Using KClO3 as an inner oxidant, MnZn-ferrite powder was synthesized by a self-propagating high-temperature synthesis (SHS) process in normal air atmosphere. The effects of the inner oxidant on combustion temperature,...Using KClO3 as an inner oxidant, MnZn-ferrite powder was synthesized by a self-propagating high-temperature synthesis (SHS) process in normal air atmosphere. The effects of the inner oxidant on combustion temperature, combustion velocity, microstructure and the phase of the product were investigated by XRD and SEM,respectively. The results show that a highly ferritized powder can be obtained as well as the highest combustion temperature and the highest combustion velocity when the inner oxidant content m equals 54(k-16).展开更多
The La-Zn substituted SrM-type ferrites with the composition of Sr1-xLaxFe12-xZnxO19 （x=0-0.4） were prepared by self-propagating high-temperature synthesis （SHS）. The single SrM phase was detected by XRD in the as...The La-Zn substituted SrM-type ferrites with the composition of Sr1-xLaxFe12-xZnxO19 （x=0-0.4） were prepared by self-propagating high-temperature synthesis （SHS）. The single SrM phase was detected by XRD in the as-received samples by controlling the Fe contents in the reagents. The substitution of La^3＋and Zn^2＋ obviously increased the magnetic properties of the as-prepared samples. The maximum improvements of Br, Hcb and （BH）m were 14.4%, 15.3% and 30.7%, respectively compared with that of the samples without La-Zn substitution. Microstructure observation by SEM showed that the SHS method benefited forming the better particle features and achieving the higher Hcj in comparison with the traditional firing method.展开更多
18CrNbTi ferritic stainless steel is a low-cost material mainly used for the fabrication of manifolds, which usually work at temperatures below 950℃. With the development of engine technology, exhaust manifolds tend ...18CrNbTi ferritic stainless steel is a low-cost material mainly used for the fabrication of manifolds, which usually work at temperatures below 950℃. With the development of engine technology, exhaust manifolds tend to work above 1 000 ℃ and this may be even higher in the future. For developing a new kind of steel to satisfy these requirements,the effects of tungsten （W）addition on the high-temperature strength and oxidation resistance of 18CrNbTi ferritic stainless steel are discussed in this study. The test results show that W enhances high-temperature strength at 1 000 ℃ and significantly improves oxidation resistance. However, W addition tends to degrade oxide layer adhesion,causing spalling during alternate hot and cold conditions.展开更多
Appropriate addition of CuO/V2O5 and the reduction of the granularity of the raw materials particle decrease the sintering temperature of NiZn ferrite from 1200 °C to 930 °C. Furthermore, the magnetic proper...Appropriate addition of CuO/V2O5 and the reduction of the granularity of the raw materials particle decrease the sintering temperature of NiZn ferrite from 1200 °C to 930 °C. Furthermore, the magnetic properties of the NiZn ferrite prepared at low temperature of 930 °C is superior to that of the NiZn ferrite prepared by sintering at high temperature of 1200 °C because the microstructure of the NiZn ferrite sintered at 930 °C is more uniform and compact than that of the NiZn ferrite sintered at 1200 °C. The high permeability of 1700 and relative loss coefficient tanδ/μi of 9.0×10?6 at 100 kHz was achieved in the (Ni0.17Zn0.63Cu0.20)Fe1.915O4 ferrite.展开更多
The Ni1–xCuxFe2O4 (x = 0.0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0) ferrites have been prepared by sol-gel method in order to obtain homogeneous crystal structure and they are sintered at high temperature. ...The Ni1–xCuxFe2O4 (x = 0.0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0) ferrites have been prepared by sol-gel method in order to obtain homogeneous crystal structure and they are sintered at high temperature. The effect of copper doping on the structural and magnetic properties of nickel ferrites sintered at 1000°C has been examined. The X-ray diffraction measurements clearly showed the formation of single phase spinel ferrite structure in all the prepared ferrite compositions. Because of the high sintering temperature the particle size is observed beyond the nano-scale range in all the compositions. The lattice parameters are found to increase with increasing doping concentration of the copper content. Magnetization results exhibit a non-collinear ferrimagnetic structure for x = 0.0 to 0.5 and Neel’s collinear ferrimagnetic structure for x = 0.5 to 0.9 suggesting a change in magnetic ordering.展开更多
