The decarburization behaviors of ultra low carbon steel in a 210-t RH vacuum degasser were investigated under practical operating conditions.According to the apparent decarburization rate constant (KC) calculated by t...The decarburization behaviors of ultra low carbon steel in a 210-t RH vacuum degasser were investigated under practical operating conditions.According to the apparent decarburization rate constant (KC) calculated by the carbon content in the samples taken from the hot melt in a ladle at an interval of 1-2 min,it is observed that the total decarburization reaction period in RH can be divided into the quick decarburization period and the stagnant decarburization period,which is quite different from the traditional one with three stages.In this study,the average apparent decarburization rate constant during the quick decarburization period is 0.306 min-1,and that of the stagnant period is 0.072 min-1.Increasing the initial carbon content and enhancing the exhausting capacity can increase the apparent decarburization rate constant in the quick decarburization period.The decarburization reaction comes into the stagnant decarburization period when the carbon content in molten steel is less than 14×10-6 after 10 min of decarburization.展开更多
A newspheroidizing process of ultra-high carbon steel ( UHCS) containing C 1·55 %, Cr 1·45 %,andAl 1·5 %in mass percent has been proposed . The effect of processing parameters on the microstructure was ...A newspheroidizing process of ultra-high carbon steel ( UHCS) containing C 1·55 %, Cr 1·45 %,andAl 1·5 %in mass percent has been proposed . The effect of processing parameters on the microstructure was ana-lyzed . The UHCS produced by this newprocess has a microstructure with recrystallizedferrite matrix andfine anduniformcarbide particles . After this spheroidizing ,the UHCS exhibits good mechanical properties at ambient tem-perature ,for exampleσb=1 100 MPa ,σs=915 MPa ,δ=8 %and high ratio ofσs/σb.展开更多
Under normal forging and annealing conditions, there are different ultra fine carbides (M3C, M23C6, M7Cj, M6C and MC) in high carbon alloy steels when alloy composition design is carried out properly. On the basis of ...Under normal forging and annealing conditions, there are different ultra fine carbides (M3C, M23C6, M7Cj, M6C and MC) in high carbon alloy steels when alloy composition design is carried out properly. On the basis of carbides transformation orderliness, the alloy composition design of the high carbon alloy steels is conducted by phase-equilibrium thermodynamic calculation for Fe-Cr-W-Mo-V-C system. The nucleation and growth of new carbides, dissolution of previous partial carbides in these steels during annealing process, all these lead to ultra-fine distribution of carbides. Due to different crystal structures of carbides and different thermodynamics as well dynamics parameters of the carbides dissolution and precipitation, the range of quenching temperature of these steels is widened, and the good temper-resistance is obtained. The characteristics of heat treatment process and microstructure variance, and the carbides transformation for different temperature are explained by the phase-equilibrium component satisfactorily. Their bend and yield strength, flexibility and toughness all are advanced markedly comparing with that of kindred steels. Results of the applications have proved that the microstructure of ultra-fine carbides in these steels played importance roles in the enhancement of edginess and fatigue crack resistance of the die and knives.展开更多
Many researchers have explored the inclusion modification mechanism to improve non-metallic inclusion modifications in steelmaking. In this study, two types of industrial trials on inclusion modifications in liquid st...Many researchers have explored the inclusion modification mechanism to improve non-metallic inclusion modifications in steelmaking. In this study, two types of industrial trials on inclusion modifications in liquid steel were conducted using ultra-low-carbon Al-killed steel with different Mg and Ca contents to verify the effects of Ca and Mg contents on the modification mechanism of Al_2O_3-based inclusions during secondary refining. The results showed that Al_2O_3-based inclusions can be modified into liquid calcium aluminate or a multi-component inclusion with the addition of a suitable amount of Ca. In addition, [Mg] in liquid steel can further reduce CaO in liquid calcium aluminate to drive its evolution into CaO–MgO–Al_2O_3 multi-component inclusions. Thermodynamic analysis confirmed that the reaction between [Mg] and CaO in liquid calcium aluminate occurs when the MgO content of liquid calcium aluminate is less than 3 wt% and the temperature is higher than 1843 K.展开更多
