The effects of deformation temperature on the transformation-induced plasticity(TRIP)-aided 304L,twinning-induced plasti-city(TWIP)-assisted 316L,and highly alloyed stable 904L austenitic stainless steels were compare...The effects of deformation temperature on the transformation-induced plasticity(TRIP)-aided 304L,twinning-induced plasti-city(TWIP)-assisted 316L,and highly alloyed stable 904L austenitic stainless steels were compared for the first time to tune the mechan-ical properties,strengthening mechanisms,and strength-ductility synergy.For this purpose,the scanning electron microscopy(SEM),electron backscattered diffraction(EBSD),X-ray diffraction(XRD),tensile testing,work-hardening analysis,and thermodynamics calcu-lations were used.The induced plasticity effects led to a high temperature-dependency of work-hardening behavior in the 304L and 316L stainless steels.As the deformation temperature increased,the metastable 304L stainless steel showed the sequence of TRIP,TWIP,and weakening of the induced plasticity mechanism;while the disappearance of the TWIP effect in the 316L stainless steel was also observed.However,the solid-solution strengthening in the 904L superaustenitic stainless steel maintained the tensile properties over a wide temper-ature range,surpassing the performance of 304L and 316L stainless steels.In this regard,the dependency of the total elongation on the de-formation temperature was less pronounced for the 904L alloy due to the absence of additional plasticity mechanisms.These results re-vealed the importance of solid-solution strengthening and the associated high friction stress for superior mechanical behavior over a wide temperature range.展开更多
Excellent weldability substantially contributes to the intrinsic quality of steels,while appropriate chemical composition plays a primary role in the essential weldability of steels.The poor weldability of ferritic st...Excellent weldability substantially contributes to the intrinsic quality of steels,while appropriate chemical composition plays a primary role in the essential weldability of steels.The poor weldability of ferritic stainless steels could be improved through modification with minor alloy elements while minimally increasing the cost.Therefore,studying the effect of minor alloy elements on the weldability of steels is of considerable importance.In this study,several steels of middle-chromium hyperpure ferritic stainless 00Cr21Ti with different Ni content(0.3%,0.5%,0.8%,and 1.0%)were developed,and their weldabilities of butt joint samples welded using the metal inert gas welding process,including the influence of welded joints on the microstructure,tensile performance,corrosion resistance,and fatigue property,were investigated.Results show that the steels with w(Ni)≥0.8%exhibit excellent mechanical properties compared with those with low-Ni content steels,further,their impact toughness at normal atmospheric temperature meets the industrial application standard and the fatigue property is similar to that of 304 austenitic stainless steel.Moreover,results show that the corrosion resistance of all the samples is almost at the same level.The results acquired in this study are supposed to be useful for the optimization of the chemical composition of stainless steels aiming to improve weldability.展开更多
Duplex stainless steels(DSSs)show better corrosion resistance with higher strength than traditional austenite stainless steels in many aggressive environments,and can be welded properly with almost every welding proce...Duplex stainless steels(DSSs)show better corrosion resistance with higher strength than traditional austenite stainless steels in many aggressive environments,and can be welded properly with almost every welding processes,if proper heat input is provided.Progresses of research works on weldability of DSSs in recent years are reviewed in this paper.Balance control of ferrite/austenite phases is most important for DSSs welding.The phases balance can be controlled with filler materials,nitrogen addition in shielding gas,heat input,post weld heat treatment,and alternating magnetic field.Too high cooling rate results in not only extra ferrite,but also chromium nitride precipitation.While too low cooling rate or heating repeatedly results in precipitation of secondary austenite and intermetallic compounds.In both situations,mechanical properties and corrosion resistance of the DSS joints deteriorate.Recommended upper and lower limits of heat input and maximum interpass temperature should be observed.展开更多
