High-nitrogen martensitic stainless steel(HNMSS)is increasingly recognized for its excellent strength-ductility balance and superior pitting resistance,largely attributed to the solid solution strengthening effect of ...High-nitrogen martensitic stainless steel(HNMSS)is increasingly recognized for its excellent strength-ductility balance and superior pitting resistance,largely attributed to the solid solution strengthening effect of nitrogen.Despite significant advancements in enhancing its mechanical properties,the precise relationship between alloying elements,particularly nickel(Ni),and microstructural evolution remains insufficiently understood.The role of Ni in HNMSS was investigated by examining the effects of two different Ni contents on microstructure and deformation mechanisms.A combination of mechanical testing and microstructural characterization was employed to assess the materials’mechanical properties and phase transformations.The key findings reveal that the steel with higher Ni content exhibits improved mechanical performance,primarily due to an increased volume fraction of retained austenite,which activates both transformation-induced plasticity and twinning-induced plasticity effects.The microstructure after deformation forms a similar multilayer core-shell structure,with twinning martensite enveloping the softer austenite,which effectively avoids the risk of cracking caused by direct collision of martensitic variants.展开更多
Pitting corrosion and crevice corrosion behaviors of high nitrogen austenitic stainless steels （HNSS） were investigated by electrochemical and immersion testing methods in chloride solution, respectively. The chemic...Pitting corrosion and crevice corrosion behaviors of high nitrogen austenitic stainless steels （HNSS） were investigated by electrochemical and immersion testing methods in chloride solution, respectively. The chemical constitution and composition in the depth of passive films formed on HNSS were analyzed by X-ray photoelectron spectrum （XPS）. HNSS has excellent pitting and crevice corrosion resistance compared to 316L stainless steel. With increasing the nitrogen content in steels, pitting potentials and critical pitting temperature （CPT） increase, and the maximum, average pit depths and average weight loss decrease. The CPT of HNSS is correlated with the alloying element content through the measure of alloying for resistance to corrosion （MARC）. The MARC can be expressed as an equation of CPT=2.55MARC-29. XPS results show that HNSS exhibiting excellent corrosion resistance is attributed to the enrichment of nitrogen on the surface of passive films, which forms ammonium ions increasing the local pH value and facilitating repassivation, and the synergistic effects of molybdenum and nitrogen.展开更多
A simple and feasible method for the production of high nitrogen austenitic stainless steels involves nitrogen gas alloying and adding nitrided ferroalloys under normal atmospheric conditions. Alloying by nitrogen gas...A simple and feasible method for the production of high nitrogen austenitic stainless steels involves nitrogen gas alloying and adding nitrided ferroalloys under normal atmospheric conditions. Alloying by nitrogen gas bubbling in Fe-Cr-Mn-Mo series alloys was carried out in MoSi2 resistance furnace and air induction furnace under normal atmospheric conditions. The results showed that nitrogen alloying could be accelerated by increasing nitrogen gas flow rate, prolonging residence time of bubbles, increasing gas/molten steel interfaces, and decreasing the sulphur and oxygen contents in molten steel. Nitrogen content of 0.69% in 18Crl8Mn was obtained using air induction furnace by bubbling of nitrogen gas from porous plug. In addition, the nickel-free, high nitrogen austenitic stainless steels with sound and compact macrostructure had been produced in the laboratory using vacuum induction furnace and electroslag remelting furnace under nitrogen atmosphere by the addition of nitrided alloy with the maximum nitrogen content of 0.81%. Pores were observed in the ingots obtained by melting and casting in vacuum induction furnace with the addition of nitrided ferroalloys and under nitrogen atmosphere. After electroslag remelting of the cast ingots, they were all sound and were free of pores. The yield of nitrogen increased with the decrease of melting rate in the ESR process. Due to electroslag remelting under nitrogen atmosphere and the consequential addition of aluminum as deoxidizer to the slag, the loss of manganese decreased obviously. There existed mainly irregular Al2O3 inclusions and MnS inclusions in ESR ingots, and the size of most of the inclusions was less than 5 um. After homogenization of the hot rolled plate at 1 150℃ × 1 h followed by water quenching, the microstructure consisted of homogeneous austenite.展开更多
The fine grained structures of nickel-free high nitrogen austenitic stainless steels had been obtained by means of cold rolling and subsequent annealing. The relationship between microstructure and mechanical properti...The fine grained structures of nickel-free high nitrogen austenitic stainless steels had been obtained by means of cold rolling and subsequent annealing. The relationship between microstructure and mechanical properties and gain size of nickel-free high nitrogen austenitic stainless steels was examined. High strength and good ductility of the steel were found. In the grain size range, the Hall-Petch dependency for yield stress, tensile strength, and hardness was valid for grain size ranges for the nickel-free high nitrogen austenitic stainless steel. In the present study, the ductility of cold rolled nickel-free high nitrogen austenitic stainless steel decreased with annealing time when the grain size was refined. The fracture surfaces of the tensile specimens in the grain size range were covered with dimples as usually seen in a ductile fracture mode.展开更多