DTA, thermal expansion, XRD, and SEM were used to evaluate the effect of quenching temperature on the mechanical properties and microstructure of a novel sintered steel Fe-6Co-1Ni-5Cr-5Mo-1C. Lattice parameters and th...DTA, thermal expansion, XRD, and SEM were used to evaluate the effect of quenching temperature on the mechanical properties and microstructure of a novel sintered steel Fe-6Co-1Ni-5Cr-5Mo-1C. Lattice parameters and the mass fraction of carbon dissolved in the matrix of the steel quenched were investigated. It is discovered that the hardness of the steel increases with quench-ing temperature in the range of 840-900°C and remains constant in the range of 900 to 1100°C. It decreases rapidly when the tem-perature is higher than 1100°C. The mass fraction of carbon dissolved in the matrix of the steel quenched at 840°C is 0.38, but when the quenching temperature is increased to 1150°C, it increases to 0.98. The carbides formed during sintering are still present at grain boundaries and in the matrix of the steel quenched at low quenching temperatures, such as 840°C. When the quenching temperature is increased to 1150°C, most of the carbides at grain boundaries are dissolved with just a small amount of spherical M23C6 existing in the matrix of the quenched steel.展开更多
In isothermal spheroidizing process, the spheroidization and growth of the carbide formed in hot-deformed high-carbon chromium cast steel at high temperature were investigated. The results showed that the spheroidizin...In isothermal spheroidizing process, the spheroidization and growth of the carbide formed in hot-deformed high-carbon chromium cast steel at high temperature were investigated. The results showed that the spheroidizing growth of carbide proceeds in such a way that the bigger carbide particles swallow the smaller ones, and the short rhabdoid carbides dissolve and are spheroidized by itself. When the samples were held at 720 ℃ for more than 3 h, the spheroidization is not obvious. The feature of the process is the size increment and the amount decrement of carbide particles. The empirical equation for growth rate of carbides was obtained. The volume fraction of carbides keeps constant. The growth process agrees well with Ostwald Ripening Law.展开更多
In this study,the spheroidization process of large-deformed steel under various conditions was researched. Steel with a high carbon content(1.0% C)was first treated thermomechanically using multipass rolling.Then it u...In this study,the spheroidization process of large-deformed steel under various conditions was researched. Steel with a high carbon content(1.0% C)was first treated thermomechanically using multipass rolling.Then it underwent spheroidization treatments at different heating temperatures,using various heating times and cooling rates.Spheroidization processes with a lower heating temperature,shorter heating time,or faster cooling rate than those of the traditional process all showed good results,indicating that the spheroidization process was promoted significantly by the large deformation process.Grain refinement and fragmentation of cementite,along with the large deformation process,promoted this spheroidization process.展开更多
This paper studied the spot welding structure of ultra-high strength steel 22MnB5.ANSYS software was adopted to simulate its static strength;BS5400 algorithm was used to calculate the fatigue life;and the grouping met...This paper studied the spot welding structure of ultra-high strength steel 22MnB5.ANSYS software was adopted to simulate its static strength;BS5400 algorithm was used to calculate the fatigue life;and the grouping method was used to test the fatigue performance of tensile shear spot weld specimens.The simulation results were in good agreement with the experimental values.Based on the validation of the simulation method,influences of different structural parameters on static strength and fatigue life were explored by adopting single factor.The results showed that within the selected structure parameter range,increase of the sheet thickness,nugget diameter,sheet width and overlapping length can lead to longer fatigue life.Besides,the fatigue life of spot weld took on a linear relationship with the overlapping length,a DoseResp relationship with the sheet thickness,and a single exponential decay relationship with the sheet width and the nugget diameter.Moreover,in order to estimate the impact from various parameters on the fatigue life of the specimens,the Taguchi orthogonal design method was applied in the simulation design.The simulating result indicated that influence of the sheet thickness on fatigue life was the most significant.In addition,the effects of nugget diameter,sheet width and overlapping length on fatigue life were reduced in turn.展开更多
