The decarburization behaviors of ultra low carbon steel in a 210-t RH vacuum degasser were investigated under practical operat- ing conditions. According to the apparent decarburization rate constant （Kc） calculated...The decarburization behaviors of ultra low carbon steel in a 210-t RH vacuum degasser were investigated under practical operat- ing 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
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
Copper and sulfur are typical residual elements or impurity elements in steel.Sufficient removal of them during steelmaking process is difficult for copper and costly for sulfur.Utilization of copper and sulfur in ste...Copper and sulfur are typical residual elements or impurity elements in steel.Sufficient removal of them during steelmaking process is difficult for copper and costly for sulfur.Utilization of copper and sulfur in steel, especially in steel scrap,has been an important issue for a long period for metallurgists.Copper and sulfur may combine to form copper sulfide,which may provide a prospect to avoid the detrimental effects of copper and sulfur in steel.Unfortunately the formation mechanism of copper sulfide in steel has not been completely clarified so far. In the present paper,solution treatment of samples containing copper and sulfur are firstly performed at 1623 K for 2.7×10~3 s followed by quenching into water.The samples are then isothermally heat-treated at 673 K,873 K, 1073 K,1273 K and 1373K for different time followed by quenching into water again.The size,morphology, constituent and crystallography of sulfide precipitates in these samples are investigated by scanning electron microscope(SEM) and TEM equipped with EDS.Fine copper sulfides(less than 100 nm) are observed to coexist with silicon oxide in samples even isothermally heat-treated at 1 373 K for 1.44×10~4 s;Film-like copper sulfides are generally observed to co-exist with iron sulfide in all samples;Plate-like copper sulfides are observed especially in sample isothermally heat-treated at 1 073 K for 1.44×10~4 s.The formation mechanisms of these copper sulfides have been discussed.展开更多
According to the balance of carbon and oxygen, a decarburization model for the RH treatment has been developed. in which the influence of the mass transfer of carbon and oxygen in the liquid steel and the stirring ene...According to the balance of carbon and oxygen, a decarburization model for the RH treatment has been developed. in which the influence of the mass transfer of carbon and oxygen in the liquid steel and the stirring energy (ε) in the vacuum vessel on decarburization rate has been considered. The conclusion that the volumetric coefficients of the mass transfer of carbon is proportional to ε(1.5) is drawn. Industrical experiment proves this model is reliable. The influence of some factors on decarburization rate has been obtained. which can provide directions for RH treatment The decarburization behavior of steel with RH-OB treatment is also studied. The OB-or-not curve, the optimized OB time and OB amount are discussed.展开更多
A Ti＋Nb bearing ultra-low carbon bake hardening sheet steel hot-rolled in the conventional austenite region and in the ferrite region with lubrication was experimentally studied. Subsequent cold rolling and continuou...A Ti＋Nb bearing ultra-low carbon bake hardening sheet steel hot-rolled in the conventional austenite region and in the ferrite region with lubrication was experimentally studied. Subsequent cold rolling and continuous annealing processes were also conducted. The results show that microstructures of ultra-low carbon bake hardening hot strips at room temperature are basically irregular polygonal ferrites. The yield strength, ultimate tensile strength, n value, and r value of the No.2 specimen hot-rolled in the ferrite region with lubrication are 243 MPa, 364 MPa, 0.29, and 1.74, respectively, which are similar to those of the No.1 specimen hot-roiled in the conventional austenite region. The elongation rate and bake hardening value of No.2 specimen are 51% and 49.4 MPa, respectively, which are greater than those of No. 1 specimen. The No.2 specimen hot-rolled in the ferrite region with lubrication exhibits good mechanical properties and relatively excellent baking hardening performance. Therefore, the hot rolling experiment of Ti＋Nb bearing ultra-low carbon bake hardening steel in the ferrite region with lubrication is feasible and can be considered in the future industrial trial production.展开更多