A series of high nitrogen austenitic stainless steels were successfully developed with a pressurized electroslag remelting furnace. Nitride additives and deoxidizer were packed into the stainless steel pipes, and then...A series of high nitrogen austenitic stainless steels were successfully developed with a pressurized electroslag remelting furnace. Nitride additives and deoxidizer were packed into the stainless steel pipes, and then the stainless steel pipes were welded on the surface of an electrode with low nitrogen content to prepare a compound electrode. Using Si3N4 as a nitrogen alloying source, the silicon contents in the ingots were prone to be out of the specification range, the electric current fluctuated greatly and the surface qualities of the ingots were poor. The surface qualities of the ingots were improved with FeCrN as a nitrogen alloying source. The sound and compact macrostructure ingot with the maximum nitrogen content of 1.21wt% can be obtained. The 18Cr18Mn2Mo0.9N high nitrogen austenitic stainless steel exhibits high strength and good ductility at room temperature. The steel shows typical ductile-brittle transition behavior and excellent pitting corrosion resistance properties.展开更多
The precipitation behavior of Cr2 N during isothermal aging in the temperature range from 700 ℃ to 950 ℃ in Fe-18Cr-12Mn-0.48N （in mass percent） high nitrogen austenitic stainless steel, including morphology and c...The precipitation behavior of Cr2 N during isothermal aging in the temperature range from 700 ℃ to 950 ℃ in Fe-18Cr-12Mn-0.48N （in mass percent） high nitrogen austenitic stainless steel, including morphology and content of precipitate, was investigated using optical microscopy, scanning electron microscopy, and transmission electron microscopy. The isothermal precipitation kinetics curve of Cr2 N and the corresponding precipitation activation energy were obtained. The results show that Cr2N phase precipitates in a cellular way and its morphology is transformed from initial granular precipitates to lamellar ones in the cell with increasing aging time. The nose temperature of Cr2 N precipitation is about 800 ℃, with a corresponding incubation period of 30 min, and the ceiling temperature of Cr2N precipitation is 950℃. The diffusionactivation energy of Cr2 N precipitation is 296 kJ/mol.展开更多
Three new bacteria HS-03, HS-043 and HS-047 isolated from different ecosystems were found capable of aerobic denitrification. The potential application of these strains in wastewater treatment under aerobic conditions...Three new bacteria HS-03, HS-043 and HS-047 isolated from different ecosystems were found capable of aerobic denitrification. The potential application of these strains in wastewater treatment under aerobic conditions was investigated, These three bacteria all presented high nitrogen removal from wastewater that more than 98% of 10 mmol/L nitrate could be removed in 12--24 h by adding cheap external carbon source and low concentration of iron as well as molybdate. The mechanism at molecular level was analyzed. The success of this aerobic denitrification applied to wastewater treatment may serve as an alternative to enhance the practical nitrogen removal from wastewater. Main biochemical and physiological features of these strains were characterized. The 16S rDNA sequences were compared with the published data in GenBank by using BLAST. The results of phenotype and genotype proved that strain HS-03 and HS-047 belonged to Pseudomonas stutzeri and Pseudomonas pseudoalcaligenes respectively. Strain HS-043 was identified as Delftia clcidovorans of which denitrifying activity has not previously been explored.展开更多
The solution-treated(ST)condition and aging precipitation behavior of 18Cr-16Mn-2Mo-1.1N high nitrogen austenitic stainless steel(HNS)were investigated by optical microscope(OM),scanning electron microscope(SEM),and t...The solution-treated(ST)condition and aging precipitation behavior of 18Cr-16Mn-2Mo-1.1N high nitrogen austenitic stainless steel(HNS)were investigated by optical microscope(OM),scanning electron microscope(SEM),and transmission electron microscope(TEM).The results show that the ST condition of 18Cr-16Mn-2Mo-1.1N HNS with wN above 1%is identified as 1100℃for 90 min,followed by water quenching to make sure the secondary phases completely dissolve into austenitic matrix and prevent the grains coarsening too much.Initial time-temperature-precipitation(TTP)curve of aged 18Cr-16Mn-2Mo-1.1N HNS which starts with precipitation of 0.05%in volume fraction is defined and the'nose'temperature of precipitation is found to be 850℃with an incubation period of 1 min.Hexagonal intergranular and cellular Cr2N with a=0.478 nm and c=0.444 nm precipitates gradually increase in the isothermal aging treatment.The matrix nitrogen depletion due to the intergranular and a few cellular Cr2N precipitates induces the decay of Vickers hardness,and the increment of cellular Cr2N causes the increase in the values.Impact toughness presents a monotonic decrease and SEM morphologies show the leading brittle intergranular fracture.The ultimate tensile strength(UTS),yield strength(YS)and elongation(El)deteriorate obviously.Stress concentration occurs when the matrix dislocations pile up at the interfaces of precipitation and matrix,and the interfacial dislocations may become precursors to the misfit dislocations,which can form small cleavage facets and accelerate the formation of cracks.展开更多
Most commercialized coronary stents are made of 316L stainless steels due to its good combination of properties, and currently some new stents are made of cobalt-based alloy owing to its higher mechanical properties. ...Most commercialized coronary stents are made of 316L stainless steels due to its good combination of properties, and currently some new stents are made of cobalt-based alloy owing to its higher mechanical properties. However, the presence of high quantity of nickel and/or cobalt elements in these materials, which are known to trigger the toxic and allergic responses, has caused many concerns. Nickel-free austenitic stainless steels have been developed in order to solve these problems. In this paper, based on the development of a new Fe- Cr-Mn-Mo-N type high nitrogen nickel-free austenitic stainless steel, properties such as mechanical property, corrosion resistance in Hankls solution, and in vitro blood compatibility including the kinetic clotting time and the platelets adhesion, were investigated in comparison to the above two conventional materials, a 316L stainless steel and a Co-28Cr-6Mo alloy. The results showed that the new high nitrogen steel possessed better combination of mechanical properties, corrosion resistance and blood compatibility than those of 316L steel and the Co-28Cr-OMo alloy, and can be a promising alternative material for manufacture of coronary stents.展开更多