Effects of nucleation sites and diffusivity enhancement of chromium on reverted transformation of AISI 304 stainless steel during annealing process were investigated.Dynamics calculation revealed that the reverted tra...Effects of nucleation sites and diffusivity enhancement of chromium on reverted transformation of AISI 304 stainless steel during annealing process were investigated.Dynamics calculation revealed that the reverted transformation of strain-inducedα’-martensite→γaustenite could were closely associated with active nucleation sites and diffusivity enhancement of chromium in nanocrystallineα’-martensite.The experimental data and the results were in accordance with 2-grain austenite/α’-martensite junctions calculated theoretically,which could result from high chromium diffusion rate in nanocrystallineα’-martensite.In addition,low temperature is not conducive to reversed transformation,while high temperature and long annealing time will lead to inhomogeneous grain size distribution.展开更多
Phase transformation is one of the factors that would significantly influence the ability to resist cavitation erosion of stainless steels. Due to the specific properties of duplex stainless steel, the heat treatment ...Phase transformation is one of the factors that would significantly influence the ability to resist cavitation erosion of stainless steels. Due to the specific properties of duplex stainless steel, the heat treatment would bring about significant phase transformations. In this paper, we have examined the previous studies on the phase transition of stainless steel, including the literature on the classification of stainless steel, spinodal decomposition, sigma phase transformation, and cavitation erosion of double stainless steel. Through these literature investigations, the destruction of cavitation erosion on duplex stainless steel can be clearly known, and the causes of failure of duplex stainless steel in seawater can be clarified, thus providing a theoretical basis for subsequent scientific research. And the review is about to help assess the possibility of using bulk heat treatment to improve the cavitation erosion (CE) behaviour of the duplex stainless steel 7MoPLUS.展开更多
Duplex stainless steels(DSSs)used in subsea structures and desalination industries require high corrosion and erosion resistance as well as excellent mechanical properties.The newly introduced cast duplex grade ASTM A...Duplex stainless steels(DSSs)used in subsea structures and desalination industries require high corrosion and erosion resistance as well as excellent mechanical properties.The newly introduced cast duplex grade ASTM A8907 A has a unique composition and is expected to have a much better resistance to corrosion and erosion compared with the super-duplex grades 5 A and 6 A.This work is a comparative study of the mechanical properties,corrosion,and erosion-corrosion resistance of super-duplex grades 5 A and 6 A and the hyper-duplex grade 7 A.The three DSSs exhibited equiaxial austenite islands in the ferrite matrix and balanced phase ratios.The hardness of the grade 7 A was nearly 15%higher than those of the super-duplex grades,which is attributed to the effect of the higher contents of W and Mn in 7 A.The impact toughness of grade 7 A was found to be lower than those of the super-duplex grades due to the carbide precipitation resulting from the partial substitution of Mo with W.The oxide layer strengthening effect of rare earth elements and the higher pitting resistance equivalent number(PREN)of grade7 A resulted in higher corrosion resistance.The harder and more passive grade 7 A showed a 35%lower material loss during erosion-corrosion.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
Austenite antibacterial stainless steels have been found to have wide applications in hospitals and food industries. In recent years epsilon copper precipitation in antibacterial stainless steels has obtained much res...Austenite antibacterial stainless steels have been found to have wide applications in hospitals and food industries. In recent years epsilon copper precipitation in antibacterial stainless steels has obtained much research interest due to its antibacterial action. The objective of this study was to determine the effects of nitrogen concentration on the precipitation of epsilon copper and antibacterial property. Two kinds of austenite antibacterial stainless steels containing copper and different nitrogen concentration (0.02 and 0.08 wt pct, respectively) were prepared and the microstructures were characterized by a combination of electron microscopy and thermodynamic analysis. A mathematical expression was deduced to predict the effect of nitrogen concentration on the activity coefficient of copper, In(fCu/f^0cu)=0.53524+4.11xN-0.48x^2N. Higher nitrogen was found to increase the free energy difference of copper concentration distribution between precipitation phase and austenite matrix, stimulate the aggregation of copper atoms from austenite, increase the precipitation amount and consequently enhance the antibacterial property of steel.展开更多
