Band 34, Heft 6 -

The flow behaviors of ultrahigh strength steel BR1500HS at elevated temperature were studied by performing hot tension tests at the temperatures of 773 K, 873 K, 1023 K and 1173 K, and strain rates of 0.01 s −1 , 0.1 s −1 and 1 s −1 on a Gleeble 3500 thermo-mechanical simulator. The true stress-strain curves were obtained and their characteristics were analyzed. Relationships among the maximum stress, temperature and strain rate were described by means of the conventional hyperbolic sine equation. The average deformation activation energy in the whole deformation temperatures was determined as Q  = 235.257 KJ/mol by regression analysis. Based on σ (d σ /d ε ) verse σ 2 curves, the values of dynamic recovery (DRV) rate coefficient, r , saturated stress, σ rec , and yield strength, σ 0 , under different deformation conditions were calculated. In order to estimate the DRV volume fractions, the modified Avrami type equation including r ( r  = 106.911351 Z −0.059 ) as a function of the temperature compensating parameter, Z , was established, and then the effects of deformation conditions on the DRV kinetics were described in details.

LiMn 2 O 4 Doped with Cr 2 O 3 spinel cathode materials were coated with Carbon Black (0, 2, 4 wt%). The cathode materials were physically characterized by X-ray diffraction (XRD), Electrochemical impedance spectra (EIS), Cyclic Voltammetry (CV) and Analysis of Charging-discharging. From the XRD analysis, the synthetic materials were spinel structure with a Fd3m space group. From the EIS studies, the coating powers possessed the least impedance and inhibited the Mn dissolution. The CV and Analysis of Charging-discharging indicated the coating improved the performance of large current charge and discharge, the capacity retention and cycle performance.

The effects of Si +4 and Zn +2 substitutions on the structural and magnetic properties of Cu 1−x Zn x+y Si y Fe 2−2y O 4 ferrites prepared by double sintering ceramic technique have been investigated. From X-ray diffraction analysis, it was found that substitution of Zn and Si enhanced sintering process and crystallization. The XRD peaks increase by increasing Zn and Si content. On the other hand, the initial permeability decreases sharply at Curie temperature for all samples, which makes Zn/Si co-doped CuFe 2 O 4 spinel ferrites a very promising candidate for magnetic switches, magnetic temperature transducers (MTT), and for fabrication of temperature sensitive controller devices. The important change of Curie temperature of CuFe 2 O 4 compound occurs by simply controlling the content of Zn and Si within CuFe 2 O 4 and results in obtaining magnetic materials with desired Curie temperature. Magnetic hysteresis loop measurements show that the samples have soft magnetic character.

In order to develop reliable constitutive equations for the simulation, the hot deformation behavior of FV520B steel was investigated through isothermal compression tests in a wide range of temperatures from 900 °C to 1100 °C at an interval of 50 °C and strain rate from 0.01 to 10 s −1 on Gleeble-1500D simulator. The effects of temperature and strain rate on deformation behavior were represented by Zener-Holloman parameter in an exponent-type equation of Arrhenius constitutive. The influence of strain was incorporated in the constitutive analysis by material constants expressed as a polynomial function of strain. The constitutive equation (considering the compensation of strain) could precisely predict the flow stress only at strain rate 0.01 s −1 except at the temperatures of 900 °C and 1000 °C, whereas the flow stress predicted by a modified equation (incorporating both the strain and strain rate) demonstrated a well agreement with the experimental data throughout the entire range of temperatures and strain rates. Correlation coefficient (R) of 0.988 and average absolute relative error (AARE) of 5.7% verified the validity of developed equation from statistical analysis, which further confirmed that the modified constitutive equation could accurately predict the flow stress of FV520B steel.

In this paper, measurement method of EAF Steelmaking decarburization rate is studied. Because of the fuel gas blown and air mixed, the composition of hot temperature off-gas is measurand unreally, and the flow rate is unknown too, the direct measurement of EAF decarburization rate by furnace gas analysis is unrealized. Firstly, the off-gas generation process is discussed. After that, dynamic concentration of CO 2 , CO, and O 2 in off-gas and EAF oxygen supply rate are monitored in real time. Finally, the concentration and volume flow rate of off-gas are obtained to measure the EAF decarburization rate indirectly. The results of the hot state experiments show that the decarburization rate in oxidization step can reach up to about 0.53 mol/s, and the forecasting carbon concentration is 1.14% corresponding to the average carbon concentration (1.43%) in finial metal samples. The measurement of decarburization rate by off-gas analysis technique can be reasonable in EAF production process.