The intergranular corrosion （IGC） behavior of high nitrogen austenitic stainless steel （HNSS） sensitization treated at 650-950℃ was investigated by the double loop electrochemical potentiodynamic reactivation （D...The intergranular corrosion （IGC） behavior of high nitrogen austenitic stainless steel （HNSS） sensitization treated at 650-950℃ was investigated by the double loop electrochemical potentiodynamic reactivation （DL-EPR） method. The effects of the electrolytes, scan rate, sensitizing temperature on the susceptibility to IGC of HNSS were examined. The results show that the addi-tion of NaCl is an effective way to improve the formation of the cracking of a passive film in chromium-depleted zones during the reactivation scan. Decreasing the scan rate exhibits an obvious effect on the breakdown of the passive film. A solution with 2 mol/L H2SO4＋1 mol/L NaCl＋0.01 mol/L KSCN is suitable to check the susceptibility to IGC of HNSS at a sensitizing temperature of 650-950℃ at a suitable scan rate of 1.667 mV/s. Chromium depletion of HNSS is attributed to the precipitation of Cr2N which results in the susceptibility to IGC. The synergistic effect of Mo and N is suggested to play an important role in stabilizing the passive film to prevent the attack of IGC.展开更多
In order to establish methods for indentification and screening of rice genotypes with high nitrogen （N） efficiency, N absorption efficiency （NAE）, N utilization efficiency （NUE） and N harvest index （NHI） in t...In order to establish methods for indentification and screening of rice genotypes with high nitrogen （N） efficiency, N absorption efficiency （NAE）, N utilization efficiency （NUE） and N harvest index （NHI） in ten rice genotypes were investgated at the elongation, booting, heading and maturity stages under six N levels in a pot experiment with soil-sand mixtures at various ratios. NAE in various rice genotypes firstly increased, peaked under a medium nitrogen rate of 0.177 g/kg and then decreased, but NUE and NHI always decreased with increasing nitrogen levels. NAE in various rice genotypes ever increased with growing process and NUE indicated a descending tendency of elongation stage〉heading stage〉maturity stage〉booting stage. N level influenced rice NAE, NUE and NHI most, followed by genotype, and the both effects were significant at 0.01 level. In addition, the interaction effects of genotype and nitrogen level on rice NAE and NUE were significant at 0.01 level, but not significant on rice NHI. Because the maximum differences of NAE and NUE were found at the elongation stage, it was thought to be the most suitable stage for identification and screening these two paremeters. Therefore, the optimum conditions for identification and screening of rice NAE, NUE and NHI in a pot experiment were the nitrogen rate of 0.157 g/kg at the elongation stage, low nitrogen at the elongation stage, and the nitrogen rate of 0.277 g/kg at the maturity stage, respectively.展开更多
Due to the excellent mechanical properties, good corrosion resistance, high biocompatibility and nickel- free character, the high nitrogen nickel-free austenitic stainless steel （HNASS） becomes an ideally alternativ...Due to the excellent mechanical properties, good corrosion resistance, high biocompatibility and nickel- free character, the high nitrogen nickel-free austenitic stainless steel （HNASS） becomes an ideally alternative material for coronary stents. Stent implantation works in harsh blood environment after a balloon dilatation, i.e., the material is used in a corrosive environment with a permanent deforma- tion. The present study attempts to investigate effects of pre-straining on high-cycle fatigue behavior and corrosion fatigue behavior of HNASS in Hank＇s solution and the relevant mechanism for coronary stents application. It is found that higher pre-straining on HNASS results in higher strength and maintains almost same corrosion resistance. Fatigue limit of 0% HNASS is 550 MPa, while corrosion fatigue limit is 475 MPa. And improvement in fatigue limit of 20% and 35% pre-strained HNASS is in comparison with the 0% HNASS, while corrosion would undermine the fatigue behavior of HNASS. In a suitable range, the pre- straining had a beneficial effect on corrosion fatigue strength of HNASS, such as nearly 300 MPa improved with 20% cold deformation. This result provides a good reference for predicting the life of HNASS stent and as well its design.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
Microstructure, hardness and fatigue properties of X30N high nitrogen stainless bearing steel were investigated. It was found that nitrogen addition could effectively reduce the amount and size of coarse carbides. The...Microstructure, hardness and fatigue properties of X30N high nitrogen stainless bearing steel were investigated. It was found that nitrogen addition could effectively reduce the amount and size of coarse carbides. The original austenite grain size was obviously refined. Additionally, more retained austenite was found in X30N steel after quenching at 1050 ℃, which could be reduced from about 30% to about 6% by cold treatment at - 73 ℃ and subsequent tempering, and thus, the ultimate hardness was increased up to about 61 HRC with reduction of austenite and precipitation of carbonitrides. Furthermore, the rolling contact fatigue lives of X30N steel ate superior to those of 440C steel, which was attributed to the enhanced hardness and a certain retained austenite in the high nitrogen steel.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
