Mao Fa Jiang

Effects of Rare Earths on the Austenite Recrystallization Behavior in X80 Pipeline Steel

In order to improve the effects of rare earths (RE) as microalloy on the recrystallization behavior in the high strength micro-alloyed steel, the X80 pipeline steels with different RE content were produced with a vacuum induction furnace, a series of hot torsion tests were performed under a range of deformation conditions, and the stress-strain curves were analyzed. The results showed that trace RE would improve the austenite recrystallization behavior. The activation energy of deformation and static recrystallization of the austenite in the X80 pipeline steel without RE additions were respectively 393 and 366 kJ/mol. When the RE addition was 0.0025 wt.%, the activation energy of deformation and static recrystallization were reduced by 33 and 29 kJ/mol respectively. But when the RE addition was increased to 0.0220 wt.%, RE would significantly inhibit the dynamic recrystallization of the austenite, the activation energy of deformation would be increased by 35 kJ/mol, but the activation energy of static recrystallization would reduce by 15 kJ/mol.

Sulphur Removal from Sulphur Containing Phase(CaS) in Ladle Slag by Oxidizing Roasting

Slag is the main by-product of iron and steelmaking process. Ladle slag, melted fully after secondary refining, usually contains rich CaO, Al2O3 and 2CaO·SiO2 phase, which has a potential value to recycle into steelmaking process as the substitution of lime. However, reuse of ladle slag is easy to induce an accumulation effect of sulphur or phosphorus. In this present work, CaS powder was used to replace the sulphur containing phase in ladle slag to investigate the roasting process under different atmosphere conditions. The influence of temperature and oxygen pressure on sulphur removal mechanism and products composition has been discussed. By adding solid sulfur into molten ladle slag, the results of SEM has showed that sulphur element in ladle slag existed as independent CaS phase. Roasting experiments showed that lower oxygen pressure and higher reaction temperature were beneficial for CaS changing into CaO, it was very important to design the optimum roasting route for sulphur removal from the ladle slag.

Electrochemical Behavior of 430 Ferritic Stainless Steel in HCl Solution with Different Concentration of Hydrochloric Acid

The hydrochloric acid pickling process which is widely applied in carbon steel pickling ensures high speeds with little pollution. In this research, hydrochloric acid pickling process was introduced into stainless steel pickling to improve the surface integrity. Research indicated that the impedance spectrum obtained from 430SS in HCl solution consisted of a capacitive loop at high frequencies and an inductive loop at low frequencies. As the concentration of hydrochloric acid rose, the radiuses of the capacitive loop decreased.And the corrosion potential of 430SS in hydrochloric acid solution moved to positive direction with band to a narrow 0.1V.And high HCl concentration more markedly influenced the charge-transfer resistance.

Study on Separation of Niobium and Iron from Low Grade Niobium Ore

The separation of niobium and iron from the low grade niobium ore was researched by the technology process of reductive roasting and magnetic separation. Experiments of reductive roasting and magnetic separation were carried out in order to investigate the separation effect at different conditions of roasting temperature and addition amount of coal powders. The results show that the separation of niobium and iron can be realized, meanwhile the niobium can be enriched in the magnetic tailings. The main mineral phase of niobium in magnetic tailings changes into NbC from (Ce,Nd)NbTiO5 when the roasting temperature exceeds 1150°C. By magnetic separation after roasting with adding 37.5% coal powders at 1050°C, w(T.Fe) of the reduced iron is 86.11%, the percentage metallization is 87.6%, and the yield ratio of iron is 77.4%. Meanwhile, w(Nb2O5) of the magnetic tailings is 7.35% which is 2.4 times higher than low grade niobium ore, and the yield ratio of niobium is 98.1%.

Effects of TiO2 on the Viscocity and Solidification Temperature of Mold Fluxes for the Stainless Steel

Effects of TiO2 on the viscous characteristic of mold fluxes for the stainless steel were investigated by the rotary viscometer, TEM and XRD. The results showed that with the increasing amount of additive TiO2, the viscosity and solidification temperature of mold fluxes could decrease gradually, and then increase rapidly. The viscosity and solidification temperature of mold fluxes were minimum of 0.30Pa.s (1300°С ) and 1198°С respectively, as amount of additive TiO2 was 10mass%. The viscosity of mold fluxes could be decreased by the additive TiO2 which played the role of network modifier, and could be increased by the precipitation of perovskite (CaTiO3) crystals as amount of additive TiO2 was more than the critical value. The growth of cuspidine and wollastonite crystals could be restrained, and the precipitation of perovskite and melilite crystals could be promoted by the additive TiO2. In this study, the solubility of additive TiO2 was more than 20mass% in mold fluxes at 1350°С .

