Through long-term production and maintenance practice,various types of stacking steel in the 2250mm hot rolling coiler of Ma Steel were tracked and analyzed,and the causes of stacking steel were summarized.Cor-respond...Through long-term production and maintenance practice,various types of stacking steel in the 2250mm hot rolling coiler of Ma Steel were tracked and analyzed,and the causes of stacking steel were summarized.Cor-responding measures were formulated to effectively reduce the probability of stacking steel.展开更多
Hypo-peritectic steels are widely used in various industrial fields because of their high strength,high toughness,high processability,high weldability,and low material cost.However,surface defects are liable to occur ...Hypo-peritectic steels are widely used in various industrial fields because of their high strength,high toughness,high processability,high weldability,and low material cost.However,surface defects are liable to occur during continuous casting,which includes depression,longitudinal cracks,deep oscillation marks,and severe level fluctuation with slag entrapment.The high-efficiency production of hypo-peritectic steels by continuous casting is still a great challenge due to the limited understanding of the mechanism of peritectic solidification.This work reviews the definition and classification of hypo-peritectic steels and introduces the formation tendency of common surface defects related to peritectic solidification.New achievements in the mechanism of peritectic reaction and transformation have been listed.Finally,countermeasures to avoiding surface defects of hypo-peritectic steels duiring continuous casting are summarized.Enlightening certain points in the continuous casting of hypo-peritectic steels and the development of new techniques to overcome the present problems will be a great aid to researchers.展开更多
The dynamic recrystallization (DRX) behavior of high-grade X80/X100 pipeline steels with different Nb contents was investi- gated through single pass compression experiment using a Gleeble 1500 thermomechanical simu...The dynamic recrystallization (DRX) behavior of high-grade X80/X100 pipeline steels with different Nb contents was investi- gated through single pass compression experiment using a Gleeble 1500 thermomechanical simulator. By the regression of stress-sWain data obtained in the experiment, the deformation activation energy of DRX was identified, and the critical strain was calculated with the Po- liak-Jonas (P-J) method. Based on the analysis, the occurrence condition and kinetics of DRX were determined. The results show that as the Nb content increases from 0.08wt% to 0.095wt%, the activation energy of recrystallization raises from 365 to 395 kJ/mol. The critical swain of DRX can be determined more accurately by the P-J method, and the ratios of critical swain to peak sWain of XS0 and X100 pipeline steels are 0.51 and 0.49, respectively, which are similar to the results achieved by other researchers and calculated with empirical formulae.展开更多
Power loss of Fe-3%Sigrain-oriented silicon steelwas measured after ballscribing with different spacing using a self-designed tool.Three different sections of power loss,including hysteresis loss,abnormalloss,and eddy...Power loss of Fe-3%Sigrain-oriented silicon steelwas measured after ballscribing with different spacing using a self-designed tool.Three different sections of power loss,including hysteresis loss,abnormalloss,and eddy current loss,were measured and calculated,respectively.The loss variation and ratio were analyzed based on the experimentaldata.At 1.0 T,hysteresis loss of tested steelwith scribing spacing of 8 mm descends by 8.2% compared to samples without scribing,which is similar to the totalloss variation,and abnormalloss descends by 16.8%.At 1.0 T,hysteresis loss ratio of the steelwith scribing spacing of 16 mm ascends from 55.7% to 57.9%,and eddy current loss increases from 17.4% to 24.1%,while abnormalloss descends from 26.9% to 23.7%.The experimentalresults show that the reduction of power loss after scribing is mainly due to decreasing of hysteresis loss and abnormalloss.展开更多
Using TEM (transmisson electron microscopy), electron diffraction, EDX (energy dispersive X-ray) analysis and physicochemical phase analysis, the morphology, crystal structure, size distribution and chemical compo...Using TEM (transmisson electron microscopy), electron diffraction, EDX (energy dispersive X-ray) analysis and physicochemical phase analysis, the morphology, crystal structure, size distribution and chemical composition of precipitates in the microstructure of high strength Nb-microalloyed Xl00 pipeline steel were investigated, and the strengthening effect of precipitation was quantitatively calculated with Ashhy-Orowan correction model. The precipitates obtained in X100 pipeline steel can be divided into two kinds: "complex" and "single" particles by morphology. The EDX analysis of "single" precipitates reveals that the chemical composition matches well with particle dimensions, especially the Nb to Ti ratio regularly decreases with the increase of particle size. The yield strength increments in the way of precipitation strengthening of X100 pipeline steel reached about 52 MPa, suggesting that the precipitation strengthening is not the dominative strengthening mechanism for X100 pipeline steel.展开更多