In order to understand the effect of Mo element on the high-temperature fatigue behavior of 15CrNbTi ferritic stainless steel, the stress-controlled fatigue tests have been performed for both 15CrNbTi and 15Cr0.5MoNbT...In order to understand the effect of Mo element on the high-temperature fatigue behavior of 15CrNbTi ferritic stainless steel, the stress-controlled fatigue tests have been performed for both 15CrNbTi and 15Cr0.5MoNbTi ferritic stainless steels at 800 ℃ in laboratory air. The fatigue test results indicate that the fatigue resistance of 15Cr0.5MoNbTi steel is manifestly higher than that of 15CrNbTi steel at the maximum stress below 57 MPa; the 15Cr0.5MoNbTi steel possesses a fatigue limit of 35 MPa, which is higher than that of 15CrNbTi steel. The TEM observations reveal that the Mo element can suppress the formation of coarsened Fe3Nb3C precipitates and result in the fatigue resistance enhancement. The dislocation networks formed during the cyclic load favor to improve the fatigue resistance of 15Cr0.5MoNbTi steel at 800 ℃.展开更多
For steam tubes used in thermal power plant,the inner and outer walls were operated in high-temperature steam and flue gas environments respectively.In this study,structure,microstructure and chemical composition of o...For steam tubes used in thermal power plant,the inner and outer walls were operated in high-temperature steam and flue gas environments respectively.In this study,structure,microstructure and chemical composition of oxide films on inner and outer walls of exservice low Cr ferritic steel G102 tube and exservice high Cr ferritic steel T91 tube were analyzed.The oxide film was composed of outer oxide layer,inner oxide layer and internal oxidation zone.The outer oxide layer on the original surface of tube had a porous structure containing Fe oxides formed by diffusion and oxidation of Fe.More specially,the outer oxide layer formed in flue gas environment would mix with coal combustion products during the growth process.The inner oxide layer below the original surface of tube was made of Fe–Cr spinel.The internal oxidation zone was believed to be the precursor stage of inner oxide layer.The formation of internal oxidation zone was due to O diffusing along grain boundaries to form oxide.There were Fe–Cr–Si oxides discontinuously distributed along grain boundaries in the internal oxidation zone of G102,while there were Fe–Cr oxides continuously distributed along grain boundaries in that of T91.展开更多
The beneficial effects of niobium addition on properties such as high-temperature strength, toughness, and formability of ferritic stainless steels have been addressed. Based on the Thermo-Calc analysis, precipitation...The beneficial effects of niobium addition on properties such as high-temperature strength, toughness, and formability of ferritic stainless steels have been addressed. Based on the Thermo-Calc analysis, precipitation of niobium carbonitride and solubility of niobium have been predicted and characterized via scanning electron microscope （SEM） and transmission electron microscope （TEM） observations. It is shown that addition of niobium has a beneficial effect on improving the high-temperature strength, toughness, formability, and corrosion resistance of ferritic stainless steel. Soluted niobium is very effective in improving the high-temperature strength, which is beneficial to reducing the sticking propensity during hot rolling. Although niobium increases the recrystallization temperature, niobium-added ferritic stainless steels show a high mean r value, or a high plastic strain ratio, as long as the annealing temperature is high enough. Furthermore, because niobium helps to inhibit the formation of chromium carbides, ferritic stainless steel can keep an effective chromium content in the matrix, leading to improved corrosion resistance. Applications of these ferritic stainless steels for construction and home appliances have also been presented.展开更多