The microstructure and properties of high carbonic-chromium cast steel subjected to different hot deformation ratios were studied. The experimental results show that the microstructure and properties of high carbonic-...The microstructure and properties of high carbonic-chromium cast steel subjected to different hot deformation ratios were studied. The experimental results show that the microstructure and properties of high carbonic-chromium cast steel are obviously improved after hot deformation, and the best mechanical properties of the cast steel can be obtained under hot deformation ratio of 40 %-50 %, which leads to the morphology change of eutectic carbide and the precipitation of granular carbides.展开更多
To investigate the seismic performance of a composite frame comprised of steel reinforced ultra high-strength concrete (SRUHSC) columns and steel reinforced concrete (SRC) beams, six interior frame joint specimens wer...To investigate the seismic performance of a composite frame comprised of steel reinforced ultra high-strength concrete (SRUHSC) columns and steel reinforced concrete (SRC) beams, six interior frame joint specimens were designed and tested under low cyclically lateral load.The effects of the axial load ratio and volumetric stirrup ratio were studied on the characteristics of the frame joint performance including crack pattern, failure mode, ductility, energy dissipation capacity, strength degradation and rigidity degradation.It was found that all joint specimens behaved in a ductile manner with flexural-shear failure in the joint core region while plastic hinges appeared at the beam ends.The ductility and energy absorption capacity of joints increased as the axial load ratio decreased and the volumetric stirrup ratio increased.The displacement ductility coefficient and equivalent damping coefficient of the joints fell between the corresponding coefficients of the steel reinforced concrete (SRC) frame joint and RC frame joint.The axial load ratio and volumetric stirrup ratio have less influence on the strength degradation and more influence on the stiffness degradation.The stiffness of the joint degrades more significantly for a low volumetric stirrup ratio and high axial load ratio.The characteristics obtained from the SRUHSC composite frame joint specimens with better seismic performance may be a useful reference in future engineering applications.展开更多
The semi-solid high carbon steel T12 was rolled in a closed box groove under a certain condition by the rheo-rolling equipment, and the microstructural morphology of the semi-solid T12 before and after deformation was...The semi-solid high carbon steel T12 was rolled in a closed box groove under a certain condition by the rheo-rolling equipment, and the microstructural morphology of the semi-solid T12 before and after deformation was investigated by optical mi- croscope to analyze and summarize the microstructure evolution law of T12 deformed in semi-solid state. The experiment results show that the grain shape before deformation of the semi-solid T12 steel displays globule or ellipse by the electromagnetic stirring, the distribution of solid and liquid phases is homogeneous. But the microstructure of semi-solid product after rheo-rolling exhibits macrosegregation that the distribution of liquid and solid phases changes, the liquid phases divorce from the solid phases. In the transverse section, most of the solid phases get together in the center of the specimen, the liquid phases flow to the surface or the edge of the specimen, and the grains occur plastic deformation while reduction increased. In longitudinal section, the middle micro- structure of the specimen is more homogeneous than that at the head or tail, the head microstructure is similar to the tail and the size of the grains is not homogeneous.展开更多