The influence of welding speed on the joint microstructures of an austenitic stainless steel(ASS)produced by friction stir welding(FSW)was investigated.The FSW process was conducted using a rotational speed of 400 r/m...The influence of welding speed on the joint microstructures of an austenitic stainless steel(ASS)produced by friction stir welding(FSW)was investigated.The FSW process was conducted using a rotational speed of 400 r/min and welding speeds of 50 and 150 mm/min.The study was carried out using electron backscattered diffraction(EBSD)technique in different regions of the resultant stir zones(SZs).The results show that the texture of the advancing side(AS)was mainly composed of C{001}〈110〉and cube{001}〈100〉texture components along with partial B/B{112}〈110〉component.Moving from the AS toward the center and the retreating side(RS),the cube texture component disappeared and the A;/A*{111}(112)component developed and predominated the other components.Higher welding speed greatly affected and decreased the intensity of the textures in the resultant SZs.Moreover,higher welding speed(lower heat input)resulted in lower frequency of cube texture in the AS.展开更多
In recent years, with attention paid to global environmental problems, there have been requirements for continuous improvement of automobile fuel economy and exhaust gas purification rate. The properties of the ferrit...In recent years, with attention paid to global environmental problems, there have been requirements for continuous improvement of automobile fuel economy and exhaust gas purification rate. The properties of the ferritic stainless steels (FSS) used to make automobile parts have been improved. This paper introduces the construction of automotive exhaust systems and describes their main failure behaviors and corrosion evaluation procedures.展开更多
Some new Ni-saving 25Cr duplex stainless steels(DSS)have been developed.The results indicate that the alloy has a balanced ferrite-austenite relation after hot forge and solid solution treatment at 1 000℃. The elemen...Some new Ni-saving 25Cr duplex stainless steels(DSS)have been developed.The results indicate that the alloy has a balanced ferrite-austenite relation after hot forge and solid solution treatment at 1 000℃. The elements W and Cu have a marked effect on the microstructure of the alloy.The pitting potential of the steel adding W and Cu elements reaches the maximum value of 435 mV.The tensile strength and percentage of area reduction of all steels in this paper are 800 -900 MPa and 60%-70%,respectively.The tensile elongations of the alloys are all above 30%.The experimental steels have good corrosion and mechanical property.展开更多
The investigation on toxicity of stainless steel has been reviewed. Many countries have established laws to guarantee food safety of stainless steel containers. The development of food safety standards with respect to...The investigation on toxicity of stainless steel has been reviewed. Many countries have established laws to guarantee food safety of stainless steel containers. The development of food safety standards with respect to the use of stainless steels in China has been analyzed. Influence of stainless steel grades and food ingredients on the release of metal ions has been reviewed briefly. The effect of surface condition on the release of metal ions has also been analyzed. Finally, the food safety issues with respect to the use of stainless steel products have been presented systematically.展开更多
An improved three-dimensional (3-D) experimental visualization methodology is presented tor evaluating the fracture mechanisms of ferritic stainless steels by in-situ tensile testing with an environmental scanning e...An improved three-dimensional (3-D) experimental visualization methodology is presented tor evaluating the fracture mechanisms of ferritic stainless steels by in-situ tensile testing with an environmental scanning electron microscope (ESEM). The samples were machined with a radial notched shape and a sloped surface. Both planar surface deformation and sloping surface deformation-induced microvoids were observed during dynamic tension experiments, where a greater amount of information could be obtained from the sloping surface. The results showed that microvoids formed at the grain boundaries of highly elongated large grains. The microvoids nucleated in the severely deformed regions grew nearly parallel to the tensile axis, predominantly along the grain boundaries. The microvoids nucleated at the interface of particles and the matrix did not propagate due to the high plasticity of the matrix. The large microvoids propagated and showed a zigzag shape along the grain boundaries,seemingly a consequence of the fracture of the slip bands caused by dislocation pile-ups. The final failure took place due to the reduction of the load-beating area.展开更多
