The effect of high pressure heat treatment on microstructure and compressive properties of low carbon steel were investigated by optical microscope,transmission electron microscope,hardness tester and compression test...The effect of high pressure heat treatment on microstructure and compressive properties of low carbon steel were investigated by optical microscope,transmission electron microscope,hardness tester and compression test methods.The results show that martensite appears in low carbon steel at 1-5GPa GPa and 950°C for 15 minutes treatment,high pressure heat treatment can improve the hardness and compressive properties of the steel,the yield strength of the steel increases with increasing pressure,and its compressive properties are better than that treated under normal pressure quenching.展开更多
The cathodic reaction mechanisms in CO2 corrosion of low-Cr steels were investigated by potentiodynamic polarization and galvanostatic measurements.Distinct but different dominant cathodic reactions were observed at d...The cathodic reaction mechanisms in CO2 corrosion of low-Cr steels were investigated by potentiodynamic polarization and galvanostatic measurements.Distinct but different dominant cathodic reactions were observed at different p H levels.At the higher p H level(p H>~5),H2 CO3 reduction was the dominant cathodic reaction.The reaction was under activation control.At the lower pH level(pH<~3.5),H+reduction became the dominant one and the reaction was under diffusion control.In the intermediate area,there was a transition region leading from one cathodic reaction to another.The measured electrochemical impedance spectrum corresponded to the proposed cathodic reaction mechanisms.展开更多
Embrittlement of a Cr-Mo2.25CrlMo steel stemming from neutron irradiation at 270℃ is studied by virtue of small punch testing in conjunction with scanning electron microscopy. The ductile-brittle transition temperatu...Embrittlement of a Cr-Mo2.25CrlMo steel stemming from neutron irradiation at 270℃ is studied by virtue of small punch testing in conjunction with scanning electron microscopy. The ductile-brittle transition temperature determined by the small punch test is much lower than that determined by the standard Charpy test. There is some irradiation-induced embrittlement effect after the steel is irradiated for 46 days with a neutron dose rate of 1.05×10^18dpa/s （displacement per atom per second）.展开更多
The catalytic conversion of biomass platform chemicals using abundant non-noble metal nanocatalysts is a challenging topic.Here,high-density cobalt oxide nanoparticles loaded on biomass-derived porous N-doped carbon(N...The catalytic conversion of biomass platform chemicals using abundant non-noble metal nanocatalysts is a challenging topic.Here,high-density cobalt oxide nanoparticles loaded on biomass-derived porous N-doped carbon(NC)was fabricated by a tandem hydrothermal pyrolysis and mild nitrate decomposition process,which is a green and cheap preparation method.The Co_(3)O_(4) nanoparticles with the average size of 12 nm were uniformly distributed on the porous NC.The nanocomposites also possessed large surface area,high N content,good dispersibility in isopropanol,and furfural absorbability.Due to these characteristics,the novel cobalt nanocatalyst exhibited high catalytic activity for producing furfuryl alcohol,yielding 98.7%of the conversion and 97.1%of the selectivity at 160℃ for 6 h under 1 bar H2.The control experiments implied that both direct hydrogenation and transfer hydrogenation pathways co-existed in the hydrogenation reaction.The excellent catalytic activity of Co_(3)O_(4)@NC was attributed to the cooperative effects of porous NC and Co_(3)O_(4) nanoparticles.This approach provides a new idea to design effective high-density nonnoble metal oxide nanocatalysts for hydrogenation reactions,which can make full use of sustainable natural biomass.展开更多
Cold-stretched pressure vessels from austenitic stainless steels(ASS) are widely used for storage and transportation of liquefied gases,and have such advantages as thin wall and light weight.Fatigue is an important co...Cold-stretched pressure vessels from austenitic stainless steels(ASS) are widely used for storage and transportation of liquefied gases,and have such advantages as thin wall and light weight.Fatigue is an important concern in these pressure vessels,which are subjected to alternative loads.Even though several codes and standards have guidelines on these pressure vessels,there are no relevant design methods on fatigue failure.To understand the fatigue properties of ASS 1.4301(equivalents include UNS S30400 and AISI 304) in solution-annealed(SA) and cold-stretched conditions(9% strain level) and the response of fatigue properties to cold stretching(CS),low-cycle fatigue(LCF) tests were performed at room temperature,with total strain amplitudes ranging from -.4% to -.8%.Martensite transformations were measured during the tests.Comparisons on cyclic stress response,cyclic stress-strain behavior,and fatigue life were carried out between SA and CS materials.Results show that CS reduces the initial hardening