The seismic performance of steel reinforced ultra-high-strength concrete columns(SRSHC) with various shear-span ratios(λ) were studied through a series of experiments.The concrete compressive cube strength value of e...The seismic performance of steel reinforced ultra-high-strength concrete columns(SRSHC) with various shear-span ratios(λ) were studied through a series of experiments.The concrete compressive cube strength value of experimental specimens ranged from 92.9 MPa to 108.1 MPa.The main experimental variables affecting seismic performance of specimens were axial load ratio and stirrup reinforcement ratio.The columns(λ=2.75) subjected to low cyclic reversed lateral loads failed mainly in the flexural-shear mode failure and columns(λ≤2.0) subjected to low cyclic reversed lateral loads failed mainly in the shear mode failure.Shear force-displacement hysteretic curves and skeleton curves were drawn.Coefficient of the specimen displacement ductility was calculated.Experimental results indicate that ductility decreases with axial pressure ratio increasing,and increases with stirrup reinforcement ratio increasing.Limit values of axial pressure ratio and minimum stirrup reinforcement ratio of columns are proposed to satisfy definite ductility requirement.The suggested values provide a reference for engineering application and for the amendment of the current Chinese design code of steel reinforced concrete composite structures.展开更多
For better processing performance of high carbon low alloy steel wire rod,an investigation about the influence of cementite lamellar spacing on wire ’easy drawing’ performance is completed.It is pointed out that too...For better processing performance of high carbon low alloy steel wire rod,an investigation about the influence of cementite lamellar spacing on wire ’easy drawing’ performance is completed.It is pointed out that too thin cementite lamellar spacing(<80 um) reduces the strain hardening level of wire drawing, and reduce the torsion performance of drawn wire at same time.For the wire or wire rod from industrial production,compared with the micro-structure with troostite,the micro-structure with sorbite or sorbite mixed with pearlite is more suitable to the drawing process with high reduction ratio.展开更多
The key manufacturing technologies associated with composition, microstructure, mechanical properties, casting quality and key process control for large martensitic stainless steel castings are involved in this paper....The key manufacturing technologies associated with composition, microstructure, mechanical properties, casting quality and key process control for large martensitic stainless steel castings are involved in this paper. The achievements fully satisfeid the technical requirements of the large 700 MW stainless steel hydraulic turbine runner for the Three Gorges Hydropower Station, and become the major technical support for the design and manufacture of the largest 700 MW hydraulic turbine generator unit in the world developed through our own efforts. The characteristics of a new high yield to tensile strength (R p0.2/R m ) ratio and high obdurability martensitic stainless steel with ultra low carbon and high cleanliness are also described. Over the next ten years, the large martensitic stainless steel castings and advanced manufacturing technologies will see a huge demand in clean energy industry such as nuclear power, hydraulic power at home and abroad. Therefore, the new high yield o tensile strength (R p0.2/R m ) ratio and high obdurability martensitic stainless steel materials, the fast and flexible manufacturing technologies of large size castings, and new environment friendly sustainable process will face new challenges and opportunities.展开更多
We investigated phase transition and precipitation of ultra-high strength steel(UHSS)in a new "short process" with controlled rolling and controlled cooling.Thermalexpansion test combined with metallographic...We investigated phase transition and precipitation of ultra-high strength steel(UHSS)in a new "short process" with controlled rolling and controlled cooling.Thermalexpansion test combined with metallographic observation was used to research the continuous cooling transformation(CCT)curve.Moreover,the microstructuraltransformation and precipitation law was revealed by morphologicalobservation and alloying elements by electron probe micro-analyzer(EPMA).Transmission electron microscopy(TEM)was utilized to analyze the composition and grain orientation of microstructure.The study showed that the measured criticaltransformation temperatures of Ac1 and Ac3 were 746 and 868 ℃,respectively.The CCT curve indicated that the undercooled austenite was transformed into proeutectoid ferrite and bainite with HV 520 in a broad range of cooling rate 0.1^(-1) ℃·s^(-1).When subjected to a cooling rate of 1 ℃·s^(-1),the undercooled austenite was divided into small-sized blocks by formed