用局部法评定焊接接头的疲劳性能

采用16Mn钢非承载十字焊接接头疲劳试验结果对使用Dang Van准则的疲劳评定局部方法进行了研究。结果表明，有限元分析中应力集中区单元尺寸对局部参量计算有明显影响，为获得比较合理的预测结果需对焊趾应力集中区所划分的单元尺寸限定，当接头焊趾半径在0．15-0．8mm变化时应选择最小单元尺寸0．32-0．62mm计算局部参量；在此基础上Dang Van准则可以对焊态接头做出合理的评定，但Dang Van建议的卢值偏安全。此外，通过计算发现焊趾半径只影响局部很小区域(约0．5mm内)的应力集中分布，在某一深度(约0．5mm)后存在稳定的应力集中，因而建议采用距应力集中区最大应力处某一深度的应力参数计算Dang Van局部参量可能更为合理，这将减小局部参数对焊趾半径及单元尺寸的依赖性。     

Destabilising persistent coal froth using silicone oil

Persistent froth is becoming more and more common in coal and mineral flotation plants and presents safety and operational challenges. No effective method has been developed to destabilise persistent froth. As a new initiative, this study examined the structural difference between persistent foam and coal froth, based on which a solution was developed to maximumly destabilise coal froth. Destabilisation test, oscillatory rheology measurement and scanning electron microscopy (SEM) analysis indicated that the coal froth was more stable than the foam due to the formation of thin capillaries and tightly arranged coal particles on bubble surfaces. Although 107 µm silicone oil droplet could completely destabilise the foam at 2 mmol/L concentration, it only destabilised less than 50% coal froth even at 6 mmol/L concentration. To maximumly destabilise the coal froth formed by −38 and −20 µm particles, 24 and 18 µm silicone oil droplets were required to pass through the thin capillaries and enter the bubble films, respectively. However, smaller silicone oil droplets could not bridge the bubble films to destabilise coal froth and therefore a critical droplet size occurred depending on the size of particles stabilising the froth.     

Continuous size fractionation of magnetic nanoparticles by using simulated moving bed chromatography

The size fractionation of magnetic nanoparticles is a technical problem, which until today can only be solved with great effort. Nevertheless, there is an important demand for nanoparticles with sharp size distributions, for example for medical technology or sensor technology. Using magnetic chromatography, we show a promising method for fractionation of magnetic nanoparticles with respect to their size and/or magnetic properties. This was achieved by passing magnetic nanoparticles through a packed bed of fine steel spheres with which they interact magnetically because single domain ferro-/ferrimagnetic nanoparticles show a spontaneous magnetization. Since the strength of this interaction is related to particle size, the principle is suitable for size fractionation. This concept was transferred into a continuous process in this work using a so-called simulated moving bed chromatography. Applying a suspension of magnetic nanoparticles within a size range from 20 to 120 nm, the process showed a separation sharpness of up to 0.52 with recovery rates of 100%. The continuous feed stream of magnetic nanoparticles could be fractionated with a space-time-yield of up to 5 mg/(L∙min). Due to the easy scalability of continuous chromatography, the process is a promising approach for the efficient fractionation of industrially relevant amounts of magnetic nanoparticles.     

Effects of surfactant and particle size on the microstructure and strength of Si3N4 foams with high porosity

The highly porous Si₃N₄ ceramic foams were prepared by direct foaming with mixed surfactants. The surface tension and viscosity of slurries were tailored by different carbon chain length of surfactants and different mean Si₃N₄ particle size to achieve the pore size controlling. The nearly linear relationship between the pore size and the ratio of surface tension to viscosity was observed, which indicates that the pore size could be precisely tailored by the slurry properties. Si₃N₄ ceramic foams with porosity of nearly 94%, mean pore size of 110–230 µm, and compressive strength of 1.24–3.51 MPa were obtained.     

H2O(g)对富氧燃烧超细颗粒物生成特性影响

为实现富氧燃烧技术的广泛推广,对煤粉燃烧在富氧气氛下的颗粒物排放特性进行了研究。在1800 K管式炉内进行煤焦燃烧试验,研究了富氧气氛下H₂O(g)体积分数(0、5%、10%、20%、30%)对煤焦燃烧超细颗粒物的影响;采用荷电低压撞击器(ELPI+)获得超细颗粒物质量和数量浓度粒径分布并进行分析。结果表明,H₂O(g)对超细颗粒物质量浓度和数量浓度粒径分布无影响,但会导致超细颗粒物的峰值波动。超细颗粒物总数量由最小粒径超细颗粒物决定,5种水蒸气浓度下EL?PI+第1级撞击器收集到的超细颗粒物数量占比均超过65%。超细颗粒物总质量由最大粒径超细颗粒物决定,5个水蒸气浓度下ELPI+第7级撞击器收集到的超细颗粒物质量占比均超过94%。低H₂O(g)浓度会抑制超细颗粒物生成,H₂O(g)体积分数为5%时的抑制作用最显著;高H₂O(g)浓度会促进超细颗粒物生成。这是因为一方面H₂O(g)与煤焦发生气化反应,使煤焦颗粒周围产生还原性气氛,促进矿物质还原为单质,进一步促进矿物质蒸发;另一方面气化反应是吸热反应,会降低煤焦颗粒燃烧温度,同时H₂O(g)加入也导致烟气热容增加进一步降低,煤焦燃烧温度抑制煤中矿物质的蒸发,导致超细颗粒物生成减少,是2种作用相互竞争的结果。此外,H₂O(g)的加入使超细颗粒物平均粒径增大,0~5%H₂O(g)时超细颗粒物平均粒径增大最迅速。     