Aging precipitation and solid solution heat treatment were carried out on three steels which have chromium content of 18%, manganese content of 12%, 15%, 18%, and nitrogen content of 0.43%, 0.53%, 0.67%, respectively....Aging precipitation and solid solution heat treatment were carried out on three steels which have chromium content of 18%, manganese content of 12%, 15%, 18%, and nitrogen content of 0.43%, 0.53%, 0.67%, respectively. The mechanisms of precipitation and solid solution of high nitrogen anstenitic stainless steel were studied using the scanning electron microscopy, transmission electron microscopy, electron probe micro analysis and mechanical testing. The results show that, Cr2N is the primary precipitate in the tested stainless steels instead of Cr23C6. Cr2N nucleates at austenitic grain boundaries and grows towards inner grains with a lameUar morphology. By means of pre-precipitation of Cr2N at 800 ~C, the microstructure of the steels at solid solution state can be refined, thus improving the strength and plasticity. After the proposed treatment, the tensile strength, the proof strength and the elongation of the tested steel reach 881 MPa, 542 MPa and 54%, respectively.展开更多
High nitrogen and nickel-free austenitic stainless steel has received much recognition worldwide because it can solve the problem of ＂nickel-allergy＂ and has outstanding mechanical and physical properties. In this a...High nitrogen and nickel-free austenitic stainless steel has received much recognition worldwide because it can solve the problem of ＂nickel-allergy＂ and has outstanding mechanical and physical properties. In this article, 0Cr17Mn11Mo3N was prepared by powder injection molding （PIM） technique accompanied with solid-nitriding. The results show that the critical solid loading can achieve up to 64vol% by use of gas-atomized powders with the average size of 17.4 μm. The optimized sintefing conditions are determined to be 1300℃,2 h in flowing nitrogen atmosphere, at which the relative density reaches to 99% and the N content is as high as 0.78wt%. After solution annealing at 1150℃for 90 rain and water quench, the 0.2% yield strength, ultimate tensile strength （UTS）, elongation, reduction in area, and hardness can reach as high as 580 MPa, 885 MPa, 26.0%, 29.1%, and Hv 222, respectively.展开更多
Some municipal solid waste （MSW） can be used as the fuel. Combustion of MSW with high nitrogen content is successfully conducted in a lab-scale vortexing fluidized-bed incinerator （VFBI）. Pigskin with 16.5 wt.% ni...Some municipal solid waste （MSW） can be used as the fuel. Combustion of MSW with high nitrogen content is successfully conducted in a lab-scale vortexing fluidized-bed incinerator （VFBI）. Pigskin with 16.5 wt.% nitrogen content was used to simulate the high nitrogen content kitchen waste, and silica sand was used as the bed material. The effects of operating conditions, such as the bed temperature, freeboard temperature, excess oxygen ratio, and static bed height on the CO and NO concentrations at the exit of combustor and cyclone were investigated. The experimental results show that the freeboard temperature is the most important factor for CO emission. The order of operating conditions impact on the NO emission is： （1） excess oxygen ratio; （2） bed temperature; （3） freeboard temperature; and （4） static bed height. Utilizing cyclone can significantly reduce the CO emission concentration when the CO concentration released from the freeboard is higher than 50 ppm. On the other hand, the cyclone has no significant effect on the NO emission. Despite having high nitrogen content, a low conversion from fuel-N to NO was attained. Compared with other types of combustors, VFBI reduces the CO and NO emission concentrations much better when burning MSW with high nitrogen content.展开更多
Cytocompatibility of high nitrogen nickel-free stainless steel （HNS） with different nitrogen content was evalu- ated and compared with a conventional austenitic stainless steel 317L. The MTT assay （3-（4,5-dimethyl...Cytocompatibility of high nitrogen nickel-free stainless steel （HNS） with different nitrogen content was evalu- ated and compared with a conventional austenitic stainless steel 317L. The MTT assay （3-（4,5-dimethylthiazol- 2-yl）-2,5-diphenyltetrazolium bromide） was performed on MG63 osteoblasts to assess the cytotoxicity. The expression of selected marker typical of differentiated osteoblasts, such as alkaline phosphatase activity （AKP）, was also monitored in MG63 cells cultured on the tested materials. As a result, HNS had higher cell growth than 317L; meanwhile the cytocompatibility was increased with increasing nitrogen content. Furthermore, HNS enhanced osteoblasts differentiation, as confirmed by AKP activity. Overall these facts indicated that HNS had higher cytocompatibility than 317L and the nitrogen content contributed to the higher cytocompatibility of HNS. The influence of nitrogen on surface energy further explained the cytocompatibility of HNS.展开更多
During the high nitrogen steel （HNS） melting process, the absorption reaction of nitrogen in the liquid steel by blowing NH3 and N2 was investigated respectively. In order to obtain higher content of nitrogen in ste...During the high nitrogen steel （HNS） melting process, the absorption reaction of nitrogen in the liquid steel by blowing NH3 and N2 was investigated respectively. In order to obtain higher content of nitrogen in steel, the liquid steel should be deoxidized and desulfurized because the oxygen and sulfur as surface activity element are not favorable to the absorption of nitrogen in melting process. Based on the metallurgical thermodynamics, the coupling reaction of NH3 with oxygen can improve the generation of activity nitrogen atom in liquid steel. Nitrogen atom is easier to be absorbed than nitrogen molecule. At the same time, blowing ammonia gas can remove the oxygen from liquid steel and decrease the inclusion in the steel. Experiments of HNS melting were carried out in a 10 kg induction furnace, and the results indicated that for liquid steel containing the same content of alloys and blowing the same mole of nitrogen, the absorption effect of nitrogen by blowing NH3 is obviously higher than that of blowing N2. The technical process of melting HNS by blowing NH3 under normal pressure is feasible in industrial production.展开更多
基金supported by the National Natural Science Foundation of China(Grant Nos.52171010,52325406,51821001 and U1960203).
