Grain growth characteristics and magnetic properties of rapidly quenched silicon steel ribbons

High silicon-iron ribbons with 6.5 and 4.5 wt Pct silicon concentrations prepared by a rapid quenching roll technique were studied. As a result, a (100) cube-on-face texture was obtained by annealing at temperatures between 1050 °C and 1150 °C for ribbons with thickness below 130 μm. Minimum iron losses W_12.5/50 obtained for 4.5 and 6.5 wt Pct ribbons were 0.51 and 0.34 W/kg, respectively. This paper is based on a presentation made at the symposium “Physical Metallurgy of Electrical Steels” held at the 1985 annual AIME meeting in New York on February 24–28, 1985, under the auspices of the TMS Ferrous Metallurgy Committee.     

Microstructural investigation of a rapidly solidified 12Cr-Mo-V steel

Rapidly solidified martensitic stainless steel (11.59Cr-0.98Mo-0.28V (in wt pct) ribbons have been produced by the melt-spinning process. The microstructure of the ribbons showed three distinct zones: a columnar, a cellular, and a cellular-dendritic zone. The height of the columnar grain zone is independent of the process parameters such as the wheel material or the wheel velocity. Due to a high level of undercooling and a high growth velocity of the solid/liquid interface, the rapid solidification process is found to suppress the formation of δ-ferrite and enhance the formation of austenite. The austenite is transformed into martensite upon cooling. In comparison with conventional solidification, a reduction in the initial austenite grain size has been found to result in a very fine lath martensite (M) structure. Investigations of the texture within the ribbons along the growth direction show a weak fiber texture. Transmission electron microscopy (TEM) has revealed a [111]_M1 ‖ [001]_M2 and (011)_M1 ‖ (110)_M2 orientation relationship between two neighboring martensite laths. The observed orientation relationship is a result of a superposition of both the Kurdjumov-Sachs (K-S) and Nishiyama-Wasserman (N-W) orientation relations.     

Steady state creep behaviour of a rapidly solidified and further processed Al-5 wt% Ti alloy

The steady state creep behaviour of rapidly solidified and further processed Al-5 wt% Ti alloy has been studied in the temperature range 573–673 K. The experiememtald ata exhibited apparent stress exponents of 7–8 and an apparent activation energy of 240 kJ mol⁻¹. The results are analyzed using the semi-empirical power law, the substructure invariant model and an exponential law. The semi-empirical power law with a threshold stress and a stress exponent of 5 is found to be the best representation for steady state creep of such alloys. By analyzing literature data on the metallic/ intermetallic dispersion strengthened aluminium alloys, a modification in the dimensionless constant, A = 8.3 × 10³ exp[−104√(b/L)], is suggested to account for the influence of dispersion on creep kinetics. It is proposed that the attractive dislocation-particle interaction originates from the dissociation of lattice dislocations into interfacial dislocations when they enter the matrix-particle interface at high temperatures for climb by-pass.     

气体雾化快凝W9高速钢粉末的组织特征

研究了颗粒粒度不同的气体雾化W9Mo3Cr4V高速钢粉末的组织、形貌及结构.结果表明:粉末由铁素体和奥氏体基体和分布在周围的MC及M2C型碳化物组成,基体组织为等轴晶及树枝晶,碳化物在空间上呈连续网状或树枝状分布;粉末中相的含量与粉末粒度相关,随高速钢粉末粒度减小,组织中的铁素体和MC型碳化物含量增加,奥氏体和M2C型碳化物含量减少.     

6.5%Si电工钢的特性及应用

介绍高硅（6．5％Si）电工钢的特性及生产方式,同时叙述了该牌号电工钢国内外的发展及应用情况．高硅电工钢的研制和开发具有重要的现实意义．     

Grain boundaries in rapidly solidified and annealed Fe-6.5 mass% Si polycrystalline ribbons with high ductility

The type and frequency of grain boundaries in rapidly solidified and subsequently annealed ribbons of Fe-6.5 mass% Si alloy have been determined to discuss the origin of high ductility of the annealed ribbons. The electron channelling pattern (ECP) technique for crystallographic orientation determination was applied. Ribbons subjected to slight annealing after the solidification have a random grain orientation distribution and contain higher frequencies (86–87%) of high-energy boundaries or so called random boundaries. On the other hand, rapidly solidified and fully annealed ribbons with a large grain size of 600 μm and {100} texture contain low-energy boundaries such as low-angle and low Σ, coincidence boundaries in high frequencies. Nearly one half of the boundaries are of low-energy type. Some coincidence boundaries such as Σ5, Σ13 and S 25 occur 3–8 times more frequently than those predicted for a polycrystal with randomly oriented grains. Similarly, low-angle boundaries compose 25% of the total boundaries in the fully annealed ribbon. The inverse cubic root Σ dependence of the frequency for the coincidence boundaries has been discussed. The high ductility of fully annealed Fe-6.5 mass% Si alloy polycrystalline ribbons is attributed to a high frequency of the low-energy boundaries with strong resistance to intergranular fracture.     