A review is given concerning some of the recent industrial developments of stainless steels. In austenitic stainless steels,two different directions of alloy development are noticeable:low nickel austenitic stainless ...A review is given concerning some of the recent industrial developments of stainless steels. In austenitic stainless steels,two different directions of alloy development are noticeable:low nickel austenitic stainless steels and high nitrogen stainless steels.In these two cases the aims are different,particularly in terms of strength,but the philosophy of alloy development and the scientific approaches are very similar and they all revolve about the role of nitrogen as an alloying element and how this affects strength,ductility and corrosion resistance. There is now a broad and useful basis of information as to how nitrogen affects solid solution hardening,grain boundary hardening and work hardening and how to make use of these effects in developing materials required by the world market. In the field of corrosion resistance,ferritic,duplex and austenitic stainless steels compete with each other and now there is a growing body of information concerning the relative corrosion resistance based on laboratory data. However,for practical applications and for alloy selection,more than just laboratory data are needed,and thus,the first results are presented here of a many years comparison of the corrosion resistance of 24 commercial stainless steels exposed to corrosion in outdoors marine atmosphere.Hope is expressed to involve in the near future even more steels from a wider range of manufacturers in such corrosion studies.This might help consumers in appropriate alloy selection.It might also help steel makers in developing appropriate stainless steel grades.展开更多
The effect of thermal aging on the fatigue crack growth(FCG) behavior of Z3CN20?09M cast duplex stainless steel with low ferrite content was investigated in this study. The crack surfaces and crack growth paths wer...The effect of thermal aging on the fatigue crack growth(FCG) behavior of Z3CN20?09M cast duplex stainless steel with low ferrite content was investigated in this study. The crack surfaces and crack growth paths were analyzed to clarify the FCG mechanisms. The microstructure and micromechanical properties before and after thermal aging were also studied. Spinodal decomposition in the aged ferrite phase led to an increase in the hardness and a decrease in the plastic deformation capacity, whereas the hardness and plastic deformation capacity of the austenite phase were almost unchanged after thermal aging. The aged material exhibited a better FCG resistance than the unaged material in the near-threshold regime because of the increased roughness-induced crack closure associated with the tortuous crack path and rougher fracture surface; however, the tendency was reversed in the Paris regime because of the cleavage fracture in the aged ferrite phases.展开更多
The grades of ultra-pure ferritic stainless steels, especially the grades used in automobile exhaust system, were reviewed. The dependence of properties on alloying elements, the refining facilities, and the mechanism...The grades of ultra-pure ferritic stainless steels, especially the grades used in automobile exhaust system, were reviewed. The dependence of properties on alloying elements, the refining facilities, and the mechanism of the reactions in steel melts were described in detail. Vacuum, strong stirring, and powder injection proved to be effective technologies in the melting of ultra-pure ferritic stainless steels. The application of the ferritic grades was also briefly introduced.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
The effect of aging temperature on erosion corrosion (E-C) behavior of 17-4PH stainless steels in dilute sulphuric acid slurry containing solid particles was studied by using self-made rotating E-C apparatus. The ef...The effect of aging temperature on erosion corrosion (E-C) behavior of 17-4PH stainless steels in dilute sulphuric acid slurry containing solid particles was studied by using self-made rotating E-C apparatus. The effect of impact velocity on EC behavior of 17 4PH steels at different aging temperatures was analyzed. Surface micrographs of the specimens after E C test were observed by using scanning electron microscope (SEM). The results showed that under the condition of the same solution heat treatment, when aging temperature ranged from 400 ℃ to 610℃, the hardness reached the highest value near the temperature 460℃. The characteristics of E-C for 17-4PH stainless steels at different aging temperatures were as follows: pure erosion (wear) was dominant, corrosion was subordinate and at the same time corrosion promoted erosion. The effect of aging temperature on E-C rate of 17-4PH steels was not significant at low impact velocity, but it was found that E-C resistance of 17-4PH steels aged near 460℃ was the most excellent due to the best precipitation strengthening effect of fine and dispersed e-Cu phase. With a prerequisite of appropriate corrosion resistance, the precipitation hardening could significantly improve the E-C resistance of the materials.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