Titanium is the impurity in some special steel grades.The existence of titanium decreases the grain size,depresses the yield strength,and results in the low quality of these steels in various properties.Thus,titanium ...Titanium is the impurity in some special steel grades.The existence of titanium decreases the grain size,depresses the yield strength,and results in the low quality of these steels in various properties.Thus,titanium should be removed to the minimum.Based on the industrial production of ultra low carbon Al-Si killed steel,the physical-chemical behavior of titanium was investigated in vacuum degassing refining（RH）process with and without desulfurization.The influences of titanium content in hot metal,ladle slag composition,and ladle slag quantity,etc,on titanium content of refined liquid steel were discussed.The results showed that the partition ratio of titanium between ladle slag and liquid steel is in inverse proportion to the 4/3square of aluminum content.The maximum partition ratio of titanium between top slag and liquid steel can be obtained by adjusting an optimum slag composition including contents of FeOxand Al2O3and the slag basicity,and the suitable range of them should be controlled higher than 6%,less than 20%,and within 1.5to 3.0,respectively.Moreover,desulfurization refining by RH decreases the partition ratio of titanium between ladle slag and liquid steel significantly.To ensure the titanium content stably less than 15×10-6 in a 300tladle,the titanium content in hot metal must be less than 500×10-6 and the thickness of basic oxygen furnace（BOF）slag carrying over must be less than 50mm.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
800 MPa grade new ultra-low carbon bainitic （NULCB） steel is the recently developed new generation steel. The microstructure in the coarse-grained heat affected zone （CGHAZ） of NULCB steel under laser welding cond...800 MPa grade new ultra-low carbon bainitic （NULCB） steel is the recently developed new generation steel. The microstructure in the coarse-grained heat affected zone （CGHAZ） of NULCB steel under laser welding conditions was investigated by thermal simulation. The influence of the cooling time from 800℃ to 500℃.t8/5 （0.3-30 s）, on the microstructure of the CGHAZ was discussed. The experimental results indicate that the microstructnre of the CGHAZ is only the granular bainite which consists of bainitic ferrite （BF） lath and M-A constituent while t8/5 is 0.3-30 s. The M-A constituent consists of twinned martensite and residual austenite, and the change of the volume fraction of the residual austenite in the M-A constituent is very small when t8/5 is between 0.3 and 30 s. The morphology of the M-A constituent obviously changes with the variation of t8/5.As t8/5 increases, tile average width, gross and shape parameter of the M-A constituent increase, while the line density of the M-A constituent decreases.展开更多
The formation mechanism of the spheroidal carbide in the ultra-low carbon ductile cast iron fabricated by the metal mold casting technique was systematically investigated. The results demonstrated that the spheroidal ...The formation mechanism of the spheroidal carbide in the ultra-low carbon ductile cast iron fabricated by the metal mold casting technique was systematically investigated. The results demonstrated that the spheroidal carbide belonged to eutectic carbide and crystallized in the isolated eutectic liquid phase area. The formation process of the spheroidal carbide was related to the contact and the intersection between the primary dendrite and the secondary dendrite of austenite. The oxides of magnesium, rare earths and other elements can act as heterogeneous nucleation sites for the spheroidal carbide. It was also found that the amount of the spheroidal carbide would increase with an increase in carbon content. The cooling rate has an important influence on the spheroidal carbide under the same chemical composition condition.展开更多
The deactivation of a Ni-Mo-W/Al_2O_3 catalyst during ultra-low-sulfur diesel production was investigated in a pilot plant. The reasons of catalyst deactivation were analyzed by the methods of elemental analysis, BET ...The deactivation of a Ni-Mo-W/Al_2O_3 catalyst during ultra-low-sulfur diesel production was investigated in a pilot plant. The reasons of catalyst deactivation were analyzed by the methods of elemental analysis, BET and TG-MS. The results showed that the catalyst deactivation rate was notable at the beginning of run, and then gradually reached a steady state after 448 h. In the initial period the catalyst deactivation may mainly be caused by the formation of the carbon deposits. The carbon deposits blocked the catalyst pores and the accessibility of active center decreased. The TG-MS analysis identified three types of carbon species deposited on the catalysts, viz.: the low temperature carbon deposit with high H/C atomic ratio, the medium temperature carbon deposit, and the high temperature carbon with low H/C atomic ratio. The amount of high temperature carbon deposits on the catalyst determined the overall activity and, therefore the high temperature carbon was a major contributor to the deactivation of Ni-Mo-W catalyst.展开更多
