60Si_2Mn-Cr弹簧钢中夹杂物演变行为分析

针对某钢厂60Si_2Mn-Cr弹簧钢的生产工艺,取不同工位处的钢样,研究夹杂物的转变效果。实验表明:微铝工艺生产钢中的夹杂物逐渐转变为Al_2O_3-SiO_2-CaO-MgO复合氧化物夹杂,形状逐渐趋于球状夹杂物尺寸逐渐减小,最终铸坯中夹杂物的平均尺寸为4.6μm。通过热力学计算,得到了不同工位下夹杂物的SiO_2+CaO-MgO-MnO+Al_2O_3相图,在中间包和铸坯中的夹杂物大多数处于1500-1 600℃温度下的液相区,减小高硬度夹杂物的危害,提高了弹簧钢的质量。     

板坯连铸机内钢液流动和夹杂物行为

采用数值模拟方法研究了板坯连铸机内钢液流动和夹杂物传输行为。数值结果表明，由于夹杂物的上浮速度远小于钢液流速，因此钢水的流动直接影响着结晶器内夹杂物分布。夹杂物具有与钢液流场相似的上下两个回流区的结构；在液面处，大粒径夹杂物的浓度较大；在窄面处，小粒径夹杂物的浓度较大。     

电解提取风电齿轮钢夹杂物研究

采用小样电解法对风电齿轮钢18CrNiMo7-6中的夹杂物进行了系统的分析检测,通过对齿轮钢中夹杂物的电解、提取、分离,较为完整地将钢中的夹杂物电解并收集,借助SEM-EDS对所收集的夹杂物进行了定性分析。结果表明:通过小样电解法可以较为完整地得到风电齿轮钢18CrNiMo7-6中夹杂物的三维形貌;Al2O3、Al2O3-SiO2类夹杂物多呈不规则多边形状,平均尺寸分别为29.7μm、15.81μm,A l2O3-MgO-CaO-SiO2复合类夹杂物通常为包裹形态的球状,平均尺寸为13.1μm,Ca O类夹杂物通常呈块状,平均尺寸为11.7μm,MnS类夹杂物形貌多呈长条状或纺锤状,平均尺寸为18.8μm,Ca S类夹杂物通常呈规则长条状,平均尺寸为9.2μm;与传统金相法相比,小样电解法在观察钢中夹杂物真实的三维形貌和尺寸时是更为行之有效的方法。     

CO_2保护浇注对45号钢钢水洁净度的影响研究

针对连铸过程中二次氧化的问题,某厂分别采用Ar和CO2保护浸入式水口,对比分析钢中洁净度水平,试验表明:在两种保护浇注条件下,钢中夹杂物去除情况较好,钢中夹杂物的面积百分比保持在10-5级别,保护浇注后为(4~5)×10-5,夹杂物粒径集中在1~5μm;夹杂物和大型夹杂物的类型及组成不变,采用CO2代替Ar进行保护浇注不会影响钢液洁净度,并且大型夹杂物平均质量减少可达16.6%。     

湍流状态下钢液中夹杂物的分形长大过程

应用DLA模型研究了各向异性湍流下夹杂物的凝聚过程.结果表明:伴随着种子集团的增大,种子集团相邻位置也不断增多,这有利于提高种子集团凝聚速度,最后得到的凝聚体与钢中簇状夹杂物的形貌相似.在各向异性湍流作用下,夹杂物的生长表现出各向异性,且湍流较弱方向为夹杂物优先生长方向.     

诱导晶内铁素体形核的夹杂物控制

结合晶内铁素体的形核机制与异质形核理论,系统介绍了可以诱发晶内铁索体形核的夹杂物的类型和尺寸范围.分析认为,诱导IGF的有效形核核心一般为复合夹杂物,夹杂物上须有与IGF共格品面错配度较小的析出相.内部氧化物与边缘析出相形成的凹形边缘为IGF的形核提供了有利条件.诱导IGF形核的夹杂物类型不同,几何尺寸也有所差异,但均...     

冷却速率对钢中MnS+Al_2O_3复合夹杂物包裹率的影响研究

通过实验室试验研究钢中MnS+Al_2O_3复合夹杂物的生成以及不同冷却速率对MnS+Al_2O_3复合夹杂物包裹率的影响。结果表明:被推动到钢液凝固前沿的Al_2O_3,会为MnS析出提供异质形核质点;随着冷却速率的增加,复合夹杂物的尺寸从4μm降至2.5μm左右,MnS+Al_2O_3复合夹杂物包裹率逐渐降低。本次试验研究为得到较优包裹程度的实验条件以及进一步改善钢材性能提供一定的理论分析。     

