Strengthening Mechanisms in Mechanically Milled Oxide-Dispersed Iron Powders

Nanocrystalline iron and oxide dispersion-strengthened (ODS) iron powders (Fe, Fe-Y₂O₃, and Fe-Y₂O₃-Ti) were prepared by mechanical milling for periods ranging from 1 to 40 hours. The as-milled powders were examined for changes in their particle sizes, crystallite sizes, hardness values, and phases present as a function of milling time. Both the particle and the crystallite sizes of all the three compositions decreased with milling time, while the hardness values of all the three powders increased with milling time because of the crystallite size refinement. At the same crystallite size, the hardness values of Fe-Y₂O₃ and Fe-Y₂O₃-Ti powders were higher than that of the Fe powders. Though, the presence of 40 nm Y₂O₃ could be established for 2-hour milling, such particles were not resolvable in 40-hour-milled powders. However, SAD patterns confirmed the presence of complex oxide dispersoids in the Fe-Y₂O₃ and Fe-Y₂O₃-Ti powders. The variation of hardness value with the crystallite size and as a function of the milling time can be rationalized on the basis of Hall–Petch crystallite size strengthening in combination with dispersion strengthening (in Fe-Y₂O₃- and Fe-Y₂O₃-Ti-milled powders) due to dispersoids. The observed double-positive slopes in the Hall–Petch relationship can be explained in terms of an increase in misorientation angle between the crystallites with increasing milling time due to the crystallite rotation driven by disclination dipoles.     

Carbothermal Reduction of Iron Ore Applying Microwave Energy

This paper presents the results of a study on carbothermal reduction of iron ore made under the microwave field in equipment specially developed for this purpose. The equipment allows the control of radiated and reflected microwave power, and therefore measures the microwave energy actually applied to the load in the reduction process. It also allows performing energy balances and determining the reaction rate with high levels of confidence by simultaneously measuring temperature and mass of the material upon reduction with high reproducibility. We used a microwave generator of 2.45 GHz with variable power up to 3000 W. Self‐reducing pellets under argon atmosphere, containing iron ore and petroleum coke, with 3.5 g of mass and 15 mm of diameter were declined. We obtained the kinetic curves of reduction of iron ore and of energy consumption to the process in the maximum electric field, in the maximum magnetic field and at different values of power/mass. The data allow analyzing how the microwave energy was actually consumed in the reduction of ore.     

Effect of Gas Atmosphere on Carbothermal Reduction and Nitridation of Titanium Dioxide

This article examined the reduction/nitridation of rutile in the He-N₂, Ar-N₂, and He (Ar)-H₂-N₂ gas mixtures, as well as pure nitrogen, in the temperature-programmed and isothermal experiments in a fixed-bed reactor. The extents of reduction and nitridation were determined from the off gas composition and LECO analysis. The off-gas composition was monitored using the infrared sensor (CO, CO₂, and CH₄) and dew point analyzer (H₂O). The phase composition of the reduced samples was analyzed using X-ray diffraction (XRD). The temperature and gas composition had a strong effect on the rutile reduction. The reduction was the fastest in the H₂-N₂ gas mixture, followed by a reduction in nitrogen; the rate of reduction/nitridation in the He-N₂ gas mixture was marginally higher than in the Ar-N₂ gas. The rate of titania reduction/nitridation in the He (Ar)-H₂-N₂ gas increased with the replacement of He (Ar) with hydrogen. The article also discusses the mechanisms of reduction/nitridation in different gas atmospheres.     

钛精矿碳热还原制备碳氮化钛的研究

以钛精矿和石墨为原料,在氮气气氛下通过碳热还原法制备出碳氮化钛(Ti CN)粉体。结合XRD、SEM、化学成分分析和TG-DSG综合热分析研究了配碳量及反应温度对钛精矿碳热还原进程的影响。研究结果表明,配碳量的增加影响逐级还原反应温度以及反应总失重,当配碳量达到23%时碳氮化钛产物中出现游离碳。钛精矿碳热还原过程中铁氧化物优先还原,钛氧化物经逐级还原形成Ti CN,还原顺序为Ti O2→Ti4O7→Ti3O5→Ti N→Ti(C,N,O)→Ti CN。得到的碳氮化钛粉体呈微米级不规则形状。     

On the Behaviour of Hematite and Graphite Blend during Ball Milling and Heating Up Reduction of Milled Mixture