An induction levitation melting （ILM） refining process is performed to remove most microsized inclusions in ultra-low carbon steel （UCS）. Nanosized, spheroid shaped sulfide precipitates remain dispersed in the UCS...An induction levitation melting （ILM） refining process is performed to remove most microsized inclusions in ultra-low carbon steel （UCS）. Nanosized, spheroid shaped sulfide precipitates remain dispersed in the UCS. During the ILM process, the UCS is molten and is rotated under an upward magnetic field. With the addition of Ti additives, the spinning molten steel under the upward magnetic field ejects particles because of resultant centrifugal, floating, and magnetic forces. Magnetic force plays a key role in removing sub-micrometer-sized particles, composed of porous aluminum titanate enwrapping alumina nuclei. Consequently, sulfide precipitates with sizes less than 50 nan remain dispersed in the steel matrix. These findings open a path to the fabrication of clean steel or steel bearing only a nanosized strengthen- ing phase.展开更多
The hot deformation experiments of ultra-low carbon steel in ferrite range were carried out in a hot simulator in order to research hot deformation behaviors of ultra-low carbon steel in ferrite range at low temperatu...The hot deformation experiments of ultra-low carbon steel in ferrite range were carried out in a hot simulator in order to research hot deformation behaviors of ultra-low carbon steel in ferrite range at low temperature. The results show that the influences of deformation parameters on flow stress are different to those in austenitic deformation. The deformation characteristic parameters were calculated for ultra-low carbon steel in ferrite region. The flow stress equation for ultra-low carbon steel in ferritic deformation at low temperature was obtained.展开更多
Stress relaxation was chosen as the best method for monitoring the precipitation process. Tests were carried out on an ultra-low carbon bainitic steel containing Mn, Nb and B over 800~950℃. Specimens were solu- tion ...Stress relaxation was chosen as the best method for monitoring the precipitation process. Tests were carried out on an ultra-low carbon bainitic steel containing Mn, Nb and B over 800~950℃. Specimens were solu- tion treated at 1250℃ for a certain holding period. A prestain of 20% was applied at a strain rate of 0.1/s. The exper- imental results are displayed by a set of stress vs. 1g(time) curves different from the typical stress relaxation curves. There are two singularities forming a stress plateau on the stress vs.1g(time) curves when precipitates could be observed. Suppose the first one is the start of precipitation (Ps), and the second represcnts the fihish (Pf). As a result Precipitation-Time-Temperature relationship is described as C-shape curves based on two points. This mechanical method is suitable and precise for measuring precipitates in microalloyed steels during hot working.展开更多
A mathematical model was established and applied to simulate thedecarburization of RH-MFB process in Pansteel Company. Study of theeffects of w_[C]0, w_[O]0, Ar flowrate, evaluation rate the MFB lanceblowing parameter...A mathematical model was established and applied to simulate thedecarburization of RH-MFB process in Pansteel Company. Study of theeffects of w_[C]0, w_[O]0, Ar flowrate, evaluation rate the MFB lanceblowing parameters on the decarburization process was car- Ried out.The results showed that this model could give the quantitativeunderstanding of the process, especially the behavior of MFB Lanceblowing. This model has realized the optimum process of RH-MFBrefining for ultra-low carbon steels in Pansteel.展开更多
Microwave-absorbing polymeric composites based on single-walled carbon nanotubes （SWNTs） are fabricated via a simple yet versatile method, and these SWNT-epoxy composites exhibit very impressive microwave absorption...Microwave-absorbing polymeric composites based on single-walled carbon nanotubes （SWNTs） are fabricated via a simple yet versatile method, and these SWNT-epoxy composites exhibit very impressive microwave absorption perfor- mances in a range of 2 GHz-18 GHz. For instance, a maximum absorbing value as high as 28 dB can be achieved for each of these SWNT-epoxy composites （1.3-mm thickness） with only 1 wt% loading of SWNTs, and about 4.8 GHz bandwidth, corresponding to a microwave absorption performance higher than 10 dB, is obtained. Furthermore, such low and appro- priate loadings of SWNTs also enhance the mechanical strength of the composite. It is suggested that these remarkable results are mainly attributable to the excellent intrinsic properties of SWNTs and their homogeneous dispersion state in the polymer matrix.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 operat- ing 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.
