An investigation was made of the activity of MgO, α_(MgO), in molten electrorefining slags with CaF_2 base of the concentrations N_(Al_2O_3)≤0.16, N_(MgO)≤0.30 and N_(CaO)≤0.30 at 1600 and 1650℃, and of the influence of MgO, Al_2O_3 and CaO contents on it as well. The diagrams of iso-activity for systems CaF_2-MgO-Al_2O_3 and CaF_2-MgO-CaO-Al_2O_3 (N_(Al_2O_3)=0.07) were constructed. It was found that the α_(MgO) increases rapidly with the increase of N_(MgO). However, the behaviour of Al_2O_3 is quite changeable, at 1600℃ it decreases violently the activity coefficient of MgO, γ_(MgO); at 1650℃ acts as one to increase γ_(MgO) if N_(MgO)<0.15 and is insensitive to α_(MgO) in the limits of N_(MgO) about 0.16. In the present study, α_(MgO) referred to solid as a function of component contents in the system CaF_2-MgO-Al_2O_3 at 1600 and 1650℃ may be expressed as follows: At 1600℃ α_(MgO)=2.89N_(MgO)-2.07N_(MgO)~2+0.081N_(MgO)~3-(55.23N_(Al_2O_3)-644.3N_(Al_2O_3)~2+2427N_(Al_2O_3)~3)N_(MgO)-56.12N_(Al_2O_3)N_(MgO)~2+373.1N_(Al_2O_3)N_(MgO)~3 At 1650℃ α_(MgO)=0.898N_(MgO)+2.73N_(MgO)~2-2.42N_(MgO)~3+(60.8N_(Al_2O_3)-120.8N_(Al_2O_3)~2+350N_(Al_2O_3)~3)N_(MgO)-77.5N_(Al_2O_3)N_(MgO)~2+ 1036N_(Al_2O_3N_(MgO)~3 In system CaF_2-MgO-CaO-Al_2O_3(N_(Al_2O_3)=0.07), CaO is found to be increasing γ_(MgO) at 1600℃ and varied its effect at 1650℃ with various N_(MgO). The expres-sion of α_(MgO) at 1650℃ in this system may be shown as: α_(MgO)= 4.67N_(MgO)-30.7N_(MgO)~2+70.1N_(MgO)~3- N_(CaO)(17.5N_(MgO)-208.4N__(MgO)~2+521N_(MgO)~3)

The phase diagram of the ternary Gd-Co-Ni system with Gd content≤24 wt-% at room temperature has been determined by X-ray powder method. Four single phase regions: α_1, β_1, α_2(α-Gd_2Co_(17)) and β_2[β-Gd_2(Co,Ni)_(17)], and five twophase regions: α_1+β_1, α_1+β_2, α_1+α_2, β_1+β_2 and α_2+β_2, and two three-phase regions: α_1+β_1+β_2 and α_1+α_2+β_2 are found. X-ray analysis showed that maximum solubility of Gd in β_1-phase is about 8 wt-%.

The existence of superledges on the broad faces of bainite formed isothermally at 320 and 420℃ has been observed with TEM on the specimens of a Si-modifled AISI 4340 steel. The height, α, and the width, b, of the superledges are about 320—850 and 1500—1800 A respectively. From the thickening rate of bainire, 0.006μm/s, the width of the superledge, b, is calculated to be approximately 0.5μm, this being of the same order of magnitude as width of the superledges observed. These ledges did exist at the habit plane and act as the growing superledges, ε-carbide and cementite were also found in bainite formed during 320 and 420℃ reaction. The orientation relationship between ε and α is the Jack relationship. Therefore, the existence of a eutectoid decomposition γ→α+ε at about 350℃, as suggested by Hehemann, is questionable. As the holding duration was prolonged there appeared cementite existing between γ and α phases. The orientation relationship between Fe_3C and γ is the Pitsch, Fe_3C and α-the Isaichev and γ/α is K-S relationship, from which the orientation relationship among γ-α- γ(or γ-α-Fe_3C) can also be established. However, it is uncertain whether or not the carbides are interphase boundary precipitates. The results have shown that part of the γ/α interface boundaries extended in a curve shape. The morphology of such interfaces and the existence of the growing superledges indicate that the growing interface is not a coherent one, so it is difficult to ascribe the growing mechanism of bainite to coherent shearing mechanism and it is more likely that bainite grows through the lengthening of the ledges.

