Effect of dispersed particles on microstructure evolved in iron under mechanical milling followed by consolidating rolling

The microstructure and the strength of an iron mechanically milled with various amounts of oxygen (i.e., 0.2, 0.6, and 1.5 mass pct) were studied. The samples were subjected to a mechanical milling in an argon atmosphere for 100 hours followed by consolidating bar rolling to a total reduction of about 86 pct at 700 °C. The microstructure of the steels sensitively changed depending on the oxygen content, i.e., on the volume fraction of the oxide particles. The average grain size decreased from about 0.7 to 0.2 μm with an increase in the amount of oxygen. Moreover, the misorientation distributions of the grain boundaries were different in the samples with various amounts of oxygen. A relatively large fraction of low-angle boundaries arranged crosswise to the rolling axis was registered in the samples with 0.2 and 0.6 pct oxygen, while the near random distribution of the boundary misorientations was obtained in the specimens with 1.5 pct oxygen. The effect of dispersed particles on the structure evolution and the relationship between microstructures and some mechanical properties are discussed.     

Annealing behavior of submicrocrystalline oxide-bearing iron produced by mechanical alloying

The structural changes upon annealing of an ultrafine-grained iron containing dispersed oxides were studied. The starting material was subjected to mechanical milling followed by consolidating bar rolling. The fine-grained microstructures were essentially stable against discontinuous grain growth and/or primary recrystallization during annealing at temperatures up to 800 °C, where the specimens maintain a very fine ferrite grain size. The annealing behavior is mainly characterized by normal grain growth accompanied by recovery. The grain-growth kinetics correlates with the oxide coarsening. Both the grain growth and the oxide coarsening can be enhanced by an increase in the temperature. The static restoration/recrystallization processes operating in the ultrafine-grained matrices, as well as the effect of dispersed oxides particles, are discussed in some detail.     

Some aspects on porous properties of iron oxides containing foreign oxides reduced by hydrogen

The objective of this study is to prepare suitable iron ores for industrial reduction processes. Therefore, the properties of porous, green and indurated hematite compacts as well as iron ore were investigated by quantitatively measuring pore volume, BET surface area and pore size distribution. Furthermore, the influence of foreign oxides on porous properties was investigated. Based on these data, the mechanism of sintering process of the compacts was discussed. The results obtained here suggest that the porosity of the compacts after almost 100 pct reduction does not depend upon whether the compacts were indurated or not. Therefore, it would be concluded that indurating the compact is not necessary for pulverized iron ores containing foreign oxides when reduced in the process such as a fluidized bed system.     

Structure and mechanical properties of iron subjected to surface severe plastic deformation by attrition: II. Mechanical properties of nano- and submicrocrystalline iron

Depth-sensing indentation is used to study the effect of grain refinement to submicro- and nanograins on the mechanical properties (hardness, plasticity, Young’s modulus) of armco iron subjected to severe plastic deformation by attrition in argon. In contrast to fcc metals, where the hardness increases and the plasticity decreases as the grain size decreases to 20 nm, the hardness of bcc iron decreases from 5.8 to 3.7 GPa and plasticity δ _A increases from 0.82 to 0.87 as the grain size decreases from 50 to 20 nm.     

Self-lubeicating iron coatings containing oxides,carbides, and borides

Conclusions It is shown that the wear resistance of multicomponent composite coatings is higher than that of some quenched constructional, alloy, and tool steels.Translated from Poroshkovaya Metallurgiya, No. 2(182), pp. 26–29, February, 1978.     

Structure and mechanical properties of iron after surface severe plastic deformation under friction with simultaneous nitrogen saturation: II. The mechanical properties of nano- and submicrocrystalline iron saturated with nitrogen during deformation

The effect of structure refinement of iron to submicro- and nanograins during intense plastic deformation under friction (SPDF) with simultaneous nitrogen saturation on the mechanical characteristics (hardness, plasticity, Young??s modulus) has been studied by nanoindentation. The nitrogen saturation of iron during SPDF is shown to increase the hardness of micro- and submicrocrystalline regions of the surface layer as compared to SPDF in argon as a result of solid-solution hardening. A high nitrogen concentration in an ??-Fe[N] solid solution weakly affects the mechanical properties of nanocrystalline iron with grain sizes d < 50 nm, in which deformation is controlled by grain-boundary sliding.     

机械球磨制备Al-Pb合金

通过对Al-Pb混合粉进行不同时间的机械球磨，采用扫描电镜、电子探针对混合粉颗粒的形貌和组织结构进行了观察，并测试了球磨粉末的显微硬度和致密性能，结果表明：在机械球磨过程中，Al-Pb混合粉的颗粒尺寸初期增大，随后逐渐减小，最后趋于稳定；Al-Pb混合粉形成了层片状的复合粉，随球磨时间延长，层片变薄，最后层片组织断裂为细小弥散的颗粒；随球磨时间延长，Al-Pb复合粉的硬度增大，压制密度降低。最后将球磨6小时的Al-20Pb复合粉用挤压比为4的模具进行包套挤压，得到了高致密度的Al-20Pb合金材料，其孔隙度只有3％左右。该合金中Pb相的尺寸平均只有几个微米，且分布比较均匀。     

氢化燃烧合成与机械合金化复合制备LaMg_(11.5)Ni_(0.5)储氢材料

采用氢化燃烧合成和机械球磨复合制备了LaMg11.5Ni0.5三元储氢材料,物相分析可知,该体系由MgH2、Mg、Mg2NiH4,Mg2NiH0.3,LaH2以及少量LaNi5H0.3构成.氢化燃烧合成产物LaMg11.5Ni0.5经20h球磨后,在423K时,100s内达到饱和吸氢量3.42%(质量分数);在523K时,1 800s内放氢基本完全,放氢量为3.29%(质量分数).研究表明,该产物在523K时的放氢过程受界面移动过程控制.     

