Li-hua Zhao

Synthesis of steel slag ceramics： chemical composition and crystalline phases of raw materials

Two types of porcelain tiles with steel slag as the main raw material (steel slag ceramics) were synthesized based on the CaO-Al2O3-SiO2 and CaO-MgO-SiO2 systems, and their bending strengths up to 53.47 MPa and 99.84 MPa, respectively, were obtained. The presence of anorthite, α-quartz, magnetite, and pyroxene crystals (augite and diopside) in the steel slag ceramics were very different from the composition of traditional ceramics. X-ray diffraction (XRD) and electron probe X-ray microanalysis (EPMA) results illustrated that the addition of steel slag reduced the temperature of extensive liquid generation and further decreased the firing temperature. The considerable contents of glass-modifying oxide liquids with rather low viscosities at high temperature in the steel slag ceramic adobes promoted element diffusion and crystallization. The results of this study demonstrated a new approach for extensive and effective recycling of steel slag.

Control of the precipitation of TiN inclusions in gear steels

In the 20CrMnTi steel production process, the nitrogen content increased by 19 × 10−6 and 29 × 10−6, respectively, during ladle furnace (LF) refining and during the casting process from ladle to tundish. The protective casting is the key to decrease the N content. The results of thermodynamic calculations and a growth kinetics investigation show that TiN formation occurs only when the solidification fraction is greater than 0.533 under the controlled conditions used in this study for the manufacture of 20CrMnTi steel; the radius of TiN particles decreases as the Ti and N contents decrease and as the cooling rate increases. Furthermore, the theory of austenite grains controlled by second-phase particles was analyzed. The elemental analysis results showed that the Ti content was controlled at 0.04wt%–0.06wt% and the N content decreased to 0.005wt%, which satisfy the requirements for grain refinement but can also effectively prevent the precipitation of TiN inclusions in 20CrMnTi steel.

Thermodynamic analysis and formula optimization of steel slag-based ceramic materials by FACTsage software

Using steel slag as a main raw material of ceramics is considered as a high value-added way. However, the relationship among the initial composition, ceramic microstructure, and macroscopic properties requires further study. In this paper, a series of ceramics with different slag ratios (0–70wt%) were designed, and the software FACTsage was introduced to simulate the formation of crystalline phases. The simulation results indicate that mullite is generated but drastically reduced at the slag ratios of 0–25wt%, and anorthite is the dominant crystalline phase in the slag content of 25wt%-45wt%. When the slag ratio is above 45wt%, pyroxene is generated more than anorthite. This is because increasing magnesium can promote the formation of pyroxene. Then, the formula with a slag content of 40wt% was selected and optimized. X-ray diffraction results were good consistent with the simulation results. Finally, the water absorption and bending strength of optimized samples were measured.

Coordinated control of carbon and oxygen for ultra-low-carbon interstitial-free steel in a smelting process

Low residual-free-oxygen before final de-oxidation was beneficial to improving the cleanness of ultra-low-carbon steel. For ultra-low-carbon steel production, the coordinated control of carbon and oxygen is a precondition for achieving low residual oxygen during the Ruhrstahl Heraeus (RH) decarburization process. In this work, we studied the coordinated control of carbon and oxygen for ultra-low-carbon steel during the basic oxygen furnace (BOF) endpoint and RH process using data statistics, multiple linear regressions, and thermodynamics computations. The results showed that the aluminum yield decreased linearly with increasing residual oxygen in liquid steel. When the mass ratio of free oxygen and carbon ([O]/[C]) in liquid steel before RH decarburization was maintained between 1.5 and 2.0 and the carbon range was from 0.030wt% to 0.040wt%, the residual oxygen after RH natural decarburization was low and easily controlled. To satisfy the requirement for RH decarburization, the carbon and free oxygen at the BOF endpoint should be controlled to be between 297 × 10-6 and 400 × 10-6 and between 574 × 10-6 and 775 × 10-6, respectively, with a temperature of 1695 to 1715°C and a furnace campaign of 1000 to 5000 heats.

Effect of electric pulse on the crystal structure of solidified copper ingots

To obtain advanced quality pure copper, the microstructure of solidified copper was optimized by imposing electric pulse on liquid copper in this study. Experiments were performed to determine the effect of electric pulse voltage, arrangement mode of electrodes, and energy input on the microstructure of solidified copper. The results show that, when the energy input of electric pulse is bigger than 28.95 kJ per ton copper, the percent of fine grains increases noticeably with the increase of energy input; but when the energy input of electric pulse is smaller than 28.95 kJ per ton copper, the percent of fine grains decreases with the increase of energy input. The influence order of above factors on grain refinement is electric pulse voltage > arrangement mode of electrodes > energy input. According to the above experimental results, the optimum process conditions are chosen as the voltage being 400 V and the energy input greater than 28.95 kJ per ton copper. Meanwhile, the best arrangement mode of electrodes should be that, one electrode is immerged in the middle of liquid copper in the crystallizer, and the other is connected to the inner wall of the crystallizer, which is divided into two electrode poles for the symmetrical electric field distribution.