20CrMnTi连铸瞬态与平均冷速条件下凝固原位观察

 宽淬透性带和大尺寸TiN析出物严重危害20CrMnTi齿轮钢的产品质量,其控制的关键基础是掌握连铸过程中凝固组织演变行为机理。传统高温激光共聚焦扫描显微镜(HT-CSLM)原位观察研究通常将糊状区冷却速率设定为固定值,这不能有效反映连铸凝固过程中冷却速率的变化。为此,以国内某钢厂20CrMnTi 160 mm×160 mm小方坯为研究对象,首先通过二维切片凝固传热计算,确定内弧表面下方20、40、60 mm位置处糊状区的热历程、瞬态与平均冷却速率,进而设计HT-CSLM试验升温与降温方案。然后,开展这些位置处糊状区瞬态与平均冷却速率条件下HT-CSLM试验,研究揭示不同冷却条件下20CrMnTi的凝固过程、δ晶粒生长动力学和包晶相变机制。最后,通过电子探针分析(EPMA),考察冷却条件对凝固组织尺寸的影响规律。结果表明,由于凝固潜热的补偿,内弧皮下20、40、60 mm位置处初始凝固阶段冷却速率较小,凝固中后期逐渐增大,且越深入方坯内部越显著。这些位置处的平均冷却速率分别为102.81、44.63和34.93 ℃/min。δ晶粒率先从钢液中析出,其平均生长速率随着冷却速率的提升而增大。在瞬态冷却速率条件下,随着凝固的进行,瞬时生长速率呈增大的趋势,但是在平均冷却速率条件下瞬时生长速率则略微降低。这是因为在瞬态冷却速率条件下,糊状区冷却速率由慢至快,不断补偿了凝固潜热,同时初始形核数量少,生长空间大,溶质过冷度的影响相对较弱。当熔体温度降低至包晶相变临界温度时,δ晶粒快速转变为γ晶粒,即发生块状转变,导致固相率迅速增加,且伴随有部分γ晶粒快速聚合。整体上讲,包晶相变临界温度随着冷却速率的增大而降低,但是也受溶质初始含量的影响。此后,剩余液相向γ相转变,直至完全凝固。晶粒半径随着冷却速率的提升而减小,且在平均冷却速率条件下比瞬态冷却速率条件更小,这取决于初始凝固阶段的形核数量。     

锡或锑在无取向电工钢中的研究进展

近年来,在节能减排背景之下,国内外众多研究者对无取向电工钢磁性能的提升做了大量研究。为了探索无取向电工钢磁性能提升的方法,对锡或锑对无取向电工钢磁性能的作用机制(晶粒尺寸和晶体织构的控制)进行分析。基于该作用机制,介绍锡或锑的添加对无取向电工钢磁性能的影响。经研究发现,适量的锡或锑在晶界偏聚,不会阻碍晶界的移动并且致使晶粒尺寸降低;与此同时,锡或锑在晶界偏聚不仅抑制{111}织构在原始晶界处形核及生长,还降低(100)晶粒表面能,促进(100)晶粒生长。因此,适量添加锡或锑,可使无取向电工钢铁损下降、磁感提升。最后结合生产工艺,建议无取向电工钢的研究方向应为稀土含量对高牌号无取向硅钢夹杂物尺寸和数量分布的影响,锡或锑的添加量和常化工艺参数(常化时间、常化温度)对常化晶粒尺寸的影响。     

GCr15钢激光淬火层的奥氏体晶粒尺寸

ＧＣｒ１５钢激光淬火层的晶粒尺寸可在很大范围内变化，从约３０μｍ到小于２μｍ。以激光光斑为中心，相距越远，晶粒尺寸越细小，晶粒尺寸的变化与激光加热时理论推导的温度场存在对应关系。激光扫描速度对激光淬火层的奥氏体晶粒尺寸有显著的影响，原始组淬火层体晶粒尺寸影响较小，ＧＣｒ１５钢激光淬火层奥氏体晶粒尺寸的研究为激光淬火工艺的制订提供了重要的参考依据。     

Microstructures and Plastic Anisotropy of As—Cast Low Carbon Steel Strips

对比研究了低碳钢带铸材不同处理状态钢带和薄板铸坯中不同位置切片的组织特征、晶体学织构和15％工程应变条件下的塑性异向性．结果表明，带铸材试样中存在{111}与{114}特征织构，织构强度均较弱；铸坯切片中存在{111}与{001}特征织构，并且因局部凝固冷速不同存在明显的织构强度差异．两组低碳钢的法向异向性与平均晶粒尺寸的对数之间尽管均存在线性关系，但斜率明显不同．分析表明法向异向性的晶粒尺寸依存性与钢带中织构的强弱有关，由此提出了“有效织构强度比”的概念，从塑性变形理论的角度解释了微观组织对塑性异向性的影响．