钢包内气泡的形成与运动过程的数值模拟

 以钢包精炼底吹氩气过程中氩气泡为研究对象,运用VOF模型追踪氩气与钢液的界面,在层流条件下三维数值模拟了氩气泡的生成和运动过程。采用Tecplot进行模拟结果的后处理,研究了不同气体流量条件对气泡脱离直径的影响以及气泡的运动特性。模拟结果显示,氩气泡的形成历经膨胀、脱离两个阶段,气泡脱离直径随着气体流量的增加而增加,针对2 mm直径的孔口,其鼓泡流量上限为1.325 L/min。气泡从孔口脱离后历经近似球形、扁平的椭球形、规则的椭球形和不规则的球帽形的形状变化;气体流量越大,气泡的变形程度越剧烈,气泡位于钢包高度中上部位置时,全部呈现近似规则的球形,不随流量的改变而改变。     

T型结晶器抽锭电渣重熔高速钢90 mm方锭新工艺

 晶界处碳化物严重影响高速工模具钢的红硬性和耐磨性能,电渣重熔工艺能够有效地改善钢锭中碳化物尺寸及分布。传统电渣重熔生产较小钢锭的截面尺寸约为[?]200 mm,减小钢锭截面尺寸和增大冷却速率将会进一步减轻碳化物的偏析程度,但将降低生产效率、提高生产成本。采用双极串联、T型结晶器、抽锭电渣重熔新工艺生产90 mm方锭,并与相同熔化速度传统电渣重熔生产[?]200 mm钢锭进行对比试验。对钢锭成分、低倍、夹杂物、显微组织进行检验分析结果表明,90 mm方钢锭中碳化物尺寸和分布明显优于[?]200 mm钢锭,碳化物在后序锻造或轧制过程中更容易被破碎。新工艺电耗也低于传统电渣重熔工艺。     

预变形量对超低碳钢烘烤硬化性能的影响

对超低碳钢进行了不同预变形量的单向拉伸及烘烤处理,研究了不同预变形量对试验钢烘烤硬化(BH)性能的影响,并用透射电镜观察了不同预变形量时试验钢中位错的形貌。结果表明:预变形量在0%～4%时,随着预变形量的增大BH值增大;预变形量在4%～8%时,随着预变形量的增大BH值降低;预变形量在8%～15%时,随着预变形量的增大BH值又有所提高;4%预变形量所对应的BH值最大,8%预变形量所对应的BH值最小;4%预变形量时的位错密度大于8%预变形量时的。     

浅析焦炭反应性与高炉冶炼

总结了焦炭反应性与高炉冶炼关系的认知历程,阐述了不同反应性焦炭对高炉冶炼过程的影响以及不同反应性焦炭生产的技术手段和研究现状。通过对不同反应性焦炭与高炉冶炼过程适用性的讨论,提出了应根据高炉的冶炼条件和矿石的还原性能来规定适宜的焦炭反应性。     

RH工艺及吹气孔堵塞对钢液混匀的影响

以某厂210tRH为原型,建立模型与原型尺寸比为1：4的物理模型。测量了不同吹气量、不同浸渍管插入深度及不同真空室液位高度等操作工艺条件下的混匀时间,讨论了吹气孔堵塞对RH混匀的影响。结果表明：当吹气量大于800L／min、浸渍管浸入深度大于560mm、真空室液位高度大于315mm、吹气孔堵塞不大于3个时均有利于RH钢液混匀。在试验基础上对现场操作工艺进行改进,提高了RH精炼效率。     

Effect of casting speed on microstructure,corrosion behaviour and in vivo bone reaction of Mg-rare earth alloys

In this study, two casting speeds of 10 and 30 r/min were used in vertical twin-roll casting(TRC) to obtain Mg-rare earth(MgRE) alloys, and their microstructures, corrosion behaviours and in vivo bone reactions were investigated in detail. The results indicated that the roll-castings of TRC-30 r/min exhibited a finer grain size and higher volume fraction of non-crystallization than those in castings of TRC-10 r/min. Moreover, the results of electrochemical impedance spectroscopy(EIS) and potentiodynamic polarization indicated that the castings of TRC-30 r/min displayed a higher corrosion resistance compared with those in the castings of TRC-10 r/min. Animal tests showed that a higher degree of newly formed bone tissues was achieved by implants of TRC-30 r/min. Additionally, in vivo tests displayed that degradation properties of the TRC-30-r/min implants were better than those of the TRC-10-r/min implants; furthermore, the degradation layer was a two-layer structure, and P and Ca were enriched in the outer degradation layer. In summary, these findings elucidated that casting speed has a substantial effect on the microstructure and degradation property of Mg-based implants, and the degradation property performs better with increased casting speed.     