Exhaust emission regulations of the automotive are enforced in each country to prevent air pollution and global warming,and the restriction standard tends to become severer.Various techniques such as the combustion im...Exhaust emission regulations of the automotive are enforced in each country to prevent air pollution and global warming,and the restriction standard tends to become severer.Various techniques such as the combustion improvement of gasoline,upgrades of the catalyst,and the thermal capacity decreases in the exhaust lines are adopted to suit the regulations,and these lead to an increase of the maximum temperature of the exhaust gas. Recently,ferritic stainless steels are mainly used to parts of exhaust lines,as their thermal expansion coefficient is small,and the cyclic oxidation resistance and the thermal fatigue property are better than austenitic stainless steels. This paper presents newly developed heat-resistant stainless steels from Nisshin Steel for exhaust lines usage,and describes the currents of the steel development that could be envisaged in the future.With regard to improving the high-temperature strength of ferritic stainless steels,the addition of Nb,Mo and Cu is effective in solution hardening and precipitation hardening at 700℃,while the addition of Nb,Mo and W is effective in mainly solution hardening at 900℃.The addition of Cr,Si and Mn suppress the breakaway oxidation in air at 950℃up to 200 h of ferritic stainless steels containing 14%Cr.Especially,the addition of 0.8%or higher Mn would effectively improve the adherence of oxide scale.It is confirmed that ferritic stainless steels,NSSHR-1(14Cr-lMn-0.9Si-Nb) and NSSHR-2(10Cr-0.9Si-Nb-Ti ),is having a superior heat resistance,formability and cost performance compared to conventional Type441 and Type439 respectively.展开更多
18Mn18Cr0.5N steel specimens were preheated at the temperatures from 1100 to 1250°C for 5 min,and then cooled to 950°C and compressed.The cracking behaviors were investigated using optical microscopy and sca...18Mn18Cr0.5N steel specimens were preheated at the temperatures from 1100 to 1250°C for 5 min,and then cooled to 950°C and compressed.The cracking behaviors were investigated using optical microscopy and scanning electron microscopy.The results showed that the hot workability of 18Mn18Cr0.5N steel gradually decreased with increasing preheating temperature between 1100 and 1200°C,and quickly deteriorated up to 1250°C.Above 1200°C,delta ferrite particles appeared in 18Mn18Cr0.5N steel,promoted cavity coalescence on grain boundary,and accelerated surface crack formation during the hot working process.展开更多
Stable austenitic structure in medical stainless steels is basically required for surgical implantation. A weak magnetism was found in a high nitrogen nickel-free austenitic stainless steel for cardiovascular stent ap...Stable austenitic structure in medical stainless steels is basically required for surgical implantation. A weak magnetism was found in a high nitrogen nickel-free austenitic stainless steel for cardiovascular stent application. This magnetic behavior in high nitrogen stainless steel was investigated by optical microscopy, X-ray diffraction （XRD）, electron probe microanalysis （EPMA） and superconducting quantum interference device （SQUID）. The results showed that the magnetism came from the composition segregation of ferrite formation elements such as Cr and Mo in the steel and some 6-ferrites were locally formed during the pressurized electroslag remelting process. The magnetism of high nitrogen stainless steel could be eliminated by a proper high temperature gas nitriding （HTGN）.展开更多
文摘Using KClO3 as an inner oxidant, MnZn-ferrite powder was synthesized by a self-propagating high-temperature synthesis (SHS) process in normal air atmosphere. The effects of the inner oxidant on combustion temperature, combustion velocity, microstructure and the phase of the product were investigated by XRD and SEM,respectively. The results show that a highly ferritized powder can be obtained as well as the highest combustion temperature and the highest combustion velocity when the inner oxidant content m equals 54(k-16).
基金Project supported by the Key Project for Science and Technology of Zhejiang Province
文摘The La-Zn substituted SrM-type ferrites with the composition of Sr1-xLaxFe12-xZnxO19 （x=0-0.4） were prepared by self-propagating high-temperature synthesis （SHS）. The single SrM phase was detected by XRD in the as-received samples by controlling the Fe contents in the reagents. The substitution of La^3＋and Zn^2＋ obviously increased the magnetic properties of the as-prepared samples. The maximum improvements of Br, Hcb and （BH）m were 14.4%, 15.3% and 30.7%, respectively compared with that of the samples without La-Zn substitution. Microstructure observation by SEM showed that the SHS method benefited forming the better particle features and achieving the higher Hcj in comparison with the traditional firing method.