The effect of the run-out table cooling patterns on the microstructure and mechanical properties of Nb microalloyed steel plates was investigated by hot rolling experiment. The results showed that the mixed microstrue...The effect of the run-out table cooling patterns on the microstructure and mechanical properties of Nb microalloyed steel plates was investigated by hot rolling experiment. The results showed that the mixed microstrueture containing ferrite, bainite and significant amounts of retained austenite can be obtained through three kinds of cooling patterns on the run-out table under the same hot rolling condition. Three kinds of cooling patterns possess different austenite transformation kinetics, which leads to variations in microconstituent characteristics. The yield strength increases, the tensile strength decreases and the total elongation tends to increase as the cooling patterns Ⅰ , Ⅱ and Ⅲ were applied respectively. The yield strength, the total elongation and the product of tensile strength and ductility reach the maximum values (547 MPa, 37. 2% and 28 384 MPa% respectively) for the steel plate processed by cooling pattern Ⅲ.展开更多
The microstructure in welding heat-affected zones of 5 wt.% manganese steels was studied, and its effect on impact toughness was analyzed. The simulated coarse-grained heat-affected zone (CGHAZ) had the lowest impact ...The microstructure in welding heat-affected zones of 5 wt.% manganese steels was studied, and its effect on impact toughness was analyzed. The simulated coarse-grained heat-affected zone (CGHAZ) had the lowest impact toughness of ~39 J at — 40℃ because of coarse-grained structure and least volume fraction of retained austenite (RA) of 1.2 vol.%. The impact toughness of simulated intercritical heat-affected zone (ICHAZ) and fine-grained heat-affected zone (FGHAZ) were ~165 and ~45 J, respectively, at — 40℃. The effective grain size of simulated FGHAZ was smaller than that of the simulated ICHAZ. Furthermore, microstructural investigation revealed that the simulated FGHAZ and ICHAZ had similarity in volume fraction and stability of RA. However, tempered martensite was present in ICHAZ and absent in FGHAZ. It is proposed that the presence of tempered martensite contributed to good impact toughness in simulated ICHAZ.展开更多
Numerical and physical models have been built and validated to study the multiphase flow inside three ladle shrouds and a four-strand tundish.A conventional straight ladle shroud and two types of trumpet-shaped ladle ...Numerical and physical models have been built and validated to study the multiphase flow inside three ladle shrouds and a four-strand tundish.A conventional straight ladle shroud and two types of trumpet-shaped ladle shroud(TLS)have been comparatively investigated.The maximum velocity at ladle shroud outlet reduces from 1.3 to 0.5 m/s,which indicates a quieter tundish pool.It is demonstrated that the use of a TLS can also decrease the maximum surface velocity from 0.16 to 0.13 m/s,which reduces the tendency of forming tundish open eye.The flow pattern and mixing behavior are improved inside the tundish,especially in enlarging the plug volume from 6.61%to 9.04%.The difference between the near and far outlets is narrowed when the TLS is applied.A computational program was developed to calculate characteristic parameters of different ladle shroud designs,and a dimensionless index was proposed to evaluate their mass and inner volume.Plant trials have been carried out,and the results showed that TLS can reduce level fluctuation in the pouring zone,which is beneficial to promoting better protective performance from secondary contamination and heat loss during continuous casting.展开更多
In this study, the effect of isothermal temperature on microstructure and mechanical properties of a high Al-low Si TRIP steel was investigated using scanning electron microscopy, transmission electron microscopy, X-r...In this study, the effect of isothermal temperature on microstructure and mechanical properties of a high Al-low Si TRIP steel was investigated using scanning electron microscopy, transmission electron microscopy, X-ray diffraction, electron back scattered diffraction, and tensile test. The results show that typical microstructure containing ferrite, bainite, and retained austenite can be obtained when two-stage heat treatment process was utilized. When annealing temperature is 840 ℃ and austempering temperature is 400 ℃, the tensile strength is 542 MPa and the product of strength and elongation is 17,685 MPa%. The morphologies and stability of the retained austenite in low silicon/high aluminum TRIP steel were finally discussed.展开更多