The effect of microstructure on mechanical properties of an iron-base superalloy after prolonged exposure at 750℃ has been investigated by means of mechanical properties test, phase analysis, X-ray or electron diffraction, EDS and, especially, SEM observation on 3-dimensional morphology of the phases precipitated. After an exposure up to 200h, the high temperature strength and plasticity of the alloy are still satisfactory. The γ'-phase remained stable till 1000 h aging. The σ-phase was found as needle-like precipitates as a result of 500 h exposure, and it was then grown into plates, accompanied with the precipitation of Laves- or μ-phase after aged for 2000 h. As the exposure went on, TiC became the Lavesphase. It is regarded that the precipitation of the needle-like σ-phase is contributable to the decending of the high temperature endurance of the alloy aged for 200h, however, its high temperature plasticity and stress-rupture are little affected.

Tritium autoradiography was employed for the identification of: 1. the hydrogen distribution in irons with different purities; 2. the diffusion behavior uof hydrogen in metal under local load for different stress stand; 3. the distribution of tritium in the W alloys, 95%W-3.5%Ni-1.5%Fe, a kind of two-phase alloys consisted from W particles and binder of solution 54.2%Ni-27.1%Fe-20.5%W with high specific gravity and 4. the hydrogen distribution of different zones for the weld joint. It was found that the hydrogen distribution of iron is dependent on the purity of iron and the hydrogen solubility in the iron, however, grain boundary of high purity iron cannot be provided preferred sites for hydrogen accumulation site, but grain orientation difference is sensitive for tritium tracer. Tritium redistribution of hydrogen in different purity iron under different plastic deformation by the stress induced hydrogen segregation on the iron. Tritium distribution on the W-Ni-Fe sintcring alloys, even without etching, it is primarily accumulated on the interface of binding phase, which is dependent on relative solubility in two-phase alloys. The distribution of tritium on the different zone of the weld joint shows that hydrogen in the austenite weld, fusion zone. Overheat affected zone of matrix and matrix is different, which is closely connection of the carbon segregation of weld process and structure defect of matrix.

The preyielding microstrain process in polycrystalline 3%Si-Fe has been investigated with the method of displaying slip bands through electrolytic etching. Three different microstrain stages were found after analysis of the relations between the stress and the percentage of yielding grain and the average number of slip band per yielding grain. Plotted the starting stress at each microstrain stage against the reciprocal square root of grain diameter, three straight lines with different slop were obtained. Consideration of the Hall-Peteh relation, the Brown's microstrain theory and the upper yield point theory, the experimental results were discussed.

The effect of cyclic stress on the strength of creep rupture and recurrent creep rupture as well as low cycle fatigue of a cast nickel-base superalloy with high Al and Ti contents has been studied under different temperature and stress. It was found that the temperature is the main factor influenced upon the creepfatigue interaction. There are three temperature ranges leading to damage of creep, fatigue or combination of creep-fatigue individuaUy. The tested results were identified by some SEM fractographs.

A study was made of the activation process of LaNi_5 under various temperatures and pressures. Three periods of the process seem easily to be distinguished, namely, the incubation period, the increment and decrement periods of H_2 absorption with prolongation of the exposure time. The different features among them were discussed and approximate expressions of the hydrogenating rate were given.