In order to investigate the effect of dynamic recrystallization (DRX) behavior on dynamic softening behavior of wrought Ti-10V-2Fe-3Al titanium alloy, a series of laboratory scale isothermal hot compression tests with a height reduction of 60% were performed in a temperature range of 948 K~1023 K in the ( σ + β ) phase field, and a strain rate range of 0.01~10 s −1 on a Gleeble-3500 thermo-mechanical simulator. The flow curves show a continuous softening at all strain rate after peak stress. The constitutive equation and the DRX kinetic mold were established to study the dynamic softening based on the flow curves. By the regression analysis for conventional hyperbolic sine equation, the activation energy was determined as Q  = 479.4169 kJ·mol −1 , According to the strain hardening rate curves (d σ /d ε versus σ ), two characteristic parameters including the critical strain for DRX initiation ( ε c ) and the strain for peak stress ( ε p ) were identified, and the linear dependence of the critical strain ( ε c ) for DRX initiation on the strain for peak stress ( ε p ) can be specified by the equation: ε c  = 0.5667 ε p . A modified Avrami type equation XDRX=1-exp[ -βd(ε-εcε0.5) kd]$${X_{DRX}} = 1 - exp[{\rm{-}}{\beta _{\rm{d}}}({{\varepsilon {\rm{-}}{\varepsilon _{\rm{c}}}} \over {{\varepsilon _{0.5}}}}){\rm{}}{k_d}]$$ was introduced to characterize the evolution of DRX volume fraction. The evolution of DRX volume was described as the following: for a fixed strain rate, the strain required for the same amount of DRX volume fraction increases with decreasing deformation temperature, in contrast, for a fixed temperature, it increases with increasing strain rate. Finally, the impact of dynamic recrystallized behavior on degree of dynamic softening became weaker and weaker with the increasing of temperature for the strain rate of 0.01 s −1 , 0.1 s −1 , 1 s −1 and 10 s −1 , due to the volume of α phase decreased with the increasing of temperature.

Dechlorination and defluorination from zinc oxide dust by microwave sulfating roasting was investigated in this study. According to proposed reactions in the process, detailed experiments were systematically conducted to study the effect of roasting temperature, holding time, air and steam flow rates on the efficiency of the removal of F and Cl. The results show that 92.3% of F and 90.5% of Cl in the fume could be purified when the condition of the roasting temperature of 650 °C, holding time at 60 min, air flow of 300 L/h and steam flow of 8 ml/min was optimized. Our investigation indicates that microwave sulfating roasting could be a promising new way for the dechlorination and defluorination from zinc oxide dust.

The cause of material degradation of an ASTM A-124 grade carbon steel tube belonging to a heat exchanger has been investigated. Visual examination, followed by an in-depth microstructural characterization using optical microscopy, energy dispersive X-ray, and scanning electron microscopy, was carried out for understanding the primary cause of material degradation. Based on the results of an extensive examination as well as the background information provided on the heat exchanger, it was determined that the steel tubes were predominantly damaged by the mechanism of crevice corrosion facilitated by the presence of mill scale. It is concluded that the heat exchanger tubes were not properly investigated for defects after their fabrication. Based on the situation, the proper cleaning method was selected for preventing further corrosion in the system. A chemical cleaning process was designed using acid pickling along with an inhibitor and a surfactant.