Photocalorimetric cooling rate measurements on a Ni-5 wt% A1 alloy rapidly solidified by melt spinning

Binary Ni-5 wt%Al alloy ribbons have been rapidly solidified by melt spinning and their cooling rates measured by a photocalorimetric method in which photographic colour density is calibrated against ribbon temperature. The cooling rates have been measured as a function of melt spinning process parameters such as wheel speed, gas ejection pressure and melt superheat. Heat transfer coefficients and Nusselt numbers have been calculated from the measured cooling rates using both Newtonian and non-Newtonian heat flow analyses. Cooling rates during melt spinning are found to be in the range 1.10⁵–5.10⁵ Ks⁻¹, and increase linearly with increasing wheel speed, with relatively little effect of varying gas ejection pressure or melt superheat. Heat transfer coefficients and Nusselt numbers are found to be in the range 6.10⁴–2.10⁵ Wm⁻²K⁻¹ and 0.07–0.2 respectively. The increase in cooling rate with increasing wheel speed results partly from a decrease in melt spun ribbbon thickness and partly from an increase in heat transfer coefficient caused by improved thermal contact between ribon and wheel.     

Oxidation behavior of a fine-grained rapidly solidified 18-8 stainless steel

The cyclic oxidation behavior of a fine-grained, rapidly solidified 303 stainless steel was determined at 900 °C in pure oxygen. The rapidly solidified alloy exhibited superior resistance to oxidation compared with that of a wrought 304 stainless steel; its oxidation resistance was as good as that of a wrought 310 stainless steel, even though the latter alloy contained more Cr and Ni. The matrix of the rapidly solidified steel contained a uniform dispersion of fine MnS precipitates (0.2 to 0.5 μm), which were effective in inhibiting grain growth at elevated temperatures. The enhanced resistance to oxidation of the rapidly solidified alloy is attributed to two factors: (1) the formation and growth of protective Cr₂O₃ and SiO₂ scales were promoted by the fine alloy grain size (5 to 8 =gmm) and by the presence of the MnS dispersion, and (2) the adherence of the scale was increased by the formation of intrusions of SiO₂ from the external scale into the alloy, which formed around MnS precipitates and along closely-spaced alloy grain boundaries, and which acted to key the scale mechanically to the alloy.     

The microstructure and phase relationships in rapidly solidified type 304 stainless steel powders

The microstructure and relative amounts of fcc and bcc phases have been studied for rapidly solidified Type 304 stainless steel powders produced by vacuum gas atomization (VGA) and centrifugal atomization (CA). The VGA powder solidifies with a cellular microstructure while the CA powder has a dendritic microstructure. The volume fraction of fcc phase in the CA powder is found to increase from 40 Pct to 97 Pct with increasing particle size from 30 to 125 μm. In the VGA powder, the volume fraction of fcc phase is found to decrease from about 90 Pct to 77 Pct over the same range of particle sizes. The origins of the fcc and bcc phases in each powder are considered. It is concluded that bcc is present as both a primary crystallization phase in the smaller CA particles (<75 μm) and as compositionally stabilized eutectic ferrite at the cell walls of particles of both CA and VGA powders in which fcc was the primary crystallization phase.     

粉末轧制法制备Fe-6.5%Si硅钢片的研究

采用粉末轧制法制备了Fe-6.5%(质量分数)Si硅钢片,并对其密度、物相组成和磁性能进行了测试分析.研究表明:在一定的轧制成形和烧结条件下,所制备的Fe-6.5%Si硅钢片的饱和磁感应强度Bs为1.8T;高频铁损W2/10k为69W/kg.     

Parametric studies of the hot isostatic pressing of rapidly solidified 304 stainless steel powder

The increasing importance of powder materials fabrication by use of hot isostatic pressing (HIP) has led to recent emphasis on analytical techniques for describing and understanding the process. Understanding of particle consolidation during the HIP process has been attempted through the modelling of densification behavior by considering the deformation of a representative particle due to forces transmitted through the particle contacts. However, the properties of HIPed material have not been thoroughly investigated in terms of their deformation maps and HIP parameters. Mechanical properties of a compact can be quite different depending on the location of various deformation map boundaries. Diffusional creep is involved not only in densification but also in bonding at particle contacts. HIP pressure increases mechanical contact and enhances density but not particle bonding per se. Discrepancies between experimental and calculated data points for shorter HIP times may have been affected by oxide film layer on the original powder.     

