In a typical process, C-Mn steel was annealed at 800℃ for 180 s, and then cooled rapidly to obtain the ferrite-martensite microstructure. After pre-straining, the specimens were baked and the corresponding bake-harde...In a typical process, C-Mn steel was annealed at 800℃ for 180 s, and then cooled rapidly to obtain the ferrite-martensite microstructure. After pre-straining, the specimens were baked and the corresponding bake-hardening （BH） values were determined as a function of pre-strain, baking temperature, and baking time. The influences ofpre-strain, baking temperature and baking time on the microstructure evolution and bake-hardening behavior of the dual-phase steel were investigated systematically. It was found that the BH value apparently increased with an increase in pre-strain in the range from 0 to 1%; however, increasing pre-strain from 1% to 8% led to a decrease in the BH value. Furthermore, an increase in baking temperature favored a gradual improvement in the BH value because of the formation of Cottrell atmosphere and the precipitation of carbides in both the ferrite and martensite phases. The BH value reached a maximum of 110 MPa at a baking temperature of 300℃. Moreover, the BH value enhanced significantly with increasing baking time from 10 to 100 min.展开更多
The purpose of this study was to investigate the suitability of palm diacylglycerol （PDAG）-enriched formulations for bakery shortening. Three types of palm diacylglycerol olein （PDAGOL） at different degree of unsa...The purpose of this study was to investigate the suitability of palm diacylglycerol （PDAG）-enriched formulations for bakery shortening. Three types of palm diacylglycerol olein （PDAGOL） at different degree of unsaturation （PDAGOL1V56, PDAGOLIV62 and PDAGOLIV64） were used as main raw materials blended with palm stearin （PS）. The blending compositions ranged from 30% to 70% of PDAGOLIV56/PS, PDAGOLIV62/PS and PDAGOLIV64/PS, respectively. The physicochemical properties of all binary blend systems were characterized for fatty acid composition （FAC）, slip melting point （SMP） and solid fat content （SFC）. The selected bakery shortening formulations were further characterised for polymorphic form of fat crystal and thermal behavior, using X-ray diffractometer （XRD） and differential scanning calorimetry （DSC）. Bakery shortening enriched with diacylglycerol that were produced from 40DS56 （40% PDAGOLIV56/60% PS）, 40DS62 （40% PDAGOL1V62/60% PS） and 40DS64 （40% PDAGOLIV64/60% PS） had 45%-50% unsaturated fatty acid and crystallized in β ＋ β polymorphs; thus they were suitable for shortening system. Based on product＇s baking performance, it could be found that all Madeira cakes prepared from bakery shortening enriched with diacylglycerol had higher specific cake volume as compared to commercial shortening （CS）. In customer acceptance test, Madeira cake made from 40DS56 shortening scored the highest rating for all sensory attributes, including overall customer acceptability. It had given an indication that 40DS56 shortening formulation was the most suitable fat blends to be used as bakery shortening.展开更多
The influences of high temperature pre-straining (HT-PS) on the natural aging and bake hardening of Al?Mg?Si alloys were investigated by Vickers microhardness measurements, differential scanning calorimetry (DSC) anal...The influences of high temperature pre-straining (HT-PS) on the natural aging and bake hardening of Al?Mg?Si alloys were investigated by Vickers microhardness measurements, differential scanning calorimetry (DSC) analysis and transmission electron microscopy (TEM) characterization. The results show that pre-straining at 170 °C immediately after quenching can effectively resolve the rather high T4 temper hardness caused by the conventional room temperature (RT) pre-straining treatment, and give a better bake hardening response (BHR) after paint-bake cycle. HT-PS 7% at 170 °C for 10 min is chosen as the optimum process as it provides lower T4 temper hardness and better BHR. The simultaneous introduction of dislocations and Cluster (2) can significantly suppress the natural aging and promote the precipitation of β″ phase, and reduce the effects of deformation hardening by dynamic recovery.展开更多
The effects of copper on the ageing precipitation behavior of as-quenched and pre-aged AA6016 aluminum alloy were studied by differential scanning calorimetry （DSC）, Vickers hardness measurement and transmission ele...The effects of copper on the ageing precipitation behavior of as-quenched and pre-aged AA6016 aluminum alloy were studied by differential scanning calorimetry （DSC）, Vickers hardness measurement and transmission electronic microscopy （TEM）. The results indicate that the addition of copper facilitates the growth of clusters （GP I） to the critical size during pre-ageing. Therefore, the addition of copper accelerates the transition from GP I （pre-β＂） to GP II （β＂） during final artificial ageing, and finally results in the favorable paint-bake response. However, the one with the copper level of 0.3% does not show significant baking hardening response as expected. Pre-aging can also reduce the detrimental effect due to natural aging of copper-containing alloys.展开更多
