Band 36, Heft 10 -

The effects of deformation temperature and cooling rate on the micro-structure evolution of umbrella-bone steel was investigated using a Gleeble thermal-mechanical testing machine and dynamic continuous cooling transformation (CCT) curves. The results show that fast cooling which lowers the starting temperature of ferrite transformation leads to finer ferrite grains and more pearlite. Low temperature deformation enhances the hardening effect of austenite and reduces hardenability, allowing a wider range of cooling rates and thus avoiding martensite transformation after deformation. According to the phase transformation rules, the ultimate tensile strength and reduction in area of the wire rod formed in the optimized industrial trial are 636 MPa and 73.6 %, respectively, showing excellent strength and plasticity.

Hydrophilic silica aerogel nanoparticles surface was modified with hexamethyldisilazane. Then, the resultant modified nanoparticles were used in random copolymerization of styrene and butyl acrylate via activators generated by electron transfer for atom transfer radical polymerization. Conversion and molecular weight determinations were performed using gas and size exclusion chromatography respectively. Addition of modified nanoparticles by 3 wt% results in a decrease of conversion from 68 to 46 %. Molecular weight of copolymer chains decreases from 12,500 to 7,500 g.mol –1 by addition of 3 wt% modified nanoparticles; however, PDI values increase from 1.1 to 1.4. Proton nuclear magnetic resonance spectroscopy results indicate that the molar ratio of each monomer in the copolymer chains is approximately similar to the initial selected mole ratio of them. Increasing thermal stability of the nanocomposites is demonstrated by thermal gravimetric analysis. Differential scanning calorimetry also shows a decrease in glass transition temperature by increasing modified silica aerogel nanoparticles.

Low softening point temperature glassy frit, reinforcing silica, wollastonite and dicumyl peroxide were incorporated into ethylene-propylene-diene (EPDM) rubber matrix in different amounts in order to obtain ceramifiable composites. Kinetics of vulcanization of the mixes was measured. Mechanical properties, micromorphology, thermal properties and combustibility of the vulcanizates were studied as well as compression strength of the ceramic residue obtained after heat treatment. Studies show that optimal amount of glassy frit from the point of view of ceramification effectiveness in dispersed mineral phase is 40 % wt.

Pyrite cinder is a solid waste generated by the sulfuric acid industry and is considered environmentally hazardous. It contains abundant iron, such as Fe 2 O 3 and Fe 3 O 4 , and nonferrous metals, such as zinc, lead and copper. In order to try and recycle this material as a source of Fe units, preparation of direct reduction iron (DRI) using pyrite cinder was investigated by coal-based grate rotary kiln process. This process includes chloridizing and reduction roasting. The results show that 97 % lead was removed after the chloridizing process. Copper was only detached in chloridizing process with the removal rate of 78.49 %. Furthermore, the removal of zinc was carried out in both chloridizing and reduction process, and the removal rate of 96.76 % was achieved after reduction roasting. The final product representing a metallization degree of 93.36 % with compressive strength of 1,198 N/pellet was obtained after the oxidized pellets were reduced at 1,050 °C for 80 min.

With toluene soluble fraction of coal tar pitch, polycarbosilane and pyridine borane as raw materials, the modification coal tar pitch was synthesized by a liquid method. The B-Si-doped carbon materials were obtained by carbonization treatment at 800–1,600 °C for 1 h. The effects of carbonization temperatures on the composition, microstructure and oxidation resistance of the B-Si-doped carbon materials were investigated by XRD, SEM and TG-DSC. The results showed that the B-Si-doped carbon materials were composed of B 2 O 3 and carbon. SiC crystal grains appeared when the carbonization temperatures were over 1,200 °C. The higher the carbonization temperatures were, the larger the SiC grain sizes of B-Si-doped carbon materials became. But oxidation rate of larger grain sizes of SiC was slow during oxidation. It was difficult to form a protective glassy film on the surface of the materials rapidly. Therefore, the B-Si-doped carbon materials obtained by carbonization at 1,200 °C showed better oxidation resistance. Oxidation resistance mechanism of B-Si-doped carbon materials was illustrated. The SiO 2 produced by the oxidation of SiC and B 2 O 3 formed protective glassy film, which had self-healing and anti-oxidation synergism.

The closure process of voids was very crucial for diffusion bonding, voids behaviors in Mg/Al bonding process were investigated, and the control mechanisms of diffusion at different predominant process parameters were discussed in this paper. Finite element simulation was utilized to investigate the influence of thermal residual stresses on the appearance of secondary voids. The results showed that: the dominant mechanism of void closure was plastic deformation in the initial stage of Mg/Al diffusion bonding. Numerical results indicated that secondary voids could be easily generated in the regions where tensile residual stress gradient achieves the maximum, corresponding to area that Al 3 Mg 2 layer at the nearby Al/Al 3 Mg 2 interface, the segregation of voids deteriorated the performances of the bonded joints.