Silver or copper ions are often chosen as antibacterial agents. But a few reports are concerned with these two antibacterial agents for preparation of antibacterial stainless steel (SS). The antibacterial properties...Silver or copper ions are often chosen as antibacterial agents. But a few reports are concerned with these two antibacterial agents for preparation of antibacterial stainless steel (SS). The antibacterial properties and corrosion resistance of AISI 420 stainless steel implanted by silver and copper ions were investigated. Due to the cooperative antibacterial effect of silver and copper ions, the Ag/Cu implanted SS showed excellent antibacterial activities against both Gram-negative Escherichia coli (E. coli) and Gram-positive Staphylococcus aureus (S. aureus) at a total implantation dose of 2~ 1017 ions/cm2. Electrochemical polarization curves revealed that the corrosion resistance of Ag/Cu implanted SS was slightly enhanced as compared with that of un-implanted SS, The implanted layer was characterized by X-ray photoelec- tron spectroscopy (XPS). Core level XPS spectra indicate that the implanted silver and copper ions exist in metallic state in the implanted layer.展开更多
基金Saeed Sadeghpour would like to thank Jane,Aatos Erkon säätiö(JAES),and Tiina ja Antti Herlinin säätiö(TAHS)for their financial support on Advanced Steels for Green Planet Project.The authors would also like to greatly thank the members of the“Formability Laboratory”and“Advanced Steels and Thermomechanically Processed Engineering Ma-terials Laboratory”for their help and support。
文摘The effects of deformation temperature on the transformation-induced plasticity(TRIP)-aided 304L,twinning-induced plasti-city(TWIP)-assisted 316L,and highly alloyed stable 904L austenitic stainless steels were compared for the first time to tune the mechan-ical properties,strengthening mechanisms,and strength-ductility synergy.For this purpose,the scanning electron microscopy(SEM),electron backscattered diffraction(EBSD),X-ray diffraction(XRD),tensile testing,work-hardening analysis,and thermodynamics calcu-lations were used.The induced plasticity effects led to a high temperature-dependency of work-hardening behavior in the 304L and 316L stainless steels.As the deformation temperature increased,the metastable 304L stainless steel showed the sequence of TRIP,TWIP,and weakening of the induced plasticity mechanism;while the disappearance of the TWIP effect in the 316L stainless steel was also observed.However,the solid-solution strengthening in the 904L superaustenitic stainless steel maintained the tensile properties over a wide temper-ature range,surpassing the performance of 304L and 316L stainless steels.In this regard,the dependency of the total elongation on the de-formation temperature was less pronounced for the 904L alloy due to the absence of additional plasticity mechanisms.These results re-vealed the importance of solid-solution strengthening and the associated high friction stress for superior mechanical behavior over a wide temperature range.
文摘Excellent weldability substantially contributes to the intrinsic quality of steels,while appropriate chemical composition plays a primary role in the essential weldability of steels.The poor weldability of ferritic stainless steels could be improved through modification with minor alloy elements while minimally increasing the cost.Therefore,studying the effect of minor alloy elements on the weldability of steels is of considerable importance.In this study,several steels of middle-chromium hyperpure ferritic stainless 00Cr21Ti with different Ni content(0.3%,0.5%,0.8%,and 1.0%)were developed,and their weldabilities of butt joint samples welded using the metal inert gas welding process,including the influence of welded joints on the microstructure,tensile performance,corrosion resistance,and fatigue property,were investigated.Results show that the steels with w(Ni)≥0.8%exhibit excellent mechanical properties compared with those with low-Ni content steels,further,their impact toughness at normal atmospheric temperature meets the industrial application standard and the fatigue property is similar to that of 304 austenitic stainless steel.Moreover,results show that the corrosion resistance of all the samples is almost at the same level.The results acquired in this study are supposed to be useful for the optimization of the chemical composition of stainless steels aiming to improve weldability.
