还原碳化法制备超细碳化铬粉末

以纳米Cr_2O_3和乙炔黑为原料,经高温还原碳化制备超细Cr_3C_2粉末,研究反应温度、反应时间以及配碳量对Cr_3C_2粉末的粒度与游离碳含量的影响。通过热力学计算,只有当温度高于1 350 K时还原碳化反应才有可能进行,采用纳米Cr_2O_3可显著降低反应温度,在1 573 K下焙烧6 h碳化率即达到98.20%;Cr_3C_2粉末的游离碳含量随配碳量增加而显著提高,配碳量(质量分数)为理论配碳量的1.05倍时制得游离碳含量为0.23%、氧含量为0.91%(均为质量分数)、平均粒度为1μm的Cr_3C_2粉末,该粉末达到硬质合金及热喷涂应用的要求。     

碳化硼陶瓷力学性能及其影响因素

碳化硼的力学性能与其他陶瓷材料一样,对结构十分敏感.在工艺控制过程上看,不可能制得结构完全相同的材料,文献报道的计算式和数据亦非常分散.作者测定了用热压方法制得的碳化硼陶瓷(表现密度为2.1～2.3g/cm~3,晶粒度为12μm)的抗弯强度、抗压强度、弹性(弯曲)模量和泊松比.同时,通过文献检索,搜集了各种公式和数据,并对本实验结果进行了综合分析,得出了有关的计算式和性能值.     

烧结温度对碳化硅陶瓷力学性能的影响

采用硼、碳助剂无压烧结制备碳化硅陶瓷。针对烧结温度与碳化硅烧结体密度、抗弯强度以及硬度之间的关系进行了试验研究,并对不同温度下制备的烧结体进行了显微结构形貌观察和XRD图谱分析。结果表明,烧结温度在2190～2220℃范围内可以制备密度高、力学性能好的碳化硅陶瓷。其相对密度超过96%;抗弯强度接近400MPa;维氏硬度23GPa以上。在试验温度范围内,密度与抗弯强度之间的关系近似为线性关系,密度越高抗弯强度和硬度性能越好。     

Effect of distribution of B4C on the mechanical behaviour of Al-6061/B4C composite

In this work, the effect of mixing parameters on the distribution of B₄C in 6061-Al alloy and its correlation with mechanical behaviour was studied. 6061-Al alloy powder was mixed with 10 mass-% B₄C powder in a ball mill and powder rotator mixer by varying mixing time from 1 to 5?h. Mixing was performed in both wet and dry conditions in a ball mill while only dry condition was used in the powder rotator mixer. The green compacts were sintered at 630°C. The quadrat method was used to quantify the distribution of B₄C particles in the microstructures of sintered Al/B₄C composite. The results showed that the distribution was improved with mixing time but the density, hardness and compression strength of Al/B₄C composites were reduced with time during ball milling. On the other hand, the distribution of reinforcement, density, hardness and compressive strength of Al/B₄C composites was improved with mixing time in the powder rotator mixer.     

碳含量对脱β层硬质合金组织和性能的影响

本文通过一步烧结法制备了三种不同含碳量的WC-Ti(C,N)-(Ti,W)C-(Ta,Nb)C-Co脱β层硬质合金,通过扫描电镜(SEM),电子探针微区分析仪(EPMA)分析合金的微观组织和成分分布,以及测定维氏硬度HV30,断裂韧性KIC等性能指标,研究碳含量对其微观组织和物理力学性能的影响,研究结果表明:在三个合金的表层均形成了缺Ti,Ta,Nb的立方相,而富Co粘结相的脱β层。微量的C含量变化对合金的组织和性能产生重要的影响,合金的脱β层厚度和WC的平均晶粒度均随着C含量的增加而增大。随着碳含量的增加,维氏硬度HV30降低,断裂韧性KIC增加。     