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.
文摘Copper and sulfur are typical residual elements or impurity elements in steel.Sufficient removal of them during steelmaking process is difficult for copper and costly for sulfur.Utilization of copper and sulfur in steel, especially in steel scrap,has been an important issue for a long period for metallurgists.Copper and sulfur may combine to form copper sulfide,which may provide a prospect to avoid the detrimental effects of copper and sulfur in steel.Unfortunately the formation mechanism of copper sulfide in steel has not been completely clarified so far. In the present paper,solution treatment of samples containing copper and sulfur are firstly performed at 1623 K for 2.7×10~3 s followed by quenching into water.The samples are then isothermally heat-treated at 673 K,873 K, 1073 K,1273 K and 1373K for different time followed by quenching into water again.The size,morphology, constituent and crystallography of sulfide precipitates in these samples are investigated by scanning electron microscope(SEM) and TEM equipped with EDS.Fine copper sulfides(less than 100 nm) are observed to coexist with silicon oxide in samples even isothermally heat-treated at 1 373 K for 1.44×10~4 s;Film-like copper sulfides are generally observed to co-exist with iron sulfide in all samples;Plate-like copper sulfides are observed especially in sample isothermally heat-treated at 1 073 K for 1.44×10~4 s.The formation mechanisms of these copper sulfides have been discussed.
文摘According to the balance of carbon and oxygen, a decarburization model for the RH treatment has been developed. in which the influence of the mass transfer of carbon and oxygen in the liquid steel and the stirring energy (ε) in the vacuum vessel on decarburization rate has been considered. The conclusion that the volumetric coefficients of the mass transfer of carbon is proportional to ε(1.5) is drawn. Industrical experiment proves this model is reliable. The influence of some factors on decarburization rate has been obtained. which can provide directions for RH treatment The decarburization behavior of steel with RH-OB treatment is also studied. The OB-or-not curve, the optimized OB time and OB amount are discussed.
基金supported by the"11th five" National Science and Technology Support Project of China (No.2006BAE03A13)
文摘A Ti＋Nb bearing ultra-low carbon bake hardening sheet steel hot-rolled in the conventional austenite region and in the ferrite region with lubrication was experimentally studied. Subsequent cold rolling and continuous annealing processes were also conducted. The results show that microstructures of ultra-low carbon bake hardening hot strips at room temperature are basically irregular polygonal ferrites. The yield strength, ultimate tensile strength, n value, and r value of the No.2 specimen hot-rolled in the ferrite region with lubrication are 243 MPa, 364 MPa, 0.29, and 1.74, respectively, which are similar to those of the No.1 specimen hot-roiled in the conventional austenite region. The elongation rate and bake hardening value of No.2 specimen are 51% and 49.4 MPa, respectively, which are greater than those of No. 1 specimen. The No.2 specimen hot-rolled in the ferrite region with lubrication exhibits good mechanical properties and relatively excellent baking hardening performance. Therefore, the hot rolling experiment of Ti＋Nb bearing ultra-low carbon bake hardening steel in the ferrite region with lubrication is feasible and can be considered in the future industrial trial production.
