A needle valve is a key component of a diesel injector.The needle valve body of the diesel engine, made of R18CrNi8 steel, cracked and failed during the working process.The cracking failure reasons for the carburized ...A needle valve is a key component of a diesel injector.The needle valve body of the diesel engine, made of R18CrNi8 steel, cracked and failed during the working process.The cracking failure reasons for the carburized injector valve body through chemical composition analysis, metallographic examination, scanning electron microscope(SEM) analysis, and energy spectrum analysis, were investigated.The results reveal that the original material of the needle valve is in conformity with the manufacturing requirement.Due to the high carburizing quenching temperature, the best carburized layer structure was not obtained, and the machining defect from which the crack emanated was not identified.The cracks expanded and eventually led to fracture under the action of altered stress and the high-temperature combustion environment during the operation of the engine.展开更多
Targeting the single tuyere and double tuyere methods of argon blowing for Baosteel' s 300 t ladle furnace, the 3D continuity equation, the N-S equation and the turbulent k-ε double-equation were used to model the f...Targeting the single tuyere and double tuyere methods of argon blowing for Baosteel' s 300 t ladle furnace, the 3D continuity equation, the N-S equation and the turbulent k-ε double-equation were used to model the form of the molten steel flow and the dead areas under six different argon blowing conditions. The different flow field forms and the degree of mixing under different argon blowing methods were compared. The results demonstrate that when large ladles are operated via different methods of argon blowing, the spray from the centre of a single tuyere forms a symmetrical vortex, while when a double tuyere sprays, there is basically no clear vortex. In regards to the amount of argon blowing that will produce the best blend of molten steel, the amount of dead area reduction will not be clearly noticeable if there is an excessive argon blowing amount.展开更多
Using the equation of continuity and the double equation of Navier-Stokes and k-ε, numerical modeling on a single outlet continuous casting tundish has been carried out during the process of non-thermal flow coupling...Using the equation of continuity and the double equation of Navier-Stokes and k-ε, numerical modeling on a single outlet continuous casting tundish has been carried out during the process of non-thermal flow coupling. The flow field distribution inside the tundish was calculated and the viscosity response time was calculated with the mass transfer equation based on the flow field distribution. The flow characteristics of the molten steel inside the tundish were analyzed, with the results of the numerical modeling compared to the hydraulic modeling. The results showed that the Resident Time Distribution (RTD) curves in the latter anatomosed comparatively better. This certified the validity established by the mathematical model. Numerical modeling was carried out on both large and small tundishes during the processes of thermal flow coupling and also thermal non-flow coupling. The results showed that in regards to large tundishes with relatively simple flow processes, using numerical modeling for thermal flow coupling is necessary.展开更多
Based on a series of related investigations, a mechanism for the formation of longitudinal surface cracks on a continuous casting slab of high-carbon steel was investigated. High-temperature tensile tests performed on...Based on a series of related investigations, a mechanism for the formation of longitudinal surface cracks on a continuous casting slab of high-carbon steel was investigated. High-temperature tensile tests performed on slab samples,metallographic and scanning electron microscopy studies, as well as heat flux and shell thickness in continuous casting predicted on the basis of a mathematical model were conducted. The results showed that high- carbon steel exhibited a much lower liquidus temperature and a wider brittle temperature range immediately after solidification compared with those of low-carbon steel. Concentrations of elements K and Na, which are contained in the mold fluxes, were not observed in the cracks during this study. The calculated results showed that the heat flux and the shell thickness were uneven along the mold width and that the shell was thinner and close to the center line of the slab surface. The longitudinal cracks were observed in situ using confocal laser scanning microscopy, to first occur close to the solidification front,where the ductility was extremely low;in addition ,the shell growth was slower than in other regions, which led to a thinner shell and depressed shrinkage owing to a lack of lubrication by the mold fluxes below the meniscus. Furthermore, the pouring temperature of high-carbon steel is - 100 ~C lower than that of low-carbon steel,so the formation of a stable liquid flux near the meniscus within a short time at the beginning of casting is difficult. The amounts of liquid slag film and crystalline slag film were insufficient to provide adequate lubrication between the shell and the mold, which resulted in greater friction force that induced or aggravated cracks. Therefore, the homogeneity of mold fluxes and initial solidification in the mold should be improved to reduce the concentration of slab surface defects.展开更多
In this study,normalized 00 Cr13 Ni5 Mo low-carbon martensitic stainless steel was tempered at temperatures ranging between 500-700 ℃ for 8 h and its mechanical properties were determined. The results show that the m...In this study,normalized 00 Cr13 Ni5 Mo low-carbon martensitic stainless steel was tempered at temperatures ranging between 500-700 ℃ for 8 h and its mechanical properties were determined. The results show that the mechanical properties vary with a variation in the tempering temperature. Samples tempered at 650 ℃exhibited a good combination of properties and a low yield ratio. Scanning electron microscopy observations and Xray diffraction analysis revealed that the tempering process involved carbide precipitation,austenitic inversion,and quenching,and the properties of materials changed with a change in the tempering temperature.展开更多
In this study, the effect of vanadium addition(0.25%) on microstructure and hydrogen embrittlement(HE) was investigated in grade 12.9 bolt steels, and hydrogen diffusion was analyzed by hydrogen permeation.The results...In this study, the effect of vanadium addition(0.25%) on microstructure and hydrogen embrittlement(HE) was investigated in grade 12.9 bolt steels, and hydrogen diffusion was analyzed by hydrogen permeation.The results show that the addition of 0.25% vanadium in bolt steels can significantly improve the HE resistance.Vanadium addition can form a large number of vanadium precipitates, resulting in the uniform distribution of hydrogen and reduction of hydrogen accumulated at local grain boundaries, which promotes the inhibition of hydrogen-induced cracking.展开更多
文摘A needle valve is a key component of a diesel injector.The needle valve body of the diesel engine, made of R18CrNi8 steel, cracked and failed during the working process.The cracking failure reasons for the carburized injector valve body through chemical composition analysis, metallographic examination, scanning electron microscope(SEM) analysis, and energy spectrum analysis, were investigated.The results reveal that the original material of the needle valve is in conformity with the manufacturing requirement.Due to the high carburizing quenching temperature, the best carburized layer structure was not obtained, and the machining defect from which the crack emanated was not identified.The cracks expanded and eventually led to fracture under the action of altered stress and the high-temperature combustion environment during the operation of the engine.