冷轧压下率对TRIP钢组织与力学性能的影响

研究了含铝TRIP钢在相同的热处理条件和不同冷轧压下率时的组织和力学性能。结果表明,随着冷轧压下率增加,材料组织细化,屈服强度连续升高;而抗拉强度和伸长率则由于晶粒细化以及TRIP效应,先升高后降低。冷轧压下率74%时材料的综合性能最佳,此时带状组织的危害也有所减轻或消失。     

纳米钨铜复合粉末的制备与微观形貌

首先采用高浓度湿磨法制备超细WO3-CuO混合粉末,800℃空气中焙烧90min后得到CuWO4-WO3前驱体粉末,再通过氢气还原获得超细W-Cu复合粉末。将该复合粉末与直接还原超细WO3-CuO混合粉末所得的W-Cu复合粉末进行对比,并研究还原温度对W-Cu复合粉末的微观形貌、成分与粒度的影响。结果表明:经过30h高浓度湿磨,WO3-CuO混合粉末的中位径由44.88μm降至0.28μm,焙烧后得到的CuWO4-WO3粉末平均粒径小于0.7μm且分散良好。由CuWO4-WO3还原获得的W-Cu复合粉末细小、分散均匀,还原温度对其形貌影响不大,由WO3-CuO混合粉末直接还原得到的W-Cu复合粉末由大量W-Cu纳米颗粒构成,随还原温度升高,纳米W-Cu颗粒逐渐长大。     

Effect of mechanical activation on carbothermal reduction of chromite with graphite

Abstract

The carbothermal reduction of mechanically activated chromite with graphite under an argon atmosphere was investigated at temperatures between 1100 and 1400°C and the effects of the mechanical activation on chromite structure were analysed by X-ray diffraction, scanning electron microscopy and specific surface area measurement. An increase in specific surface area resulted in more contact points. The activation procedure led to amorphisation and structural disordering in chromite, and accelerated the degree of reduction and metallisation in the mixture of chromite and graphite.

On a effectué une investigation de la réduction carbothermique avec du graphite, de la chromite activée mécaniquement, en atmosphère d’argon, à des températures entre 1100 et 1400°C, et l’on a analysé les effets de l’activation mécanique sur la structure de la chromite par diffraction des rayons x, par microscopie électronique à balayage et par mesure de la surface spécifique. Une augmentation de la surface spécifique résultait en des points de contact plus nombreux. La procédure d’activation menait à une structure plus amorphe et en désordre de la chromite et accélérait le degré de réduction et de métallisation dans le mélange de chromite et de graphite.     

Y_2O_3对硬质合金晶粒尺寸和摩擦磨损性能的影响

研究了稀土Y2O3对WC-10Co硬质合金晶粒尺寸、矫顽力的影响,对比了Y2O3含量0.10%(质量分数,下同)和0.30%硬质合金的摩擦磨损性能。结果表明:微量Y2O3能细化WC晶粒,有效改善合金的硬度,影响硬质合金的磁性能。低于0.15%时,WC-10Co合金晶粒尺寸随着Y2O3增加而明显细化,硬度显著增加;Y2O3含量达到0.2%以上,WC-10Co合金的晶粒尺寸基本稳定,硬度也变化不大。在相同条件下,细晶粒0.30%Y2O3的WC-10Co硬质合金比0.10%Y2O3的WC-10Co硬质合金的摩擦因数稍高,但磨损体积损失低于0.10%Y2O3合金。     

Direct chromium alloying by smelting reduction of mill scale and low grade chromite ore

Direct alloying is the process in which all of the elements needed for alloying can be reduced from their oxides in a furnace or a ladle. This process is one way of reducing the amounts of energy and materials, reducing the loss of alloying elements, and improving working condition. Mill scale produced in rolling mills is considered a rich iron source (> 67% Fe) with minimum impurities. In this paper, iron high-Cr alloy was produced by a direct alloying with chromium in carbo- thermal reduction using fine of low grade chromites ore and mill scale. The smelting experimental heats were carried out in a 5?kg pilot plant submerged electric arc furnace. The charging materials and reduction parameters were varied and the optimum conditions for obtaining alloy with the highest metallic yield and the highest iron and chromium recovery were determined. When using coke as the reducing agent in stoichiometric amounts, for a mixture of mill scale (55%) and chromite ore (45%), 89.1% of the iron and 72.5% of the chromium were recovered, producing iron high-Cr alloy containing 17.9%Cr, 3.73%C, 0.46%Mn and 1.47%Si. The maximum iron and chromium recoveries obtained were 99.3% and 72.5%, respectively when using excess carbon. The present study clarifies the possibility of using a mixture of chromite ore , mill scale and coke as the precursor for direct chromium alloying. This method offers an alternative process route with cheaper raw materials and fewer process steps (by avoiding the step of ferrochrome production) for producing high chromium iron or steel alloys.     

