Grain refinement of copper by the addition of iron and by electromagnetic stirring

The effect of iron additions in the range of 0.57 to 7.5 wt pet on the grain size of electromagnetically levitated copper-iron alloys was investigated. The samples were solidified while levitated or quenched in water from the molten state. The addition of iron was found to be effective in reducing the grain size of copper, and the average grain size decreased as the iron content was increased up to the peritectic liquid composition of about 2.8 wt pet Fe. Beyond this composition, the grain size of the samples solidified in the levitated state was insensitive to the iron content, whereas that of the quenched samples continuously decreased with increasing iron content. The results indicate that electromagnetic stirring causes fragmentation of copper dendrites in the hypoperitectic region, and hence enhances grain refinement. In the hyperperitectic region, on the other hand, the stirring has a detrimental effect on the grain refinement by agglomerating the primary iron particles which act as heterogeneous nucleation sites for the copper matrix.     

Effects of the intensity and frequency of electromagnetic vibrations on the microstructural refinement of hypoeutectic Al-Si alloys

An experimental apparatus that uses a superconducting magnet and enables the simultaneous application of an alternating electric field with a frequency of up to 50 kHz and a magnetic field of up to 10 T was designed and assembled. Electromagnetic vibrations were induced in Al-7 wt pct Si alloy during solidification by simultaneous application of the two fields. The thorough investigation, which was carried out over wide ranges of intensity (an electromagnetic pressure range of 0 to 2.25×10⁵ Pa) and frequency (0 to 50 kHz), clarified the effects of the two main parameters on the microstructural refinement brought about by electromagnetic vibrations. Low-intensity vibrations changed the highly columnar dendritic structure into one composed of large, equiaxed dendrites. As the intensity, and consequently, the magnetic pressure were increased, at about 0.93×10⁵ Pa, fine isolated grains started to appear and dominated the structure as the pressure was increased further. At low frequencies, the structure was one with large, equiaxed dendrites, which disintegrated to form a fine and homogeneous structure as the frequency was increased. At about 1.5 kHz, the trend reversed and the structure gradually became a completely columnar dendritic one at frequencies higher than 10 kHz. Metallographic observations showed that the cavitation phenomenon has been a main factor behind the observed microstructural refinement. The effects of mechanical vibrations of the experimental apparatus were also investigated and found to have no contribution to the observed effects.     

Grain refinement induced by electromagnetic stirring: A dendrite fragmentation criterion

The influence of electromagnetic stirring (EMS) on grain refinement has been studied for two copper-base alloys (Cu-1 wt pct Ni-1 wt pct Pb-0.2 wt pct P and Cu-4 wt pct Zn-4 wt pct Sn-4 wt pct Pb) solidified in a Bridgman furnace. Metallographic inspection of the specimens, temperature measurements during solidification, and numerical simulations performed with CALCOSOFT revealed that the efficiency of EMS is strongly dependent upon the penetration of the liquid in the mushy zone and therefore upon the position of the convection vortices with respect to the liquidus front. In particular, the low-concentration alloy could be grain refined only at high power and when the coil was moved close to the liquidus front. These results were analyzed on the basis of a dendrite fragmentation criterion similar to Flemings’ criterion for local remelting of the mushy zone. Considering that the component of the fluid flow velocity along the thermal gradient, , must be larger than the casting speed, V _c , dendrite fragmentation occurs if

Grinding gray cast iron chip

Studies have been made on the grinding conditions for SCh21-40 gray cast iron chip of sizes from 10 × 2 × 0.2 to 20 × 5 × 0.5 mm in vibrating mills containing various media. During dry grinding, the mean particle size falls for 6 h, but after 7 h there is agglomeration. Grinding in the presence of distilled water is most effective when the mill body cooling system is switched off. The grinding in that case is accelerated by a factor of 1.5–2.Deceased.Translated from Poroshkovaya Metallurgiya, No. 11 (359), pp. 7–11, November, 1992.     

Structural analysis by Rietveld refinement of calcium and lanthanum phosphosilicate apatites

Britholites with the general formula Ca10-xLnx(PO4)6-x(SiO4)xF2, (0≤x≤6) are considered to be promising matrices for the confinement of the by-products in the nuclear industry. A thermodynamic study sh...     

Studies on induction hardening of gray iron and ductile iron

The effect of induction case hardening of a gray cast iron (FG 260) and SG iron (600/3) as a function of applied induction power has been studied. The influence of various operating parameters on the penetration depth has been analysed. The case depth as a function of applied power and the associated changes in microstructure has been investigated. The case depth of SG iron was found to be twice than the gray iron due to higher resistivity of the material and increase in depth of penetration. Both hardness and the depth of penetration increased with increase in applied power associated with martensitic case formation. The surface hardness of both the irons varies between 600 to 800 VHN. The core microstructure in both the irons displayed pearlitic matrix. In the case of SG iron, the nodule size, sphericity and nodularity have reduced in the induction hardened case compared to the core.     

Structure refinement of pure iron during low-temperature high-pressure deformation

The structural evolution of iron (99.97%) during high-pressure torsion at the liquid-nitrogen temperature is studied by transmission electron microscopy and durometry. Twinning and deformation microband formation become operative low-deformation mechanisms along with dislocation slip because of a low dislocation mobility; as a result, deformation is nonuniform and inhomogeneous. Low-angle misorientations are retained up to the limiting achieved strains; therefore, a homogeneous submicrocrystalline structure, which forms in iron deformed at room temperature, does not form in this case. The structure refinement in iron during low-temperature deformation reaches a steady state.     

