Volume 34, Issue 1 -

This work focused on the determination of boron diffusion coefficient through the Fe 2 B layers on AISI 1026 steel using a mathematical model. The suggested model solves the mass balance equation at the (Fe 2 B/substrate) interface. This thermochemical treatment was carried out in the temperature range of 1123–1273 K for a treatment time ranging from 2 to 8 h. The generated boride layers were characterized by different experimental techniques such as light optical microscopy, scanning electron microscopy, XRD analysis and the Daimler-Benz Rockwell-C indentation technique. As a result, the boron activation energy for AISI 1026 steel was estimated as 178.4 kJ/mol. Furthermore, this kinetic model was validated by comparing the experimental Fe 2 B layer thickness with the predicted one at a temperature of 1253 K for 5 h of treatment. A contour diagram relating the layer thickness to the boriding parameters was proposed to be used in practical applications.

The hot ductility of 20CrMnTi steel with x % copper ( x  = 0, 0.34) was investigated. Results show that copper can reduce its hot ductility, but there is no significant copper-segregation at the boundary tested by EPMA. The average copper content at grain boundaries and substrate is 0.352% and 0.318% respectively in steel containing 0.34% copper tensile-tested at 950 °C. The fracture morphology was examined with SEM and many small and shallow dimples were found on the fracture of steel with copper, and fine copper sulfide was found from carbon extraction replicas using TEM. Additionally, adding 0.34% copper caused an increase in the dynamic recrystallization temperature from 950 °C to 1000 °C, which indicates that copper can retard the dynamic recrystallization (DRX) of austenite. The detrimental influence of copper on hot ductility of 20CrMnTi steel is due mainly to the fine copper sulfide in the steel and its retarding the DRX.

The hot ductility of 20CrMnTi steel with x % tin, y % copper and z ppm boron ( x  = 0, 0.02; y  = 0, 0.2; z  = 0, 60) was investigated. The results show that tin and copper in 20CrMnTi steel are detrimental to its hot ductility while adding boron can eliminate the adverse effect and enhance hot ductility greatly. Tin is found to segregate to the boundaries tested by EPMA in 20CrMnTi steel containing tin and copper and tin-segregation is suppressed by adding boron, moreover, copper was found not to segregate to boundaries, however, fine copper sulfide was found from carbon extraction replicas using TEM. The adverse effect of tin and copper on the hot ductility was due mainly to tin segregation and fine copper sulfide in the steel. The proeutectoid ferrite film precipitating along the austenite grain boundary causes the ductility trough of the three examined steels. Tin and copper in 20CrMnTi steel can retard the occurrence of dynamic recrystallization (DRX) while boron-addition can compensate for that change. The beneficial effect of boron on 20CrMnTi steel containing tin and copper might be ascribed to the fact that boron segregates to grain boundaries, accelerates onset of DRX, retards austenite/ferrite transformation and promotes intragranular nucleation of ferrite.

The paper presents and analyzes the experimental results of the effect of elevated temperatures on the engineering properties of steel 42CrMo4. Experimental data relating to the mechanical properties of the material, the creep resistance as well as Charpy impact energy. Temperature dependence of the mentioned properties is also shown. Some of creep curves were simulated using rheological models and an analytical equation. Finally, an assessment of fracture toughness was made that was based on experimentally determined Charpy impact energy. Based on the obtained results it is visible that the tensile strength (617 MPa) and yield strength (415 MPa) have the highest value at the room temperature while at the temperature of 700 °C (973 K) these values significantly decrease. This steel can be considered resistant to creep at 400 °C (673 K), but at higher temperatures this steel can be subjected to low levels of stress in a shorter time.

The paper presents research results of isothermal oxidation of Ti-46Al-7Nb-0.7Cr-0.1Si-0.1Ni intermetallic alloy with Al 2 O 3 coating. Oxidation was carried out in air and in the atmosphere with the content 9%O 2  + 0.2%HCl + 0.08%SO 2  + N 2 at 750 °C. Mass changes of the specimens were recorded after 50, 100, 300 and 500 hours. The surface morphology of the oxidized samples were studied using Scanning Electron Microscopy (SEM), Wavelength Dispersive Spectroscopy (WDS) and Energy Dispersive Spectroscopy (EDS). The results obtained showed that the corrosion resistance of the examined alloy is better in air. The oxidation in the atmosphere of 9%O 2  + 0.2%HCl + 0.08%SO 2  + N 2 causes the formation of eruptions of Al 2 O 3 and TiO 2 mixture, however, in air the forming oxide layer is suppressed by the deposited protective Al 2 O 3 coating.

The effect of cooling rate on boron removal and solidification behavior of Al-Si alloy with different silicon contents were studied during solar grade silicon purification. It is found that the boron removal rate is controlled by kinetic factor. A method is proposed to calculate apparent segregation coefficient of solidification process that spans over a temperature range. This apparent segregation coefficient is used to evaluate purification effect in alloy system with changing segregation coefficients. When average solidification temperature decreases, the apparent segregation coefficient of boron decreases. The average width and mass of primary silicon flakes decrease with increasing cooling rate. Impurity elements form intermetallic compound phases such as α-Al 8 SiFe 2 and π-Al 8 Si 6 Mg 3 Fe in eutectic matrix.

