Structure of IF steel in continuous annealing

The recovery and recrystallization kinetics of IF titanium steel is studied by investigating the microstructure, measuring the coercive force, and analyzing the residual stress. The results are familiar, except for the initial and final temperatures of these processes, which are specific to the steel employed. We assume that, on heating cold-rolled IF steel in the range 550?C650°C, the dislocation density is unchanged on account of retardation by small TiC particles. Formulas are derived for the coercive force as a function of the grain size and may be used for monitoring purposes.     

Coercive force and microstructure in a Zr-permalloy

An alloy containing 80.0 pct Ni, 12.65 pct Fe, 6.74 pct Mo, 0.36 pct Zr, and 0.25 pct Mn by weight was cast, homogenized, and successively cold rolled into thin strips with area reductions of 0, 50, 75, and 90 pct. Annealed samples were studied by optical and electron microscopy, electron diffraction, and magnetic testing to determine the effects of cold work and annealing upon the microstructure and magnetic properties of the alloy. Cold work produced a high initial hardness together with high coercive force. Recrystallization of the cold worked structures occurred upon annealing at 600°C (873 K) and above and caused significant and parallel decreases in hardness and coercive force. The activation energy for recrystallization was found to be 80.5 kcal/g mole (337.0 kJ/g mole) for the 50, 75, and 90 pct cold worked specimens. After annealing at 600°C (873 K), a small number of spherical Ni₄Mo particles were observed, but the particles produced little change in magnetic properties apparently because of their relatively coarse size and large spacing. Beginning at 700°C (973 K) ribbon-shaped particles of a Ni₅Zr intermetallic compound also precipitated out of solid solution. Both the Ni₄Mo and Ni₅Zr precipitates were the result of a homogeneous continuous precipitation reaction within the grains. A peak in coercive force at 800°C (1073 K) is attributed to domain wall pinning associated with the fine distribution of rodlike Ni₅Zr particles. Cold working 90 pct and aging at 800°C (1073 K) was found to increase coercive force by almost 60 pct from the minimum produced by complete recrystallization. Annealing, however, decreased hysteresis and improved squareness.     

Preparation and Properties of Iron Powder Plated with Nickel and Cobalt

The magnetic properties (magnetic induction and coercive force) of iron powder coated with nickel and cobalt as a result of chemical deposition from hypophosphite electrolytes are studied. Thermogravimetry, differential thermal and x-ray phase analyses are used to study in detail the kinetics and mechanism of high-temperature oxidation in air (up to 1200°C) for the original and coated powders. The phase composition of oxide films on specimens annealed at all temperatures of the DTA-curve peaks is determined. The possibility of increasing the high-temperature oxidation resistance of iron powder coated with nickel or cobalt is demonstrated.     

Manufacture of magnetic cores from various iron powders

Conclusions Coercive force measurements were made on grades PZh4M3, PZhCh3SV, PZhCh3MV, NC 100.24, PZhR(0) and PZhÉ iron powders and magnetic cores heat treated in the temperature range 750–1200°C. Iron powders of large specific surface are characterized by greater coercive forces compared with powders of small specific surface. Grades PZhCh3SV, PZhCh3MV, NC 100.24, and PZhR(0) iron powders are suitable for the manufacture of magnetic cores after they have been alloyed with elements decreasing internal stresses in alloys. Sintered magnetic cores from PZhÉ electrolytic iron powder meet all the requirements of TU 16-538.225-74 without alloying. The properties of grades EMP300M, PM282N, KiP 270.MS, and SC 100.26 iron powders were assessed. KiP 270.MS and SC 100.26 powders possess the same properties as PZhCh3SV, PZhCh3MV, and NC 100.24 powders, but in grade SC 100.26 powder high oxygen contents are not permissible. Consequently, magnetic cores made from this powder will exhibit high coercivity. Grades EMP300M and PZhR(0) iron powders are similar in all their properties, and the magnetic characteristics of cores made from them will therefore also be comparable. Grade PM282N iron powder is produced by the electrolysis of solutions and characterized by a dendritic particle shape. Owing to the large specific surface of the particles of this powder, its coercive force will be 25–30 A/m greater than that of PZhÉ. In the manufacture of magnetic cores from this powder recourse must therefore be had to alloying with silicon in order to decrease their coercivity.Translated from Poroshkovaya Metallurgiya, No. 6(234), pp. 73–78, June, 1982.     