文摘High-nitrogen martensitic stainless steel(HNMSS)is increasingly recognized for its excellent strength-ductility balance and superior pitting resistance,largely attributed to the solid solution strengthening effect of nitrogen.Despite significant advancements in enhancing its mechanical properties,the precise relationship between alloying elements,particularly nickel(Ni),and microstructural evolution remains insufficiently understood.The role of Ni in HNMSS was investigated by examining the effects of two different Ni contents on microstructure and deformation mechanisms.A combination of mechanical testing and microstructural characterization was employed to assess the materials’mechanical properties and phase transformations.The key findings reveal that the steel with higher Ni content exhibits improved mechanical performance,primarily due to an increased volume fraction of retained austenite,which activates both transformation-induced plasticity and twinning-induced plasticity effects.The microstructure after deformation forms a similar multilayer core-shell structure,with twinning martensite enveloping the softer austenite,which effectively avoids the risk of cracking caused by direct collision of martensitic variants.
基金supported by the National Natural Science Foundation of China and Baosteel Group Corporation (No.50534010)
文摘Pitting corrosion and crevice corrosion behaviors of high nitrogen austenitic stainless steels （HNSS） were investigated by electrochemical and immersion testing methods in chloride solution, respectively. The chemical constitution and composition in the depth of passive films formed on HNSS were analyzed by X-ray photoelectron spectrum （XPS）. HNSS has excellent pitting and crevice corrosion resistance compared to 316L stainless steel. With increasing the nitrogen content in steels, pitting potentials and critical pitting temperature （CPT） increase, and the maximum, average pit depths and average weight loss decrease. The CPT of HNSS is correlated with the alloying element content through the measure of alloying for resistance to corrosion （MARC）. The MARC can be expressed as an equation of CPT=2.55MARC-29. XPS results show that HNSS exhibiting excellent corrosion resistance is attributed to the enrichment of nitrogen on the surface of passive films, which forms ammonium ions increasing the local pH value and facilitating repassivation, and the synergistic effects of molybdenum and nitrogen.
基金Item Sponsored by National Natural Science Foundation of China(50534010)
文摘A simple and feasible method for the production of high nitrogen austenitic stainless steels involves nitrogen gas alloying and adding nitrided ferroalloys under normal atmospheric conditions. Alloying by nitrogen gas bubbling in Fe-Cr-Mn-Mo series alloys was carried out in MoSi2 resistance furnace and air induction furnace under normal atmospheric conditions. The results showed that nitrogen alloying could be accelerated by increasing nitrogen gas flow rate, prolonging residence time of bubbles, increasing gas/molten steel interfaces, and decreasing the sulphur and oxygen contents in molten steel. Nitrogen content of 0.69% in 18Crl8Mn was obtained using air induction furnace by bubbling of nitrogen gas from porous plug. In addition, the nickel-free, high nitrogen austenitic stainless steels with sound and compact macrostructure had been produced in the laboratory using vacuum induction furnace and electroslag remelting furnace under nitrogen atmosphere by the addition of nitrided alloy with the maximum nitrogen content of 0.81%. Pores were observed in the ingots obtained by melting and casting in vacuum induction furnace with the addition of nitrided ferroalloys and under nitrogen atmosphere. After electroslag remelting of the cast ingots, they were all sound and were free of pores. The yield of nitrogen increased with the decrease of melting rate in the ESR process. Due to electroslag remelting under nitrogen atmosphere and the consequential addition of aluminum as deoxidizer to the slag, the loss of manganese decreased obviously. There existed mainly irregular Al2O3 inclusions and MnS inclusions in ESR ingots, and the size of most of the inclusions was less than 5 um. After homogenization of the hot rolled plate at 1 150℃ × 1 h followed by water quenching, the microstructure consisted of homogeneous austenite.
基金Item Sponsored by Key Program of National Natural Science Foundation of China (50534010)
文摘The fine grained structures of nickel-free high nitrogen austenitic stainless steels had been obtained by means of cold rolling and subsequent annealing. The relationship between microstructure and mechanical properties and gain size of nickel-free high nitrogen austenitic stainless steels was examined. High strength and good ductility of the steel were found. In the grain size range, the Hall-Petch dependency for yield stress, tensile strength, and hardness was valid for grain size ranges for the nickel-free high nitrogen austenitic stainless steel. In the present study, the ductility of cold rolled nickel-free high nitrogen austenitic stainless steel decreased with annealing time when the grain size was refined. The fracture surfaces of the tensile specimens in the grain size range were covered with dimples as usually seen in a ductile fracture mode.
