Advanced Materials Research Vols. 284-286

Abstract: It can reduce the grain boundary segregation effectively, and improve the solidification microstructure, as well as cause the migration and redistribution of elements by adding the pulse electric field during the solidification process of the Fe-C-S alloy melt. Where, the element S migrates from the positive polarity to the negative polarity, while the migration law of the element C is reverse to that of the element S. The principal ingredient of the inclusion in solidification microstructure after treatment is FeS and a small amount of MnS, while FeS is distributed at the edge and in the centre area of the whole sample spherically.

Abstract: For high grade pipeline steel, elimination of Al₂O₃ inclusions can improve the susceptibility of hydrogen-induced cracking (HIC) and stress corrosion cracking (SCC). In the present work, the transformation of Al₂O₃ inclusions with slag-metal reaction was studied by controlling ladle slag and relative technologies in LF-RH refining process. It is found that Al₂O₃ inclusions decrease with increasing refining time, and no pure Al₂O₃ inclusions exist in molten steel at the end of secondary refining; the remained inclusions in molten steel are liquid calcium aluminates and semi-liquid CaO-MgO-Al₂O₃ complex inclusions. The analysis of thermodynamic equilibrium proves that CaO and MgO in slag can be reduced by aluminum in molten steel, which is the source of calcium and magnesium in molten steel.

Abstract: It is impossible to keep pipelines free from defects in the manufacturing, installation and servicing processes. In this paper, pre-tension deformation is used to imitate the defects of the part of material and the electric method is used to measure the distance of the fatigue crack. Experimental investigations were carried out on the fatigue crack propagation characteristics of X60 pipeline steel after different degrees of pre-tension deformation Test results show that the fatigue crack propagation was augmented with the pre-tension deformation increase, especially the crack propagation at the near threshold section. The results of quantitative analysis show, the pre-tension deformation reduced the fatigue crack propagation threshold and increased the crack propagation coefficient; consequently the fatigue performance of the part of mechanical damnification was degenerate.

Abstract: The reduction of different basicity BF charge with gases of different H₂ ratio has been determined to simulate different BF technology. The results reveal: reduction rate (R & r) and metallization rate of charge increase with the H₂ ratio increasing, and the temperature increasing while the reducing time becomes longer simultaneously. The direct reduction degree of charge in Hydrogen-enrichment BF is very low, thus the energy consumption of Ironmaking could be reduced. There is certain difference between metallization rate and reduction degree due to reduction kinetics. The mass loss rate of coke increases sharply with the H₂ ratio increasing, the H₂ ratio of gas should be selected an appropriate value.

Abstract: The use of high strength line pipe steels is beneficial for the reduction the cost of gas transmission pipelines by enabling high pressure transmission of large volumes of gas. The high strength line pipe steels will become the preferred materials for modern natural gas transmission pipeline. It was well known that manganese was an important element in the high strength line pipe steels. In this paper, a simple spectrophotometric method was described for determination of manganese in high strength line pipe steels. The method was based on the oxidation-reduction reaction between ammonium persulfate and manganese(II) producing manganese(VII) in the presence of silver nitrate as a catalyst. The characteristic wavelength of maximum absorption of manganese(VII) was obtained locating at 530 nm. Under the optimum reaction conditions the absorption value was proportional to the concentration of manganese in the range of 0.18%~2.0% (R² = 0.9997), and the relative standard deviation was less than 3.0% (n=5). The proposed method was applied successfully to determine manganese in API grade X80 line pipe steel and API grade X70 line pipe steel samples.

Abstract: The freeboard, which is an important region in COREX melter gasifier, has drawn more and more attentions, and as a key parameter for COREX melter gasifier operation, the temperature in freeboard must be within a certain range. In this paper, the temperature field of freeboard is simulated with computational fluid dynamics(CFD). The results show that the temperature in bottom is lower than that in upper. The temperature when oxygen nozzles are open is higher than that when oxygen nozzles are off, and the temperature under different operation conditions is all about 1000 °C.

Abstract: A new, high efficient comprehensive utilization technology with non-pollution, low energy consumption, and strong feedstock adaptability is investigated with the view to developing an efficient smelting process of vanadium-bearing titanomagnetite by non-BF route. It includes three major steps in this process: selective chlorination of the concentrates for extraction vanadium using industrial chloride wastes, direct reduction for producing DRI at medium temperature, and separation of hot metal from slag at elevated temperature. In this paper, it focuses on the extraction of vanadium from vanadium-bearing titanomagnetite by selective chlorination. The mechanisms of selective chlorination for extracting vanadium is discussed from the view of thermodynamics analyses and it is found that the reasonable temperature is over the temperature range of 900K~1300K if chlorine potential (logp_Cl2) and oxygen potential (logp_O2) are controlled at a certain region (hatched region A). Furthermore, some preliminary experimental are conducted and the results show that it is possible to extract vanadium from vanadium-bearing titanomagnetite by selective chlorination and extraction ratio can reach up to 30% under 1100K after 2 hours calcination.

Abstract: The effect of Nb microalloying on microstructure transformation of coarse-grained heat-affected zone of high strength low alloy steels were investigated utilizing different heat input welding simulation. For the low-Nb steel, the microstructures of coarse-grained heat-affected zone mainly consisted of acicular ferrite, bainite and grain boundary ferrite for small heat input welding; the amount of acicular ferrite decreased whereas grain boundary ferrite, polygonal ferrite and pearlite increased with increasing heat input. In constrast, for the high-Nb steel, granular bainite was the dominant microstructure. The formation of granular bainitic microstructure was associated with the solid solution of Nb, which suppressed ferrite transformation and promoted the formation of granular bainite. The hardness of coarse-grained heat-affected zone increased with increasing Nb content, and decreased with decreasing heat input, which was attributed to the microstructural change.

Abstract: High silicon steel containing 6.5 wt% Si was prepared by pulse electrodepositon in KCl-NaCl-NaF-SiO₂ molten salt followed by diffusion annealing. The composition, the phase and the evolution of texture during the different production step were analyzed by glow discharge optical emission spectroscopy (GDOES), X-ray diffraction analysis (XRD) and the orientation distribution function (ODF). The results showed that the silicon content of the high silicon steel was about 6.5wt%. The high silicon steel was composed of a-Fe and Fe₃Si. After diffusion annealing the undesirable g-fibre type texture {111} <110> and {111} <112> weakened, both easy magnetization direction Goss texture ({110} <001>) and cube texture {100} <001> were intensified.

Abstract: A physical thermal model was established in this study, and the gas temperature in the model was measured with temperature sensors under different experimental conditions. The results show that the packed bed, cohesive zone, dripping zone and raceway in melter gasifier can be roughly distinguished by temperature gradient analysis along the vertical direction. The changes of different zones in the COREX melter gasifier were also investigated in this paper under different operation conditions.