稀土处理对含铝中锰钢中夹杂物的调控机理

铝脱氧中锰钢精炼过程中易形成尖晶石类夹杂物,这类硬质夹杂物会恶化中锰钢的疲劳性能,易导致钢材功能失效引发事故。采用稀土Ce处理对中锰钢中尖晶石类硬质夹杂物进行改质处理。为了阐明夹杂物的改质机理,开展了高温模拟实验。实验结果表明,Ce处理后,尖晶石夹杂物转变为稀土夹杂物,且随着TO含量的降低,稀土夹杂物类型为CeAlO₃→CeAlO₃+Ce₂O₂S→Ce₂O₂S。铈对尖晶石夹杂物的变质机理为：铈添加到钢中后,尖晶石夹杂物中镁和铝不断被铈替代(含锰尖晶石夹杂物中锰优先被置换),尖晶石结构遭到破坏,从而形成CeAlO₃。当钢中氧含量低,相对硫含量较高时,钢中硫将参与置换反应,置换出夹杂物中的氧,因此尖晶石夹杂物和CeAlO₃夹杂物最终转变为Ce₂O₂S。最后通过热力学模型计算得出,将钢中尖晶石夹杂物完全改质为稀土夹杂物的最低铈含量与钢中氧含量呈线性关系,当钢中铈质量分数为氧质...     

高压定轮中的夹杂物应力场数值模拟

以某水电站泄洪底孔事故闸门定轮为例,采用ABAQUS有限元分析软件建立了含有不同弹性模量和泊松比夹杂物的高压定轮与轨道接触有限元模型,比较分析了各种夹杂物对高压定轮的影响.结果表明,不同夹杂物对定轮性能有不同的影响,该方法对控制定轮中非金属夹杂物含量、最大限度改善定轮的力学性能提供了依据.     

Ca处理对55SiMnMo夹杂物行为变化的研究

研究了Consteel电弧炉-LF-VD-连铸工艺生产55SiMnMo时钙处理对钢中夹杂物行为变化的影响,对显微夹杂物、夹杂物成分变化及大型夹杂物进行分析。结果表明,喂钙线后2 min时钙处理并未反应完全,VD结束后夹杂物钙处理变性效果明显且钙主要与夹杂物表面反应。对Mg-Al-Ca类夹杂物成分分析得出,钙线的加入使钢中夹杂物Ca含量明显增加,(Al2O3)由VD入位80%～90%降低至中间包中的40%～60%,(Mg)最终降低至10%以下。钙处理对大型夹杂物影响较小。     

非对称二流中间包夹杂物碰撞长大行为研究

采用数值模拟方法考察了非对称二流中间包内夹杂物碰撞长大行为,计算结果表明:挡墙对中间包流场影响较大,有利于控制中间包内钢液湍流流动;安装挡墙后中间包内湍动能耗散率分布更均匀,最大湍动能耗散率为无挡墙时最大值的I/5;挡墙对中间包夹杂物空间分布影响较大;挡墙的安装有利于提高夹杂物去除率,可有效地增强对直径＞ 50的大尺寸...     

Estimation of thermal and mass diffusivity in a porous medium of complex structure using a lattice Boltzmann method

The thermal and mass diffusivity in a porous medium of complex structure is studied by using the lattice Boltzmann method. The media under consideration include two-dimensional medium with an array of periodically distributed circular and square cylinders, three-dimensional granular medium of overlapping or non-overlapping spherical and cubical inclusions of different size, and randomly generated fibrous medium. The calculated effective diffusivities are in good agreement with existing analytical and numerical results when the inclusions, regardless of their shapes, are not overlapped. For the medium of overlapping inclusions, the effective diffusivity deviates from existing correlations as the inclusion fraction increases. In particular, the deviation increases dramatically if the thermal diffusivity of the inclusion is greater than that of the fluid in the medium for enhanced thermal conduction. A new empirical correlation between the effective diffusivity and the volume fraction for the medium of overlapping inclusions is proposed.     

Effect of particle size on sodium distribution and sodium removal by water washing of Zhundong coal

The utilization of Zhundong (ZD) coal has been limited by its high sodium content. In the paper, the effect of particle size on the distribution of the sodium contained in the coal and the sodium removal from the coal was addressed. The results indicate that the water-soluble sodium content and insoluble sodium content increased and the acid-soluble sodium decreased with increasing particle size. The occurrence modes of the sodium contained correlate closely to the properties of ZD coal. The water-soluble sodium and water-soluble chlorine contained in ZD coal may exist in the form of sodium chloride. Due to the competitive effects between adsorbing capability of the leachate and the diffusing capability of sodium ion, the removal sodium rate increases first and then decreases with increasing particle size.     