Nanocrystalline polymeric complex (Ni 0.5 Zn 0.4 Cu 0.1 ) ferrite substituted cobalt (Co) ferrite system has been synthesized by chemical co precipitation method. The dielectric properties of polymeric spinel ferrite system (Ni 0.5 Zn 0.4 Cu 0.1 Fe 2 O 4 ) x (CoFe 2 O 4 ) 1–x have been investigated. Some of the dielectric parameters such as dielectric permittivity ε′ and loss tangent (tan δ) were studied as a function of frequency in the range 1 Hz–1 MHz and of temperature in the range 230–410 K. Excessive dependency of dielectric properties on frequency and temperature with the presence of two relaxation mechanisms, which are called as major and minor, have been observed. From Argand diagram analysis α and Δε values for these two kinds of relaxation curves have been determined for all the samples in the measured temperatures. The reported dielectric properties are thought to be meaningful for future applications.

A new approach to concentrate V-containing spinel phase from vanadium slag by super gravity was investigated. The samples obtained by the gravity coefficient G ≥ 1050, time t ≥ 30 min and temperature T ≥ 1523 K appear significant layers and V-containing spinel phase presents gradient size distribution in the sample along the super gravity. The mechanism of moving speed of V-containing spinel particles in super gravity field was also discussed, and the conclusion indicates that the moving speed of V-containing spinel particles is proportional to the square of the V-containing spinel particle size. As a result, large size V-containing spinel particles move a farther distance than the small ones and gather at the bottom of the sample. Under the hypothesis that the vanadium and silicon exist in the slag in terms of V 2 O 3 and SiO 2 , with the parameter of G = 1050, t = 30 min, T = 1523 K, the mass fraction of V 2 O 3 and SiO 2 in the concentrate is 18.92% and 7.42%, while that of the tailing is 6.86% and 24.48% respectively. Considering that the mass fraction of V 2 O 3 and SiO 2 is 13.34% and 15.25% in the parallel sample, the recovery ratio of V in the concentrate is 74.60%, while the removal ratio of Si is 75.59% by centrifugal concentration.

Previously published sulphide capacity data and thermodynamic arguments have been employed to calculate the phosphate capacities and the phosphorus partition ratios between a molten carbon saturated iron alloy and binary CaF 2 -MgO slags and also ternary CaF 2 -CaO-MgO slags at 1450 °C. For the CaF 2 -MgO binary system, a linear relationship was found between the phosphate and the sulphide capacities as follows: log  = 1.2 log C s  + 25.2. For the ternary CaF 2 -CaO-MgO system at 1450 °C, the logarithm of the calculated phosphate capacities ranged from 19.47 to 20.15. With the addition of CaO, the phosphate capacities initially increased, reached a maximum and then decreased slightly. The addition of MgO to the CaF 2 -CaO system resulted in a decrease in the phosphate capacity. The calculated phosphorus partition ratios increased slightly with increasing mole fraction of CaO in the ternary system.

Thermodynamic properties as lattice parameters, thermal expansion, heat capacities C p and C v , bulk modulus, and Gruneisen parameter of ionic halides TlCl and TlBr in solid and liquid phases were studied using classical molecular dynamics simulation (MD) with interionic Vashistha-Rahman (VR) model potential. In addition to the static and transport properties which have been previously reported by the author [13], this study further confirms that temperature dependence of the calculated thermophysical properties of TlCl and TlBr are in agreement with the available experimental data at both solid and liquid phases in terms of providing an alternative rigid ion potential. The results give a fairly good description of TlCl and TlBr in the temperature range 10–1000 K.

In order to find material parameters of established Zener-Hollomon constitutive equations and predict high-temperature flow stress of alloy 2618-Ti, the hot compressive deformation behaviors of the alloy were investigated at temperatures ranging from 300 to 500 °C at intervals of 50 °C and at constant strain rates of 0.001, 0.01, 0.1 and 1 s −1 using a Gleeble-3500 thermomechanical simulator. The material constants α , n , A and activation energy Q of alloy 2618-Ti were calculated by constitutive equations. The results show that the true stress-true strain curve exhibits a peak stress at a very small strain at every testing temperature. The peak flow stresses of alloy 2618-Ti calculated using the proposed constitutive equations agree well with experimental results. The activation energy of hot deformation for alloy 2618-Ti is 306.8 kJ/mol, while it is only 181 kJ/mol for alloy 2618.

CaO-CaF 2 -SiO 2 system is a base system for commercial mould fluxes. Thermodynamic properties of CaOCaF 2 -SiO 2 are essential for understanding the properties of mould fluxes and developing new mould fluxes. Thermodynamics of two sub-binary systems CaO-CaF 2 and CaOSiO 2 were modeled in the present work. A thermodynamic model for description of liquid slag presented by Björkvall et al. was extended to incorporate fluorine ion into model framework. The activities of components in CaO-CaF 2 and CaO-SiO 2 were calculated and good agreements between experimental and calculated activities were achieved. Phase diagrams for CaO-CaF 2 and CaO-SiO 2 systems were also well reproduced by the present calculation.

Water modeling experiments were carried out to investigate the mixing time and fluid flow phenomena in a shaking ladle, which is widely used in production of low and medium carbon ferromanganese and ferrochrome and also other metallurgical processes. Mixing time was determined by electrical conductivity probe method. A new concept of CSS-MT (critical shaking speed based on mixing time) was defined, which was different from the previous CSS-WH (critical shaking speed based on wave height). And the influences of bath depth and eccentricity on the CSS-MT were studied. The results showed that the mixing behaviors in shaking ladle can be categorized into shallow water type and deep water type, and the mixing efficiency of the former is poor and should be avoided in the industry practice. For the deep water type, the CSS-MT increases with increasing of bath depth and is approximately 15 rpm greater than the CSS-WH obtained from Ishii’s empirical formula. A larger eccentricity is helpful to decrease the critical shaking speed within certain limitations which is 30 mm; however, it is useless for increasing the eccentricity when it is above the limitation.