Recently, large sized CaO-Alz 03 inclusions with low melting temperature have been the main reason for lowering mechanical properties of high strength low alloy (HSLA) steel plates. New philosophy, i.e. refining by ...Recently, large sized CaO-Alz 03 inclusions with low melting temperature have been the main reason for lowering mechanical properties of high strength low alloy (HSLA) steel plates. New philosophy, i.e. refining by top slag with relatively low basicity and Al2O3 content, was proposed to control such kind of inclusions. Firstly, the characteristics of refining slag, such as component activities and sulphide capacity (Cs) of CaO-Al2O3-SiO2-MgO slag, were studied through thermodynamic calculation. Then, slag-metal equilibrium experiments were carried out in laboratory to investigate the exact chemical composition of refining slag together with thermodynamic analysis. Finally, industrial trials were done to verify the desulphurization ability and inclusions control in steel refined by the new slag. Thermodynamic calculations indicated that the slags with basicity of 3.5 and Al2O3 content of 200/oo and basicity of 5.0 and Al2O3 content of 20 % or 25 % have high values of CaO activity, sulphide capacity and ratio of MgO activity to Al2O3 activity. Laboratory equilibrium experiments showed that the slag with basicity of about 4.5 and A12 03 content of about 20% is helpful for increasing the melting temperature of inclusions in steel. After introducing such kind of refining slag in industrial trials, the sulphur content in eight heats of steel is below 20 ×l0-6 , which meets the requirement of HSLA steel, and most inclusions distribute in relatively high melting zone (≥1773 K) of CaO- Al2O3-MgO(-SiO2) quasi-ternary diagram. New philosophy of top refining slag is feasible to control low melting point inclusions of CaO-Al2O3 system in HSLA steel.展开更多
A numerical simulation of the thermal stress field of the solidified shell in the mold during continuous casting of peritectic steel slab was calculated.The results showed,owing to the volume contraction caused by the...A numerical simulation of the thermal stress field of the solidified shell in the mold during continuous casting of peritectic steel slab was calculated.The results showed,owing to the volume contraction caused by the peritectic reaction,the thermal stress on the wide surface of the solidified shell was larger for the peritectic steel slab than that for the non-peritectic steel,and the maximum thermal stress on the wide face was at the 200-400mm position away from the central line.With increment of slab width,the thermal stress increased and the maximum value moved towards the central line.In addition,the thermal stress was also affected by the casting operation parameters.In the present work,the proper drawing speed was around 1.2m/min for the wide slab of 3200mm×150mm,with the cooling intensity of 5500L/min and the superheat degree of 15℃ to 25℃.展开更多
The significance of different deoxidation practises on the ductility and impact toughness of next generation of microalloyed heavy plates was elucidated to explore the best deoxidation practice in obtaining required m...The significance of different deoxidation practises on the ductility and impact toughness of next generation of microalloyed heavy plates was elucidated to explore the best deoxidation practice in obtaining required mechanical properties,which was judged by the combined effects of composition,size and number density of inclusions on the ductility of the experimental high-strength low alloy steel.The impurity contents,i.e.,total O+N+S contents,of 82×10^(-6)(Al-killed)and 118×10^(-6)(Zr-killed)have been induced to characterize both the steels.Ductility was characterized using tensile and Charpy V-notch testing.The number,size and composition of the inclusions were characterized using a field emission scanning electron microscope with an energy dispersive spectrometer.In the Al-killed steel,the inclusion structure consisted of titanium nitrides,stringer calcium aluminates and elongated manganese sulfides,whereas in the Zr-killed steel,the inclusion structure consisted of mainly fine spherical oxide inclusions with sulphide shells.The impurity content did not have a significant effect on the number density of inclusions,as with higher and lower impurity content,the number of inclusions was 83.7 and 78.8 