不同预热温度WC增强镍基合金堆焊层的微结构演化与摩擦学性能

目的 研究不同预热温度(200、400 ℃)条件下硬质颗粒增强镍基合金堆焊层的微观组织结构演化机理,以及对其力学性能、磨损性能的影响规律。方法 采用等离子弧焊接技术在42CrMo钢基体表面堆焊硬质WC颗粒增强镍基强化层,利用X射线衍射(XRD)、扫描电子显微镜(SEM)、硬度计和摩擦磨损试验机,分析不同预热温度堆焊层的物相组成、微观组织形貌、力学性能和磨损性能,建立堆焊层制备工艺–微观组织结构–力学性能–磨损性能之间的强映射关系。结果 堆焊层主要由γ-Ni/Fe、WC、W2C、M7C3、M23C6、Ni2W4C、Cr3C2等物相组成,在预热温度200 ℃下堆焊层二次碳化物析出较少,发生了严重的WC颗粒沉降现象;在预热温度400 ℃下,堆焊层析出了大量的二次碳化物,WC颗粒沉降减弱,组织均匀性提高。在400 ℃下预热,相较于200 ℃下预热,堆焊层的磨损质量减少了51.85%,磨损率减少了51.89%。结论 高预热温度和长保温时间可促进WC颗粒界面反应,驱动大面积二次碳化物的析出,有效缓解WC颗粒沉降,改善凝固组织中WC颗粒的分布均匀性,从而显著提高堆焊层的硬度和耐磨性。     

Construction of WS2 triangular nanoplates array for hydrogen evolution reaction over a wide pH range

As a classic transition metal dichalcogenide, WS₂ has been synthesized by a variety of methods towards different applications. However, few of them are vertically grown self-templated structures, besides, all the reported WS₂ for hydrogen evolution reaction (HER) are in acidic media. Herein, we use a simple method to synthesize a new morphological WS₂ triangular nanoplates array through the sulfuration of hydrothermally obtained WO₃ nanowires on carbon cloth (WS₂TN/CC). The WS₂TNs are equilateral triangle with large surface area that grown vertically on carbon fiber. The WS₂TN/CC exhibits good catalytic activity and stability as electrocatalyst for HER in acidic media and firstly in both neutral and alkaline media. The overpotential of 196, 150 and 193 mV are needed to afford current density of 10 mA cm⁻² in acidic, neutral and alkaline media, respectively.     

Effects of sintering curves on microstructure,physical and mechanical properties and on low temperature degradation of zirconia-toughened alumina

The objective of this work was to study two-step sintering as a means of controlling the microstructure of coarse Al₂O₃ matrix composites containing submicrometric and nanometric inclusions of ZrO₂ ranging from 0–30 wt. % by weight based on commercially available powders and evaluate its hydrothermal degradation as function of a water vapour pressure and its mechanical properties. The results showed that two-step sintering allowed a more efficient microstructural control than single-step sintering, resulting in good mechanical properties. The highest flexural strength was achieved for ZTA samples sintered in two-stage sintering conditions TSS2 with T1 = 1560 °C for 3 h, T2 = 1460 °C for 8 h. The studied composites showed good resistance to hydrothermal degradation compared to composites sintered in single step sintering conditions.     

New understanding on formation mechanism of CaFe2O4 in Fe2O3 -Fe3O4-CaO-SiO2 system during sintering Process: Phase transformation and morphologies evolution

The complex calcium ferrite is the main binder phase of high basicity, high iron and low silicon sinter used in blast furnace (BF), and its formation amount and structure are important factors affecting sinter quality. This work research on the phase transformation and morphologies evolution of Fe₂O₃ -Fe₃O₄-CaO-SiO₂ systems roasted 900 °C ? 1200 °C in air atmosphere to understand the formation process of calcium ferrite. In CaO-Fe₃O₄ system, the prolonged roasting time and higher temperature promotes that CaFe₅O₇, CaFe₃O₅, and Ca₂Fe₂O₅ gradually transformed into the stable existence of CaFe₂O₄. In CaO-Fe₃O₄ system, the higher temperature promotes that the combination of Fe₃O₄ and CaO formed the stable CaFe₃O₅ with orthorhombic structure. The replacement reaction between the newly formed CaFe₃O₅ phase and the unreacted CaO phase occur to form Ca₂Fe₂O₅. In CaO-Fe₃O₄-SiO₂ system, FeSiO₃ can be combined with Fe₃O₄ to form Fe₂SiO₄ and Fe₂O₃. Under the action of high temperature, FeSiO₃ and CaO undergo displacement reaction to form the unstable CaSiO₃, the new formation of CaSiO₃ can be easily combined with CaO to form the stable Ca₂SiO₄. With the further increase of temperature, the complex calcium ferrite is formed in calcium silicate layer. The final product complex calcium ferrite and calcium silicate exist at the same time. The formation of calcium silicate has an unfavorable effect on formation of complex calcium ferrite in the sintering process.