Progress of Sm-Fe-N Anisotropic Magnets

A reduction and diffusion method (R/D) is used to make a mother alloy of Sm-Fe-N anisotropic magnets. Reduction of 0.5wt% of samarium content compared to the conventional powder increases magnetization. Milling condition and surface treatment improve the squareness of demagnetization curve, the aging property and the heat resistance. The maximum energy product of 292 kJ/m³ is obtained with the powder. High coercive force is maintainable even if the powder is exposed for 300h in 80 °C 90%RH. The maximum energy product of 141 kJ/m³ is obtained with an injection molded anisotropic magnet. The aging property estimated by irreversible flux loss is comparable to the conventional MQP-B magnets. The heat resistance temperature (T_−5%) at which die initial irreversible flux loss becomes −5% is 125-more than 150 °C for Sm-Fe-N magnets and 150–170 °C for hybrid magnets. The magnetic properties of bonded HDDR Nd-Fe-B magnet were improved by substituting for Nd-Fe-B powder with Sm-Fe-N powder. A new technology to make anisotropic bonded Sm-Fe-N thin cylinder magnets by an injection molding using unsaturated polyester (UP) resin was developed.     

Correlation between microstructure and coercivity of amorphous (fe0.82b0.18)0.90tb0.05la0.05 alloy ribbons

Amorphous alloys of (Fe_0.82B_0.18)_0.90Tb_0.05La_0.05 develop intrinsic coercive forces of about 9 kOe when crystallized at 650 °C. In this work we have investigated the relationship between coercive force and microstructure for these alloys using X-ray and electron diffraction, electron microscopy, and by differential thermal analysis (DTA). The DTA reveals that upon heating, an exothermal process (probably an atomic rearrangement) occurs before crystallization begins. Annealing between the temperatures of 577 °C and 611 °C produces microcrystals of α-Fe, Fe₃B, and R₆Fe₂₃ (R = Rare Earth). Mainly Fe₃B and R Fe₂₃ and a small amount of a-Fe appear in crystalline form between 627 °C and 752 °C, and the crystalline size increases with the temperature. Small amounts of La and an unidentified phase are also present in this temperature interval. Above 752 °C, the La and the unidentified phase disappear, the Fe₃B transforms to a-Fe and Fe₂B, and the grains of α-Fe and R₆Fe₂₃ grow appreciably. The high coercivity of ribbons annealed between 650 °C and 700 °C seems related to the single magnetic domain nature of the small crystallized grains, 100 to 300A. The decrease in coercivity observed by annealing above 700 °C is apparently related to the increase in grain size.     

Magnetic Properties of Nanocrystalline Powder Cores Fabricated by Mechanically Crushed Powders

Fe73.5Cu1Nb3Si15.5B7 nanocrystalline powder cores with different particle sizes ranging from 10 to 125μm were fabricated by cold-pressing techniques.The cores exhibited increased core loss Pcvand decreased initial permeabilityμiwith addition of fine powders below 50μm in size,and the content should be less than 40mass%.It was thought to be closely related to the high coercive force Hcdue to the stresses generated during the crushing process and high demagnetization fields of small powders.Furthermore,modifying the alloy compositions by adding defined amount of Ni could improve the soft magnetic properties,including superior characteristics of permeability under high direct current(DC)bias field and comparable low core loss at high frequency.     

THE COERCIVE FORCE OF FINE IRON POWDERS

Abstract

The intrinsic coercive force of compacts prepared from hydrogen-reduced ferric oxide powder has been studied as a function of particle size in the range 200–800 Å. For well-dispersed powder the coercive force increases sharply with particle size to a value of 970 oersteds, where the nominal particle size is 260 Å.; above this value the coercive force decreases sharply. An electron-microscope study of powders in the neighbourhood of the maximum shows that the experimentally determined coercive force is in good agreement with recent theory. X-ray line-broadening experiments indicate that packing effects, rather than strain anisotropy within particles, control the coercive force of compacts. A linear variation with packing density is obtained for all particle sizes investigated.     

Reactive hot pressing of nonstoichiometric uranium dioxide

High density UO_2+x pellets have been produced by reactive hot pressing uranyl oxalate at temperatures up to 700°C. Rapid densification occurred during the decomposition reactions resulting in densities in the range 90 to 92 pct of the theoretical. A density of 98 pct of the theoretical value was achieved by further hot-pressing at 650° to 700°C for 30 min. This densification behavior can be related to the nonstoichiometry and submicron sized particles of UO_2+x produced in the decomposition reactions. The kinetics of hot-pressing of powder compacts of this UO_2+x were studied in the temperature range 500° to 700°C. The results were analyzed utilizing models proposed by Fryer. The activation energy of 53 kcal per mole, obtained from this analysis is the same as that for creep of nonstoichiometric urania in the temperature range 975° to 1400°C, suggesting that the mechanism controlling the rate of the final stage of densification may be a creep process.     