电石渣为钙源的硅热法炼镁煅烧过程

电石渣是化工行业用乙炔法生产乙炔气或聚氯乙烯树脂的工业废渣,其主要成分为Ca(OH)2,是高碱性物质,属于较难处理的工业废弃物.现有处理电石渣的工艺都存在不足之处,因此电石渣的综合利用是近年来研究的重点与热点问题.本文提出以电石渣为钙源的硅热法炼镁工艺,可综合利用电石渣,将其与菱镁石、萤石和硅铁制成预制球团,用于真空热...     

Effect of nickel additions on the oxidation kinetics of double titanium and chromium carbide powder

The effect of powdered nickel additions (10–33 mass %) on the oxidation kinetics of double titanium-chromium carbide produced by the method of self-propagating high-temperature synthesis, and also that of plating the synthesized carbide powder with nickel (26 mass %) was studied. The effect of nickel concentration and powder particle size on the oxidation resistance at different temperatures was different. However, it can be stated that plating the carbide powder with nickel increased its oxidation resistance at all temperatures in the range 600–1000°C, excepting 700°C. The degree of oxidation of the carbide and nickel constituents were estimated. Activation energies for the initial and parabolic stages of oxidation were determined. Translated from Poroshkovaya Metallurgiya. Nos. 1/2(411), pp. 76–82, January–February, 2000.     

冷轧压下率和退火温度对H62黄铜组织性能的影响

利用OM、SEM和室温拉伸试验系统研究了冷轧压下率和退火温度对黄铜组织性能的影响.结果表明:随压下率和退火温度的增加,H62黄铜晶粒尺寸均逐渐增大,强度逐渐降低,伸长率先上升后下降;400℃退火时,α相开始发生再结晶,β相沿α相晶界均匀分布,500℃及以上退火时,α相已完成再结晶,β相将逐渐回溶到α基体中;H62黄铜在56.5%的冷轧压下,600℃退火时能获得最优的力学性能.     

“前驱体+真空碳热还原”法制备超细Mo_2C粉末的研究

利用"前驱体+真空碳热还原"法制备了超细Mo_2C粉末,采用XRD、FESEM等表征手段研究配碳量、合成温度以及保温时间对Mo_2C粉末微观形貌和物相组成的影响。结果表明:在配碳量为150%(质量分数)、合成温度1 150℃、保温2.0 h条件下制备的超细Mo_2C粉末,粒径约为100~500 nm。     

纳米镍粉的粒度分析

纳米材料的性质强烈依赖于其颗粒和晶粒的大小，测量纳米颗粒或晶粒尺寸无论从粉体制备还是从应用上都具有重要的意义。本文针对纳米镍粉进行了一系列粒度分析研究，包括SEM、TEM、激光粒度分析法、比表面分析法、X射线衍射法和X射线小角度散射法(SAXS)。不同的研究手段得到的纳米镍粉的粒径不尽相同。比较各种研究手段得到的结果可以知道其准确程度，并且针对不同的分析要求可选择不同的方法。     

