The influence of processing parameters ofrelaxation-precipitation-controlling phase transformation (RPC) technique, finish rollingtemperature, reduction ratio and relaxing time on the microstructure was studied byther...The influence of processing parameters ofrelaxation-precipitation-controlling phase transformation (RPC) technique, finish rollingtemperature, reduction ratio and relaxing time on the microstructure was studied bythermo-simulation for a low carbon Nb and Ti containing micro-alloyed steel. The microstructure wasinvestigated by optical microscope, transmission electron microscope and electron back scatterdiffraction (EBSD). The statistical results of the packet size were calculated. It shows that, afterRPC process, the steel is a composite microstructure of bainite and matensite. The bestthermo-simulation process for refinement in this experiment is deformation for 30 percent at 850 degC, and then relaxing at this temperature for 60 s to 200 s. Increasing the reduction ratio from 30percent to 60 or decreasing the deformation temperature to 800 deg C would cause the best relaxationtime to become shorter, increasing the deformation temperature to 900 deg C would cause therefinement effect to be weak.展开更多
Thermal simulation test, TEM (Transmission Electron Microscope) and nanobeamEDS (Energy Dispersed x-ray Spectrum) techniques were used to investigate the precipitation behaviorof Nb, Ti, Mo etc. in HSLA (High Strength...Thermal simulation test, TEM (Transmission Electron Microscope) and nanobeamEDS (Energy Dispersed x-ray Spectrum) techniques were used to investigate the precipitation behaviorof Nb, Ti, Mo etc. in HSLA (High Strength Low Alloy) steel. The strain induced precipitationoccurred during the isothermal relaxation stage after deformed in the non-recrystallizationtemperature region. After 30% predeformation at 850 and 900℃, there are two kinds of particles,(Ti,Nb)(C,N) and a few Nb(C,N), to precipitate during holding. The content of Nb in particles riseswith the relaxation time increasing. During the final holding stage, some Nb and Ti atoms in thelattice sites of the precipitates would be replaced by Mo atoms, and the Mo content in theprecipitates increases with the relaxation time. The results were compared with the refinementeffect of microstructures caused by relaxation-precipitation controlling transformation (RPC)processing.展开更多
The structure variation of deformed austenite during the relaxation stage after deformation at various temperatures in an Nb-B ultra low carbon bainitic steel and Fe-Ni alloy was studied by the thermo-simulation. Opti...The structure variation of deformed austenite during the relaxation stage after deformation at various temperatures in an Nb-B ultra low carbon bainitic steel and Fe-Ni alloy was studied by the thermo-simulation. Optical microscope and TEM were applied to analyze the microstructure after RPC （Relaxation-precipitation-controlling phase transformation technique） and the evolution of dislocation configuration. The particle tracking autoradiography （PTA） technique, revealing the distribution of boron, was employed to show the change of boron segregation after different relaxation times. The results indicate that during the relaxation stage the recovery occurs in the deformed austenite, the dislocations rearrange and subgrains form. During the subsequent cooling the boron will segregate at the boundaries of subgrains.展开更多
The ultra-fine bainitic microstructure of a 900 MPa low carbon bainitic Cu-Ni-Mo-B steel was obtained by a newly developed relaxation precipitation control （RPC） phase transformation processing. In a pan-cake like p...The ultra-fine bainitic microstructure of a 900 MPa low carbon bainitic Cu-Ni-Mo-B steel was obtained by a newly developed relaxation precipitation control （RPC） phase transformation processing. In a pan-cake like prior-austenite grain, the micro- structure consisted of lath bainite, a little of abnormal granular bainite, and acicular ferrite. The effect of zirconium carbonitrides on the austenite grain coarsening behavior was studied by transmission electron microscopy （TEM）. The results show that, the lath is narrower with increasing cooling rate. The ratio of all kinds of bainitic microstructure is proper with the intermediate cooling rate; and Zr-containing precipitates distribute uniformly, which restrains austenite grain growing in heat-affected welding zone.展开更多
文摘The influence of processing parameters ofrelaxation-precipitation-controlling phase transformation (RPC) technique, finish rollingtemperature, reduction ratio and relaxing time on the microstructure was studied bythermo-simulation for a low carbon Nb and Ti containing micro-alloyed steel. The microstructure wasinvestigated by optical microscope, transmission electron microscope and electron back scatterdiffraction (EBSD). The statistical results of the packet size were calculated. It shows that, afterRPC process, the steel is a composite microstructure of bainite and matensite. The bestthermo-simulation process for refinement in this experiment is deformation for 30 percent at 850 degC, and then relaxing at this temperature for 60 s to 200 s. Increasing the reduction ratio from 30percent to 60 or decreasing the deformation temperature to 800 deg C would cause the best relaxationtime to become shorter, increasing the deformation temperature to 900 deg C would cause therefinement effect to be weak.
基金This work was financially supported by the national key basic research and development program of China (No.G1998061507).
文摘Thermal simulation test, TEM (Transmission Electron Microscope) and nanobeamEDS (Energy Dispersed x-ray Spectrum) techniques were used to investigate the precipitation behaviorof Nb, Ti, Mo etc. in HSLA (High Strength Low Alloy) steel. The strain induced precipitationoccurred during the isothermal relaxation stage after deformed in the non-recrystallizationtemperature region. After 30% predeformation at 850 and 900℃, there are two kinds of particles,(Ti,Nb)(C,N) and a few Nb(C,N), to precipitate during holding. The content of Nb in particles riseswith the relaxation time increasing. During the final holding stage, some Nb and Ti atoms in thelattice sites of the precipitates would be replaced by Mo atoms, and the Mo content in theprecipitates increases with the relaxation time. The results were compared with the refinementeffect of microstructures caused by relaxation-precipitation controlling transformation (RPC)processing.
基金This work is financially supported by the National Natural Science Foundation of China (No. 50471089)
文摘The structure variation of deformed austenite during the relaxation stage after deformation at various temperatures in an Nb-B ultra low carbon bainitic steel and Fe-Ni alloy was studied by the thermo-simulation. Optical microscope and TEM were applied to analyze the microstructure after RPC （Relaxation-precipitation-controlling phase transformation technique） and the evolution of dislocation configuration. The particle tracking autoradiography （PTA） technique, revealing the distribution of boron, was employed to show the change of boron segregation after different relaxation times. The results indicate that during the relaxation stage the recovery occurs in the deformed austenite, the dislocations rearrange and subgrains form. During the subsequent cooling the boron will segregate at the boundaries of subgrains.
基金supported by the National High-Technology Research and Development Program of China (No.2003AA331020)
文摘The ultra-fine bainitic microstructure of a 900 MPa low carbon bainitic Cu-Ni-Mo-B steel was obtained by a newly developed relaxation precipitation control （RPC） phase transformation processing. In a pan-cake like prior-austenite grain, the micro- structure consisted of lath bainite, a little of abnormal granular bainite, and acicular ferrite. The effect of zirconium carbonitrides on the austenite grain coarsening behavior was studied by transmission electron microscopy （TEM）. The results show that, the lath is narrower with increasing cooling rate. The ratio of all kinds of bainitic microstructure is proper with the intermediate cooling rate; and Zr-containing precipitates distribute uniformly, which restrains austenite grain growing in heat-affected welding zone.