文摘Targeting the single tuyere and double tuyere methods of argon blowing for Baosteel' s 300 t ladle furnace, the 3D continuity equation, the N-S equation and the turbulent k-ε double-equation were used to model the form of the molten steel flow and the dead areas under six different argon blowing conditions. The different flow field forms and the degree of mixing under different argon blowing methods were compared. The results demonstrate that when large ladles are operated via different methods of argon blowing, the spray from the centre of a single tuyere forms a symmetrical vortex, while when a double tuyere sprays, there is basically no clear vortex. In regards to the amount of argon blowing that will produce the best blend of molten steel, the amount of dead area reduction will not be clearly noticeable if there is an excessive argon blowing amount.
文摘Using the equation of continuity and the double equation of Navier-Stokes and k-ε, numerical modeling on a single outlet continuous casting tundish has been carried out during the process of non-thermal flow coupling. The flow field distribution inside the tundish was calculated and the viscosity response time was calculated with the mass transfer equation based on the flow field distribution. The flow characteristics of the molten steel inside the tundish were analyzed, with the results of the numerical modeling compared to the hydraulic modeling. The results showed that the Resident Time Distribution (RTD) curves in the latter anatomosed comparatively better. This certified the validity established by the mathematical model. Numerical modeling was carried out on both large and small tundishes during the processes of thermal flow coupling and also thermal non-flow coupling. The results showed that in regards to large tundishes with relatively simple flow processes, using numerical modeling for thermal flow coupling is necessary.
文摘Based on a series of related investigations, a mechanism for the formation of longitudinal surface cracks on a continuous casting slab of high-carbon steel was investigated. High-temperature tensile tests performed on slab samples,metallographic and scanning electron microscopy studies, as well as heat flux and shell thickness in continuous casting predicted on the basis of a mathematical model were conducted. The results showed that high- carbon steel exhibited a much lower liquidus temperature and a wider brittle temperature range immediately after solidification compared with those of low-carbon steel. Concentrations of elements K and Na, which are contained in the mold fluxes, were not observed in the cracks during this study. The calculated results showed that the heat flux and the shell thickness were uneven along the mold width and that the shell was thinner and close to the center line of the slab surface. The longitudinal cracks were observed in situ using confocal laser scanning microscopy, to first occur close to the solidification front,where the ductility was extremely low;in addition ,the shell growth was slower than in other regions, which led to a thinner shell and depressed shrinkage owing to a lack of lubrication by the mold fluxes below the meniscus. Furthermore, the pouring temperature of high-carbon steel is - 100 ~C lower than that of low-carbon steel,so the formation of a stable liquid flux near the meniscus within a short time at the beginning of casting is difficult. The amounts of liquid slag film and crystalline slag film were insufficient to provide adequate lubrication between the shell and the mold, which resulted in greater friction force that induced or aggravated cracks. Therefore, the homogeneity of mold fluxes and initial solidification in the mold should be improved to reduce the concentration of slab surface defects.
文摘In this study,normalized 00 Cr13 Ni5 Mo low-carbon martensitic stainless steel was tempered at temperatures ranging between 500-700 ℃ for 8 h and its mechanical properties were determined. The results show that the mechanical properties vary with a variation in the tempering temperature. Samples tempered at 650 ℃exhibited a good combination of properties and a low yield ratio. Scanning electron microscopy observations and Xray diffraction analysis revealed that the tempering process involved carbide precipitation,austenitic inversion,and quenching,and the properties of materials changed with a change in the tempering temperature.
文摘In this study, the effect of vanadium addition(0.25%) on microstructure and hydrogen embrittlement(HE) was investigated in grade 12.9 bolt steels, and hydrogen diffusion was analyzed by hydrogen permeation.The results show that the addition of 0.25% vanadium in bolt steels can significantly improve the HE resistance.Vanadium addition can form a large number of vanadium precipitates, resulting in the uniform distribution of hydrogen and reduction of hydrogen accumulated at local grain boundaries, which promotes the inhibition of hydrogen-induced cracking.