Superior machinability of steel enhanced with BN and MnS particles

The strategy that replacing part of MnS with BN was proposed in order to decrease the sulfur content in sulfur based free-cutting steel. The effects of BN and MnS inclusions on the microstructure and machinability of the steel were systematically investigated. The results show that most of the BN and MnS inclusions exist individually in the steel and only a small amount of them are in a composite state forming either isolated particles or clusters of particles. In the case of multi-phased steel, the theoretical calculation predicts that the volume of large BN particles should be 0.7 times of the volume of large MnS particles. The machinability of this type of BN and MnS alloy steel over a wide range of cutting speeds ranging from a low speed appropriate for drilling to a high speed appropriate for turning is confirmed as being equal to or superior to that of an MnS reference steel, even though the sulfur content in the composite steel is only half that of the MnS steel. The aptitude for cutting effect of 240 ppm nitrogen and 115 ppm boron in the composite steel is demonstrated to be equivalent or even better than 1000 ppm sulfur in MnS free-cutting steel.

Experimental study on sulfur removal from ladle furnace refining slag in hot state by blowing air

In view of the present problem of sulfur enrichment in the metallurgical recycling process of ladle furnace (LF) refining slag, a simple and efficient method of removing sulfur from this slag was proposed. The proposed method is compatible with current steelmaking processes. Sulfur removal from LF refining slag for SPHC steel (manufactured at a certain steel plant in China) by blowing air in the hot state was studied by using hot-state experiments in a laboratory. The FactSage software, a carbon/sulfur analyzer, and scanning electron microscopy in conjunction with energy-dispersive X-ray spectroscopy were used to test and analyze the sulfur removal effect and to investigate factors influencing sulfur removal rate. The results show that sulfur ions in LF refining slag can be oxidized into SO2 by O2 at high temperature by blowing air into molten slag; SO2 production was observed to reach a maximum with a small amount of blown O2 when the temperature exceeded 1350°C. At 1370°C and 1400°C, experimental LF refining slag is in the liquid state and exhibits good fluidity; under these conditions, the sulfur removal effect by blowing air is greater than 90wt% after 60 min. High temperature and large air flow rate are beneficial for removing sulfur from LF refining slag; compared with air flow rate, temperature has a greater strongly influences on the sulfur removal.

Study on Adjustment and Optimization of LF Refining Slag of Spring Steel 55SiCrA

The spring steel 55SiCrA produced in a domestic steel factory is deoxidized by Si with “100 t EAF-LF-VD-CC”. The fluoric content (CaF2 = 17.41–22.15%) and the binary basicity (R = 1.9–3.0) of applied LF refining slag are high. To avoid environmental pollution caused by fluorine, meanwhile guarantee the speed of melting slag and smelting effect on molten steel, the structure of refining slag was adjusted. A new fluorine-free slag system was obtained by changing slagging process, adjusting adding amounts of slag-making materials, such as lime, calcium carbide, silicon carbide and so on. This new fluorine-free slag was applied in industrial tests. The results showed that this new fluorine-free slag could meet smelting demands well. The average mass fraction of oxygen content of spring steel 55SiCrA billets could decreased from 11 × 10−6 to 9 × 10−6 and the plasticity of inclusions also changed better. All compositions of observed inclusion in billets were within the 1400 °C liquidus in Al2O3-SiO2-CaO-MgO-MnO phase diagram.

The Research on the Relationship Between Gas Movement Behaviors and Circulation Flow of the Molten Steel in RH

Circulating kinetic energy has important influences on process of rapid decarburization rate in RH. A physical model of 300 t RH in 1:6 ratio is established to study the relationship between gas behaviors and circulating kinetic energy in this paper. The studies showed that the circulating kinetic energy of liquid steel has the exponential relationship with the bubble velocity and gas volume fraction (17–26%). However, the proportion that the circulating kinetic energy accounted for the total energy is less than 1%, when the void fraction in the up leg is lower than 22% or the bubble velocity less than 0.5 m/s. Therefore, in order to avoid appearing lowest energy value and take advantage of gas-driven energy, must satisfy threes below requests. Ensuring the void fraction is greater than 22%. The vacuum chamber bubble residence time is around 0.15 s. And the bubble rising velocity is not less than 0.5 m/s. Satisfying the above conditions can optimize flow effect of molten steel and improve the decarbonization rate.

Study on the Respirable Particulate Matter Generated from the Petroleum Coke and Coal Mixed-Fired CFB Boiler

The dust generated from the fuel combustion is one of the important sources for air pollution. This paper has made a comprehensive research on the particulate matter generated from the petroleum coke and coal mixed-fired circulating fluidized bed (CFB) boiler. Four kinds of ash were studied including the ash from the electrostatic precipitator(ESP), the ash from the bag filter, PM10 collected at the entrance of the ESP and the export of the bag filter. The results of the analysis of particle size show that PM10 of the entrance present the three peaks distribution due to the different formation mechanisms. The chemical composition analysis was conducted to deduce the formation mechanisms based on the current PM formation theory in combustion. The result indicates that there are two kinds of micron particles found, some are fuel generated, others are limestone generated. The bigger the particles are, the more limestone generated particles can be found.