mm^(-2),respectively.However,the size distribution of the inclusions,especially the coarse inclusions with their longest length greater than 8μm,differsmuch from each other.The number density of coarse inclusions differs from 0.8 to 1.1 mm^(-2) with processing,and in Al-killed steel,55.5% of the coarse inclusions were titanium nitrides or manganese sulfides,whereas in Zr-killed steel,only 22.5% of the coarse inclusions were titanium nitrides and manganese sulfides.Coarse titanium nitrides were especially detrimental to the impact toughness.The number density of them should be below 0.33 mm-2 in order to guarantee the best possible toughness in the steel in question.The average crystallographic grain size detected by electron backscattered diffraction of Zr-killed steel(4.28±2.70μm)was smaller than that of Al-killed steel(6.00±4.80μm).As a result from the grain refinement and sulphide shape control,Zr-killed steel exhibited superior impact toughness(223±70 J)at -80℃ as compared with Al-killed steel(153±68 J).Thus,Zr-killed steel was observed to provide good performance in terms of mechanical properties as compared with Al-killed steel.展开更多
For plate quenching on a roller quenching machine, heat transfer process is investigated. According to the practical online experiment of plate center temperature, average heat transfer coefficient under different con...For plate quenching on a roller quenching machine, heat transfer process is investigated. According to the practical online experiment of plate center temperature, average heat transfer coefficient under different conditions and temperature fields are analyzed by numerical simulation. The results show that, at the water temperature of 15 ℃, the instantaneous maximum quenching cooling rate is 17.6 ℃/s for the plate of 50 mm in thickness in roller quenching process. In the temperature range of 400-850 ℃, the maximum is 12.1 ℃/s. With the plate surface temperature decreasing, surface heat transfer coefficient increases at first, and reaches the maximum value of about 15 000 W/(m^2·K), and then decreases. The calculated heat transfer coefficients are applied to analyze plate temperature field of different thicknesses, and the difference between the calculated and measured temperature is less than 5%.展开更多
An experimental mold was built to study the flow in a flow control mold under high speed continuous casting. The effect of the magnetic field on the flow was investigated using mercury. The results show that the magne...An experimental mold was built to study the flow in a flow control mold under high speed continuous casting. The effect of the magnetic field on the flow was investigated using mercury. The results show that the magnetic field can not only dampen the flow of liquid metal but also change its direction, and then redistribute the flow in the mold. When maintaining a constant distance between magnets, the fluctuation of the free surface is dampened because of the increasing magnetic flux density. The flow at the free surface is improved, and the penetration depth of the downward stream is reduced. The decrease in the dis- tance between magnets promotes the brake effect and the flow is dampened in the upper eddy.展开更多
文摘Through long-term production and maintenance practice,various types of stacking steel in the 2250mm hot rolling coiler of Ma Steel were tracked and analyzed,and the causes of stacking steel were summarized.Cor-responding measures were formulated to effectively reduce the probability of stacking steel.
基金financially supported by the Fundamental Research Funds for the Central Universities(No.FRF-TP-19-017A3)the National Natural Science Foundation of China(No.51874026)。
文摘Hypo-peritectic steels are widely used in various industrial fields because of their high strength,high toughness,high processability,high weldability,and low material cost.However,surface defects are liable to occur during continuous casting,which includes depression,longitudinal cracks,deep oscillation marks,and severe level fluctuation with slag entrapment.The high-efficiency production of hypo-peritectic steels by continuous casting is still a great challenge due to the limited understanding of the mechanism of peritectic solidification.This work reviews the definition and classification of hypo-peritectic steels and introduces the formation tendency of common surface defects related to peritectic solidification.New achievements in the mechanism of peritectic reaction and transformation have been listed.Finally,countermeasures to avoiding surface defects of hypo-peritectic steels duiring continuous casting are summarized.Enlightening certain points in the continuous casting of hypo-peritectic steels and the development of new techniques to overcome the present problems will be a great aid to researchers.