The electrical resistivity measurements of the amorphous (Fe_(1-x)Co_x)_(78)Si_(9.5)B_(12.5)(x=0—1.0) alloys were made by a fourprobe technique at temperature range from 4.2 to 300K. It was found that the resistivity minima have been observed over the whole concentration range for x=0—1.0. The temperature T_(min) at which the resistivity is minimum increased with increaing Co content, and approached to the maximum at x=0.9. Below T_(min) the resistivity can be described by a logarithmic temperature dependence over the whole content. In the temperature range between T_(min) and 100K the resistivity has a T~2 temperature dependence and follows T_(3/2) temperature dependence above 100K. In summary, the temperature dependence of the electrical resistivity for all content may be expressed at temperature range (9.5—100K) by ρ/ρ_(min)=ρ_0+AlnT+BT~2. A Kondo-type resistivity minimum has been observed in these alloys, A T~2 temperature dependence of resistivity may originate from electron-phonon scattering.

An investigation was made of the effect of creep fracture toughness on the crack initiation and growth of two low-alloy heat resistant steels 25Cr2Mo1V and 12Cr1MoV. It was found that the resistance to creep crack initiation and growth of steel 25Cr2Mo1V, with a higher creep rupture strength, is much lower than that of 12Cr1MoV. This resistance is increased with the increase of the creep fracture toughness. For steel 25Cr2Mo1V, the creep rupture strength decreases slightly, and the creep fracture toughness and the resistance to crack initiation and growth increase along with the raise of the tempering temperature. As the steels are in tough or brittle state, the initiation and growth of creep crack are varied. In the tough state, cracking is both transgranular and intergranular around the notch tip. The transgranular crack may be either occurred in carbide inside the grains or nucleated at grain boundary and then propagated into grain. However, the intergranular crack may be formed by nucleation, growth and interlinkage of voids. Cracks may be propagated along grain boundaries and penetrated through the grains yet they are discontinuous. In the brittle state, cracks occur along grain boundaries only. They originate from the interlinkage of voids and cause eventually to brittle fracture.

Fine structure of tempered martensite of ultra-high strength steel 30CrMnSiNi2A was investigated under TEM. It was found that two kinds of martensite, the twinned type and the dislocated type were existed in the quenched state. Fracture toughness of this steel tempered below 400℃ depends primarily on the species and morphology of the products of martensite decomposition and has little concerned with the presence of twinned martensite. The severe embrittlement at 400℃ temper is attributed to the elimination of the homogeneously distributed χ-Fe_2C with the simultaneous preferred precipitation of the brittle Fe_3C phase. The high temperature temper brittleness at 550℃ is induced by the solute segregation(as alloyed carbide)along grain boundary as well as dislocation pinning by fine precipitates. Upon further increase in tempering temperature however, the precipitate phases are more or less spheroidized which, together with the matrix recovery, cause the fracture toughness to increase.

Some observations of voids formation were carried out by using low carbon steel with three kinds of heat-treatment, namely, normalizing, annealing and spheroidizing. Based on these observations and computations, some analytical results have been made to show strain dependency of voids nucleation rate and voids growth rate.

The metallurgical factors influenced the hot-rolled plates or coils on to form the fracture delamination have been investigated. The fragile micro-planes, including stretched inclusions, dendritic segregations, etc., which occur in steel and parallel to the rolling direction, seem to be the inherent factor. As the segregation of these micro-planes accumulated beneath the fracture surface, such delamination is formed under through thicknessstress in the propagation of fracture. The intergranular embrittlement zone is due to the temper brittleness produced by phosphorus and other impurities which diffused from intragrain to grain boundary in the slow cooling period after coiling. Delamination cracks propagate as mode of cleavage when (100) texture parallel to plate surface obtained by low temperature( References | Related Articles | Metrics

An attempt was made to develop the new method of magnetic seeding for concentration of Dong'anshan hematite ore, on which the influence of such factors as magnetic seed dose rate, stirring time, dose rate and proportion of collector-agglomerant, density and speed of repulping pulp conditioning, quality of water, pH of medium, etc. has been systematically investigated and discussed. It was shown that the vigorous stirring and high density contribute to agglomeration magnetic seeding process. A diagramatic flowsheet illustrating the separation process by magnetic seeding and its classification was established. A concentration grade of 66.85% Fe and recovery of 99,02% as well as waste tailing of 0.67% Fe were obtained by using this new method from a synthetic mineral mixture of hematite and quartz(1:1). And also concentrates containing 53.1% Fe and recovery of 95.3% were yielded from Dong'anshan crude ore assaying 32%Fe. This results have been verified by the tests of same procedure for Sijiayin hematite ore. Preliminary industrial practice seems to make sure of that the separation process utilizing the magnetic seeding would have potential possibility for concentration of Dong'anshan hematite or other similar ores.

