Advanced Materials Research Vols. 284-286

Abstract: Through the mathematical model of RH vacuum decarburization, the decarburization mechanism of argon gas bubble surface was studied. By the RH equipment of Shougang Qian’an Iron and Steel Co. Ltd for background, the calculated results of this model showed that the decarburization quantity of argon gas bubble surface was about 8% that of overall decarburization. In the initial conditions was constant, the ascension of argon flowrate will promote the decarburization quantity of argon gas bubble surface, free surface and splash droplet surface as well as reducing the decarburization quantity of internal liquid steel decarburization. Based on the commercial production data, it was found the best opportunity of ascension blow argon flowrate to acquire lower carbon content in relatively shorter time.

Abstract: Nozzle blockage is easy to take place in continuous casting process when producing 38CrMoAl steel due to high content of aluminum ([Al]=0.7%~1.1%). Slag-steel reaction will lead to large transformation for composition of molten steel and performance of slag on the condition of traditional high content of SiO2 in slag. And it will reduce the cleanliness of steel as well. The control target of refining slag and tundish powder has been gotten through the analysis of refining & continuous casting characteristics of high aluminum steel. Based on this, the content of Si and Al in molten steel can be controlled accurately, and the cleanliness of steel has gone to a higher level. Moreover, mold powder with high basicity and vitrification ensures the stability of slag after sorbing Al2O3 inclusions in theory. Continuous casting can be carried out successfully with the control of inclusion morphology through slag washing during tapping. Industrial practice shows that Si content is 0.25%~0.40%, Al content is 0.80%~1.00%, S content is below 0.004% and T[O] is below 0.0015% in steel products. Moreover, casting bloom with good surface quality is achieved, and the rate of bloom without cleaning is as high as 100%. With all these countermeasures, 38CrMoAl steel can be continuously cast for more than 6 heats.

Abstract: As a raw material, Indonesia vanadium-titanium sinters are being applied to the blast furnace process for iron making in the typical iron and steel plant. In order to keep the health running of blast furnace process, in this work we have investigated the softening and melting properties of Indonesia vanadium-titanium sinters. We found that the content of vanadium-titanium magnetite in sinter is correlated with the softening and melting ranges for those sinters considered here. With the increasing of the vanadium-titanium magnetite in sinter, the starting softening temperature increases gradually and the final softening temperature increases as well, thereby the softening range becomes narrow. Both starting and final melting temperatures begin to ascent, and the variation of melting range is not obvious. In addition, we also found that the coke is wetted by the molten slag and iron. From the viewpoint of blast furnace process, the softening and melting zone has to move downward. In this zone of blast furnace the contact area of solid-liquid phase will get larger because of the close contract among the molten slag, iron and coke. On one hand, this kind of behavior can definitely speed up the reduction of iron oxide. On the other hand, it simultaneously worse the ventilation properties and affect the normal running of air flow, because a lot of iron and slag can not be got smoothly into the hearth through coke layer.

Abstract: This paper is written to discuss the Gleeble simulation experiment of micro-carbon steel rolled in ferrite region. By measuring the resistances under different rolling temperatures, rolling speeds and rolling deformation, the matrix of micro-carbon steel is established, after that, the matrix is also regressed and the result proves that the accordance of the matrix is good. This show the matrix established can be used to calculate the rolling parameters of micro-carbon steel.

Abstract: The ability of IMC-80BH corrosion inhibitor is proven to be excellent in earlier indoor static and flowing evaluation and it is worthwhile to determine the inhibitor concentration to maintain the optimum concentration for the sake of effective gas well protection. A improved concentration determination method is aboratively investigated. The maximum absorption wavelengths, buffer solution, reaction time and additive dosage of chromogenic reagent XD are detected successively and the standard curve of liquid phase behaves better than oil gas. The sample verification demonstrates that such determination measurement is reliable and precise. The four representative gas wells including G8-7, S59, W26-5 and G49-6 in service are also determined. The determination result offered substantial basis to analyze and select appropriate inhibitor injection program and dosage.