Rare earth elements（REE） are a set of seventeen chemical elements in the periodic table, which have been found in a variety classes of minerals in the world. The global demand for REE and their compounds has increas...Rare earth elements（REE） are a set of seventeen chemical elements in the periodic table, which have been found in a variety classes of minerals in the world. The global demand for REE and their compounds has increased in high-tech applications over the past decades due to their chemical, catalytic, electrical, magnetic, and optical properties. After mining, comminution and ore beneficiation, hydrometallurgical and pyrometallurgical processes are carried out to recover REE compounds. The concentrate cracking is a process wherein the structure of a REE mineral is modified in order to dissolve REE in a weak acid solution. This would be accomplished through various techniques such as alkaline cracking and acid baking. The cracked concentrate is then leached to dissolve REE in a solution and subsequently recover those via neutralization, precipitation or solvent extraction methods. This paper reviewed the cracking and leaching methods applied to REE concentrates to produce an intermediate product for further REE separation.展开更多
After 2% predeformation,the baking treatment with different schedule was carried out for low silicon TRIP steel sheet with niobium.The effects of baking temperature and time on microstructures and mechanical propertie...After 2% predeformation,the baking treatment with different schedule was carried out for low silicon TRIP steel sheet with niobium.The effects of baking temperature and time on microstructures and mechanical properties were investigated.The results showed that with increasing the baking temperature and time,the volume fraction of retained austenite decreases,and the volume fraction of tempered martensite increases; as baking temperature ranges from 80 ℃ to 170 ℃,the bake-hardening（BH）value increases obviously,while from 170 ℃ to 230 ℃,the variation of BH value is very slight; as baking time ranges from 2 min to 20 min,the BH value increases significantly,while the BH value decreases when baking time exceeds 20 min.So that when the baking temperature is 170 ℃ and the baking time is 20 min,the low silicon TRIP steel sheet exhibits good bake-hardening behavior,and the highest BH value is above 70 MPa.展开更多
Hot rolling, cold rolling and continuous annealing processes of Ti bearing and Ti＋ Nb stabilized ultra-low-carbon bake hardened steels were experimentally studied. The microstructure and texture evolution, as well as...Hot rolling, cold rolling and continuous annealing processes of Ti bearing and Ti＋ Nb stabilized ultra-low-carbon bake hardened steels were experimentally studied. The microstructure and texture evolution, as well as the morphology, size and distribution of second phase precipitates during hot rolling, cold rolling and continuous annealing were also analyzed. The results showed that the size of NbC precipitates in Ti＋Nb stabilized ultra-low-carbon bake hardened steel was smaller than that of TiC precipitates in Ti bearing ultra-low-carbon bake hardened steel, which made the average grain size of Ti＋ Nb stabilized ultra-low-carbon bake hardened steel finer than that of Ti bearing ultra-low-carbon bake hardened steel; for the yield strength, the former was higher than the latter; but for the r value which reflects the deep-drawing performance, the former was lower than the latter.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
This paper describes pre-treatment methods to improve the bake-hardening response of naturally aged AA6022 （Al-0.6Mg-1.0Si）, which is an alloy used in automotive body panels. These methods are used to accelerate the...This paper describes pre-treatment methods to improve the bake-hardening response of naturally aged AA6022 （Al-0.6Mg-1.0Si）, which is an alloy used in automotive body panels. These methods are used to accelerate the artificial aging process, which proceeds 30-day period of natural aging. The precipitation behavior of the sheets of this aluminum alloy was analyzed by differential scanning calorimetry （DSC） and electrical conductivity measurements, and subsequently confirmed by microstructure observations by transmission electron microscopy （TEM）. Tensile tests and microhardness measurements were performed to determine the mechanical properties of the samples. Under simulated paint-baking conditions （30 min at 170℃）, the microhardness and the yield strength （YS） of the pre-strained ＋ pre-aged samples were found to be I13 HV and 225 MPa, respectively. These values are considerably higher than those of pre-aged samples, and they did not decrease significantly during the initial stage of artificial aging.展开更多