文摘18CrNbTi ferritic stainless steel is a low-cost material mainly used for the fabrication of manifolds, which usually work at temperatures below 950℃. With the development of engine technology, exhaust manifolds tend to work above 1 000 ℃ and this may be even higher in the future. For developing a new kind of steel to satisfy these requirements,the effects of tungsten （W）addition on the high-temperature strength and oxidation resistance of 18CrNbTi ferritic stainless steel are discussed in this study. The test results show that W enhances high-temperature strength at 1 000 ℃ and significantly improves oxidation resistance. However, W addition tends to degrade oxide layer adhesion,causing spalling during alternate hot and cold conditions.
基金Project (Grant No. 50471041) supported by the National NaturalScience Foundation of China
文摘Appropriate addition of CuO/V2O5 and the reduction of the granularity of the raw materials particle decrease the sintering temperature of NiZn ferrite from 1200 °C to 930 °C. Furthermore, the magnetic properties of the NiZn ferrite prepared at low temperature of 930 °C is superior to that of the NiZn ferrite prepared by sintering at high temperature of 1200 °C because the microstructure of the NiZn ferrite sintered at 930 °C is more uniform and compact than that of the NiZn ferrite sintered at 1200 °C. The high permeability of 1700 and relative loss coefficient tanδ/μi of 9.0×10?6 at 100 kHz was achieved in the (Ni0.17Zn0.63Cu0.20)Fe1.915O4 ferrite.
文摘The Ni1–xCuxFe2O4 (x = 0.0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0) ferrites have been prepared by sol-gel method in order to obtain homogeneous crystal structure and they are sintered at high temperature. The effect of copper doping on the structural and magnetic properties of nickel ferrites sintered at 1000°C has been examined. The X-ray diffraction measurements clearly showed the formation of single phase spinel ferrite structure in all the prepared ferrite compositions. Because of the high sintering temperature the particle size is observed beyond the nano-scale range in all the compositions. The lattice parameters are found to increase with increasing doping concentration of the copper content. Magnetization results exhibit a non-collinear ferrimagnetic structure for x = 0.0 to 0.5 and Neel’s collinear ferrimagnetic structure for x = 0.5 to 0.9 suggesting a change in magnetic ordering.
基金supported by the National Natural Science Foundation of China (No. 51134010)
文摘In order to understand the effect of Mo element on the high-temperature fatigue behavior of 15CrNbTi ferritic stainless steel, the stress-controlled fatigue tests have been performed for both 15CrNbTi and 15Cr0.5MoNbTi ferritic stainless steels at 800 ℃ in laboratory air. The fatigue test results indicate that the fatigue resistance of 15Cr0.5MoNbTi steel is manifestly higher than that of 15CrNbTi steel at the maximum stress below 57 MPa; the 15Cr0.5MoNbTi steel possesses a fatigue limit of 35 MPa, which is higher than that of 15CrNbTi steel. The TEM observations reveal that the Mo element can suppress the formation of coarsened Fe3Nb3C precipitates and result in the fatigue resistance enhancement. The dislocation networks formed during the cyclic load favor to improve the fatigue resistance of 15Cr0.5MoNbTi steel at 800 ℃.
基金supported by the National Natural Science Foundation of China (Nos.51901113 and 51775300)the State Key Laboratory of Tribology in Tsinghua University, and the State Key Lab of Advanced Welding and Joining in Harbin Institute of Technology (No.AWJ-21M03)。
文摘For steam tubes used in thermal power plant,the inner and outer walls were operated in high-temperature steam and flue gas environments respectively.In this study,structure,microstructure and chemical composition of oxide films on inner and outer walls of exservice low Cr ferritic steel G102 tube and exservice high Cr ferritic steel T91 tube were analyzed.The oxide film was composed of outer oxide layer,inner oxide layer and internal oxidation zone.The outer oxide layer on the original surface of tube had a porous structure containing Fe oxides formed by diffusion and oxidation of Fe.More specially,the outer oxide layer formed in flue gas environment would mix with coal combustion products during the growth process.The inner oxide layer below the original surface of tube was made of Fe–Cr spinel.The internal oxidation zone was believed to be the precursor stage of inner oxide layer.The formation of internal oxidation zone was due to O diffusing along grain boundaries to form oxide.There were Fe–Cr–Si oxides discontinuously distributed along grain boundaries in the internal oxidation zone of G102,while there were Fe–Cr oxides continuously distributed along grain boundaries in that of T91.