文摘Duplex stainless steels(DSSs)show better corrosion resistance with higher strength than traditional austenite stainless steels in many aggressive environments,and can be welded properly with almost every welding processes,if proper heat input is provided.Progresses of research works on weldability of DSSs in recent years are reviewed in this paper.Balance control of ferrite/austenite phases is most important for DSSs welding.The phases balance can be controlled with filler materials,nitrogen addition in shielding gas,heat input,post weld heat treatment,and alternating magnetic field.Too high cooling rate results in not only extra ferrite,but also chromium nitride precipitation.While too low cooling rate or heating repeatedly results in precipitation of secondary austenite and intermetallic compounds.In both situations,mechanical properties and corrosion resistance of the DSS joints deteriorate.Recommended upper and lower limits of heat input and maximum interpass temperature should be observed.
文摘Effects of nucleation sites and diffusivity enhancement of chromium on reverted transformation of AISI 304 stainless steel during annealing process were investigated.Dynamics calculation revealed that the reverted transformation of strain-inducedα’-martensite→γaustenite could were closely associated with active nucleation sites and diffusivity enhancement of chromium in nanocrystallineα’-martensite.The experimental data and the results were in accordance with 2-grain austenite/α’-martensite junctions calculated theoretically,which could result from high chromium diffusion rate in nanocrystallineα’-martensite.In addition,low temperature is not conducive to reversed transformation,while high temperature and long annealing time will lead to inhomogeneous grain size distribution.
文摘Phase transformation is one of the factors that would significantly influence the ability to resist cavitation erosion of stainless steels. Due to the specific properties of duplex stainless steel, the heat treatment would bring about significant phase transformations. In this paper, we have examined the previous studies on the phase transition of stainless steel, including the literature on the classification of stainless steel, spinodal decomposition, sigma phase transformation, and cavitation erosion of double stainless steel. Through these literature investigations, the destruction of cavitation erosion on duplex stainless steel can be clearly known, and the causes of failure of duplex stainless steel in seawater can be clarified, thus providing a theoretical basis for subsequent scientific research. And the review is about to help assess the possibility of using bulk heat treatment to improve the cavitation erosion (CE) behaviour of the duplex stainless steel 7MoPLUS.
文摘Duplex stainless steels(DSSs)used in subsea structures and desalination industries require high corrosion and erosion resistance as well as excellent mechanical properties.The newly introduced cast duplex grade ASTM A8907 A has a unique composition and is expected to have a much better resistance to corrosion and erosion compared with the super-duplex grades 5 A and 6 A.This work is a comparative study of the mechanical properties,corrosion,and erosion-corrosion resistance of super-duplex grades 5 A and 6 A and the hyper-duplex grade 7 A.The three DSSs exhibited equiaxial austenite islands in the ferrite matrix and balanced phase ratios.The hardness of the grade 7 A was nearly 15%higher than those of the super-duplex grades,which is attributed to the effect of the higher contents of W and Mn in 7 A.The impact toughness of grade 7 A was found to be lower than those of the super-duplex grades due to the carbide precipitation resulting from the partial substitution of Mo with W.The oxide layer strengthening effect of rare earth elements and the higher pitting resistance equivalent number(PREN)of grade7 A resulted in higher corrosion resistance.The harder and more passive grade 7 A showed a 35%lower material loss during erosion-corrosion.
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.
文摘Austenite antibacterial stainless steels have been found to have wide applications in hospitals and food industries. In recent years epsilon copper precipitation in antibacterial stainless steels has obtained much research interest due to its antibacterial action. The objective of this study was to determine the effects of nitrogen concentration on the precipitation of epsilon copper and antibacterial property. Two kinds of austenite antibacterial stainless steels containing copper and different nitrogen concentration (0.02 and 0.08 wt pct, respectively) were prepared and the microstructures were characterized by a combination of electron microscopy and thermodynamic analysis. A mathematical expression was deduced to predict the effect of nitrogen concentration on the activity coefficient of copper, In(fCu/f^0cu)=0.53524+4.11xN-0.48x^2N. Higher nitrogen was found to increase the free energy difference of copper concentration distribution between precipitation phase and austenite matrix, stimulate the aggregation of copper atoms from austenite, increase the precipitation amount and consequently enhance the antibacterial property of steel.