文摘The dynamic recrystallization (DRX) behavior of high-grade X80/X100 pipeline steels with different Nb contents was investi- gated through single pass compression experiment using a Gleeble 1500 thermomechanical simulator. By the regression of stress-sWain data obtained in the experiment, the deformation activation energy of DRX was identified, and the critical strain was calculated with the Po- liak-Jonas (P-J) method. Based on the analysis, the occurrence condition and kinetics of DRX were determined. The results show that as the Nb content increases from 0.08wt% to 0.095wt%, the activation energy of recrystallization raises from 365 to 395 kJ/mol. The critical swain of DRX can be determined more accurately by the P-J method, and the ratios of critical swain to peak sWain of XS0 and X100 pipeline steels are 0.51 and 0.49, respectively, which are similar to the results achieved by other researchers and calculated with empirical formulae.
基金Funded by the National Natural Science Foundation of China(Nos.51174057 and 51404159)the National High Technology Research and Development Program(No.2012AA03A503)Research Fund for the Doctoral Program of Higher Education of China(No.20130042110040)
文摘Power loss of Fe-3%Sigrain-oriented silicon steelwas measured after ballscribing with different spacing using a self-designed tool.Three different sections of power loss,including hysteresis loss,abnormalloss,and eddy current loss,were measured and calculated,respectively.The loss variation and ratio were analyzed based on the experimentaldata.At 1.0 T,hysteresis loss of tested steelwith scribing spacing of 8 mm descends by 8.2% compared to samples without scribing,which is similar to the totalloss variation,and abnormalloss descends by 16.8%.At 1.0 T,hysteresis loss ratio of the steelwith scribing spacing of 16 mm ascends from 55.7% to 57.9%,and eddy current loss increases from 17.4% to 24.1%,while abnormalloss descends from 26.9% to 23.7%.The experimentalresults show that the reduction of power loss after scribing is mainly due to decreasing of hysteresis loss and abnormalloss.
文摘Using TEM (transmisson electron microscopy), electron diffraction, EDX (energy dispersive X-ray) analysis and physicochemical phase analysis, the morphology, crystal structure, size distribution and chemical composition of precipitates in the microstructure of high strength Nb-microalloyed Xl00 pipeline steel were investigated, and the strengthening effect of precipitation was quantitatively calculated with Ashhy-Orowan correction model. The precipitates obtained in X100 pipeline steel can be divided into two kinds: "complex" and "single" particles by morphology. The EDX analysis of "single" precipitates reveals that the chemical composition matches well with particle dimensions, especially the Nb to Ti ratio regularly decreases with the increase of particle size. The yield strength increments in the way of precipitation strengthening of X100 pipeline steel reached about 52 MPa, suggesting that the precipitation strengthening is not the dominative strengthening mechanism for X100 pipeline steel.
文摘The effect of the run-out table cooling patterns on the microstructure and mechanical properties of Nb microalloyed steel plates was investigated by hot rolling experiment. The results showed that the mixed microstrueture containing ferrite, bainite and significant amounts of retained austenite can be obtained through three kinds of cooling patterns on the run-out table under the same hot rolling condition. Three kinds of cooling patterns possess different austenite transformation kinetics, which leads to variations in microconstituent characteristics. The yield strength increases, the tensile strength decreases and the total elongation tends to increase as the cooling patterns Ⅰ , Ⅱ and Ⅲ were applied respectively. The yield strength, the total elongation and the product of tensile strength and ductility reach the maximum values (547 MPa, 37. 2% and 28 384 MPa% respectively) for the steel plate processed by cooling pattern Ⅲ.
基金Authors gratefully acknowledge the support from National Natural Science Foundation of China (No. 2015AA03A501).
文摘The microstructure in welding heat-affected zones of 5 wt.% manganese steels was studied, and its effect on impact toughness was analyzed. The simulated coarse-grained heat-affected zone (CGHAZ) had the lowest impact toughness of ~39 J at — 40℃ because of coarse-grained structure and least volume fraction of retained austenite (RA) of 1.2 vol.%. The impact toughness of simulated intercritical heat-affected zone (ICHAZ) and fine-grained heat-affected zone (FGHAZ) were ~165 and ~45 J, respectively, at — 40℃. The effective grain size of simulated FGHAZ was smaller than that of the simulated ICHAZ. Furthermore, microstructural investigation revealed that the simulated FGHAZ and ICHAZ had similarity in volume fraction and stability of RA. However, tempered martensite was present in ICHAZ and absent in FGHAZ. It is proposed that the presence of tempered martensite contributed to good impact toughness in simulated ICHAZ.