stage,but prolongs the softening period in the cyclic stress response.Martensite transformation helps form a stable regime and subsequent secondary hardening.The stresses of monotonic and cyclic stress-strain curves are improved by CS,which leads to a lower plastic strain and a much higher elastic strain.The fatigue resistance of the CS material is better than that of the SA material,which is approximately 1?03 to 2?04 cycles.The S-N curve of the ASME standard for ASS is compared with the fatigue data and is justified to be suitable for the fatigue design of cold-stretched pressure vessels.However,considering the CS material has a better fatigue resistance,the S-N curve will be more conservative.The present study would be helpful in making full use of the advantages of CS to develop a new S-N curve for fatigue design of cold-stretched pressure vessels.展开更多
Compared with the traditional atm ospheric carburization, low-pressure carburization has the benefits of producing no surface oxidation and leaving fine, uniformly dispersed carbides in the carburized layer. However, ...Compared with the traditional atm ospheric carburization, low-pressure carburization has the benefits of producing no surface oxidation and leaving fine, uniformly dispersed carbides in the carburized layer. However, the process param eters for low-pressure carburization of 16Cr3NiWMoVNbE steel have yet to be optimized. Thus, we use the saturation-value method to optimize these parameters for aviation-gear materials. Toward this end, the m icrostructure and properties of 16Cr3NiWMoVNbE steel after different carburization processes are studied by optical microscopy, scanning electron microscopy, transm ission electron microscopy, and electron probe microanalysis. Considering the saturated austenite carbon concentration, we propose a model of carbon flux and an alloy coefficient for low -pressure carburization to reduce the carbon concentration in austenite and avoid the surface carbide network. At the early stage of carburization (30 s), the gas-solid interface has a higher concentration gradient. The averaging method is not ideal in practical applications, but the carbon flux measured by using the segm ented average m ethod is 2.5 times that measured by the overall average method, which is ideal in practical applications. The corresponding carburization tim e is reduced by 60%. By using the integral average method, the actual carburization time increases, which leads to the rapid form ation of carbide on the surface and affects the entire carburization process. Nb and Wcombine with C to form carbides, which hinders carbon diffusion and consumes carbon, resulting in a sharp decrease in the rate of C diffusion in austenite (the diffusion rate is reduced by 52% for 16Cr3NiWMoVNbE steel). By changing the diffusion coefficient model and comparing the hardness gradient of different processes, the depth of the actual layer is found to be very similar to the design depth.展开更多
The mechanical and fatigue properties of SA508-Ⅳ steel with martensite and granular bainite, respectively, were studied. The mechanical tests results showed that the ultimate tensile strength and impact toughness of ...The mechanical and fatigue properties of SA508-Ⅳ steel with martensite and granular bainite, respectively, were studied. The mechanical tests results showed that the ultimate tensile strength and impact toughness of the specimen with martensite were 830 MPa and 158 J, respectively, and those of the specimen with granular bainite were 811 MPa and 115 J, respectively. The former had higher tensile strength and impact toughness than the latter. The impact tests results showed that the former belonged to typical dimple fracture, while the latter belonged to brittle fracture. The fatigue tests results showed that the fatigue life of the specimen with martensite was 2717 cycles, and that of the specimen with granular bainite was 1545 cycles under the strain amplitude of ± 0.45%. The specimen with martensite had fewer crack initiation points, narrower fatigue striations separation, and larger volume fraction of high-angle grain boundaries than the latter. The fewer crack initiation points meant fewer fatigue cracks, the narrower fatigue striations separation meant slower crack propagation rate, and the larger volume fraction of high-angle grain boundaries could more effectively hinder fatigue crack propagation. Based on these facts, the fatigue life of the specimen with martensite was higher than that of the specimen with granular bainite.展开更多
文摘The effect of high pressure heat treatment on microstructure and compressive properties of low carbon steel were investigated by optical microscope,transmission electron microscope,hardness tester and compression test methods.The results show that martensite appears in low carbon steel at 1-5GPa GPa and 950°C for 15 minutes treatment,high pressure heat treatment can improve the hardness and compressive properties of the steel,the yield strength of the steel increases with increasing pressure,and its compressive properties are better than that treated under normal pressure quenching.