脉冲电磁场凝固组织细化和均质化技术研究与应用进展

由于金属凝固过程中选分结晶的作用,不可避免地会出现成分不均匀现象。连铸过程中由于强制冷却,这种成分不均匀现象更为严重。这不仅影响了铸坯和铸锭后续加工性能,并影响了最终产品质量和性能的均匀性和稳定性。研究和生产实践表明,细化凝固组织是解决成分不均匀性的有效手段。脉冲电磁场因能耗低、施加方便、细晶效果显著,近年来得到了广泛关注,有望成为冶金界广泛应用的凝固组织细化和均质化技术。分别介绍脉冲电流、脉冲磁场和脉冲磁致振荡3种脉冲电磁场凝固组织细化和均质化技术的研究现状和应用进展。     

An investigation of the effects caused by electromagnetic vibrations in a hypereutectic Al-Si alloy melt

In order to investigate the mechanism by which electromagnetic vibrations affect the solidification structure of metallic alloys, an experimental apparatus which enables the simultaneous application of electric and magnetic fields under different cooling conditions (ranging from rapid to furnace cooling) is developed. The objective is followed by inducing vibrations in a hypereutectic Al-Si alloy melt containing suspended silicon particles and interrupting the process at different temperatures before and after the start of solidification by water quenching. Interrupting the process at temperatures higher than the liquidus has revealed the effects of vibrations independent of the influences of the nucleation and growth phenomena. Establishing the conditions for obtaining identical cooling rates in experiments with different experimental conditions has lead to the exclusion of effects resulting from the differences in cooling rates and recognition of the effects caused only by electromagnetic vibrations. It is found that the application of either of the two fields alone has no significant effect on the solidified structure, while profound effects are observed when the two fields are applied simultaneously. An increase in the number of suspended silicon particles and a reduction in their average size are the effects noticed before the start of solidification. In this research, it has for the first time been clearly verified, through microscopic observation of the quenched samples, that these effects are brought about by the cavitation phenomenon. After the start of solidification, particles are locally agglomerated and expelled toward the surrounding walls under a combined influence of electromagnetic vibrations and pinch force squeezing the liquid. The final structure obtained is composed of an almost completely eutectic matrix surrounded by agglomerates of silicon particles along the outer surface.     

Effect of inoculating addition on machinability of gray cast iron

Gray cast irons were inoculated with FeSi75+RE and FeSi75+Sr inoculants. The changes of apex angle of the drills before and af-ter being used were used to evaluate machinability of gray cast irons. Effect of FeSi75+RE and FeSi75+Sr inoculants on mechanical proper-ties, machinability and sensibility of gray cast iron used in cylinder block were investigated. Experimental results showed that gray cast iron treated with 60%FeSi75+40% RE inoculants exhibited tensile strength consistently at about 295 MPa along with good hardness and im-proved metallurgical quality. While gray cast iron inoculated with 20%FeSi75+80% Sr inoculants exhibited the best machinability, the low-est cross-section sensibility and the least microhardness difference. The tool flank wear of the drill increased correspondingly with the in-crease of the microhardness difference of the matrix, indicating the great effect of homogeneity of the matrix on the machinability of gray cast iron.     

Modeling stress development during the solidification of gray iron castings

A method has been developed to predict stress development in gray iron foundry castings. A new yield function, based on theoretical developments by Frishmuth and McLaughlin,⁹ and on experiments by Coffin¹⁰ was implemented as a user-written element in a commercial finite element package. The yield function takes into account the strong dependence of the yield stress in cast irons on the loading path. Stresses resulting from thermal displacements in the cooling casting are computed using the new yield function in an elastic-viscoplastic stress analysis. In earlier work, techniques were developed to represent the mold in the thermal analysis by sets of boundary conditions on the surface of the part. For this work, a second user-written element was used to apply force-displacement boundary conditions on the surface of the casting to represent the mechanical constraint of the mold. The properties for this element were based on soil mechanics considerations. Example problems are given, showing a substantial difference in the computed stresses when using the present formulation, in comparison to results obtained with the more usual von Mises yield function. Formerly at the University of Illinois.     

A new unidirectional solidification method to study gray cast iron

A new unidirectional solidification (US) method to study gray cast iron was developed. It is based on the combination of the classical Bridgman-type technique and the directional casting technique. By means of this method, it is possible to achieve, among others, the following aims:

灰铸铁手工电弧焊的焊补

介绍了铸件在制造和使用过程中出现的各种缺陷和损坏,利用手工电弧焊焊补,从灰铸铁的鉴别,焊接性能出发,对焊补方法及操作技能做了深入分析,在生产中实践取得较好的社会经济效益.     

Solidification of low-silicon iron under the action of nanosecond electromagnetic pulses

When low-silicon iron solidifies in the presence of nanosecond electromagnetic pulses, the influence of the irradiation time on the process is considered, as well as its influence on the structure and properties (hardness, density, local microhardness, corrosion resistance, and wear resistance) of the gray iron that forms. Extending the irradiation time increases the initial temperature of austenite solidification and reduces the eutectic and eutectoidal transformation temperatures. The dependences of the iron’s physicomechanical properties on the irradiation time include maxima or minima in the range 10–15 min. For example, the thermal conductivity doubles in that range.     

Relationship between the electromagnetic and physicochemical properties of carbonyl iron powder

Summary The relationship is examined between the electromagnetic properties of carbonyl iron powder and some factors involved in the manufacture of this powder. The electromagnetic properties depend on the onion skin structure of the powder particles and the chemical composition and particle size of the powder.Translated from Poroshkovaya Metallurgiya, No. 7 (43), pp. 38–44, July, 1966.