At the late stage of continuous casting (CC) ladle teeming, sink vortex can suck the liquid slag into tundish, and cause negative influences on the cleanliness of molten steel. To address this issue, a two-phase fluid mechanical modeling method for ladle teeming was proposed. Firstly, a dynamic model for vortex suction process was built, and the profiles of vortex flow field were acquired. Then, based on the level set method (LSM), a two-phase 3D interface coupling model for slag entrapment was built. Finally, in combination with high-order essentially non-oscillatory (ENO) and total variation diminishing (TVD) methods, a LSM-based numerical solution method was proposed to obtain the 3D coupling evolution regularities in vortex suction process. Numerical results show that the vortex with higher kinetic energy can form an expanded sandglass-shape region with larger slag fraction and lower rotating velocity; there is a pressure oscillation phenomenon at the vortex penetration state, which is caused by the energy shock of two-phase vortex penetration coupling.
The global steel production has been growing for the last 50 years, from 200 Mt in 1950s to 1 240 Mt in 2006. Iron and steel making industry is one of the most energy-intensive industries, with an annual energy consumption of about 24 EJ, 5% of the world＇s total energy consumption. The steel industry accounts for 3%-4% of totat world greenhouse gas emissions. Enhancing energy efficiency and employing energy saving/recovering technologies such as coke dry quechning （CDQ） and top pressure recovery turbine （TRT） can be short-term approaches to the steel industry to reduce greenhouse gas emission. The long-term approaches to achieving a significant reduction in CO2 emissions from the steel industry would be through developing and applying CO2 breakthrough technologies for iron and steel making, and：through increasing use of renewable energy for iron and steel making. Thus, an overview of new CO2 breakthrough technologies for iron and steel making was made.
The Lüders deformation behavior in a medium Mn transformation-induced plasticity (TRIP) steel is investigated at different temperatures ranging from 25 to 300 °C. It demonstrates that the Lüders band appears at all testing temperatures but with varied Lüders strains which do not change monotonically with temperature. The martensitic transformation is simultaneously observed within the Lüders band in varying degrees depending on the testing temperature. It is well verified that the martensitic transformation is not responsible for the formation of Lüders band, and a reasonable explanation is given for the non-monotonic variation of Lüders strain with increasing temperature.
The hot deformation behavior of GH4945 superalloy was investigated by isothermal compression test in the temperature range of 10001200 ℃with strain rates of 0.001 10.000 s 1 toa total strain of 0.7. Dynamic recrystallization is the primary softening mechanism for GH4945 superalloy during hot deformation. The constitutive equation is established, and the calculated apparent activation energy is 458. 446 kJ/moh The processing maps at true strains of 0.2, 0.4 and 0.6 are generally similar, dem- onstrating that strain has little influence on processing map. The power dissipation efficiency and in- stability factors are remarkably influenced by deformation temperature and strain rate. The optimal hot working conditions are determined in temperature range of 1082 -1131 ℃ with strain rates of 0.0040.018 s-1. Another domain of11341150 ℃ and 0. 018 0.213s ^- can also be selected as the optimal hot working conditions. The initial grains are replaced by dynamically reerystallized ones in optimal domains. The unsafe domains locate in the zone with strain rates above 0, 274 s^- 1, mainly characterized by uneven microstructure. Hot working is not recommended in the unsafe domains.
The grain refinement and macrosegregation control of GCrl5 bearing steel were investigated under a type of rarely-used electromagnetic stirring, vertical electromagnetic stirring （V-EMS）, in continuous casting. V-EMS can create an upward electromagnetic force and generate longitudinal loop convection, which ena- bles the better mixing of the upper part with the lower part of the liquid steel. The results showed that ap- plying V-EMS can enlarge the region of the equiaxed grain, decrease the secondary dendrite arm spacing （SDAS） and reduce the segregation of both carbon and sulfur. After applying V-EMS, liquid steel with a high solute concentration is brought to the dendrite tips, making the dendrite arms partially melt. The length of the dendrite fragment is approximately 1.8 mm, 10 to 12 times the SDAS. Upon increasing the amount of cooling water from 2.0 to 3.5 m3/h, the dendrite fragments exhibit an obvious aggregation fol- lowing V-EMS. Finally, a criterion for dendrite fragmentation under V-EMS was derived based on the dendrite fragmentation theory of Campanella et al.