基金financially supported by the National Natural Science Foundation of China (No. 51371034)Fundamental Research Funds for the Central Universities (No. 06500118)
文摘The cathodic reaction mechanisms in CO2 corrosion of low-Cr steels were investigated by potentiodynamic polarization and galvanostatic measurements.Distinct but different dominant cathodic reactions were observed at different p H levels.At the higher p H level(p H>~5),H2 CO3 reduction was the dominant cathodic reaction.The reaction was under activation control.At the lower pH level(pH<~3.5),H+reduction became the dominant one and the reaction was under diffusion control.In the intermediate area,there was a transition region leading from one cathodic reaction to another.The measured electrochemical impedance spectrum corresponded to the proposed cathodic reaction mechanisms.
文摘Embrittlement of a Cr-Mo2.25CrlMo steel stemming from neutron irradiation at 270℃ is studied by virtue of small punch testing in conjunction with scanning electron microscopy. The ductile-brittle transition temperature determined by the small punch test is much lower than that determined by the standard Charpy test. There is some irradiation-induced embrittlement effect after the steel is irradiated for 46 days with a neutron dose rate of 1.05×10^18dpa/s （displacement per atom per second）.
基金The work was supported by the Scientific Research Foundation of Zhejiang Sci-Tech University(19212450-Y).
文摘The catalytic conversion of biomass platform chemicals using abundant non-noble metal nanocatalysts is a challenging topic.Here,high-density cobalt oxide nanoparticles loaded on biomass-derived porous N-doped carbon(NC)was fabricated by a tandem hydrothermal pyrolysis and mild nitrate decomposition process,which is a green and cheap preparation method.The Co_(3)O_(4) nanoparticles with the average size of 12 nm were uniformly distributed on the porous NC.The nanocomposites also possessed large surface area,high N content,good dispersibility in isopropanol,and furfural absorbability.Due to these characteristics,the novel cobalt nanocatalyst exhibited high catalytic activity for producing furfuryl alcohol,yielding 98.7%of the conversion and 97.1%of the selectivity at 160℃ for 6 h under 1 bar H2.The control experiments implied that both direct hydrogenation and transfer hydrogenation pathways co-existed in the hydrogenation reaction.The excellent catalytic activity of Co_(3)O_(4)@NC was attributed to the cooperative effects of porous NC and Co_(3)O_(4) nanoparticles.This approach provides a new idea to design effective high-density nonnoble metal oxide nanocatalysts for hydrogenation reactions,which can make full use of sustainable natural biomass.