The energy dissipation rate (EDR) is an important parameter for characterizing the behavior of inclusion coagulation in agitated molten metal. To clarify the inclusion coagulation mechanism, we review previous water model studies by particularly focusing on the relation between the impeller torque and the EDR of the fluid, which indicates the ratio of energy dissipated in the viscous medium to the energy inputted by the rotating impeller. In the present study, simulations coupled with experiments were performed to determine the relation between the torque and the effective EDR for water and liquid Al in crucibles with and without baffles.

Dynamic recrystallization (DRX) behavior of a vanadium microalloyed steel pipe was systematically investigated at temperatures range of 850–1,200 °C and a strain rate of 5 s −1 on a Gleeble-3800 thermo-simulation machine. Constitutive equation was obtained by characteristic points of DRX which derived from the strain hardening rate and stress curves. DRX kinetics model was established for determining the recrystallization volume fraction ( X ). Effect of dynamic precipitation of V(C, N) imposed on DRX at temperatures from 850–1,000 °C was analyzed. Results show that true stress-strain curves exhibited no clearly defined stress peaks with typical dynamic recovery behavior. X increased from 43.9 % to 100 % with increasing deformation temperature, which was in reasonable agreement with the observation of microstructure. Moreover, the calculation pinning force of V(C, N) precipitates was weaker than the recrystallization driving force, revealing that V(C, N) precipitates could effectively retard rather than prevent the progress of DRX.

This paper highlights the effect of 70 %NaCl–30 %KCl salt mixture on compression creep properties of 12Cr1MoV alloys at 100 MPa (948.15 K, 973.15 K and 998.15 K) in air using bare specimens and specimens in corrosive environment. The corrosive specimens were also tested at 923.15 K (150 MPa, 175 MPa and 200 MPa). Experimental results showed that the specimen in chloride mixture showed relatively high compression creep strain and steady-state creep rates compared with the bare specimen, and this effect accelerated with the increased temperature, especially when it was above 973.15 K. The creep mechanisms of the specimen in chloride mixture were inferred from gliding and climbing of dislocations of the stress exponent. Damage of hot corrosion in creep deformation was found to be associated with the layer fracture attributing to the initiation and propagation from the intergranular cracks and reduction of the bare area caused by the internal transgranular attack of chloride mixture.

In order to improve the understanding of the hot flow behaviors of as-extruded 7050 aluminum alloy, a series of isothermal compression tests with a fixed height reduction of 60 % were performed at the temperatures of 573 K, 623 K, 673 K and 723 K, and the strain rates of 0.01 s −1 , 0.1 s −1 , 1 s −1 and 10 s −1 on a Gleeble-1500 thermo-mechanical simulator. Based on both nonlinear and linear estimations of work hardening rate versus strain curves, two phenomenological models have been developed to predict the flow stress values under different hot forming conditions up to the peak stress. The suitability levels of these two models were evaluated by comparing both the correlation coefficient ( R ) and the average absolute relative error ( AARE ). R -value and AARE -value for the linear phenomenological model are 0.9995 and 2.18 %, respectively, while the R -value and AARE -value for the nonlinear model are 0.9901 and 10.60 %, respectively. The results showed that the predictions of these two models were in good agreement with the experimental data for 7050 aluminum alloy. Fewer materials constants were involved in the linear model, and the predicting ability of the linear model is stronger than the nonlinear model.

Solubility of nitrogen gas into pure copper at temperature range of 1,993–2,443 K was studied with using a levitation melting apparatus. The solubility which was dissolved content of nitrogen equilibrated with nitrogen gas with a pressure of 101.3 kPa increased with the temperature of molten copper. However, the solubility was approximately 1.5 mass ppm even at 2,443 K. Absorption of nitrogen gas into pure copper obeyed the Sieverts’ law and was expressed as: 12N2gas=N_ $${1 \over 2}{{\rm{N}}_2}\left({{\rm{gas}}} \right) = \underline {\rm N} $$ Here, the underlined element was expressed as the element dissolved into a molten copper. The relation between this reaction Gibbs energy, ΔrG0 ${\Delta _{\rm{r}}}{G^0}$ [J], and thermodynamic temperature of the molten copper, T [K], was given as: ΔrG0=61573+48.75T $${\Delta _{\rm{r}}}{G^0} = 61573 + 48.75T$$