Solidification structures of high carbon rectangular billet with a size of 180 mm × 240 mm in different secondary cooling conditions were simulated using cellular automaton-finite element (CAFE) coupling model. The adequacy of the model was compared with the simulated and the actual macrostructures of 82B steel. Effects of the secondary cooling water intensity on solidification structures including the equiaxed grain ratio and the equiaxed grain compactness were discussed. It was shown that the equiaxed grain ratio and the equiaxed grain compactness changed in the opposite direction at different secondary cooling water intensities. Increasing the secondary cooling water intensity from 0.9 or 1.1 to 1.3 L/kg could improve the equiaxed grain compactness and decrease the equiaxed grain ratio. Besides, the industrial test was conducted to investigate the effect of different secondary cooling water intensities on the center carbon macrosegregation of 82B steel. The optimum secondary cooling water intensity was 0.9 L/kg, while the center carbon segregation degree was 1.10. The relationship between solidification structure and center carbon segregation was discussed based on the simulation results and the industrial test.

In the study, magnesium oxide acting as modifier was added to V-bearing steelmaking slag to concentrate vanadium, and then the effect of magnesium oxide on the formation of V-concentrating phase during cooling was investigated. Experimental results show that, in the case of the original slag, di-calcium silicate along with most of vanadate and phosphate in the slag forms solid solution, calcium ferrite which contains small part of vanadium in the slag and matrix without vanadium in turn precipitate during slowly cooling; For the sample with 8% MgO addition, two new phases (merwinite and V-concentrating phase) generate during slowly cooling, and the amount of di-calcium silicate decreases. Merwinite phase doesn’t contain vanadium, and V-concentrating phase (Ca 3 (V,P) 2 O 8 ·nCa 2 SiO 4 ) contains 17–19% V 2 O 5 by mass; For the sample with 16% MgO addition, another new phase (monticellite) precipitates from liquid slag, the phase of di-calcium silicate disappears, and most of vanadium concentrates in V-concentrating phase-Ca 3 (V,P) 2 O 8 ·nCa 2 SiO 4 (18–21%V 2 O 5 ).

The present work studied the carbides in forged and annealed H13 hot work die steel. The carbides were examined by scanning electron microscopy (SEM), energy dispersive spectrometer (EDS) and X-ray diffraction (XRD) and analyzed with quantitative chemical analysis method. The carbide types, qualities and compositions in dependence on temperatures were thermodynamically calculated by Thermo-Calc software and compared with the experimental results. In the final, methods for carbide improvement were discussed. The results are as follows. The primary carbides and the carbide segregation are improved after the hot-forging operation. The carbides in the hot-forged and annealed H13 steel are M 7 C 3 , M 6 (C, N) and M(C, N) which is accordance with the calculated results. Trace Mg added to the H13 steel leads to an increase of primary carbide nucleation and a decrease of primary carbide size.

The aim of this study is the recovery of rice husk waste by researching usability in industry as an alternative to wood. In this study urea formaldehyde resin was used mainly as binding agent for wood-panel used in industry. For the preparation of composite material, ground powder rice husks were mixed with urea formaldehyde resin used in different proportions (65/50, 75/50, 80/50, 85/50, 95/50 by mass of filler/binder). Each particleboard produced in 393.15 K and 9.8 MPa pressure was tested by means of three point bending strength, shore hardness and limited oxygen index (LOI) tests. Particleboard made with 75/50 paddy husk/urea formaldehyde composition material formed of 11.40 MPa specimens showed the highest strength. Limited oxygen index value increased by increasing the filler material usage. The highest LOI value was recorded as 40%. Besides, fire point of particleboards which have the best three point bending strength has been analyzed at environmental atmosphere and 493.15 K has been measured as fire point. The results of the tests showed that this material maybe used instead of wooden plate. The usage of agricultural wastes like these in processing of particleboard will give economically benefits and slow down waste products.

Electron beam melting (EBM) technology has been considered as one of the key steps for preparing high purity tungsten, and reasonable setting of process parameters is the premise. In this paper, the optimum process parameters obtained from thermal equilibrium calculation and evaporation loss control of tungsten are presented. Effective power is closely related to melting temperature, and the required power for maintaining the superheating melt linearly increases with the increase of melt superheat temperature. The evaporation loss behavior of tungsten is significantly influenced by melting rate and melting temperature. Analysis of experiments show that the best results are realized at melting rate of 1.82 g/s, melting temperature of 4200 K, and the corresponding melting power of 130 kW, in which the main impurity elements in tungsten, such as As, Cd, Mg and Sn, present high removal ratio of 90%, 95%, 85.7% and 90%, respectively.