Cheng Jun Liu

Effect of Zr addition on toughness and microstructure of coarse grained heat affected zone in Al deoxidised low carbon steel

The effect of Zr addition on the toughness and microstructure of coarse grained heat affected zone (CGHAZ) in Al deoxidised low carbon steel was investigated. In this present work, the specimens (Zr free and Zr added) were subjected to weld thermal cycle with heat input of 54, 80 and 100 kJ cm− 1 at 1350°C peak temperature using thermal simulator. The typical inclusions were characterised by scanning electron microscopy, and the chemical composition of the inclusions was determined by energy dispersive spectroscopy. The nanoscale precipitates were analysed by transmission electron microscopy and energy dispersive spectroscopy. It was verified that the occurrence of Zr in steel mostly exists in the form of oxide inclusions, but a few in the form of solid solution state and Zr containing precipitates when the concentration of Zr is 0.015%. The improvement of CGHAZ toughness is obtained when the heat input is 80–100 kJ cm− 1. The possible reasons about the effects of Zr on the toughness of CGHAZ, including Zr containing inclusions, precipitates and microstructure characteristics, were also discussed.

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.

Influence of zirconium on mechanical properties and phase transformation in low carbon steel

The influence of zirconium on the mechanical properties and phase transformation was investigated in low carbon steel. First, the steels are subjected to a special thermomechanical regime, and the hot rolled plates were used to characterise the tensile properties and impact toughness. Second, the phase transformation behaviour of the steels with various Zr contents was evaluated by both dilatometry and metallography. Finally, to confirm the existence of Zr containing precipitates in the Zr added steels, transmission electron microscopy and energy dispersive spectroscopy were used. It was verified that plenty of fine spherical (Nb,Ti,Zr)C, which is identified to be nearly 10 nm, can be formed when the concentration of Zr is in the range of 0.015–0.030%. The effects of zirconium on the phase transformation, including proeutectoid ferrite and pearlite transformation, and mechanical properties evolution were also identified and discussed.

Evaluation of surface tension of Ce-bearing slag based on calcium aluminate system

The surface tension of the Ce-bearing calcium aluminate slag was studied by the modified Butler’s equation. By taking the slag structure into account, the parameter related to AlO4-tetrahedron has been modified, imparting the model with good reproducibility. Ce2O3 and Li2O were surfactants. Ce2O3 can decrease the surface tension because of the decrease in the total ion moment of the slag and the weaker interactions between Ce3+ and O2−. Li+ had the weakest ionic potential, and increasing Li2O content decreased the total ion moment, which led to the decrease in the surface tension. The dissociated Ca2+ ions showed stronger absorption of the anions in the surface, so the surface tension increased with increasing the content of CaO. Increasing the value of w(CaO)/w(Al2O3) decreased the surface tension, because of the decrease in the total polymerised anions in the slag and the increase in the total ion moment.

Corrosion of hot-rolled 430 stainless steel in HCl-based solution

The mixtures of hydrochloric acid and hydrogen peroxide were employed as the environmental friendly pickling solution for 430 hot-rolled stainless steel in this study. Increase of HCl concentration accelerates the corrosion rate of base metal, however aggravates the intergranular attack in sole hydrochloric acid solution. Addition of oxidant (H2O2) boosts the corrosion potential of stainless steel significantly resulting in the change of electrode action. At high oxidant content (0.6 mol l−1 H2O2), a corrosion product film accumulates onto the surface and the corrosion is then governed by the mass-transport at the film/stainless steel interface. The random dissolving of metal ions because of the film leads to brightening of stainless steel surface and the local corrosion is suppressed.

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 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.

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.

Effects and Mechanisms of Niobium on the Fracture Toughness of Heavy Rail Steel

Heavy rail steel was prepared by the process of vacuum induction furnace smelting, forge work and rolling. Effects and mechanisms of niobium on the fracture toughness of heavy rail steel were investigated. In addition, the appropriate range of niobium content for heavy rail steel was determined. With the niobium content increasing, both the austenite grain size and pearlite laminae distance of heavy rail steel were decreased gradually at first and then increased rapidly. When the niobium content was low, the precipitates containing niobium predominantly appeared in the cementite, which improved the toughness of heavy rail steel by fining the austenite grain size and pearlite laminae distance; when the niobium content > 0.024%, the fine dispersed precipitates containing niobium mainly occurred in the ferrite, which improved the toughness of heavy rail steel by pining dislocations and inhibiting crack growth; with the niobium content increasing, both the quantity and size of precipitates containing niobium were increased gradually; when the niobium content > 0.073%, most precipitates containing niobium could not pin dislocations and inhibit crack growth because the particles size was too big, thus the fracture toughness of heavy rail steel was bad. So the optimum range of the niobium content could improve the fracture toughness of heavy rail steel. In the present study, when the niobium content was about 0.053%, the fracture toughness of heavy rail steel was the best. The maximum plane-strain fracture toughness was 49.88 MPam1/2.

Experimental Study on the Effective Separation of Chromium-Iron Ions in Multi-Component Solution System by Ihleite Method

As one of the raw material resources in China, chromium salt production has been paid to close attention. Alkali process of chromium salt produces serious environmental pollution, while acid production of chromium salt has separation problems of chromium-iron ions. The separation process of chromium-iron ions in acidic solution by the combination technology of hydrothermal method and ihleite method is studied in this paper. which finds that: with the increase of reaction temperature or with the extension of reaction time, precipitation rate of iron increases, while loss rate of chromium decreases.