基金The funding of National Natural Science Foundation of China(No.52004024)is highly appreciated.
文摘Numerical and physical models have been built and validated to study the multiphase flow inside three ladle shrouds and a four-strand tundish.A conventional straight ladle shroud and two types of trumpet-shaped ladle shroud(TLS)have been comparatively investigated.The maximum velocity at ladle shroud outlet reduces from 1.3 to 0.5 m/s,which indicates a quieter tundish pool.It is demonstrated that the use of a TLS can also decrease the maximum surface velocity from 0.16 to 0.13 m/s,which reduces the tendency of forming tundish open eye.The flow pattern and mixing behavior are improved inside the tundish,especially in enlarging the plug volume from 6.61%to 9.04%.The difference between the near and far outlets is narrowed when the TLS is applied.A computational program was developed to calculate characteristic parameters of different ladle shroud designs,and a dimensionless index was proposed to evaluate their mass and inner volume.Plant trials have been carried out,and the results showed that TLS can reduce level fluctuation in the pouring zone,which is beneficial to promoting better protective performance from secondary contamination and heat loss during continuous casting.
基金supported by the National High Technology Research and Development Program (No. 2012AA03A508)the National Natural Science Foundation of China (No. 51271051)
文摘In this study, the effect of isothermal temperature on microstructure and mechanical properties of a high Al-low Si TRIP steel was investigated using scanning electron microscopy, transmission electron microscopy, X-ray diffraction, electron back scattered diffraction, and tensile test. The results show that typical microstructure containing ferrite, bainite, and retained austenite can be obtained when two-stage heat treatment process was utilized. When annealing temperature is 840 ℃ and austempering temperature is 400 ℃, the tensile strength is 542 MPa and the product of strength and elongation is 17,685 MPa%. The morphologies and stability of the retained austenite in low silicon/high aluminum TRIP steel were finally discussed.
基金Item Sponsored by National Basic Research Program of China(2010CB630806)National Natural Science Foundation of CHina(51404020)State Key Laboratory of Advanced Metallurgy(USTB)of China(41603015)
文摘Recently, large sized CaO-Alz 03 inclusions with low melting temperature have been the main reason for lowering mechanical properties of high strength low alloy (HSLA) steel plates. New philosophy, i.e. refining by top slag with relatively low basicity and Al2O3 content, was proposed to control such kind of inclusions. Firstly, the characteristics of refining slag, such as component activities and sulphide capacity (Cs) of CaO-Al2O3-SiO2-MgO slag, were studied through thermodynamic calculation. Then, slag-metal equilibrium experiments were carried out in laboratory to investigate the exact chemical composition of refining slag together with thermodynamic analysis. Finally, industrial trials were done to verify the desulphurization ability and inclusions control in steel refined by the new slag. Thermodynamic calculations indicated that the slags with basicity of 3.5 and Al2O3 content of 200/oo and basicity of 5.0 and Al2O3 content of 20 % or 25 % have high values of CaO activity, sulphide capacity and ratio of MgO activity to Al2O3 activity. Laboratory equilibrium experiments showed that the slag with basicity of about 4.5 and A12 03 content of about 20% is helpful for increasing the melting temperature of inclusions in steel. After introducing such kind of refining slag in industrial trials, the sulphur content in eight heats of steel is below 20 ×l0-6 , which meets the requirement of HSLA steel, and most inclusions distribute in relatively high melting zone (≥1773 K) of CaO- Al2O3-MgO(-SiO2) quasi-ternary diagram. New philosophy of top refining slag is feasible to control low melting point inclusions of CaO-Al2O3 system in HSLA steel.