The effect of ball milling under argon and air atmospheres on the reaction behaviour of the mixture of sintered hematite and graphite was investigated. Thermo‐gravimetry / differential thermal analysis (TG‐DTA) was adopted to determine the effect of milling time on the reduction process during heating up under Ar atmosphere. The samples were heated at a constant heating rate of 10 °C/min from room temperature up to 1100 °C and maintained at this temperature for 30 minutes. TGL (thermo‐gravimetry loss) curves showed a decrease of onset temperature of reduction with increase of milling time. XRD patterns of milled samples at room temperature revealed that the peaks of graphite disappeared after 48 hours milling. This represents the transformation of crystalline structure of graphite to the amorphous structure. By increasing the milling time to 72 hours, magnetite peaks appeared in the XRD pattern as a result of reduction of hematite with graphite during milling. However, the amount of magnetite formed during milling process increased as milling proceeded. The powders milled under Ar atmosphere became more active than the powders milled under air and consequently the carbothermic reduction of hematite in powders milled under Ar atmosphere was observed at lower temperatures compared with air‐milled powders. It was observed that the reduction time of hematite in powder mixture was decreased with increase of sintering time of hematite prior to milling.     

Study of Technology for Preparing Titanium Carbide and Calcium Metal from Perovskite Concentrate by a Carbothermal Method

Metallurgist - Substantiation of using a carbothermal method for processing flotation perovskite concentrate is presented. Results of X-ray structural studies of compacted specimens after two...     

应用三氯化钛还原滴定法测定铁矿石中的全铁

叙述了采用三氯化钛还原滴定法测定铁矿石中的全铁.通过对温度、硫磷混酸冒烟高度、还原剂等影响因素进行分析后,规范了测定操作标准并应用于全铁含量大于50％的铁矿石测定,提高了分析结果的精密度和准确度,成本低,分析周期短,取代了氯化汞法测定全铁,能够满足生产需要.     

碳化硅纳米线增强钛基复合材料的制备与性能研究

采用球磨法将Ti60合金粉末与碳化硅纳米线(SiCnw)混合,通过放电等离子活化烧结工艺制备SiCnw/Ti60复合材料。利用扫描电子显微镜、X射线衍射仪和万能力学试验机研究复合材料的组织形貌、物相结构和力学性能。结果表明,在Ti60合金中添加SiCnw后,基体晶粒尺寸显著减小,当SiCnw添加量为0.1%(质量分数)时,SiCnw/Ti60复合材料的晶粒尺寸较Ti60合金下降42%,抗拉强度提高2.7%,为1037 MPa。SiCnw在晶界处的均匀分布可起到钉扎效应,在拉伸过程中SiCnw承担了基体间的载荷传递,从而提高了SiCnw/Ti60复合材料的拉伸强度。     

铁矿石全铁含量的测定——三氯化钛还原法

试验制定三氯化钛还原法测定铁矿石中全铁含量的分析方法,并验证其使用情况。     

Hardening Through an Ultrafine Carbide Precipitation in Austenite of a Low-Carbon Steel Containing Titanium and Tungsten

Metallurgical and Materials Transactions A - In this study, a significant hardening effect was obtained in a low-carbon steel containing Ti and W by performing a 20 pct hot compressive...     

Reaction Synthesis of Titanium Matrix Composites Through Powder Metallurgy Processing Technique

Titanium matrix composites reinforced with 10, 20 and 30 vol.% of in situ TiB–TiC reinforcements were fabricated using powder metallurgy method which offers economical solution for production of high performance materials. The in situ composites were produced by reaction of sintering of uniformly blended and compacted powders of titanium and boron carbide in required proportions. XRD analysis confirmed the completion of in situ reaction. SEM studies confirmed uniform distribution and the shape of the reinforcement, TiB as whiskers and TiC as equiaxed particles. The effect of morphology and reinforcement volume on properties of the composites were evaluated by measurement of modulus, hardness, three-point bend test and compression test at ambient temperature along with unreinforced titanium. The study has revealed that the composites with increasing percentage of the reinforcements exhibited improved properties due to the presence of TiB whiskers distributed uniformly. Fractography of the three-point bend tested samples revealed the plastic mode of fracture for unreinforced titanium and the composites exhibiting mixed mode of fracture.     

钒钛铁精矿含碳球团直接还原试验

采用正交试验和单因素试验考察还原温度、配碳量(nC/nO)、还原时间对某钒钛磁铁矿精矿直接还原的影响。结果表明,影响含碳球团金属化率的主次因素依次为还原温度、配碳量、还原时间。优化工艺参数为:还原时间35min、还原温度1 350℃、配碳量1.25、水分9%、成型压力12MPa、黏结剂加入量0.4%,此工艺条件下含碳球团的金属化率达91.77%,还原后球团的主要物相组成为金属铁。     

Phosphorus Removal and Iron Recovery from High-Phosphorus Hematite Using Direct Reduction Followed by Melting Separation

To efficiently utilize high-phosphorus oolitic hematite resources, a method using direct reduction followed by melting separation was proposed. In this study, direct reduction behavior of the ore–char briquette and the melting separation behavior of the reduced briquette were investigated. Direct reduction test results show that under investigated conditions, the briquette reached a metallization rate of 80%–88% and a residual carbon value of 0.11–4.85 wt%,and apatite layers were fragmented into tiny particles, some of which were embedded in metallic iron phase. Melting separation test results show that residual carbon can significantly influence the iron recovery rate. For metallic briquettes with the abovementioned qualities, the iron recovery rate ranged from 75% to 98%. To control the phosphorus content in molten iron to be nearly 0.4 wt%, an iron recovery rate of 80% was shown to be adequate.     