文摘The influence of welding speed on the joint microstructures of an austenitic stainless steel(ASS)produced by friction stir welding(FSW)was investigated.The FSW process was conducted using a rotational speed of 400 r/min and welding speeds of 50 and 150 mm/min.The study was carried out using electron backscattered diffraction(EBSD)technique in different regions of the resultant stir zones(SZs).The results show that the texture of the advancing side(AS)was mainly composed of C{001}〈110〉and cube{001}〈100〉texture components along with partial B/B{112}〈110〉component.Moving from the AS toward the center and the retreating side(RS),the cube texture component disappeared and the A;/A*{111}(112)component developed and predominated the other components.Higher welding speed greatly affected and decreased the intensity of the textures in the resultant SZs.Moreover,higher welding speed(lower heat input)resulted in lower frequency of cube texture in the AS.
文摘In recent years, with attention paid to global environmental problems, there have been requirements for continuous improvement of automobile fuel economy and exhaust gas purification rate. The properties of the ferritic stainless steels (FSS) used to make automobile parts have been improved. This paper introduces the construction of automotive exhaust systems and describes their main failure behaviors and corrosion evaluation procedures.
文摘Some new Ni-saving 25Cr duplex stainless steels(DSS)have been developed.The results indicate that the alloy has a balanced ferrite-austenite relation after hot forge and solid solution treatment at 1 000℃. The elements W and Cu have a marked effect on the microstructure of the alloy.The pitting potential of the steel adding W and Cu elements reaches the maximum value of 435 mV.The tensile strength and percentage of area reduction of all steels in this paper are 800 -900 MPa and 60%-70%,respectively.The tensile elongations of the alloys are all above 30%.The experimental steels have good corrosion and mechanical property.
文摘The investigation on toxicity of stainless steel has been reviewed. Many countries have established laws to guarantee food safety of stainless steel containers. The development of food safety standards with respect to the use of stainless steels in China has been analyzed. Influence of stainless steel grades and food ingredients on the release of metal ions has been reviewed briefly. The effect of surface condition on the release of metal ions has also been analyzed. Finally, the food safety issues with respect to the use of stainless steel products have been presented systematically.
文摘An improved three-dimensional (3-D) experimental visualization methodology is presented tor evaluating the fracture mechanisms of ferritic stainless steels by in-situ tensile testing with an environmental scanning electron microscope (ESEM). The samples were machined with a radial notched shape and a sloped surface. Both planar surface deformation and sloping surface deformation-induced microvoids were observed during dynamic tension experiments, where a greater amount of information could be obtained from the sloping surface. The results showed that microvoids formed at the grain boundaries of highly elongated large grains. The microvoids nucleated in the severely deformed regions grew nearly parallel to the tensile axis, predominantly along the grain boundaries. The microvoids nucleated at the interface of particles and the matrix did not propagate due to the high plasticity of the matrix. The large microvoids propagated and showed a zigzag shape along the grain boundaries,seemingly a consequence of the fracture of the slip bands caused by dislocation pile-ups. The final failure took place due to the reduction of the load-beating area.
文摘A review is given concerning some of the recent industrial developments of stainless steels. In austenitic stainless steels,two different directions of alloy development are noticeable:low nickel austenitic stainless steels and high nitrogen stainless steels.In these two cases the aims are different,particularly in terms of strength,but the philosophy of alloy development and the scientific approaches are very similar and they all revolve about the role of nitrogen as an alloying element and how this affects strength,ductility and corrosion resistance. There is now a broad and useful basis of information as to how nitrogen affects solid solution hardening,grain boundary hardening and work hardening and how to make use of these effects in developing materials required by the world market. In the field of corrosion resistance,ferritic,duplex and austenitic stainless steels compete with each other and now there is a growing body of information concerning the relative corrosion resistance based on laboratory data. However,for practical applications and for alloy selection,more than just laboratory data are needed,and thus,the first results are presented here of a many years comparison of the corrosion resistance of 24 commercial stainless steels exposed to corrosion in outdoors marine atmosphere.Hope is expressed to involve in the near future even more steels from a wider range of manufacturers in such corrosion studies.This might help consumers in appropriate alloy selection.It might also help steel makers in developing appropriate stainless steel grades.