For a series of Al-0.34／%Mg-1.05／%Si-0.08／%Cu alloys, the effects of pre-treatment on natural aging, bake hardening response and plasticity were investigated using Vickers hardness test and tensile test. Differenti...For a series of Al-0.34／%Mg-1.05／%Si-0.08／%Cu alloys, the effects of pre-treatment on natural aging, bake hardening response and plasticity were investigated using Vickers hardness test and tensile test. Differential scanning calorimetry （DSC） analysis was conducted to reveal corresponding precipitation mechanisms. The results showed that pre-straining and pre-aging alone couldn＇t completely suppress natural aging and improve bake hardening response simultaneously. The sensitivity of the pre-straining and pre-aging on the mechanical properties was evaluated. It was found that pre-aging was the main factor which greatly improved bake hardening response and pre-treatment had a weak influence on plasticity in pre-treated samples. DSC analysis showed that the dissolution trough of clusters disappeared in pre-treated samples, both β”and β＇ precipitation peak shifted to lower temperature and were reduced in pre-strained and pre-aged samples. It was concluded that the formation of Mg/Si clusters was replaced by the accelerated precipitation ofβ” andβ＇ phases, which caused the suppression of natural aging and the improvement of bake hardening response （BHR）.展开更多
Specimens of two different kinds of bake hardening steels （BH-Mn and BH-P） were prepared and treated with different annealing processes （water quenching and overaging）. A novel technique of three dimensional atom ...Specimens of two different kinds of bake hardening steels （BH-Mn and BH-P） were prepared and treated with different annealing processes （water quenching and overaging）. A novel technique of three dimensional atom probe was used to investigate solute distributions in these steels. The results indicate that C concentration decreases, whereas V increases during overaging in both bake hardening steels. The conclusion that no vanadium carbides pre- cipitate during the overaging is therefore originally obtained by microanalysis in bake hardening steels. Moreover, bake hardening values of all the specimens were tested by tensile experiments with 2 0/~ pre-deformation. However, those of overaged specimens were further measured with higher levels of pre-deformation because no bake hardening phenomenon was present at 2% pre-deformation. As the pre-deformation increases from 2% to 6% and 8%, both overaged steels show bake hardening values, and the value data are almost the same.展开更多
The bake hardening （BH） behavior of transformation-induced plasticity （TRIP） and dual-phase （DP） steels after different prestrains was studied. The experimental results indicate that TRIP steel exhibits good BH ...The bake hardening （BH） behavior of transformation-induced plasticity （TRIP） and dual-phase （DP） steels after different prestrains was studied. The experimental results indicate that TRIP steel exhibits good BH ability while DP steel does not, and prestrain displays a strong effect on the BH values of both steels. The comparison of microstructures of the two steels showed that the hard second phase in the matrix might be harmful to the BH ability. For deformed specimens, baking resulted in a loss of uniform elongation, but there was no obvious decrease in uniform elongation for unprestrained specimens.展开更多
The formability of bake hardened steel （thickness 0.82 mm）, and the extra galvannealed IF steel （thickness 0.82 mm） have been studied. The suitability of the above steels for forming applications has been critical...The formability of bake hardened steel （thickness 0.82 mm）, and the extra galvannealed IF steel （thickness 0.82 mm） have been studied. The suitability of the above steels for forming applications has been critically examined. The microstructure, tensile properties, and formability parameters of the above sheet metals were determined. The manufacturing process of the steels and the significance with reference to its formability were studied.展开更多
In an anode baking horizontal flue ring furnace, the temperature distribution is one of the key factors influencing the quality of baked anode and is closely correlated with the gas flow. To understand the gas flow di...In an anode baking horizontal flue ring furnace, the temperature distribution is one of the key factors influencing the quality of baked anode and is closely correlated with the gas flow. To understand the gas flow distribution in the flue, Navier Stokes equation with " k ε " two equation turbulence model was adopted and the simulation on the gas flow was performed. The numerical simulation results showed that the even direction of gas flow should be considered in the design of flue baffles and the gas flow distribution was really uneven in the flue in practical use. By adjusting the number and location of flue baffles rationally, the even distribution of gas flow can be improved obviously.展开更多