基金Sponsored by National Natural Science Foundation of China(51104109)
文摘Titanium is the impurity in some special steel grades.The existence of titanium decreases the grain size,depresses the yield strength,and results in the low quality of these steels in various properties.Thus,titanium should be removed to the minimum.Based on the industrial production of ultra low carbon Al-Si killed steel,the physical-chemical behavior of titanium was investigated in vacuum degassing refining（RH）process with and without desulfurization.The influences of titanium content in hot metal,ladle slag composition,and ladle slag quantity,etc,on titanium content of refined liquid steel were discussed.The results showed that the partition ratio of titanium between ladle slag and liquid steel is in inverse proportion to the 4/3square of aluminum content.The maximum partition ratio of titanium between top slag and liquid steel can be obtained by adjusting an optimum slag composition including contents of FeOxand Al2O3and the slag basicity,and the suitable range of them should be controlled higher than 6%,less than 20%,and within 1.5to 3.0,respectively.Moreover,desulfurization refining by RH decreases the partition ratio of titanium between ladle slag and liquid steel significantly.To ensure the titanium content stably less than 15×10-6 in a 300tladle,the titanium content in hot metal must be less than 500×10-6 and the thickness of basic oxygen furnace（BOF）slag carrying over must be less than 50mm.
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800 MPa grade new ultra-low carbon bainitic （NULCB） steel is the recently developed new generation steel. The microstructure in the coarse-grained heat affected zone （CGHAZ） of NULCB steel under laser welding conditions was investigated by thermal simulation. The influence of the cooling time from 800℃ to 500℃.t8/5 （0.3-30 s）, on the microstructure of the CGHAZ was discussed. The experimental results indicate that the microstructnre of the CGHAZ is only the granular bainite which consists of bainitic ferrite （BF） lath and M-A constituent while t8/5 is 0.3-30 s. The M-A constituent consists of twinned martensite and residual austenite, and the change of the volume fraction of the residual austenite in the M-A constituent is very small when t8/5 is between 0.3 and 30 s. The morphology of the M-A constituent obviously changes with the variation of t8/5.As t8/5 increases, tile average width, gross and shape parameter of the M-A constituent increase, while the line density of the M-A constituent decreases.
基金financially supported by the Hebei Province Science and Technology Support Program(No.14211007D)
文摘The formation mechanism of the spheroidal carbide in the ultra-low carbon ductile cast iron fabricated by the metal mold casting technique was systematically investigated. The results demonstrated that the spheroidal carbide belonged to eutectic carbide and crystallized in the isolated eutectic liquid phase area. The formation process of the spheroidal carbide was related to the contact and the intersection between the primary dendrite and the secondary dendrite of austenite. The oxides of magnesium, rare earths and other elements can act as heterogeneous nucleation sites for the spheroidal carbide. It was also found that the amount of the spheroidal carbide would increase with an increase in carbon content. The cooling rate has an important influence on the spheroidal carbide under the same chemical composition condition.
基金financially supported by the Hydrogenation Process and Hydrogenation Catalyst Laboratory (RIPP, SINOPEC)
文摘The deactivation of a Ni-Mo-W/Al_2O_3 catalyst during ultra-low-sulfur diesel production was investigated in a pilot plant. The reasons of catalyst deactivation were analyzed by the methods of elemental analysis, BET and TG-MS. The results showed that the catalyst deactivation rate was notable at the beginning of run, and then gradually reached a steady state after 448 h. In the initial period the catalyst deactivation may mainly be caused by the formation of the carbon deposits. The carbon deposits blocked the catalyst pores and the accessibility of active center decreased. The TG-MS analysis identified three types of carbon species deposited on the catalysts, viz.: the low temperature carbon deposit with high H/C atomic ratio, the medium temperature carbon deposit, and the high temperature carbon with low H/C atomic ratio. The amount of high temperature carbon deposits on the catalyst determined the overall activity and, therefore the high temperature carbon was a major contributor to the deactivation of Ni-Mo-W catalyst.