martensite.With further increase of cooling rate,micro-hardness increased dramatically,the microstructure of specimen was mainly lathe bainite(LB),granular bainite(GB),lath martensite(LM)and residualaustenite.By diffraction test analysis,it was identified that there was K-S orientation relationship between martensite and austenite for {110}_α//{111}_γ,{111}_α//{101}_γ.EPMA clearly showed that carbon diffused adequately due to staying for a long time at high temperature with a lower cooling rate of 2 ℃·s-1.Phase transition drive force was lower and the residualaustenite existed in the block form of Martensite austenite island(M-A).With the increase of cooling rate to 10 ℃·s^(-1),the block residualaustenite reduced,the carbon content of residualaustenite increased and α phase around the residualaustenite formed into a low carbon bainite form.展开更多
A mathematical model was established and applied to simulatethe decarburization of RH-MFB process in Pansteel Company. Study of the effects of , , Ar flowrate, evacuation rate and MFB lance blowing parameters on the d...A mathematical model was established and applied to simulatethe decarburization of RH-MFB process in Pansteel Company. Study of the effects of , , Ar flowrate, evacuation rate and MFB lance blowing parameters on the decarburization process was carried out. The results showed that this model could give the quantitative understanding of the process, especially the behavior of MFB lance blowing. This model has realized the optimum process of RH-MFB refining for ultra-low carbonsteels in Pansteel.展开更多
文摘The decarburization behaviors of ultra low carbon steel in a 210-t RH vacuum degasser were investigated under practical operating conditions.According to the apparent decarburization rate constant (KC) calculated by the carbon content in the samples taken from the hot melt in a ladle at an interval of 1-2 min,it is observed that the total decarburization reaction period in RH can be divided into the quick decarburization period and the stagnant decarburization period,which is quite different from the traditional one with three stages.In this study,the average apparent decarburization rate constant during the quick decarburization period is 0.306 min-1,and that of the stagnant period is 0.072 min-1.Increasing the initial carbon content and enhancing the exhausting capacity can increase the apparent decarburization rate constant in the quick decarburization period.The decarburization reaction comes into the stagnant decarburization period when the carbon content in molten steel is less than 14×10-6 after 10 min of decarburization.
基金Item Sponsored by Provincial Natural Science Foundation of Hebei Province of China (500023)
文摘A newspheroidizing process of ultra-high carbon steel ( UHCS) containing C 1·55 %, Cr 1·45 %,andAl 1·5 %in mass percent has been proposed . The effect of processing parameters on the microstructure was ana-lyzed . The UHCS produced by this newprocess has a microstructure with recrystallizedferrite matrix andfine anduniformcarbide particles . After this spheroidizing ,the UHCS exhibits good mechanical properties at ambient tem-perature ,for exampleσb=1 100 MPa ,σs=915 MPa ,δ=8 %and high ratio ofσs/σb.
文摘Under normal forging and annealing conditions, there are different ultra fine carbides (M3C, M23C6, M7Cj, M6C and MC) in high carbon alloy steels when alloy composition design is carried out properly. On the basis of carbides transformation orderliness, the alloy composition design of the high carbon alloy steels is conducted by phase-equilibrium thermodynamic calculation for Fe-Cr-W-Mo-V-C system. The nucleation and growth of new carbides, dissolution of previous partial carbides in these steels during annealing process, all these lead to ultra-fine distribution of carbides. Due to different crystal structures of carbides and different thermodynamics as well dynamics parameters of the carbides dissolution and precipitation, the range of quenching temperature of these steels is widened, and the good temper-resistance is obtained. The characteristics of heat treatment process and microstructure variance, and the carbides transformation for different temperature are explained by the phase-equilibrium component satisfactorily. Their bend and yield strength, flexibility and toughness all are advanced markedly comparing with that of kindred steels. Results of the applications have proved that the microstructure of ultra-fine carbides in these steels played importance roles in the enhancement of edginess and fatigue crack resistance of the die and knives.