Numerical study on effect of inclusions on hydrogen segregation in steel under stress conditions

It is generally believed that hydrogen embrittlement (HE) of metallic material is closely related to the presence of hydrogen traps such as inclusions inside. Therefore, the study of hydrogen segregation in the inclusions is essential for the further understanding of the mechanism of HE phenomena. In this study, a numerical model for exploring the hydrogen transport and hydrogen segregation in inclusions under stress conditions was developed, and the effect of inclusion's shape and orientation, micro-cracks and stress magnitude on hydrogen segregation was investigated. Results showed that, inclusion's shape made a great effect on the hydrogen concentration at the inclusions/matrix interface, which became higher as inclusion closed to a globular shape. The hydrogen concentration inside the inclusions was affected by both the shape of inclusions and the angle between the orientation of inclusions and the hydrogen diffusion direction. The hydrogen segregation in inclusions with micro-cracks was much greater than that without micro-cracks, which caused 3–4 times local hydrogen concentration increase in inclusions, leading to the enhancement of HE susceptibility of the steel. The magnitude of stress did not change the regions of hydrogen segregation, but the hydrogen concentration at each region increased with the increasing stress.     

掺混甲烷对预混合丙烯火焰碳烟生成的影响

基于当量比为1.79且最高火焰温度为1 829 K的预混合丙烯火焰,研究了燃料掺混对碳烟生成的影响以及协同效应.分别将5％、20％、40％摩尔分数的甲烷混合到丙烯中,形成具有相同当量比和最高火焰温度的预混火焰.使用微孔探针采样技术和扫描电迁移率粒径谱仪,在燃烧器稳定滞止火焰中测量了碳烟粒径分布.研究发现,掺混甲烷后的火...     

Comparative study of non-metallic inclusions on the critical size for HIC initiation and its influence on hydrogen trapping

In the present work, the critical crack nucleation size and the hydrogen trapping capability of inclusion were discussed with a numerical simulation considering the factors of inclusion/matrix heterojunction. The results showed that the inclusion composition had a significant effect on hydrogen capacity and its critical nucleation size of hydrogen-induced cracking (HIC). The MnS inclusions exhibited a larger critical size tolerance of HIC nucleation (approximately 2.5 μm), but for some typical oxide inclusions, it ranged between 0.1 and 0.4 μm. In addition, two sheets of steel containing different composition, morphology, and distribution of inclusions were studied by the standard-based test and thermal desorption spectroscopy (TDS) to evaluate the HIC susceptibility and hydrogen trapping behaviour. The results complementarily demonstrated that when controlling the non-metallic inclusions into the proper size and compound with MnS into the sphere, the HIC resistance of steel could be efficiently improved.     

用直接数值模拟对移动颗粒层除尘的研究

利用气固两相流数值模拟计算模型 ,分别采用了不同粒径的移动颗粒层过滤除尘器 ,对不同粒径粉尘颗粒的碰撞次数进行统计 ,对移动床除尘中过滤介质尺寸与粉尘粒径尺寸之间的相互选择性进行了初步研究。模拟计算了在同一风速下碰撞次数与粉尘粒径以及移动层颗粒粒径之间的关系。计算统计的结果与实验结果对比发现 ,二者存在定性上的一致。研究结果表明在移动床过滤除尘器中不同粒径的过滤层对不同粒径尘粒具有明显的选择性。     

基于格子Boltzmann方法的饱和土壤渗流与传热数值模拟

本文利用随机多孔介质生成算法重构了与真实土壤外貌相近的多孔介质几何结构。通过引入不可压耦合双分布格子Boltzmann模型（lattice Boltzmann model ,LBM）对孔隙尺度下单相饱和土壤渗流和传热进行了模拟。着重讨论了不同渗流压差、孔隙率、土壤固体颗粒尺寸分布对流动与传热的影响。结果表明：土壤渗流速度与渗流压差呈线性单调递增关系,平均温度随渗流压差增加而增大,但温升速率逐渐减缓;当孔隙率增大时,渗流速度增加,且当孔隙率大于0.58时,对流换热作用迅速增强,土壤温升速率显著加快;对于相同孔隙率,当土壤固相颗粒尺寸较大时,流动出现典型优先流效应;随着土壤固相颗粒尺寸减小,土壤温度变化逐渐趋于平缓,平均温度降低。     

Mitigation of ice crystallization fouling in stationary and circulating liquid–solid fluidized bed heat exchangers

Liquid–solid fluidized bed heat exchangers are attractive ice crystallizers since they are able to mitigate ice crystallization fouling and exhibit high heat transfer coefficients. Experiments show that the fouling removal ability of stationary fluidized beds increases with decreasing bed voidage (95–80%) and increasing particle size (2–4 mm). The removal of ice crystallization fouling appears to be more effective in circulating fluidized beds, especially at high circulation rates. Fouling removal is realized by both particle–wall collisions and pressure fronts induced by particle–particle collisions. A comparison between ice crystallization experiments and impact characteristics shows that the removal rate is proportional to the impulse exerted on the wall. A model based on these phenomena is discussed and predicts the transition temperature difference for ice crystallization fouling in both stationary and circulating fluidized beds with an average absolute error of 9.2%.