Influence of Texture on Magnetic Aging of Cold Rolling Non‐oriented Silicon Steel Sheets

The relationship between magnetic aging and texture of 50W800 non‐oriented silicon steel (0.002~0.003 % C) was investigated. The Young's modulus of cementite is very close to that of {100} planes in ferrite and obviously lower than those of other crystallographic planes in ferrite. Therefore, cementite particles would precipitate in the form of disks along the {100} planes of the ferrite matrix during aging. The magnetic properties after aging at 200°C for 24 hours showed that the aging precipitation of cementite particles increased the core loss. The driving force for the wall movement of 180° stripe domains depends on the sheet texture. The texture, in which the <100> direction is parallel to the magnetizing field, is the most favourable texture component to reduce the core loss increment induced by aging.     

硅对铁基磁粉芯性能的影响研究

分别从磁滞回线、损耗、磁导率及直流偏置特性来分析硅对铁基磁粉芯性能的影响。结果表明:随着硅含量的增加,磁粉芯的饱和磁感应强度降低,纯铁粉芯的饱和磁感应强度最大;磁粉芯损耗随着硅含量的增加而逐渐减小,纯铁粉芯的损耗最大,FeSi6.5的损耗最小;纯铁粉芯的磁导率要高于铁硅磁粉芯,但随着硅含量的增加,磁导率又缓慢上升;随着硅含量的增加,磁粉芯的直流偏置特性DC-bias稳定性降低。     

Phase and structure changes during the sintering of compacts of high-speed steels obtained from powders with various rates of solidification

An investigation was made of the phase and structure transformations in compacts of high-speed steel R6M5F3 powder fractions ?630+50 μm at the temperatures of solid-phase (1160–1220°C) and liquid-phase (1240°C) sintering. The structure of the compacts was crystalline or quasicrystalline, depending on the degree of superheating and cooling rate of the melt during powder spraying. This was related to the presence of a cellular structure in particles of a critical size in the powder. Compacts of powder with the cellular structure experienced higher shrinkage during solid-phase sintering as a result of structre relaxation and recrystallization. The driving force of these processes is the change in chemical potential arising from the decomposition of highly supersaturated metastable solid solutions, and the excess grain-boundary energy of the quasicrystalline matrix structure.     

冷轧变形量和热处理工艺对电磁纯铁矫顽力的影响

试验用电磁纯铁0.5～2.5 mm冷轧板由3.5～4.5 mm热连轧电磁纯铁板(%:0.005C、0.50Al)经350 mm四辊可逆式精轧机冷轧而成。结果表明,电磁纯铁板获得较小矫顽力的最佳退火温度为850～900℃,退火升降温速度对矫顽力影响较小。当冷轧变形量由28.6%增加至88.9%时,900℃退火后纯铁板的矫顽力由29.8A/m增加到73.5 A/m,获得较小矫顽力的最佳冷轧变形量为≤45%。     

高速压制制备高密度纯铁软磁材料

以退火纯铁粉末为原料,采用粉末退火结合高速压制技术的方法制得高密度压坯(7.70 g·cm^-3),经烧结后获得高密度高性能的纯铁软磁材料.研究退火粉末的高速压制行为,以及烧结时间和烧结温度对材料磁性能和晶粒大小的影响.结果显示:退火粉末的压坯密度随压制速度的增加而增加,压坯密度最高可达到7.70 g·cm^-3,相对密度可达到98.10%.烧结温度为1450℃,烧结时间为4 h时,材料密度达到7.85 g·cm^-3,相对密度为99.96%,最大磁导率达到13.60 m H·m^-1,饱和磁感应强度为1.87 T,矫顽力为56.50 A·^m-1.     

Effects of embedding direct reduction followed by magnetic separation on recovering titanium and iron of beach titanomagnetite concentrate

Embedding direct reduction followed by magnetic separation was conducted to fully recover iron and titanium separately from beach titanomagnetite(TTM).The influences of reduction conditions,such as molar ratio of C to Fe,reduction time,and reduction temperature,were studied.The results showed that the TTM concentrate was reduced to iron and iron-titanium oxides,depending on the reduction time,and the reduction sequence at 1 200°C was suggested as follows:Fe_(2.75)Ti_(0.25)O_4→Fe_2TiO_4→FeTiO_3→FeTi_2O_5.The reduction temperature played a considerable role in the reduction of TTM concentrates.Increasing temperature from 1 100 to 1 200°C was beneficial to recovering titanium and iron,whereas the results deteriorated as temperature increased further.The results of X-ray diffraction and scanning electron microscopy analyses showed that low temperature(≤1 100°C)was unfavorable for the gasification of reductant,resulting in insufficient reducing atmosphere in the reduction process.The molten phase was formed at high temperatures of 1 250-1 300°C,which accelerated the migration rate of metallic particles and suppressed the diffusion of reduction gas,resulting in poor reduction.The optimum conditions for reducing TTM concentrate are as follows:molar ratio of C to Fe of 1.68,reduction time of 150 min,and reduction temperature of 1 200°C.Under these conditions,direct reduction iron powder,assaying 90.28 mass%TFe and 1.73 mass% TiO_2 with iron recovery of 90.85%,and titanium concentrate,assaying 46.24mass% TiO_2 with TiO_2 recovery of 91.15%,were obtained.     