云南某高磷鲕状赤铁矿提铁降磷试验研究

云南某鲕状赤铁矿磷含量高达0.87%,铁品位为45.14%。对此矿石进行单一的强磁选及反浮选试验研究,结果表明都不能获得磷品位低于0.2%,铁品位较高的铁精矿。采用强磁-反浮选及脱泥-反浮选均能获得磷品位低于0.2%,铁品位高于52%的铁精矿。脱泥-反浮选具有投资成本低,流程结构简单的优势,推荐采用此流程处理该矿石。该研究对开发此类高磷鲕状赤铁矿具有一定的借鉴意义。     

Structures and Properties of Iron Matrix Composites with Tungsten Carbide Particle by EPC-V Process

Ｍｏｄｅｒｎｉｎｄｕｓｔｒｙｍａｋｅｓｄｅｍａｎｄｓｏｎｗｅａｒｒｅｓｉｓ－ｔａｎｃｅｏｆｅｎｇｉｎｅｅｒｉｎｇｍａｔｅｒｉａｌｓ．Ａｓａｋｉｎｄｏｆｓｕｒｆａｃｅｔｒｅａｔｍｅｎｔｔｅｃｈｎｏｌｏｇｙ,ｃａｓｔｉｎｇｐｅｒｍｅａｔｉｎｇｔｅｃｈｎｏｌｏ－ｇｙｃａｎｓａｔｉｓｆｙｔｈｅｎｅｅｄｓｏｆｗｅａｒｒｅｓｉｓｔａｎｃｅｏｆｍａｔｅｒｉ－ａｌｓ,ｂｕｔｔｈｅｒｅａｒｅｍａｎｙｄｉｓａｄｖａｎｔａｇｅｓｉｎｔｒａｄｉｔｉｏｎａｌｃａｓｔｉｎｇｐｅｒｍｅａｔｉｎｇｔｅｃｈｎｏｌｏｇｙｗｈｉｃｈ…     

三氯化钛还原-重铬酸钾滴定法测定球团矿中TFe

采用碱混合熔剂熔融试样,熔融物以热水浸取盐酸酸化后,用SnCl2-TiCl3将Fe3+还原为Fe2+,以钨酸钠为指示剂指示还原终点;在硫磷混酸介质中,以二苯胺磺酸钠为指示剂,用重铬酸钾标准溶液滴定球团矿中TFe含量。该法测定TFe的绝对误差<0.15%,避免了用重铬酸钾氧化褪去钨蓝色泽时易引入的误差。     

Reduction and Swelling of Fired Hematite Iron Ore Pellets by Non-coking Coal Fines for Application in Sponge Ironmaking

In the present investigation, the reduction and swelling behaviors (in low grade coal) of fired iron ore pellets, prepared by blending hematite iron ore fines of ?100, ?18 + 25, and ?10 + 16 mesh sizes in different proportions, have been studied in the temperature range of 850–1000°C with an objective to promote massive utilization of fines in sponge ironmaking. An increase in temperature up to the range studied (850–1000°C) substantially enhanced the reduction rate and the rate was found to be highest in the first 15–30 min at all these temperatures. All the fired pellets, made by mixing iron ore particles of ± 100 mesh size, have shown approximately the same reduction rates and slightly higher swelling indices than those made from fines of ?100 mesh size only. In all the fired pellets reduced at temperatures of 850°C and 900°C, the results indicated an increase in the extent of swelling with reduction time. Reduction of fired pellets at temperatures of 950°C and 1000°C exhibited shrinkage in their reduced products, and the extent of this shrinkage increased with increase in exposure time.     

钒钛铁精矿内配碳球团直接还原的动力学

采用等温还原试验并结合热力学反应数据,对钒钛铁精矿内配碳球团直接还原的还原反应进行了分析.以还原反应发生10min为边界点,将反应过程分为前期和后期两个阶段,建立了还原过程的动力学模型.结果表明,钒钛铁精矿内配碳球团直接还原的还原度随反应温度的升高而增大.温度越高,球团在反应前期还原度的增加速率越大,达到的最终还原度越...