Advanced Materials Research Vols. 941-944

Abstract: An experimental study on hydrogen selective-reduction of niobium containing iron ore powder is discussed in this paper. It was used for this study that a homemade diffusion bed tubular resistance furnace which gas was blown from the bottom. Experimental results are reported on that when reduction times reach 2h the best reduction temperature is 950°C and that the reduction degree which is niobium containing iron ore powder can reach 90.98% and the metallization rate which is niobium containing iron ore powder can reach 86.47%. And in the best reduction condition adding LiCL catalyst, it is found that adding LiCl catalyst can promote the reduction degree and the metallization rate improved significantly. Adding LiCL catalyst's proportion is changed from 0.43% to 2.14%, the experiment results show that when adding 0.71% LiCl catalyst the catalytic effect is better and the reduction degree can reach 95.82% and the metallization rate can reach 93.73%.

Abstract: Corrosion behaviors of Q235 steel in simulate ammonium sulfate solution were studied. Effects of the ammonium sulfate concentration, Cl^- concentration, pH and the flow velocity on corrosion of Q235 steel in simulate ammonium sulfate solution were investigated by the weight-loss method, and the electrode processes were studied by polarization curves. The result showed that: (1) the corrosion rate of Q235 steel increased with the increase of Cl^- concentration firstly. When Cl^- concentration was 10000ppm, the corrosion rate reached the maximum value of 6.698 mm/a, and then, with the increase of Cl^- concentration, the corrosion rate decreased. (2)With pH increasing, the corrosion rate of Q235 steel decreased. (3)The corrosion rate increased with the increase of the concentration of ammonium sulfate firstly. When the concentration of ammonium sulfate was 5%, the corrosion rate reached the maximum value of 5.462 mm/a. And then the corrosion rate decreased. (4)The influence of the flow velocity on Q235 steel corrosion was remarkable, with the increase of the flow velocity, the corrosion rate increased rapidly.

Abstract: Brazing of commercially pure titanium to low carbon steel by using the Ag72Cu28 interlayer at different conditions was carried out in the present work in order to investigate the tensile-shear strength, microstructure and the fracture morphology of brazed joint. The results show that different intermetallic compounds such as CuTi,CuTi₂,Cu₄Ti₃ and FeTi were formed at the bonding area. It was observed that the microstructure of joint has a considerable effect on tensile-shear strength of the brazed samples and the maximum tensile-shear strength was achieved at “750°C-10min→850°C-5min”.All the fracture paths after tensile-shear tests occurred in the interface between titanium and silver-based interlayer in spite of the different fracture morphology.

Abstract: The elementary theory of functions of the basic tundish coving flux is analyzed at the beginning of this paper. Several types of the flux used in deferent steel grade include ultra-low carbon steel, low carbon steel and micro-alloyed steel. The result shows that the basic flux with CaO/SiO₂ to be 3~5 can help to control the SiO₂ be reduced by Al in steel within ±2%, and whole cleaness keeps stable with suitable component and proper process condition, marked with the T[O] content change ranged within 3ppm. But the basicity should be variable considering the productivity for different steel grade.

Abstract: In order to use GCr15 steel scrap from Wuxi, production process of reduction steel powder was studied according to its characteristic, including the effect of magnetic separation process on removing impurity, the selection of reduction process parameters. The results showed that bake in air at 500°C should be conducted to burn lubricant off. Magnetic separation on removing impurity should be conducted after burning lubricant off, and ball-milling in water should be added before wet magnetic separation. Effect of magnetic separation and recovery rate of steel scrap were comprehensive best when magnetic induction was selected at 80mT. Reduction system should be adopted at 850°C, 5 h in reducing atmosphere of dissociated ammonia.-100 mesh particle size and 20mm in material thickness should be selected. Through the above process, performance of GCr15 reduction steel powder produced by steel scrap from polishing process was as follows, TFe content was 97.18%, acid insoluble content was 0.38%, and it can be used to produce powder metallurgy structural parts. Performance of GCr15 reduction steel powder produced by steel scrap from grinding process was as follows, TFe content was 95.14%, acid insoluble content was 2.49%, and it can be used as steel powder for welding electrode.

Abstract: The main methods for manufacturing titanium clad steel are described, also the mechanisms of cold roll bonding and explosive welding are specifically analyzed. It is showed that two opposing brittle surface layers produced by scratch brushing break up and underlying base metal is extruded through cracks of the broken layers and creates an atom-to-atom bond for cold roll bonding, however, a lot of parameters affect the bonding for explosive welding. Some new ideas for manufacturing titanium clad steel is discussed herein.

Abstract: The oxidation behavior of T91 steel in Ar-10%H₂O atmosphere at 750°C was investigated. The morphology, microstructures and composition of oxide scales were examined by SEM/EDS and XRD. The results showed that the oxidation kinetics followed logarithmic law in the initial stage and parabolic law in the latter stage. At the early stage Cr-rich oxide film formed on the sample surface, which led to slow mass gain stage. In the latter oxidation stage, Fe ions diffused outward, resulting in fast oxidation stage. The oxidation scales consisted of two layers, an porous Fe₂O₃ outer layer and an denser Cr-rich inner layer. Some cracks were formed between the inner and outer layers. The oxidation mechanism of T91 in water-vapor atmosphere at high temperature was discussed in brief.

Abstract: The high temperature crept tests of T91 steel have been conducted under two different stresses and temperatures. The single crystal electron diffraction is used to identify the precipitated phase structure. The quantity and size of carbides located in boundaries and intragranular area have been obtained by quantitative metallography, respectively. The results showed that the main precipitated carbides in T91 steel are M₂₃C₆(M=Fe,Cr) and V₄C_3, which is located in the grain and at the boundary of prior austenite respectively. In comparison with the carbides at boundary, the average size of intragranular carbides was smaller while the quantity is higher. The distribution of the carbides size crept with different stresses and temperatures is in accordance with a typical Boltzmann distribution.

Abstract: Two kinds of TRIP steel with different Al and Si content were researched in this article. Different annealing atmosphere in the trial was achieved by the Hot Dip Galvanized Simulator by Iwatani. The segregation of alloying elements after annealing under different atmosphere were investigated and the compounds on the surface were shown. Furhermore, the distribution of oxides was abserved on the surface and the reactive wetting was assessed and the results after galvanizing was provided. We found out the increasing wettability was abserved under more reducing atmosphere with less Si because of a decrease oxide amount and an increase internal oxidation.

Abstract: The oxidation behavior of SUS310S austenitic stainless steels was studied in isothermal conditions at different temperatures between 800^oC and 1100^oC for 96h in air. The oxidation kinetics was analyzed, the surface and cross-section of the oxide scale grown by oxidation were characterized by using scanning electron microscopy (SEM), energy dispersive spectrometer (EDS), X-ray diffusion (XRD) and X-ray photoelectron spectroscopy (XPS). The SUS310S steel has high oxidation resistance at 800^oC and with the increase of the temperature, the parabolic rate constants is constantly increasing. Examination of the morphology and composition of oxide layers reveals a double-layer structure, The inner layer is mainly chromium oxide (Cr₂O₃) and is covered by an uneven thinness outer layer of manganese-chromium or iron-chromium spinel oxide.