基金financially supported by the Fundamental Research Funds for the Central Universities (No. FRF-TP-16-079A1)the National Science Foundation for Young Scientists of China (No. 51704021)+1 种基金the Joint Funds of National Natural Science Foundation of China (No. U1560203)supported by Beijing Key Laboratory of Special Melting and Preparation of High-end Metal Materials
文摘Many researchers have explored the inclusion modification mechanism to improve non-metallic inclusion modifications in steelmaking. In this study, two types of industrial trials on inclusion modifications in liquid steel were conducted using ultra-low-carbon Al-killed steel with different Mg and Ca contents to verify the effects of Ca and Mg contents on the modification mechanism of Al_2O_3-based inclusions during secondary refining. The results showed that Al_2O_3-based inclusions can be modified into liquid calcium aluminate or a multi-component inclusion with the addition of a suitable amount of Ca. In addition, [Mg] in liquid steel can further reduce CaO in liquid calcium aluminate to drive its evolution into CaO–MgO–Al_2O_3 multi-component inclusions. Thermodynamic analysis confirmed that the reaction between [Mg] and CaO in liquid calcium aluminate occurs when the MgO content of liquid calcium aluminate is less than 3 wt% and the temperature is higher than 1843 K.
文摘DTA, thermal expansion, XRD, and SEM were used to evaluate the effect of quenching temperature on the mechanical properties and microstructure of a novel sintered steel Fe-6Co-1Ni-5Cr-5Mo-1C. Lattice parameters and the mass fraction of carbon dissolved in the matrix of the steel quenched were investigated. It is discovered that the hardness of the steel increases with quench-ing temperature in the range of 840-900°C and remains constant in the range of 900 to 1100°C. It decreases rapidly when the tem-perature is higher than 1100°C. The mass fraction of carbon dissolved in the matrix of the steel quenched at 840°C is 0.38, but when the quenching temperature is increased to 1150°C, it increases to 0.98. The carbides formed during sintering are still present at grain boundaries and in the matrix of the steel quenched at low quenching temperatures, such as 840°C. When the quenching temperature is increased to 1150°C, most of the carbides at grain boundaries are dissolved with just a small amount of spherical M23C6 existing in the matrix of the quenched steel.
基金Item Sponsored by Guiding Programme of Science and Technology Research of Hebei of China(94122123)
文摘In isothermal spheroidizing process, the spheroidization and growth of the carbide formed in hot-deformed high-carbon chromium cast steel at high temperature were investigated. The results showed that the spheroidizing growth of carbide proceeds in such a way that the bigger carbide particles swallow the smaller ones, and the short rhabdoid carbides dissolve and are spheroidized by itself. When the samples were held at 720 ℃ for more than 3 h, the spheroidization is not obvious. The feature of the process is the size increment and the amount decrement of carbide particles. The empirical equation for growth rate of carbides was obtained. The volume fraction of carbides keeps constant. The growth process agrees well with Ostwald Ripening Law.
文摘In this study,the spheroidization process of large-deformed steel under various conditions was researched. Steel with a high carbon content(1.0% C)was first treated thermomechanically using multipass rolling.Then it underwent spheroidization treatments at different heating temperatures,using various heating times and cooling rates.Spheroidization processes with a lower heating temperature,shorter heating time,or faster cooling rate than those of the traditional process all showed good results,indicating that the spheroidization process was promoted significantly by the large deformation process.Grain refinement and fragmentation of cementite,along with the large deformation process,promoted this spheroidization process.
基金financially supported by the Beijing Natural Science Foundation(3122004)
文摘This paper studied the spot welding structure of ultra-high strength steel 22MnB5.ANSYS software was adopted to simulate its static strength;BS5400 algorithm was used to calculate the fatigue life;and the grouping method was used to test the fatigue performance of tensile shear spot weld specimens.The simulation results were in good agreement with the experimental values.Based on the validation of the simulation method,influences of different structural parameters on static strength and fatigue life were explored by adopting single factor.The results showed that within the selected structure parameter range,increase of the sheet thickness,nugget diameter,sheet width and overlapping length can lead to longer fatigue life.Besides,the fatigue life of spot weld took on a linear relationship with the overlapping length,a DoseResp relationship with the sheet thickness,and a single exponential decay relationship with the sheet width and the nugget diameter.Moreover,in order to estimate the impact from various parameters on the fatigue life of the specimens,the Taguchi orthogonal design method was applied in the simulation design.The simulating result indicated that influence of the sheet thickness on fatigue life was the most significant.In addition,the effects of nugget diameter,sheet width and overlapping length on fatigue life were reduced in turn.