Bake-hardening behaviour of carbon steel with different martensite morphologies and volume fraction was investigated. The specimens with fibrous and bulky martensite were prestrained in tension by 4%. After this, they...Bake-hardening behaviour of carbon steel with different martensite morphologies and volume fraction was investigated. The specimens with fibrous and bulky martensite were prestrained in tension by 4%. After this, they were unloaded and bake hardened at 180 ℃ for 10-160 min. It was found that dual-phase steel samples which were bake hardened at 180 ℃ for 20 rain showed an increase in the yield stress （YS） and ultimate tensile stress （UTS） but a decrease in ductility. Further increase in the bake-hardening time of 80 or 160 min has reduced the YS and UTS, but increased the ductility. △σ （increase in stress due to bake hardening）, YS and UTS values are higher for the microstructure containing fibrous martensite compared to the microstructure-containing bulky martensite. It was also observed that at a given baking temperature Aa, YS and UTS increased by volume of martensite.展开更多
基金financially supported by the National Key Project of Scientific and Technical Supporting Programs of China (No. 2011BAE13B07)
文摘In a typical process, C-Mn steel was annealed at 800℃ for 180 s, and then cooled rapidly to obtain the ferrite-martensite microstructure. After pre-straining, the specimens were baked and the corresponding bake-hardening （BH） values were determined as a function of pre-strain, baking temperature, and baking time. The influences ofpre-strain, baking temperature and baking time on the microstructure evolution and bake-hardening behavior of the dual-phase steel were investigated systematically. It was found that the BH value apparently increased with an increase in pre-strain in the range from 0 to 1%; however, increasing pre-strain from 1% to 8% led to a decrease in the BH value. Furthermore, an increase in baking temperature favored a gradual improvement in the BH value because of the formation of Cottrell atmosphere and the precipitation of carbides in both the ferrite and martensite phases. The BH value reached a maximum of 110 MPa at a baking temperature of 300℃. Moreover, the BH value enhanced significantly with increasing baking time from 10 to 100 min.
文摘The purpose of this study was to investigate the suitability of palm diacylglycerol （PDAG）-enriched formulations for bakery shortening. Three types of palm diacylglycerol olein （PDAGOL） at different degree of unsaturation （PDAGOL1V56, PDAGOLIV62 and PDAGOLIV64） were used as main raw materials blended with palm stearin （PS）. The blending compositions ranged from 30% to 70% of PDAGOLIV56/PS, PDAGOLIV62/PS and PDAGOLIV64/PS, respectively. The physicochemical properties of all binary blend systems were characterized for fatty acid composition （FAC）, slip melting point （SMP） and solid fat content （SFC）. The selected bakery shortening formulations were further characterised for polymorphic form of fat crystal and thermal behavior, using X-ray diffractometer （XRD） and differential scanning calorimetry （DSC）. Bakery shortening enriched with diacylglycerol that were produced from 40DS56 （40% PDAGOLIV56/60% PS）, 40DS62 （40% PDAGOL1V62/60% PS） and 40DS64 （40% PDAGOLIV64/60% PS） had 45%-50% unsaturated fatty acid and crystallized in β ＋ β polymorphs; thus they were suitable for shortening system. Based on product＇s baking performance, it could be found that all Madeira cakes prepared from bakery shortening enriched with diacylglycerol had higher specific cake volume as compared to commercial shortening （CS）. In customer acceptance test, Madeira cake made from 40DS56 shortening scored the highest rating for all sensory attributes, including overall customer acceptability. It had given an indication that 40DS56 shortening formulation was the most suitable fat blends to be used as bakery shortening.
基金Project(2014DFA51270)supported by the International Science and Technology Cooperation Program of ChinaProject(51421001)supported by the Foundation for Innovative Research Groups of the National Natural Science Foundation of China
文摘The influences of high temperature pre-straining (HT-PS) on the natural aging and bake hardening of Al?Mg?Si alloys were investigated by Vickers microhardness measurements, differential scanning calorimetry (DSC) analysis and transmission electron microscopy (TEM) characterization. The results show that pre-straining at 170 °C immediately after quenching can effectively resolve the rather high T4 temper hardness caused by the conventional room temperature (RT) pre-straining treatment, and give a better bake hardening response (BHR) after paint-bake cycle. HT-PS 7% at 170 °C for 10 min is chosen as the optimum process as it provides lower T4 temper hardness and better BHR. The simultaneous introduction of dislocations and Cluster (2) can significantly suppress the natural aging and promote the precipitation of β″ phase, and reduce the effects of deformation hardening by dynamic recovery.