快速凝固耐热铝合金的耐蚀性能

采用腐蚀失重法和极化曲线的测定,研究了FVS0611,FVS0812,2618,2618+Sc,2014,6061合金在人工模拟海水和海洋环境中的耐蚀性能。结果表明:2014,2618和2618+Sc合金腐蚀较严重,RS/PM生产的FVS0611,FVS0812和6061合金腐蚀速率较小,出现明显的钝化现象,并因为加工残余应力导致出现钝化-腐蚀-再钝化现象。     

Development of microalloyed steel for pipeline applications

Abstract

An experimental HSLA steel was produced by the electric arc furnace, vacuum degassing, ladle treatment and continuous casting route. The experimental steel was then rolled in a laboratory using a hot rolling schedule to simulate an industrial controlled hot rolling procedure for the production of plates as closely as possible to investigate the effect of a thermomechanical processing schedule plus the use of water quench, accelerated cooling followed by forced nitrogen gas or air as cooling media, on the mechanical properties of plates. The results showed that the controlled thermomechanical hot rolling schedule of slabs followed by the cooling of plates in either forced nitrogen gas or by accelerated cooling exhibited target properties equivalent to a steel grade API X-80.     

Microstructural characterization of rapidly solidified Al-Li-Co powders

A study of the combined effect of alloying elements and melt superheat has been carried out on the as-solidified structure of rapidly solidified Al-Li-Co powders. Three alloys,viz., Al-3 pct Li, Al-3 pct Li-0.4 pct Co, and Al-3 pct Li-0.8 pct Co were chosen, and the liquid melt in each alloy atomized from the temperatures 1173 and 1073 K, using the centrifugal atomization technique. The microstructural characterization was done using light, scanning, and transmission electron microscopy. Four types of microstructures,viz., dendritic, cellular, equiaxed-type, and featureless structures, were observed by light microscopy. The cooling rate, as determined from the same, lay in the range 10⁴ to 10⁶ Ks⁻¹, but was seen to go beyond 10⁷ Ks⁻¹ when estimated from TEM micrographs. On the micro-level, the Al-Li powders were found to exhibit dendritic structures with differing morphologies, whereas low-angle cell walls with perturbed interfaces were the main structural features observed in the Al-Li-Co alloys. Increasing both cobalt content and powder particle diameter favored transition from dendritic into cellular structure. The featureless zone was comprised mainly of elongated columnar grains (0.2 μm width and 1.5 μm length). A mechanism describing the cellular structure formation has been proposed. Aging of the melt-quenched powders at 473 K for times up to 100 hours results in the dissolution of the cellular structure. A mechanism for the same has been postulated. The difference in the superheats chosen in the present work is found not sufficient to cause drastic microstructural changes. Central Metallurgical Research and Development Institute, National Research Centre, Dokki, Cairo, Egypt     

Microstructural characterization of rapidly solidified Al-Ta alloys

Two Al-rich Al-Ta alloys containing by weight 3 and 6 pct Ta have been rapidly solidified from the melt using the ‘gun’ technique. The microstructures and the crystal structures of the phases in the as-solidified as well as those formed on subsequent decomposition of the supersaturated solid solution have been characterized. A supersaturated solid solution was obtained in both the alloys in the as-solidified condition indicating a solid solubility extension of Ta in Al to almost 6 wt pct. The supersaturated solid solutions formed in both the alloys have been found to be quite stable up to 673 K (for 1 hour). Annealing at higher temperatures resulted in the formation of rod-shaped precipitates inside the grains and massive precipitates along grain boundaries. The rod-shaped precipitates arranged in a regular pattern constitute a new metastable intermediate phase Al₇Ta having an ordered structure. The massive precipitates which form along grain boundaries constitute the equilibrium Al₃Ta phase with a tetragonal crystal structure. The transformation behavior and the morphology of the transformation products are detailed in this paper.     

谐波对硅钢片磁性能的影响

针对电机实际运行过程中存在的谐波环境,对不同谐波条件下无取向硅钢片的磁性能进行了研究。采用w(Si)为3%的高牌号无取向硅钢,在磁性测量设备上设置不同次数的谐波,对其磁性能进行了测试。试验结果表明,相对于正弦波条件下的磁性能,3次谐波能造成铁损明显上升;随着谐波次数的增加,谐波引起的铁损会降低并逐渐趋向稳定,但单次谐波对磁感无明显影响;复合多次谐波增加铁损最为显著,并且降低低场下的磁感。