基金Item Sponsored by Guiding Program of Science and Technology Research of Hebei Province of China(94122123)
文摘The microstructure and properties of high carbonic-chromium cast steel subjected to different hot deformation ratios were studied. The experimental results show that the microstructure and properties of high carbonic-chromium cast steel are obviously improved after hot deformation, and the best mechanical properties of the cast steel can be obtained under hot deformation ratio of 40 %-50 %, which leads to the morphology change of eutectic carbide and the precipitation of granular carbides.
基金National Natural Science Foundation of China Under Grant No.50878037
文摘To investigate the seismic performance of a composite frame comprised of steel reinforced ultra high-strength concrete (SRUHSC) columns and steel reinforced concrete (SRC) beams, six interior frame joint specimens were designed and tested under low cyclically lateral load.The effects of the axial load ratio and volumetric stirrup ratio were studied on the characteristics of the frame joint performance including crack pattern, failure mode, ductility, energy dissipation capacity, strength degradation and rigidity degradation.It was found that all joint specimens behaved in a ductile manner with flexural-shear failure in the joint core region while plastic hinges appeared at the beam ends.The ductility and energy absorption capacity of joints increased as the axial load ratio decreased and the volumetric stirrup ratio increased.The displacement ductility coefficient and equivalent damping coefficient of the joints fell between the corresponding coefficients of the steel reinforced concrete (SRC) frame joint and RC frame joint.The axial load ratio and volumetric stirrup ratio have less influence on the strength degradation and more influence on the stiffness degradation.The stiffness of the joint degrades more significantly for a low volumetric stirrup ratio and high axial load ratio.The characteristics obtained from the SRUHSC composite frame joint specimens with better seismic performance may be a useful reference in future engineering applications.
基金This work was financially supported by the National Natural Science Foundation of China and Baosteel (No.50174003).
文摘The semi-solid high carbon steel T12 was rolled in a closed box groove under a certain condition by the rheo-rolling equipment, and the microstructural morphology of the semi-solid T12 before and after deformation was investigated by optical mi- croscope to analyze and summarize the microstructure evolution law of T12 deformed in semi-solid state. The experiment results show that the grain shape before deformation of the semi-solid T12 steel displays globule or ellipse by the electromagnetic stirring, the distribution of solid and liquid phases is homogeneous. But the microstructure of semi-solid product after rheo-rolling exhibits macrosegregation that the distribution of liquid and solid phases changes, the liquid phases divorce from the solid phases. In the transverse section, most of the solid phases get together in the center of the specimen, the liquid phases flow to the surface or the edge of the specimen, and the grains occur plastic deformation while reduction increased. In longitudinal section, the middle micro- structure of the specimen is more homogeneous than that at the head or tail, the head microstructure is similar to the tail and the size of the grains is not homogeneous.
文摘The seismic performance of steel reinforced ultra-high-strength concrete columns(SRSHC) with various shear-span ratios(λ) were studied through a series of experiments.The concrete compressive cube strength value of experimental specimens ranged from 92.9 MPa to 108.1 MPa.The main experimental variables affecting seismic performance of specimens were axial load ratio and stirrup reinforcement ratio.The columns(λ=2.75) subjected to low cyclic reversed lateral loads failed mainly in the flexural-shear mode failure and columns(λ≤2.0) subjected to low cyclic reversed lateral loads failed mainly in the shear mode failure.Shear force-displacement hysteretic curves and skeleton curves were drawn.Coefficient of the specimen displacement ductility was calculated.Experimental results indicate that ductility decreases with axial pressure ratio increasing,and increases with stirrup reinforcement ratio increasing.Limit values of axial pressure ratio and minimum stirrup reinforcement ratio of columns are proposed to satisfy definite ductility requirement.The suggested values provide a reference for engineering application and for the amendment of the current Chinese design code of steel reinforced concrete composite structures.