基金Project(51105139)supported by the National Natural Science Foundation of ChinaProject(2010CB731706)supported by the National Basic Research Program of China
文摘The effects of copper on the ageing precipitation behavior of as-quenched and pre-aged AA6016 aluminum alloy were studied by differential scanning calorimetry （DSC）, Vickers hardness measurement and transmission electronic microscopy （TEM）. The results indicate that the addition of copper facilitates the growth of clusters （GP I） to the critical size during pre-ageing. Therefore, the addition of copper accelerates the transition from GP I （pre-β＂） to GP II （β＂） during final artificial ageing, and finally results in the favorable paint-bake response. However, the one with the copper level of 0.3% does not show significant baking hardening response as expected. Pre-aging can also reduce the detrimental effect due to natural aging of copper-containing alloys.
基金supported by the Research Initiation Grant of Queen’s University,Canada(#378140)Ontario Centers of Excellence VIP fund(#25394)
文摘Rare earth elements（REE） are a set of seventeen chemical elements in the periodic table, which have been found in a variety classes of minerals in the world. The global demand for REE and their compounds has increased in high-tech applications over the past decades due to their chemical, catalytic, electrical, magnetic, and optical properties. After mining, comminution and ore beneficiation, hydrometallurgical and pyrometallurgical processes are carried out to recover REE compounds. The concentrate cracking is a process wherein the structure of a REE mineral is modified in order to dissolve REE in a weak acid solution. This would be accomplished through various techniques such as alkaline cracking and acid baking. The cracked concentrate is then leached to dissolve REE in a solution and subsequently recover those via neutralization, precipitation or solvent extraction methods. This paper reviewed the cracking and leaching methods applied to REE concentrates to produce an intermediate product for further REE separation.
基金Item Sponsored by National Natural Science Foundation of China(50527402)
文摘After 2% predeformation,the baking treatment with different schedule was carried out for low silicon TRIP steel sheet with niobium.The effects of baking temperature and time on microstructures and mechanical properties were investigated.The results showed that with increasing the baking temperature and time,the volume fraction of retained austenite decreases,and the volume fraction of tempered martensite increases; as baking temperature ranges from 80 ℃ to 170 ℃,the bake-hardening（BH）value increases obviously,while from 170 ℃ to 230 ℃,the variation of BH value is very slight; as baking time ranges from 2 min to 20 min,the BH value increases significantly,while the BH value decreases when baking time exceeds 20 min.So that when the baking temperature is 170 ℃ and the baking time is 20 min,the low silicon TRIP steel sheet exhibits good bake-hardening behavior,and the highest BH value is above 70 MPa.
基金Item Sponsored by National Science and Technology Support 11th Five-Year Plan of China(2006BAE03A13)
文摘Hot rolling, cold rolling and continuous annealing processes of Ti bearing and Ti＋ Nb stabilized ultra-low-carbon bake hardened steels were experimentally studied. The microstructure and texture evolution, as well as the morphology, size and distribution of second phase precipitates during hot rolling, cold rolling and continuous annealing were also analyzed. The results showed that the size of NbC precipitates in Ti＋Nb stabilized ultra-low-carbon bake hardened steel was smaller than that of TiC precipitates in Ti bearing ultra-low-carbon bake hardened steel, which made the average grain size of Ti＋ Nb stabilized ultra-low-carbon bake hardened steel finer than that of Ti bearing ultra-low-carbon bake hardened steel; for the yield strength, the former was higher than the latter; but for the r value which reflects the deep-drawing performance, the former was lower than the latter.
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.
文摘This paper describes pre-treatment methods to improve the bake-hardening response of naturally aged AA6022 （Al-0.6Mg-1.0Si）, which is an alloy used in automotive body panels. These methods are used to accelerate the artificial aging process, which proceeds 30-day period of natural aging. The precipitation behavior of the sheets of this aluminum alloy was analyzed by differential scanning calorimetry （DSC） and electrical conductivity measurements, and subsequently confirmed by microstructure observations by transmission electron microscopy （TEM）. Tensile tests and microhardness measurements were performed to determine the mechanical properties of the samples. Under simulated paint-baking conditions （30 min at 170℃）, the microhardness and the yield strength （YS） of the pre-strained ＋ pre-aged samples were found to be I13 HV and 225 MPa, respectively. These values are considerably higher than those of pre-aged samples, and they did not decrease significantly during the initial stage of artificial aging.