Through study of the extraction equilibria of TbCl_3-DyCl_3-HCl-H_2O-1 mol P204 (HDEHP, kerosene solution) system, an empirical model Y=sum from i=0 to M sum from j=0 to N sum from k=0 to P (A_(ijk)x_A~ix_B~jx_C~k has been developed with M=N=P=2, where Y represents the rare earth concentration in the organic phase. As the mole fraction of TbCl_3, x_A=0.10—0.92, the acidity, x_B =1.1—3.4 mol·kg~(-1), and the total rare earth concentration, x_C=0.03—0.96 mol·kg~(-1), in the aqueous solution, the correlation coefficient of the model would be 0.9957, the average error would be 3.22% and the average error of the predictive value would be ±3.01%. The β_(Dy/Tb) was 2.69±0.056 as obtained from the experiments.From the results calculated by the model, the extraction equilibrium lines with the rare earth concentrations, acidities and mole fraction were drawn. Discussions were given.The TbCl_3-DyCl_3 model may be used for the stagewise calculations and for designing the corresponding extraction separation procedures.

A study was made of the mathematical simulation of the steady state feature of the fractional extraction on the basis of the established extraction equilibria model of TbCl_3-DyCl_3-HCl-H_2O-1 mol P 204 (HDEHP, kerosene solution) system. A BASIC program has been written for calculating the solute concentrations in phases in different stages under given conditions of fractional extraction by iteration method. The optimization process of Tbseparation was selected with the aid of established objective function by direct Seeking method. The mathematical simulation was verified by comparison with experimental one. The relative error of the purity for Tb or Dy<1.6% and of recovery<4.5%. Thus, a mathematical simulation method of modelling the extraction equilibria, simulating the steady state feature of fractional extraction and selecting the optimization process may be available for the extraction separation of any binary metal.

Taking two-phase equilibrium point of the single component system as a basic, an expression for kinetic rate constants of the binary system crystallization was derived in consideration of the changes in the chemical potential of gaseous phase and in the bond combination energy of crystalline phase after a new constituent added. The chemical potential differences caused by both partial pressure and equilibrium temperature shift have been taken into account. Hence, it may be available for any binary system with an arbitrary proportion.The computer simulation was made of the crystallization process for binary systems. It was shown that when the bond between molecules A and B is weaker than that between two A's, the segregation coefficients will be smaller than 1, adding of the new constituent makes the growth slower, and then the chemical potential of vapour must be increased to obtain the equilibrium with crystalline phase. In contrast to this, when the bond between A and B is stronger than that between two A's, the segregation coefficients will be greater than 1, adding of the new constituent makes the growth faster, and then the chemical potential of the vapour must be decreased to obtain the equilibrium with crystalline phase. In both cases, with the increasing growth rate, the segregation coefficients will approach to 1 more and more.All the simulation results seem to be in accordance with the binary system phase diagram and the model seems to be considered correctly.

A mathematical model for the heat transfer in the solidification of continuously cast slabs is proposed. A finite difference equation considering the viewpoint of the thermal equilibrium both within the unit and between the neighbour ones is derived and used in computer simulation of the solidification process of the continuously cast mould. The influence of operating parameter variations including casting speed and temperature, liquid convection in pool, mould length, etc. upon the solidification process of mould is discussed.

A method is described using the etch-pits technique for the experimental determination of the geometric structure of the grain boundary. The orientation relations between both sides of the grain boundary can be directly determined and the atomic configuration along the grain boundary can be easily drawn in theory. Owing to its simplicity, this technique seems to be available to accumulate the experiential patterns of various boundary structure.