Abstract: The effect of cooling rates after finish rolling on microstructure and properties of high strength medium carbon microalloyed steels used for fracture splitting con-rods was investigated using the methods of optical microscopy, SEM and TEM, etc. The results show that high cooling rate after finish rolling can increase the percentage of pearlite, reduce the grain size of ferrite and lamellar spacing of pearlite. The precipitations in the steel are composite phases of (V,Ti)(C,N), etc. Their granularity are about 30-170nm, and they will decrease with the speeding up cooling. The yield strength (YS) and ultimate tensile strength (UTS) are improved with increasing the cooling rate. The impact fracture surface shows distinct brittle fracture character.

Abstract: In order to make nonmetallic inclusions with low melting point and improve the fatigue resistance of gear steel, thermodynamic analysis on precipitation of nonmetallic inclusions CaO(MgO)-Al₂O₃ system was investigated in this paper. The complex deoxidation equilibria of strong deoxidizing elements such as aluminum, calcium, magnesium and so on were calculated accurately with the second order and middle term of the activity coefficient expression. Thermodynamic conditions for the precipitation of spinel inclusion (MgO•Al₂O₃) is sufficient as the acid-soluble aluminum content is 0.04% and magnesium content is less than 0.0005% in the tested gear steel 20CrMoH. The relationship between precipitation of spinel and calcium aluminate inclusions in gear steel and the composition of molten steel at 1873K indicates that, the compositions of inclusions before and after calcium treatment are C₁₂A₇ and C₃A respectively, while the reactions in ladle reach the equilibrium state.

Abstract: Electroconductive Si₃N₄–TiN ceramic was fabricated by pressureless sintering from the chief materials containing high titanium slag and Si₃N₄ powder synthesized by carbonthermal reduction nitridation method using iron ore tailing as raw materials. Phase constitutes and microstructure were analyzed by XRD and SEM. The densification, mechanical properties and electrical conductivity of Si₃N₄–TiN ceramic were also measured. Results show that the sintered samples mainly consist of Si₃N₄ and TiN. Si₃N₄ exhibits rod morphology and the grain sizes are about 1-3mm.TiN shows fine granular morphology with most of grain size being lower than 0.5mm. The electroconductive Si₃N₄–TiN ceramic has optimal properties when it is sintered at 1550°C for 2h using initial raw materials containing 20wt% TiO₂. The sintered sample’s bulk density, hardness, flexure strength and room electrical resistivity are 2.79 g·cm^-3, 8.23GPa, 66 MPa and 7.1×10^-2W·cm, respectively.

Abstract: Physical modeling using a 1:3 scale model was carried out to study the fluid flow characteristics in a delta shaped, four-strand continuous casting tundish with different types of flow control devices (FCD). The symmetric baffle with inclined holes (II shaped from top view) was not suitable in this study, while the U shaped baffle with inclined holes was suggested for the integrated fluid flow in tundish. The principles of U shaped baffle designs were proposed, and 18 types of FCD were evaluated by the residence time distribution (RTD) curve and strand consistency. The RTD curves of abnormal operations (with one strand closed) of the II shaped and U shaped baffles were also investigated.

Abstract: This study was carried out to determine the minimum Al content needed to form an Al₂O₃ scale on creep resistant ferritic steels at 650 °C. Two steels differing mainly in Al content were oxidized in air at 650 °C for 3000 h. One of the steels contained 2.3 wt% Al and the other 1.9 wt% Al. Oxidation resistance of the two steels was also compared with that of the commercial P92 steel at the same temperature. The oxidation was monitored by weight gain measurement. XRD, SEM and EDS techniques were used to analyze the scale formed on the surface of the steels. For the steel containing 2.3 wt% Al, a continuous Al₂O₃ scale was observed after 3000 h of oxidation and growth of the scale was parabolic with an extremely low rate constant of 0.00058 mg cm^-2 h^-1/2. For the steel containing 1.9 wt% Al, however, only a non-protective scale was formed, which exhibited a layer structure that consisted of an outermost porous Fe₂O₃ layer, followed by a relatively dense intermixed Fe₂O₃ and FeCr₂O₄ inner layer and then by an internal oxidation layer containing voids, Al₂O₃ and un-reacted metal particles in addition to Fe and Cr oxides; growth of this type of non-protective scale followed the logarithmic kinetics Δm_t = k_lln(αt + 1) for oxidation times up to 3000 h.