Study on the Clean Production Process of Basic Chromium Sulphate

The pollution of chromium salt industry is increasingly serious in China and becomes a worldwide problem with the rapid development of chromium salt industry. Then a new clean production process with a high recovery rate of chromium and pollution-free was proposed according to the comprehensive summary of existing processes of basic chromium sulphate. Furthermore, a small amount of slag will be discharged in this short process with lower energy consuming. The design concept is also applicable to the preparation of other chromium salts products, which will eliminate the pollution of Cr6+ during the process of chromium salt production and be helpful to the comprehensive utilization of chromium salt. In addition, the guidance of scholar research and the broad application prospects of this work cannot be neglected.

Microstructure and Precipitates of High-Pure Ferritic Stainless Steels Stabilized by Niobium and Titanium

As stabilization elements added into ferritic stainless steels, various kinds of precipitates of niobium and titanium will form and have great effect on their microstructure, which has great effect on the mechanical and corrosion properties of the final products. Combined with thermodynamic calculation by FactSage software, microstructure and precipitates of ferritic stainless steels containing different niobium and titanium were investigated by optical microscope, scanning electron microscope, transmission electron microscope and energy dispersive spectrometer. The results show that titanium mainly exists in form of TiN but niobium exists mainly in form of NbC. Moreover, a certain amount of NbN particles precipitate when there is not enough titanium to react with nitrogen. TiN particles with size of 2μm~8μm promote the recrystallization but Nb-rich precipitates with size of less than 500nm suppress the recrystallization in the process of annealing.

Effect of Melting and Refining with DC-Arc on the Yield of Alloy Element

In order to know what effect on the yield of alloy elements will be if the steel is melted/refined with the DC arc furnace, the effect of melting and refining with DC-arc on the yield of alloy element has been investigated by a melting experiment, in which the melting/refining is switched to continuous melting/refining with DC-arc after the molten metal is contact with the molten slag for 41 minutes without DC-arc, and by a contrast experiment of melting/refining with DC-arc and with an AC-arc. When DC current passes through the slag-metal interface and the slag-gas interface, the existence of the electrolysis phenomenon during the DC-arc steel melting/refining has been confirmed. Electrolysis participates in the metallurgical reaction. The phenomenon of two or more electrode reactions taking place simultaneously at both the slag-metal interface and the slag-gas interface has also been observed. The two phenomena cause the accelerating loss of the alloy-elements in the molten metal and the decreasing of concentrations of the corresponding oxides in the molten slag. The electrochemical transfer of oxygen from the molten slag to the molten metal ((O2-)=[+2e and (O2-)=1/2O2+2e) at the slag-metal interface has been observed, and causes the increasing of oxygen content in the molten metal.

Turbulent Flow of Molten Steel in Thin Slab Continuous Casting Mold

The quality of continuously casting steel is greatly influenced by turbulent flow in the mold. Understanding the unsteady flow structures in this process is an important step in avoiding failures and decreasing defects. The cassette filter function is used to deal with unsteady Navier-Stokes equation, and then the turbulent flows in the thin slab continuous casting processes are simulated with the large eddy simulation (LES) method with the Smagorinsky sub-grid scale model. Characteristics of the unsteady turbulent flow in the thin slab continuous casting processes are exhibited. The turbulent asymmetric distribution was revealed even the nozzle in the centre position. And the vortices are located at the low velocity side adjacent to the nozzle.

Effects and Mechanisms of Vanadium on Structural Transformation of BVRE Heavy Rail Steel

The different dilatometric curves of continuous cooling transformation with the different cooling rates were determined by means of Gleeble-2000 thermal simulation machine. The CCT curve of BVRE heavy rail steel was obtained by measuring the dilatometric curves and metallographic analysis. And the effects and mechanisms of vanadium on the phase transformation and microstructure of BVRE heavy rail steel were investigated. It is found that, the BVRE heavy rail steel only takes place pearlite and martensite transformation during continuous cooling. The CCT curve of BVRE heavy rail steel is moved to lower right with increasing vanadium content, which indicates that vanadium can obviously improve the stability of super cooled austenite and delay the pearlite transformation. When the content of vanadium is increased from 0.052% to 0.12%, the shortest incubation time of pearlite transformation is increased from 30s to 59s. When the cooling rate ≤ 5 ·s-1, with increasing vanadium content, both starting and finishing temperatures of pearlite transformation are decreased at different extent, meanwhile the pearlite is refined and the pearlite percentage is notably decreased. When the cooling rate is 2 ·s-1, the pearlite percentage is decreased from 65.7% to 35.9% with increasing vanadium content. When the content of vanadium is increased from 0.052% to 0.12%, the critical cooling rate of quenching is decreased from 13 ·s-1 to 7 ·s-1, thus the hardenability of BVRE heavy rail steel is improved.