The rate of reduction of iron oxides by carbon

The rate of reduction of Fe₂O₃ and FeO by coconut charcoal, coal char and coke, in an inert atmosphere within the temperature range 900 to 1200°C was investigated. The effects of pressure, particle size, and the amount of carbon were determined. The results indicate that the reaction takes place by means of the gaseous intermediates CO and CO₂, and that the overall rate is controlled by the oxidation of the carbon by CO₂. The rates of reduction of FeO and Fe₂O₃ by CO are relatively fast, and the CO₂/CO ratio for the oxidation of carbon is determined by their equilibria. The reduction of Fe₂O₃ by carbon is accomplished in two stages, with FeO forming first. The reduction of Fe₂O₃ to FeO is faster than that of FeO to Fe because its CO₂/CO equilibrium ratio is higher and hence the rate of oxidation of carbon is faster. A direct comparison was made between the rate constants for the reduction of FeO by carbon and those for the oxidation of carbon in the appropriate CO₂-CO gas mixtures, and they are in good agreement. Apparently the iron formed by the reduction does not significantly catalyze the oxidation of carbon; whereas for the reduction of NiO by carbon, the Ni formed does catalyze the oxidation of carbon.     

Reduction of iron and chromium from oxides by carbon

The reaction of iron and chromium oxides with carbon is considered. The decomposition of carbon monoxide is an important source of carbon at the surface of the iron oxides. In the reaction of Cr₂O₃ with carbon, the first stage includes dissociation of the oxides, with the liberation of atomic and molecular oxygen, and the formation of carbon oxides. Rapid reduction of chromium is ensured by the reaction of Cr₂O₃ with C₃O₂ and elementary carbon, which is produced from oxides.     

Non-Topochemical reduction of iron oxides

Non-topochemical behavior was studied during reduction of porous spheres of hematite by stages through the intermediate oxides and also continuously to iron by CO/CO₂ mixtures at temperatures of 600 to 900°C (873 to 1173 K). The behavior became more nearly topochemical as temperature increased. Shrinking occurred during the reduction of hematite to magnetite and of magnetite to wüstite, whereas swelling was observed during the reduction of wiistite to iron. Shrinking was greater, and swelling less, at higher temperatures. The total surface area of the solid decreased with increasing extent of reduction during each of the three stages. A non-topochemical model was developed which satisfies, better than previously proposed models, the reduction data for the single reactions and the three reactions occurring simultaneously. The model provides for variation in particle size and local changes in porosity and effective diffusivity. An empirical “sintering exponent” was introduced to describe changes in reacting surface area.     

Influence of pulsed mechanical activation of hematite-graphite-aluminum powder mixtures on the reduction of iron oxides

To decrease the temperature of direct iron reduction by carbon and aluminum, short-term pulsed mechanical activation (PMA) of an Fe₂O₃ + C_gr + Al powder mixture is perfumed during sound-frequency shock loading by a flat activating plunger. The PMA efficiency for powders in comparable with mechanical activation in high-energy ball mills in a decrease in the activation time and retaining the chemical purity of a powder composition.     

Gaseous reduction of iron oxides: Part III. Reduction-oxidation of porous and dense iron oxides and iron

The internal reduction of high-grade granular hematite ore in hydrogen and carbon monoxide, and also the internal oxidation of porous iron granules in CO₂-CO mixtures have been investigated. To assist the interpretation of the rate data for porous iron and iron oxides, rate measurements have been made also with dense wustite, previously grown on iron by oxidation. The iron formed by reduction of dense wustite is porous, similar to that observed when porous hematite is reduced. It is found that the rate of dissociation or formation of water vapor or carbon dioxide on the iron surface is about an order of magnitude greater than that on the surface of wustite. The results of the previous investigations using dense iron and wustite are in general accord with the present findings. The rate of reduction of hematite increases with increasing pore surface area of the reduced oxide. The results indicate that the rate of reduction of granules is controlled primarily by the formation of H₂O or CO₂ on the pore walls of wustite. The specific rate constants evaluated from internal reduction, using the total pore surface area, are about 1/50 to 1/100 of those for dense wustite. These findings indicate that with porous wustite or iron, the effective pore surface area utilized is about 1 to 2 pct of the total pore surface area. The rate of reduction in H₂-CO mixtures is in accord with that derived from the rate constants for reduction in H₂ and CO.     

Electron-microscopic investigations of highly dispersed iron powders obtained by the electroemulsion method

Conclusions Depending upon the electrolysis conditions and the rate of movement of the emulsion the form, dispersion, degree of aggregation, and specific surface of highly dispersed iron particles change. The electroemulsion method makes it possible to obtain 0.15–0.25~m metal particles close to monodispersed.Translated from Poroshkovaya Metallurgiya, No. 6(258), pp. 68–72, June, 1984.     

ICP-AES法测定冶金炉渣中氧化物及全铁

提出用ICP AES分析法测定冶金炉渣中SiO2,Al2O3,CaO,MgO,MnO,TFe,P2O5,TiO2等成分。试样经常规熔融处理及稀释后,用工作曲线法测定,各组分的测量范围0.01%～50.0%,经与化学法对照,效果满意,可取代化学方法。