基金supported by the Fundamental Research Fund for the Central Universities(No.CDJZR10130018)the Chongqing Science and Technology Commission (No.2011GZ0039)
文摘For a series of Al-0.34／%Mg-1.05／%Si-0.08／%Cu alloys, the effects of pre-treatment on natural aging, bake hardening response and plasticity were investigated using Vickers hardness test and tensile test. Differential scanning calorimetry （DSC） analysis was conducted to reveal corresponding precipitation mechanisms. The results showed that pre-straining and pre-aging alone couldn＇t completely suppress natural aging and improve bake hardening response simultaneously. The sensitivity of the pre-straining and pre-aging on the mechanical properties was evaluated. It was found that pre-aging was the main factor which greatly improved bake hardening response and pre-treatment had a weak influence on plasticity in pre-treated samples. DSC analysis showed that the dissolution trough of clusters disappeared in pre-treated samples, both β”and β＇ precipitation peak shifted to lower temperature and were reduced in pre-strained and pre-aged samples. It was concluded that the formation of Mg/Si clusters was replaced by the accelerated precipitation ofβ” andβ＇ phases, which caused the suppression of natural aging and the improvement of bake hardening response （BHR）.
基金sponsored by National Natural Science Foundation of China(50934011,50971137)National Basic Research Program of China(2010CB630802)
文摘Specimens of two different kinds of bake hardening steels （BH-Mn and BH-P） were prepared and treated with different annealing processes （water quenching and overaging）. A novel technique of three dimensional atom probe was used to investigate solute distributions in these steels. The results indicate that C concentration decreases, whereas V increases during overaging in both bake hardening steels. The conclusion that no vanadium carbides pre- cipitate during the overaging is therefore originally obtained by microanalysis in bake hardening steels. Moreover, bake hardening values of all the specimens were tested by tensile experiments with 2 0/~ pre-deformation. However, those of overaged specimens were further measured with higher levels of pre-deformation because no bake hardening phenomenon was present at 2% pre-deformation. As the pre-deformation increases from 2% to 6% and 8%, both overaged steels show bake hardening values, and the value data are almost the same.
文摘The bake hardening （BH） behavior of transformation-induced plasticity （TRIP） and dual-phase （DP） steels after different prestrains was studied. The experimental results indicate that TRIP steel exhibits good BH ability while DP steel does not, and prestrain displays a strong effect on the BH values of both steels. The comparison of microstructures of the two steels showed that the hard second phase in the matrix might be harmful to the BH ability. For deformed specimens, baking resulted in a loss of uniform elongation, but there was no obvious decrease in uniform elongation for unprestrained specimens.
文摘The formability of bake hardened steel （thickness 0.82 mm）, and the extra galvannealed IF steel （thickness 0.82 mm） have been studied. The suitability of the above steels for forming applications has been critically examined. The microstructure, tensile properties, and formability parameters of the above sheet metals were determined. The manufacturing process of the steels and the significance with reference to its formability were studied.
文摘In an anode baking horizontal flue ring furnace, the temperature distribution is one of the key factors influencing the quality of baked anode and is closely correlated with the gas flow. To understand the gas flow distribution in the flue, Navier Stokes equation with " k ε " two equation turbulence model was adopted and the simulation on the gas flow was performed. The numerical simulation results showed that the even direction of gas flow should be considered in the design of flue baffles and the gas flow distribution was really uneven in the flue in practical use. By adjusting the number and location of flue baffles rationally, the even distribution of gas flow can be improved obviously.
文摘Bake-hardening behaviour of carbon steel with different martensite morphologies and volume fraction was investigated. The specimens with fibrous and bulky martensite were prestrained in tension by 4%. After this, they were unloaded and bake hardened at 180 ℃ for 10-160 min. It was found that dual-phase steel samples which were bake hardened at 180 ℃ for 20 rain showed an increase in the yield stress （YS） and ultimate tensile stress （UTS） but a decrease in ductility. Further increase in the bake-hardening time of 80 or 160 min has reduced the YS and UTS, but increased the ductility. △σ （increase in stress due to bake hardening）, YS and UTS values are higher for the microstructure containing fibrous martensite compared to the microstructure-containing bulky martensite. It was also observed that at a given baking temperature Aa, YS and UTS increased by volume of martensite.