基金Project supported by the National Key Technology R&D Program (No.2011BAK06B0205)the International Science and Technology Cooperation Project (No. 2010DFB42960)the Key Technology Innovation Team of Zhejiang Province (No. 2010R50001),China
文摘Cold-stretched pressure vessels from austenitic stainless steels(ASS) are widely used for storage and transportation of liquefied gases,and have such advantages as thin wall and light weight.Fatigue is an important concern in these pressure vessels,which are subjected to alternative loads.Even though several codes and standards have guidelines on these pressure vessels,there are no relevant design methods on fatigue failure.To understand the fatigue properties of ASS 1.4301(equivalents include UNS S30400 and AISI 304) in solution-annealed(SA) and cold-stretched conditions(9% strain level) and the response of fatigue properties to cold stretching(CS),low-cycle fatigue(LCF) tests were performed at room temperature,with total strain amplitudes ranging from -.4% to -.8%.Martensite transformations were measured during the tests.Comparisons on cyclic stress response,cyclic stress-strain behavior,and fatigue life were carried out between SA and CS materials.Results show that CS reduces the initial hardening stage,but prolongs the softening period in the cyclic stress response.Martensite transformation helps form a stable regime and subsequent secondary hardening.The stresses of monotonic and cyclic stress-strain curves are improved by CS,which leads to a lower plastic strain and a much higher elastic strain.The fatigue resistance of the CS material is better than that of the SA material,which is approximately 1?03 to 2?04 cycles.The S-N curve of the ASME standard for ASS is compared with the fatigue data and is justified to be suitable for the fatigue design of cold-stretched pressure vessels.However,considering the CS material has a better fatigue resistance,the S-N curve will be more conservative.The present study would be helpful in making full use of the advantages of CS to develop a new S-N curve for fatigue design of cold-stretched pressure vessels.
基金financially supported by the National Key R&D Program of China (Grant No. 2016YFB0300600)the National Natural Science Foundation of China (Grant No. 51604074)
文摘Compared with the traditional atm ospheric carburization, low-pressure carburization has the benefits of producing no surface oxidation and leaving fine, uniformly dispersed carbides in the carburized layer. However, the process param eters for low-pressure carburization of 16Cr3NiWMoVNbE steel have yet to be optimized. Thus, we use the saturation-value method to optimize these parameters for aviation-gear materials. Toward this end, the m icrostructure and properties of 16Cr3NiWMoVNbE steel after different carburization processes are studied by optical microscopy, scanning electron microscopy, transm ission electron microscopy, and electron probe microanalysis. Considering the saturated austenite carbon concentration, we propose a model of carbon flux and an alloy coefficient for low -pressure carburization to reduce the carbon concentration in austenite and avoid the surface carbide network. At the early stage of carburization (30 s), the gas-solid interface has a higher concentration gradient. The averaging method is not ideal in practical applications, but the carbon flux measured by using the segm ented average m ethod is 2.5 times that measured by the overall average method, which is ideal in practical applications. The corresponding carburization tim e is reduced by 60%. By using the integral average method, the actual carburization time increases, which leads to the rapid form ation of carbide on the surface and affects the entire carburization process. Nb and Wcombine with C to form carbides, which hinders carbon diffusion and consumes carbon, resulting in a sharp decrease in the rate of C diffusion in austenite (the diffusion rate is reduced by 52% for 16Cr3NiWMoVNbE steel). By changing the diffusion coefficient model and comparing the hardness gradient of different processes, the depth of the actual layer is found to be very similar to the design depth.
基金the Beijing Municipal Natural Science Foundation under No.2162026 and the 863 Program of China under Nos.2008AA031702 and 2012AA03A507 for financial support.
文摘The mechanical and fatigue properties of SA508-Ⅳ steel with martensite and granular bainite, respectively, were studied. The mechanical tests results showed that the ultimate tensile strength and impact toughness of the specimen with martensite were 830 MPa and 158 J, respectively, and those of the specimen with granular bainite were 811 MPa and 115 J, respectively. The former had higher tensile strength and impact toughness than the latter. The impact tests results showed that the former belonged to typical dimple fracture, while the latter belonged to brittle fracture. The fatigue tests results showed that the fatigue life of the specimen with martensite was 2717 cycles, and that of the specimen with granular bainite was 1545 cycles under the strain amplitude of ± 0.45%. The specimen with martensite had fewer crack initiation points, narrower fatigue striations separation, and larger volume fraction of high-angle grain boundaries than the latter. The fewer crack initiation points meant fewer fatigue cracks, the narrower fatigue striations separation meant slower crack propagation rate, and the larger volume fraction of high-angle grain boundaries could more effectively hinder fatigue crack propagation. Based on these facts, the fatigue life of the specimen with martensite was higher than that of the specimen with granular bainite.
