基于场致二次谐波的大气压脉冲流注放电时变非均匀电场测量研究

诊断大气压脉冲流注放电空间电场是实现流注放电精准调控和揭示等离子体不稳定性机制的重要基础。基于场致二次谐波的空间电场测量方法具有非侵入式、时空分辨率高等优点。然而,流注放电时变非均匀电场对二次谐波信号产生过程的影响规律尚不完善,真实电场标定系数随流注放电不同阶段的变化规律尚不清晰。该文首先计算二次谐波信号产生规律和电场空间分布的影响;然后,基于等离子体流体模拟,分析二次谐波信号对流注放电不同阶段时变非均匀电场的敏感程度;最后,基于纳秒脉冲激光场致二次谐波电场测量平台,实验获得了重频脉冲作用下组合电极结构产生的单根负流注轴向电场演变规律,分析脉冲重复频率对空间电场的影响机制,并针对流注放电时变非均匀电场特点提出电场致二次谐波测量优化若干建议。

Failure analysis of the needle valve body of R18CrNi8 steel

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.

GIS同频同相耐压试验中母线隔离开关断口击穿过程仿真计算

GIS设备同频同相耐压试验发生意外导致试验相母线隔离开关断口击穿时,试验间隔对应母线电压可能产生畸变,间隔保护可能误动。为评估该暂态过程对运行母线及试验侧串联谐振装置的影响,有必要对断口击穿暂态过程中各个关键节点的电压、电流波形进行仿真。建立了网侧真型和试验侧真型两种ATPEMTP仿真模型,对同频同相耐压试验失败导致母线隔离开关断口击穿后的暂态过程开展仿真计算,得到该过程中过电压、过电流波形及峰值,评估了两种模型的正确性及击穿过程对同频同相耐压试验的影响。仿真结果表明,网侧真型模型能更好地反映试验失败时产生的过电压、过电流。

Numerical modeling of blow refining process of a 300t ladle furnace at Baosteel

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.

Numerical modeling of influence of thermal flow coupling on flow characteristics of molten steel

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.

Investigation of longitudinal surface cracks in a continuous casting slab of high-carbon steel

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.

Effect of tempering on the properties and microstructure of 00Cr13Ni5Mo

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.

Effect of vanadium on hydrogen embrittlement of grade 12.9 high-strength bolt steels

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.

GCr15轴承套圈组织分布特点及碳化物均匀性

利用光学显微镜(OM)和扫描电镜(SEM)对GCr15淬回火态轴承套圈不同部位的微观组织进行观察。采用定量金相分析法,对碳化物含量、形态、大小及分布进行统计,并对内外套圈纵截面进行酸蚀,观察其低倍组织。结合套圈各部位在原棒材上对应的位置,对淬回火套圈的组织分布特点及其成因进行研究。结果表明:对应于原棒材R/2处的套圈滚道面组织均匀,碳化物细小,直径<0.6μm的碳化物颗粒个数占比高达92.3%,且颗粒圆度高,在基体上呈弥散分布;滚道面较大尺寸的碳化物由晶界处的粗大的网状碳化物演变而来;套圈内圆部位存在棱角分明的碳化物,由棒材心部锻前组织中的粗大网状碳化物遗留形成,难以通过锻造及后期热处理消除。套圈内圆冲孔辗扩时,棒材心部缺陷组织流向内圆下端面,使下端面成为薄弱部位。