基金Item Sponsored by the National Natural Science Foundation of China(51174052)the Fundamental Research Funds for the Central Universities of China(110402009)
文摘A numerical simulation of the thermal stress field of the solidified shell in the mold during continuous casting of peritectic steel slab was calculated.The results showed,owing to the volume contraction caused by the peritectic reaction,the thermal stress on the wide surface of the solidified shell was larger for the peritectic steel slab than that for the non-peritectic steel,and the maximum thermal stress on the wide face was at the 200-400mm position away from the central line.With increment of slab width,the thermal stress increased and the maximum value moved towards the central line.In addition,the thermal stress was also affected by the casting operation parameters.In the present work,the proper drawing speed was around 1.2m/min for the wide slab of 3200mm×150mm,with the cooling intensity of 5500L/min and the superheat degree of 15℃ to 25℃.
基金support from the National Natural Science Foundation of China(U1532268 and U20A20279)Wuhan Science and Technology Program(Grant No.2019010701011382)+1 种基金the 111 ProjectHigher Education Discipline Innovation Project(Grant No.18018).
文摘The significance of different deoxidation practises on the ductility and impact toughness of next generation of microalloyed heavy plates was elucidated to explore the best deoxidation practice in obtaining required mechanical properties,which was judged by the combined effects of composition,size and number density of inclusions on the ductility of the experimental high-strength low alloy steel.The impurity contents,i.e.,total O+N+S contents,of 82×10^(-6)(Al-killed)and 118×10^(-6)(Zr-killed)have been induced to characterize both the steels.Ductility was characterized using tensile and Charpy V-notch testing.The number,size and composition of the inclusions were characterized using a field emission scanning electron microscope with an energy dispersive spectrometer.In the Al-killed steel,the inclusion structure consisted of titanium nitrides,stringer calcium aluminates and elongated manganese sulfides,whereas in the Zr-killed steel,the inclusion structure consisted of mainly fine spherical oxide inclusions with sulphide shells.The impurity content did not have a significant effect on the number density of inclusions,as with higher and lower impurity content,the number of inclusions was 83.7 and 78.8 mm^(-2),respectively.However,the size distribution of the inclusions,especially the coarse inclusions with their longest length greater than 8μm,differsmuch from each other.The number density of coarse inclusions differs from 0.8 to 1.1 mm^(-2) with processing,and in Al-killed steel,55.5% of the coarse inclusions were titanium nitrides or manganese sulfides,whereas in Zr-killed steel,only 22.5% of the coarse inclusions were titanium nitrides and manganese sulfides.Coarse titanium nitrides were especially detrimental to the impact toughness.The number density of them should be below 0.33 mm-2 in order to guarantee the best possible toughness in the steel in question.The average crystallographic grain size detected by electron backscattered diffraction of Zr-killed steel(4.28±2.70μm)was smaller than that of Al-killed steel(6.00±4.80μm).As a result from the grain refinement and sulphide shape control,Zr-killed steel exhibited superior impact toughness(223±70 J)at -80℃ as compared with Al-killed steel(153±68 J).Thus,Zr-killed steel was observed to provide good performance in terms of mechanical properties as compared with Al-killed steel.
基金Sponsored by National Basic Research Program(973 Program) of China(2010CB630800)
文摘For plate quenching on a roller quenching machine, heat transfer process is investigated. According to the practical online experiment of plate center temperature, average heat transfer coefficient under different conditions and temperature fields are analyzed by numerical simulation. The results show that, at the water temperature of 15 ℃, the instantaneous maximum quenching cooling rate is 17.6 ℃/s for the plate of 50 mm in thickness in roller quenching process. In the temperature range of 400-850 ℃, the maximum is 12.1 ℃/s. With the plate surface temperature decreasing, surface heat transfer coefficient increases at first, and reaches the maximum value of about 15 000 W/(m^2·K), and then decreases. The calculated heat transfer coefficients are applied to analyze plate temperature field of different thicknesses, and the difference between the calculated and measured temperature is less than 5%.
文摘An experimental mold was built to study the flow in a flow control mold under high speed continuous casting. The effect of the magnetic field on the flow was investigated using mercury. The results show that the magnetic field can not only dampen the flow of liquid metal but also change its direction, and then redistribute the flow in the mold. When maintaining a constant distance between magnets, the fluctuation of the free surface is dampened because of the increasing magnetic flux density. The flow at the free surface is improved, and the penetration depth of the downward stream is reduced. The decrease in the dis- tance between magnets promotes the brake effect and the flow is dampened in the upper eddy.