基金supported partly by the National Natural Science Foundation of China (No. 51472170)the Major State Basic Research Development Program of China (No. 2011CB932700)
文摘An induction levitation melting （ILM） refining process is performed to remove most microsized inclusions in ultra-low carbon steel （UCS）. Nanosized, spheroid shaped sulfide precipitates remain dispersed in the UCS. During the ILM process, the UCS is molten and is rotated under an upward magnetic field. With the addition of Ti additives, the spinning molten steel under the upward magnetic field ejects particles because of resultant centrifugal, floating, and magnetic forces. Magnetic force plays a key role in removing sub-micrometer-sized particles, composed of porous aluminum titanate enwrapping alumina nuclei. Consequently, sulfide precipitates with sizes less than 50 nan remain dispersed in the steel matrix. These findings open a path to the fabrication of clean steel or steel bearing only a nanosized strengthen- ing phase.
基金the Education Bureau of Hubei Province of China(No.2002A01013)
文摘The hot deformation experiments of ultra-low carbon steel in ferrite range were carried out in a hot simulator in order to research hot deformation behaviors of ultra-low carbon steel in ferrite range at low temperature. The results show that the influences of deformation parameters on flow stress are different to those in austenitic deformation. The deformation characteristic parameters were calculated for ultra-low carbon steel in ferrite region. The flow stress equation for ultra-low carbon steel in ferritic deformation at low temperature was obtained.
文摘Stress relaxation was chosen as the best method for monitoring the precipitation process. Tests were carried out on an ultra-low carbon bainitic steel containing Mn, Nb and B over 800~950℃. Specimens were solu- tion treated at 1250℃ for a certain holding period. A prestain of 20% was applied at a strain rate of 0.1/s. The exper- imental results are displayed by a set of stress vs. 1g(time) curves different from the typical stress relaxation curves. There are two singularities forming a stress plateau on the stress vs.1g(time) curves when precipitates could be observed. Suppose the first one is the start of precipitation (Ps), and the second represcnts the fihish (Pf). As a result Precipitation-Time-Temperature relationship is described as C-shape curves based on two points. This mechanical method is suitable and precise for measuring precipitates in microalloyed steels during hot working.
文摘A mathematical model was established and applied to simulate thedecarburization of RH-MFB process in Pansteel Company. Study of theeffects of w_[C]0, w_[O]0, Ar flowrate, evaluation rate the MFB lanceblowing parameters on the decarburization process was car- Ried out.The results showed that this model could give the quantitativeunderstanding of the process, especially the behavior of MFB Lanceblowing. This model has realized the optimum process of RH-MFBrefining for ultra-low carbon steels in Pansteel.
基金Project supported by the National Basic Research Program of China(Grant Nos.2012CB933401 and 2014CB643502)the National Natural Science Foundation of China(Grant Nos.21374050,51273093,and 51373078)
文摘Microwave-absorbing polymeric composites based on single-walled carbon nanotubes （SWNTs） are fabricated via a simple yet versatile method, and these SWNT-epoxy composites exhibit very impressive microwave absorption perfor- mances in a range of 2 GHz-18 GHz. For instance, a maximum absorbing value as high as 28 dB can be achieved for each of these SWNT-epoxy composites （1.3-mm thickness） with only 1 wt% loading of SWNTs, and about 4.8 GHz bandwidth, corresponding to a microwave absorption performance higher than 10 dB, is obtained. Furthermore, such low and appro- priate loadings of SWNTs also enhance the mechanical strength of the composite. It is suggested that these remarkable results are mainly attributable to the excellent intrinsic properties of SWNTs and their homogeneous dispersion state in the polymer matrix.