基金support of the CITIC-CBMM R&D Subject Foundation(No.2010-D046)CITIC-CBMM-Baosteel Technical Cooperation Projects"Development of High-quality Niobium-bearing Ferritic Stainless Steel for Home Appliances in Baosteel"
文摘The beneficial effects of niobium addition on properties such as high-temperature strength, toughness, and formability of ferritic stainless steels have been addressed. Based on the Thermo-Calc analysis, precipitation of niobium carbonitride and solubility of niobium have been predicted and characterized via scanning electron microscope （SEM） and transmission electron microscope （TEM） observations. It is shown that addition of niobium has a beneficial effect on improving the high-temperature strength, toughness, formability, and corrosion resistance of ferritic stainless steel. Soluted niobium is very effective in improving the high-temperature strength, which is beneficial to reducing the sticking propensity during hot rolling. Although niobium increases the recrystallization temperature, niobium-added ferritic stainless steels show a high mean r value, or a high plastic strain ratio, as long as the annealing temperature is high enough. Furthermore, because niobium helps to inhibit the formation of chromium carbides, ferritic stainless steel can keep an effective chromium content in the matrix, leading to improved corrosion resistance. Applications of these ferritic stainless steels for construction and home appliances have also been presented.
文摘Exhaust emission regulations of the automotive are enforced in each country to prevent air pollution and global warming,and the restriction standard tends to become severer.Various techniques such as the combustion improvement of gasoline,upgrades of the catalyst,and the thermal capacity decreases in the exhaust lines are adopted to suit the regulations,and these lead to an increase of the maximum temperature of the exhaust gas. Recently,ferritic stainless steels are mainly used to parts of exhaust lines,as their thermal expansion coefficient is small,and the cyclic oxidation resistance and the thermal fatigue property are better than austenitic stainless steels. This paper presents newly developed heat-resistant stainless steels from Nisshin Steel for exhaust lines usage,and describes the currents of the steel development that could be envisaged in the future.With regard to improving the high-temperature strength of ferritic stainless steels,the addition of Nb,Mo and Cu is effective in solution hardening and precipitation hardening at 700℃,while the addition of Nb,Mo and W is effective in mainly solution hardening at 900℃.The addition of Cr,Si and Mn suppress the breakaway oxidation in air at 950℃up to 200 h of ferritic stainless steels containing 14%Cr.Especially,the addition of 0.8%or higher Mn would effectively improve the adherence of oxide scale.It is confirmed that ferritic stainless steels,NSSHR-1(14Cr-lMn-0.9Si-Nb) and NSSHR-2(10Cr-0.9Si-Nb-Ti ),is having a superior heat resistance,formability and cost performance compared to conventional Type441 and Type439 respectively.
基金supported by the National Science and Technology Support Plan of China(No.2007BAF02B01-03)
文摘18Mn18Cr0.5N steel specimens were preheated at the temperatures from 1100 to 1250°C for 5 min,and then cooled to 950°C and compressed.The cracking behaviors were investigated using optical microscopy and scanning electron microscopy.The results showed that the hot workability of 18Mn18Cr0.5N steel gradually decreased with increasing preheating temperature between 1100 and 1200°C,and quickly deteriorated up to 1250°C.Above 1200°C,delta ferrite particles appeared in 18Mn18Cr0.5N steel,promoted cavity coalescence on grain boundary,and accelerated surface crack formation during the hot working process.
基金supported by National Natural Science Foundation of China(No.31000428)National Basic Research Program of China(973Program)(No.2012CB619101)
文摘Stable austenitic structure in medical stainless steels is basically required for surgical implantation. A weak magnetism was found in a high nitrogen nickel-free austenitic stainless steel for cardiovascular stent application. This magnetic behavior in high nitrogen stainless steel was investigated by optical microscopy, X-ray diffraction （XRD）, electron probe microanalysis （EPMA） and superconducting quantum interference device （SQUID）. The results showed that the magnetism came from the composition segregation of ferrite formation elements such as Cr and Mo in the steel and some 6-ferrites were locally formed during the pressurized electroslag remelting process. The magnetism of high nitrogen stainless steel could be eliminated by a proper high temperature gas nitriding （HTGN）.