基金supported by the National Natural Science Foundation of China(No.50534010)
文摘A series of high nitrogen austenitic stainless steels were successfully developed with a pressurized electroslag remelting furnace. Nitride additives and deoxidizer were packed into the stainless steel pipes, and then the stainless steel pipes were welded on the surface of an electrode with low nitrogen content to prepare a compound electrode. Using Si3N4 as a nitrogen alloying source, the silicon contents in the ingots were prone to be out of the specification range, the electric current fluctuated greatly and the surface qualities of the ingots were poor. The surface qualities of the ingots were improved with FeCrN as a nitrogen alloying source. The sound and compact macrostructure ingot with the maximum nitrogen content of 1.21wt% can be obtained. The 18Cr18Mn2Mo0.9N high nitrogen austenitic stainless steel exhibits high strength and good ductility at room temperature. The steel shows typical ductile-brittle transition behavior and excellent pitting corrosion resistance properties.
基金Item Sponsored by National Basic Research Programof China(2004CB619103)National Natural Science Foundation of China(50534010)
文摘The precipitation behavior of Cr2 N during isothermal aging in the temperature range from 700 ℃ to 950 ℃ in Fe-18Cr-12Mn-0.48N （in mass percent） high nitrogen austenitic stainless steel, including morphology and content of precipitate, was investigated using optical microscopy, scanning electron microscopy, and transmission electron microscopy. The isothermal precipitation kinetics curve of Cr2 N and the corresponding precipitation activation energy were obtained. The results show that Cr2N phase precipitates in a cellular way and its morphology is transformed from initial granular precipitates to lamellar ones in the cell with increasing aging time. The nose temperature of Cr2 N precipitation is about 800 ℃, with a corresponding incubation period of 30 min, and the ceiling temperature of Cr2N precipitation is 950℃. The diffusionactivation energy of Cr2 N precipitation is 296 kJ/mol.
基金The National Natural Science Foundation of China (No. 30170011)
文摘Three new bacteria HS-03, HS-043 and HS-047 isolated from different ecosystems were found capable of aerobic denitrification. The potential application of these strains in wastewater treatment under aerobic conditions was investigated, These three bacteria all presented high nitrogen removal from wastewater that more than 98% of 10 mmol/L nitrate could be removed in 12--24 h by adding cheap external carbon source and low concentration of iron as well as molybdate. The mechanism at molecular level was analyzed. The success of this aerobic denitrification applied to wastewater treatment may serve as an alternative to enhance the practical nitrogen removal from wastewater. Main biochemical and physiological features of these strains were characterized. The 16S rDNA sequences were compared with the published data in GenBank by using BLAST. The results of phenotype and genotype proved that strain HS-03 and HS-047 belonged to Pseudomonas stutzeri and Pseudomonas pseudoalcaligenes respectively. Strain HS-043 was identified as Delftia clcidovorans of which denitrifying activity has not previously been explored.
基金Item Sponsored by Key Program of National Science Foundation of China(50534010)Fundamental Research Funds for Central Universities of China(N100402015)
文摘The solution-treated(ST)condition and aging precipitation behavior of 18Cr-16Mn-2Mo-1.1N high nitrogen austenitic stainless steel(HNS)were investigated by optical microscope(OM),scanning electron microscope(SEM),and transmission electron microscope(TEM).The results show that the ST condition of 18Cr-16Mn-2Mo-1.1N HNS with wN above 1%is identified as 1100℃for 90 min,followed by water quenching to make sure the secondary phases completely dissolve into austenitic matrix and prevent the grains coarsening too much.Initial time-temperature-precipitation(TTP)curve of aged 18Cr-16Mn-2Mo-1.1N HNS which starts with precipitation of 0.05%in volume fraction is defined and the'nose'temperature of precipitation is found to be 850℃with an incubation period of 1 min.Hexagonal intergranular and cellular Cr2N with a=0.478 nm and c=0.444 nm precipitates gradually increase in the isothermal aging treatment.The matrix nitrogen depletion due to the intergranular and a few cellular Cr2N precipitates induces the decay of Vickers hardness,and the increment of cellular Cr2N causes the increase in the values.Impact toughness presents a monotonic decrease and SEM morphologies show the leading brittle intergranular fracture.The ultimate tensile strength(UTS),yield strength(YS)and elongation(El)deteriorate obviously.Stress concentration occurs when the matrix dislocations pile up at the interfaces of precipitation and matrix,and the interfacial dislocations may become precursors to the misfit dislocations,which can form small cleavage facets and accelerate the formation of cracks.