不同粒度镍粉对WC－9％Ni硬质合金性能和组织的影响

研究了不同粒度镍粉对ＷＣ－９％Ｎｉ硬质合金性能和组织的影响，并对镍聚集现象给合金材质造成的不良影响进行了讨论。     

铁精矿粉粒度对精控还原工艺的影响

本文以河北承德地区的铁精矿粉为原料,选用模拟隧道窑还原工艺制备海绵铁粉,研究了铁精矿粉粒度对精控还原工艺的影响。结果表明:铁精矿粉粒度对其还原工艺影响很大,并直接影响海绵铁粉的产品性能。在既定试验条件下,随着铁精矿粉粒度的增大,其精控还原所需最优还原温度随着增加,最佳配碳量先减少后增大,而最佳还原时间随粒度的增大呈现出先增大后减小的变化趋势。究其原因为粒度过小导致的粉体烧结和粒度过大导致的粉体芯部不易还原均会阻碍还原过程的进行。45~75μm粒度区间铁精矿粉最适合作为制备优质海绵铁粉原料,其在配碳量0.8、还原温度1150℃、还原时间4.5 h的精控还原工艺下可制得的海绵铁粉的铁含量高达97.88%。     

基于性能预报技术减少热轧带钢取样频率的探索

性能预报技术是一件具有深远影响的技术,但实现在线应用需系统考虑解决一些约束问题,目前在线应用的报道并不多见。宝钢研究了一种基于性能预报模型对现有热轧产品取样管理流程的优化方法,它通过建立带钢力学性能预报模型,将产品取样管理流程与带钢的实际生产过程相关联,对多数合格带钢实现预报替代取样,而对少数异常带钢进行有针对性地实际取样,从而达到减少取样频率的目的。基于现有生产执行系统（MES系统）的应用实践,探索出一套基于性能状态优化中间品采样频率的方案,实现了性能预报模型的大生产在线应用。该方法依托信息技术和统计技术,既实现了取样的精细化管理,又降低了运营成本。实际应用效果表明,基于性能预报模型的新取样管理方法不但没有降低可靠性,而且可以降低69%的中间品取样量;新方法在加快生产物流上效果也非常明显,可以节省23 h,这些都说明该方法是一项具有实际应用价值的技术。     

Effect of the nickel-chromium binder on the densification kinetics of chromium carbide-titanium nitride cermets in hot pressing

The paper studies the densification kinetics in hot pressing of mixtures with equimass content (50 ∶ 50) of Cr₃C₂ and TiN without a binder at 1350, 1470, and 1800°C under 16.2, 21.6, and 35.7 MPa, a mixture of Cr₃C₂-50 wt.% TiN with 5 wt.% of the Ni-Cr binder at 1300, 1350, and 1370°C under 5 and 10 MPa, and a mixture of Cr₃C₂-50 wt.% TiN with 20 wt.% of the Ni-Cr binder at 1180, 1220, and 1270 °C under 5 and 10 MPa with isothermal holding for up to 25 min. The behavior of materials in hot pressing is analyzed using the viscous flow theory for porous body. It is shown that the compaction of an alloy without a binder and with the Ni-Cr binder in hot pressing is described by a generalized equation of volume viscous flow of a porous body. It is controlled by non-linear creep with an effective activation energy of 3.2 eV in materials without a binder and by a viscous flow in alloys with a metal binder. The structure and mechanical properties of the materials obtained are studied. __________ Translated from Poroshkovaya Metallurgiya, Vol. 46, No. 5–6 (455), pp. 29–37, 2007.     

SiC粒径比对SiC_p/Al基复合材料组织及性能的影响

采用高压扭转(high pressure torsion)法将粒径比分别为1:1,1:7,1:21的SiC颗粒和纯铝粉末的混合物固结成金属基复合材料。利用金相显微镜、显微维氏硬度计、万能试验机和扫描电镜研究不同SiC粒径比对SiCp/Al复合材料显微组织和力学性能的影响。结果表明,与SiC粒径比1:1的试样相比,粒径比为1:7和1:21的试样中SiC颗粒分布更加均匀,颗粒间无明显团聚现象;大颗粒加入后对材料硬度的影响较为复杂,1:21试样硬度值最低;材料伸长率分别提高130%和113%,致密度也高于1:1的试样,材料断裂形式为韧性断裂。SiC粒径比为1:7试样的致密度、伸长率高于粒径比为1:21试样,综合性能较好。