文摘For better processing performance of high carbon low alloy steel wire rod,an investigation about the influence of cementite lamellar spacing on wire ’easy drawing’ performance is completed.It is pointed out that too thin cementite lamellar spacing(<80 um) reduces the strain hardening level of wire drawing, and reduce the torsion performance of drawn wire at same time.For the wire or wire rod from industrial production,compared with the micro-structure with troostite,the micro-structure with sorbite or sorbite mixed with pearlite is more suitable to the drawing process with high reduction ratio.
文摘The key manufacturing technologies associated with composition, microstructure, mechanical properties, casting quality and key process control for large martensitic stainless steel castings are involved in this paper. The achievements fully satisfeid the technical requirements of the large 700 MW stainless steel hydraulic turbine runner for the Three Gorges Hydropower Station, and become the major technical support for the design and manufacture of the largest 700 MW hydraulic turbine generator unit in the world developed through our own efforts. The characteristics of a new high yield to tensile strength (R p0.2/R m ) ratio and high obdurability martensitic stainless steel with ultra low carbon and high cleanliness are also described. Over the next ten years, the large martensitic stainless steel castings and advanced manufacturing technologies will see a huge demand in clean energy industry such as nuclear power, hydraulic power at home and abroad. Therefore, the new high yield o tensile strength (R p0.2/R m ) ratio and high obdurability martensitic stainless steel materials, the fast and flexible manufacturing technologies of large size castings, and new environment friendly sustainable process will face new challenges and opportunities.
基金Funded by the Scientifi c and Technological Research Program of Chongqing Municipal Education Commission(No.KJ1501324)the General Project of Chongqing Frontier and Applied Basic Research Project(No.cstc2015jcyj A90005)the Research Foundation of Chongqing University of Science and Technology(Nos.CK2013Z16&CK2014Z20)
文摘We investigated phase transition and precipitation of ultra-high strength steel(UHSS)in a new "short process" with controlled rolling and controlled cooling.Thermalexpansion test combined with metallographic observation was used to research the continuous cooling transformation(CCT)curve.Moreover,the microstructuraltransformation and precipitation law was revealed by morphologicalobservation and alloying elements by electron probe micro-analyzer(EPMA).Transmission electron microscopy(TEM)was utilized to analyze the composition and grain orientation of microstructure.The study showed that the measured criticaltransformation temperatures of Ac1 and Ac3 were 746 and 868 ℃,respectively.The CCT curve indicated that the undercooled austenite was transformed into proeutectoid ferrite and bainite with HV 520 in a broad range of cooling rate 0.1^(-1) ℃·s^(-1).When subjected to a cooling rate of 1 ℃·s^(-1),the undercooled austenite was divided into small-sized blocks by formed martensite.With further increase of cooling rate,micro-hardness increased dramatically,the microstructure of specimen was mainly lathe bainite(LB),granular bainite(GB),lath martensite(LM)and residualaustenite.By diffraction test analysis,it was identified that there was K-S orientation relationship between martensite and austenite for {110}_α//{111}_γ,{111}_α//{101}_γ.EPMA clearly showed that carbon diffused adequately due to staying for a long time at high temperature with a lower cooling rate of 2 ℃·s-1.Phase transition drive force was lower and the residualaustenite existed in the block form of Martensite austenite island(M-A).With the increase of cooling rate to 10 ℃·s^(-1),the block residualaustenite reduced,the carbon content of residualaustenite increased and α phase around the residualaustenite formed into a low carbon bainite form.
文摘A mathematical model was established and applied to simulatethe decarburization of RH-MFB process in Pansteel Company. Study of the effects of , , Ar flowrate, evacuation rate and MFB lance blowing parameters on the decarburization process was carried out. The results showed that this model could give the quantitative understanding of the process, especially the behavior of MFB lance blowing. This model has realized the optimum process of RH-MFB refining for ultra-low carbonsteels in Pansteel.