基金financially supported by the National High-Tech Research and Development Program of China (Nos. 2012AA03A507 and 2012AA050901)
文摘The effect of thermal aging on the fatigue crack growth(FCG) behavior of Z3CN20?09M cast duplex stainless steel with low ferrite content was investigated in this study. The crack surfaces and crack growth paths were analyzed to clarify the FCG mechanisms. The microstructure and micromechanical properties before and after thermal aging were also studied. Spinodal decomposition in the aged ferrite phase led to an increase in the hardness and a decrease in the plastic deformation capacity, whereas the hardness and plastic deformation capacity of the austenite phase were almost unchanged after thermal aging. The aged material exhibited a better FCG resistance than the unaged material in the near-threshold regime because of the increased roughness-induced crack closure associated with the tortuous crack path and rougher fracture surface; however, the tendency was reversed in the Paris regime because of the cleavage fracture in the aged ferrite phases.
基金Item Sponsored by National Natural Science Foundation of China Baoshan Iron and Steel Co Ltd(50534010)
文摘The grades of ultra-pure ferritic stainless steels, especially the grades used in automobile exhaust system, were reviewed. The dependence of properties on alloying elements, the refining facilities, and the mechanism of the reactions in steel melts were described in detail. Vacuum, strong stirring, and powder injection proved to be effective technologies in the melting of ultra-pure ferritic stainless steels. The application of the ferritic grades was also briefly introduced.
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.
文摘The effect of aging temperature on erosion corrosion (E-C) behavior of 17-4PH stainless steels in dilute sulphuric acid slurry containing solid particles was studied by using self-made rotating E-C apparatus. The effect of impact velocity on EC behavior of 17 4PH steels at different aging temperatures was analyzed. Surface micrographs of the specimens after E C test were observed by using scanning electron microscope (SEM). The results showed that under the condition of the same solution heat treatment, when aging temperature ranged from 400 ℃ to 610℃, the hardness reached the highest value near the temperature 460℃. The characteristics of E-C for 17-4PH stainless steels at different aging temperatures were as follows: pure erosion (wear) was dominant, corrosion was subordinate and at the same time corrosion promoted erosion. The effect of aging temperature on E-C rate of 17-4PH steels was not significant at low impact velocity, but it was found that E-C resistance of 17-4PH steels aged near 460℃ was the most excellent due to the best precipitation strengthening effect of fine and dispersed e-Cu phase. With a prerequisite of appropriate corrosion resistance, the precipitation hardening could significantly improve the E-C resistance of the materials.
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supported by the National Natural Science Foundation of China (Nos. 50771075 and 51171133) the Program for New Century Excellent Talents in University of Ministries of the Education of China (No.NECT-07-0650)
文摘Silver or copper ions are often chosen as antibacterial agents. But a few reports are concerned with these two antibacterial agents for preparation of antibacterial stainless steel (SS). The antibacterial properties and corrosion resistance of AISI 420 stainless steel implanted by silver and copper ions were investigated. Due to the cooperative antibacterial effect of silver and copper ions, the Ag/Cu implanted SS showed excellent antibacterial activities against both Gram-negative Escherichia coli (E. coli) and Gram-positive Staphylococcus aureus (S. aureus) at a total implantation dose of 2~ 1017 ions/cm2. Electrochemical polarization curves revealed that the corrosion resistance of Ag/Cu implanted SS was slightly enhanced as compared with that of un-implanted SS, The implanted layer was characterized by X-ray photoelec- tron spectroscopy (XPS). Core level XPS spectra indicate that the implanted silver and copper ions exist in metallic state in the implanted layer.