基金supported by the National Natural Science Foundation of China (No. 31000428)a funding from Chinese Academy of Sciences (No.KGCX2-YW-207)
文摘Most commercialized coronary stents are made of 316L stainless steels due to its good combination of properties, and currently some new stents are made of cobalt-based alloy owing to its higher mechanical properties. However, the presence of high quantity of nickel and/or cobalt elements in these materials, which are known to trigger the toxic and allergic responses, has caused many concerns. Nickel-free austenitic stainless steels have been developed in order to solve these problems. In this paper, based on the development of a new Fe- Cr-Mn-Mo-N type high nitrogen nickel-free austenitic stainless steel, properties such as mechanical property, corrosion resistance in Hankls solution, and in vitro blood compatibility including the kinetic clotting time and the platelets adhesion, were investigated in comparison to the above two conventional materials, a 316L stainless steel and a Co-28Cr-6Mo alloy. The results showed that the new high nitrogen steel possessed better combination of mechanical properties, corrosion resistance and blood compatibility than those of 316L steel and the Co-28Cr-OMo alloy, and can be a promising alternative material for manufacture of coronary stents.
基金supported by the National Natural Science Foundation of China (No.50534010) and Baosteel Group Corporation
文摘The intergranular corrosion （IGC） behavior of high nitrogen austenitic stainless steel （HNSS） sensitization treated at 650-950℃ was investigated by the double loop electrochemical potentiodynamic reactivation （DL-EPR） method. The effects of the electrolytes, scan rate, sensitizing temperature on the susceptibility to IGC of HNSS were examined. The results show that the addi-tion of NaCl is an effective way to improve the formation of the cracking of a passive film in chromium-depleted zones during the reactivation scan. Decreasing the scan rate exhibits an obvious effect on the breakdown of the passive film. A solution with 2 mol/L H2SO4＋1 mol/L NaCl＋0.01 mol/L KSCN is suitable to check the susceptibility to IGC of HNSS at a sensitizing temperature of 650-950℃ at a suitable scan rate of 1.667 mV/s. Chromium depletion of HNSS is attributed to the precipitation of Cr2N which results in the susceptibility to IGC. The synergistic effect of Mo and N is suggested to play an important role in stabilizing the passive film to prevent the attack of IGC.
基金supported by the National High-Tech Research&Development program(Grant No.2003AA206030)the National Natural Science Foundation of China(Grant No.30030090)
文摘In order to establish methods for indentification and screening of rice genotypes with high nitrogen （N） efficiency, N absorption efficiency （NAE）, N utilization efficiency （NUE） and N harvest index （NHI） in ten rice genotypes were investgated at the elongation, booting, heading and maturity stages under six N levels in a pot experiment with soil-sand mixtures at various ratios. NAE in various rice genotypes firstly increased, peaked under a medium nitrogen rate of 0.177 g/kg and then decreased, but NUE and NHI always decreased with increasing nitrogen levels. NAE in various rice genotypes ever increased with growing process and NUE indicated a descending tendency of elongation stage〉heading stage〉maturity stage〉booting stage. N level influenced rice NAE, NUE and NHI most, followed by genotype, and the both effects were significant at 0.01 level. In addition, the interaction effects of genotype and nitrogen level on rice NAE and NUE were significant at 0.01 level, but not significant on rice NHI. Because the maximum differences of NAE and NUE were found at the elongation stage, it was thought to be the most suitable stage for identification and screening these two paremeters. Therefore, the optimum conditions for identification and screening of rice NAE, NUE and NHI in a pot experiment were the nitrogen rate of 0.157 g/kg at the elongation stage, low nitrogen at the elongation stage, and the nitrogen rate of 0.277 g/kg at the maturity stage, respectively.
基金supported financially by the National Natural Science Foundation of China (No. 31370976)
文摘Due to the excellent mechanical properties, good corrosion resistance, high biocompatibility and nickel- free character, the high nitrogen nickel-free austenitic stainless steel （HNASS） becomes an ideally alternative material for coronary stents. Stent implantation works in harsh blood environment after a balloon dilatation, i.e., the material is used in a corrosive environment with a permanent deforma- tion. The present study attempts to investigate effects of pre-straining on high-cycle fatigue behavior and corrosion fatigue behavior of HNASS in Hank＇s solution and the relevant mechanism for coronary stents application. It is found that higher pre-straining on HNASS results in higher strength and maintains almost same corrosion resistance. Fatigue limit of 0% HNASS is 550 MPa, while corrosion fatigue limit is 475 MPa. And improvement in fatigue limit of 20% and 35% pre-strained HNASS is in comparison with the 0% HNASS, while corrosion would undermine the fatigue behavior of HNASS. In a suitable range, the pre- straining had a beneficial effect on corrosion fatigue strength of HNASS, such as nearly 300 MPa improved with 20% cold deformation. This result provides a good reference for predicting the life of HNASS stent and as well its design.
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This research is supported by the National Natural Science Foundation of China （No. 51371057）, the National Key Research and Development Plan （No. 2016YFB0300101） and Beijing Natural Science Foundation （No. 2182088）.
文摘Microstructure, hardness and fatigue properties of X30N high nitrogen stainless bearing steel were investigated. It was found that nitrogen addition could effectively reduce the amount and size of coarse carbides. The original austenite grain size was obviously refined. Additionally, more retained austenite was found in X30N steel after quenching at 1050 ℃, which could be reduced from about 30% to about 6% by cold treatment at - 73 ℃ and subsequent tempering, and thus, the ultimate hardness was increased up to about 61 HRC with reduction of austenite and precipitation of carbonitrides. Furthermore, the rolling contact fatigue lives of X30N steel ate superior to those of 440C steel, which was attributed to the enhanced hardness and a certain retained austenite in the high nitrogen steel.