Preparation of Monodispersed Iron Nanoparticles by Thermal Decomposition

Monodispersed iron nanoparticles were prepared by thermal decomposition of iron carbonyl at low temperatures of 160–180 °C in kerosene. The iron nanoparticles were spherical and their average size was decreased from 11.2 nm to 8.6 nm with increasing decomposition temperatures in the range of 160 °C to 180 °C. The as-prepared iron nanoparticles were amorphous, but the surface of the particles was easily oxidized to be spinel structured.     

Sintering mechanism of iron powder with microadditions of boron

The effect of boron on the sintering of iron powder was investigated. Boron (0–400 ppm) was added to high-purity iron powder of the German firm “Mannesmann.” Powder mixtures were pressed to compacts of identical density and sintered at different temperatures in different atmospheres. The results indicated the absence of a liquid phase and no influence of boron in the high-temperature stage of sintering. However, boron additions substantially improved sintering at low temperatures (up to 800°C) due to an effect on the interparticle contacts. With a properly selected sintering regime, microadditions of boron substantially increase the density of sintered ingots.     

IRON-COPPER-TIN SINTERED COMPACTS

Abstract

A wide range of copper and tin powder additions to iron powder sintered compacts hasbeen studied. From mechanical-property tests it has been shown that when using sinteririg temperatures of 900–1100°C in nitrogen/10% hydrogen atmospheres there is an optimum copper: tin ratio of 15:2. The mechanical properties obtained from compacts pressed from iron mixed with 4% copper+tin in this ratio and sintered at 900°C were similar to those obtained from iron ?l0% copper powder compacts sintered at 1100°C. Moreover, the iron-copper-tin components showed improved dimensional accuracy.

In a further series of experiments, it was shown that tin additions to iron-copper alloy compacts increased the solubility of iron in the liquid phase at the sintering temperature and simultaneously decreased the rate of diffusion of copper into the iron particles. At the same time, tin improved the wettability of the liquid, reducing its surface tension and allowing it to disperse more completely throughout the matrix. The mechanical properties of compacts containing larger amounts of tin were decreased by the presence of brittle compounds, although the sintering rate was increased. It is concluded that the optimum properties of iron-copper-tin compacts are obtained by making correct additions of copper and tin to the iron powder and giving careful consideration to the sintering atmosphere.     

DEHYDRIDING OF Ti–6AI–2Sn–4Zr–6Mo HYDRIDE POWDER

Abstract

A systematic investigation of temperature/pressure/time variables for dehydriding titanium alloy (Ti–6AI–2Sn–4Zr–6Mo) powder was made to determine practical processing conditions for reducing the hydrogen content of the powder to levels below 100 ppm. Studies made between 650·C (1200·F) and 871·C (1600·F) established the following conditions for obtaining the desired hydrogen contents:

Analyses of the experimental results of tests made between 650°C (1200°F) and 816°C (1500°F) indicate that at 1–0·088 μm partial pressure of hydrogen the dehydriding process is controlled by the second order reaction: 2H (gas)= H2 (gas) with an activation energy of 21 760 ± 1840 cal. At <0·088 μm partial pressure of hydrogen the process appears to be controlled by the rate of removal of H₂ molecules clinging to the powder surfaces. The type of vacuum system used for dehydriding is believed to be the major factor governing removal of these molecules.     

Sintering parameters and mechanical properties of injection moulded aluminium powder

Abstract

This paper describes the microstructural and mechanical properties of injection moulded aluminium powder. Gas atomised aluminium powder was injection moulded with wax based binder. The critical powder loading for injection moulding was 62·5 vol.-% for feedstock. Binder debinding was performed in solvent and thermal method. After debinding, the samples were sintered at different temperatures and times in high purity N₂. Metallographic studies were conducted to determine the extent of densification and the corresponding microstructural changes. The results show that gas atomised aluminium powder could be sintered to a maximum 96·2% of theoretical density. Maximum density, tensile strength and hardness were obtained when sintered at 650°C for 60 min.