulation of deformation-relaxation-accelerated cooling processing,using a Gleeble 3500 thermal-mechanical simulator.A pre-treatment of solid solution at 1200°C was implemented to minimize the influence on transformation from solid solution/precipitation qualities of 0.08%Nb in this steel.On this basis,the effect of austenite grain size and accelerated cooling start temperature were studied individually.The results indicated that the transformation of ferrite in multi-phase steel could be significantly promoted by the refinement of austenite grains and the increase of relaxation time,while the hard phase,such as lath bainite or martensite,could still be obtained with the following accelerated cooling.In contrast,more uniform lower temperature transformed microstructure could form from coarse grain austenite.The potential benefit of austenite grain size on adjusting the proportion of phases in multiphase steel was also discussed.