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）.
基金Project(50974014) supported by the National Natural Science Foundation of China
文摘Aging precipitation and solid solution heat treatment were carried out on three steels which have chromium content of 18%, manganese content of 12%, 15%, 18%, and nitrogen content of 0.43%, 0.53%, 0.67%, respectively. The mechanisms of precipitation and solid solution of high nitrogen anstenitic stainless steel were studied using the scanning electron microscopy, transmission electron microscopy, electron probe micro analysis and mechanical testing. The results show that, Cr2N is the primary precipitate in the tested stainless steels instead of Cr23C6. Cr2N nucleates at austenitic grain boundaries and grows towards inner grains with a lameUar morphology. By means of pre-precipitation of Cr2N at 800 ~C, the microstructure of the steels at solid solution state can be refined, thus improving the strength and plasticity. After the proposed treatment, the tensile strength, the proof strength and the elongation of the tested steel reach 881 MPa, 542 MPa and 54%, respectively.
文摘High nitrogen and nickel-free austenitic stainless steel has received much recognition worldwide because it can solve the problem of ＂nickel-allergy＂ and has outstanding mechanical and physical properties. In this article, 0Cr17Mn11Mo3N was prepared by powder injection molding （PIM） technique accompanied with solid-nitriding. The results show that the critical solid loading can achieve up to 64vol% by use of gas-atomized powders with the average size of 17.4 μm. The optimized sintefing conditions are determined to be 1300℃,2 h in flowing nitrogen atmosphere, at which the relative density reaches to 99% and the N content is as high as 0.78wt%. After solution annealing at 1150℃for 90 rain and water quench, the 0.2% yield strength, ultimate tensile strength （UTS）, elongation, reduction in area, and hardness can reach as high as 580 MPa, 885 MPa, 26.0%, 29.1%, and Hv 222, respectively.
基金sponsored by the National Natural Science Foundation of China (No. 99-2221-E-003-057)
文摘Some municipal solid waste （MSW） can be used as the fuel. Combustion of MSW with high nitrogen content is successfully conducted in a lab-scale vortexing fluidized-bed incinerator （VFBI）. Pigskin with 16.5 wt.% nitrogen content was used to simulate the high nitrogen content kitchen waste, and silica sand was used as the bed material. The effects of operating conditions, such as the bed temperature, freeboard temperature, excess oxygen ratio, and static bed height on the CO and NO concentrations at the exit of combustor and cyclone were investigated. The experimental results show that the freeboard temperature is the most important factor for CO emission. The order of operating conditions impact on the NO emission is： （1） excess oxygen ratio; （2） bed temperature; （3） freeboard temperature; and （4） static bed height. Utilizing cyclone can significantly reduce the CO emission concentration when the CO concentration released from the freeboard is higher than 50 ppm. On the other hand, the cyclone has no significant effect on the NO emission. Despite having high nitrogen content, a low conversion from fuel-N to NO was attained. Compared with other types of combustors, VFBI reduces the CO and NO emission concentrations much better when burning MSW with high nitrogen content.
基金supported by the National Natural Science Foundation of China (No. 31000428)the National Basic Research Program of China ("973 Program",No. 2012CB619101)
文摘Cytocompatibility of high nitrogen nickel-free stainless steel （HNS） with different nitrogen content was evalu- ated and compared with a conventional austenitic stainless steel 317L. The MTT assay （3-（4,5-dimethylthiazol- 2-yl）-2,5-diphenyltetrazolium bromide） was performed on MG63 osteoblasts to assess the cytotoxicity. The expression of selected marker typical of differentiated osteoblasts, such as alkaline phosphatase activity （AKP）, was also monitored in MG63 cells cultured on the tested materials. As a result, HNS had higher cell growth than 317L; meanwhile the cytocompatibility was increased with increasing nitrogen content. Furthermore, HNS enhanced osteoblasts differentiation, as confirmed by AKP activity. Overall these facts indicated that HNS had higher cytocompatibility than 317L and the nitrogen content contributed to the higher cytocompatibility of HNS. The influence of nitrogen on surface energy further explained the cytocompatibility of HNS.
文摘During the high nitrogen steel （HNS） melting process, the absorption reaction of nitrogen in the liquid steel by blowing NH3 and N2 was investigated respectively. In order to obtain higher content of nitrogen in steel, the liquid steel should be deoxidized and desulfurized because the oxygen and sulfur as surface activity element are not favorable to the absorption of nitrogen in melting process. Based on the metallurgical thermodynamics, the coupling reaction of NH3 with oxygen can improve the generation of activity nitrogen atom in liquid steel. Nitrogen atom is easier to be absorbed than nitrogen molecule. At the same time, blowing ammonia gas can remove the oxygen from liquid steel and decrease the inclusion in the steel. Experiments of HNS melting were carried out in a 10 kg induction furnace, and the results indicated that for liquid steel containing the same content of alloys and blowing the same mole of nitrogen, the absorption effect of nitrogen by blowing NH3 is obviously higher than that of blowing N2. The technical process of melting HNS by blowing NH3 under normal pressure is feasible in industrial production.