Nb is often considered to be a powerful alloying element for controlling the recrystallization process in microalloyed high strength steels. However, Nb can be presented either as solute in solution, where it is thought to exhibit a strong solute drag effect, or as NbC precipitates, which are thought to be effective at pinning grain boundaries. Therefore, it is very important to quantitatively measure Nb in solution or in NbC precipitates. A quantitative analysis method of Nb in solution and in precipitates was proposed. The test procedure involved chemical dissolution, filtration and inductively coupled plasma atomic emission spectroscopic (ICP-AES) analysis. The amount of Nb in solution in Nb-microallyed steels under different treatment conditions was evaluated. The results show that the niobium and carbon contents in steels have a great effect on niobium dissolution kinetics. The solute Nb is more effective to retard dynamic recrystallization, while the NbC precipitates are more effective to inhibit static recrystallization. The results may help to comprehend effect of Nb in steels, and provide some guides in the design of new high strength Nb-bearing steels.
To achieve ultrasonic casting of 35CrMo steel, the waveguide unit for introducing ultrasound into liquid steel was studied numerically and experimentally. The structure and length of the ultrasonic waveguide were optimized by modal analysis. The simulation results showed that a T-shaped waveguide unit matched the vibrational system better than an L-shaped unit. The performance of T-shaped waveguide unit was optimized when the length of the ultrasound radiator was 135 mm. The performance of the T-shaped waveguide unit was investigated in ultrasonic casting experiments, and the effect of ultrasound on the microstructure of 35CrMo steel was examined. The experimental results showed that the T-shaped waveguide was able to successfully introduce ultrasound into the 35CrMo melt. In addition, the use of a silicon nitride ceramic radiator avoided high-temperature corrosion in the molten metal. The microstructure of the treated area was significantly refined and equiaxed grains were obtained. The results represented a novel method for ultrasonic casting of steel.
The microstructures and mechanical properties of Cr13 super martensitic stainless steel after different heat treatments were studied. The results show that the structures of the steel after quenching are of lath martensite mixed with a small amount of retained austenite. With the raising quenching temperature, the original austenite grain size increases and the lath martensite gradually becomes thicker. The structures of the tempered steel are mixtures of tempered martensite and reversed austenite dispersed in the martensite matrix. The amount of reversed austenite is from 7.54% to 22. 49%. After different heat treatments, the tensile strength, the elongation and the HRC hardness of the steel are in the range of 813 1 070 MPa, 10.1%21.2% and 21.3332.37, respectively. The steel displays the best comprehensive mechanical properties after the sample is quenched at 1 050 ℃ followed by tempering at 650 ℃.
Hot deformation behavior of superaustenitic stainless steel S32654 was investigated with hot compression tests at temperatures of 950-1250 C and strain rates of 0. 001-10 s-1. Above 1150 ℃, with strain rate lower than 0.1 s -1 , the flow curves exhibit nearly steady state behavior, while at higher strain rate, continuous flow softening occurs. To provide a precise prediction of flow behavior for the alloy, the constitutive modeling considering effect of strain was derived on the basis of the obtained experimental data and constitutive relationship which incorporated Ar- rhenius term and hyperbolic sine type equation. The material constants α, n, Q and lnA are found to be functions of the strain and can be fitted employing eighth-order polynomial. The developed constitutive model can be employed to describe the deformation behavior of superaustenitic stainless steel S32654.
The hydrogen induced cracking （HIC） behavior of a high deformability pipeline steel was investigated with three different dual-phase microstructures, ferrite and bainite （F＋B）, ferrite and martensite/austenite islands （F＋M/A） and ferrite and martensite （F＋M）, respectively. The HIC test was conducted in hydrogen sulfide （H2S）-saturated solution. The results showed that the steels with F＋B and F＋M/A dual-phase microstructures had both higher deformability and better HIC resistance, whereas the harder martensite phase in F＋M microstructure was responsible for the worst HIC resistance. The band-like hard phase in dual-phase mi- crostructure was believed to lead to increasing susceptibility to HIC.
The possible decomposition of metastable austenite during the partitioning process in the high-end quenching and partitioning (Q&P) steels is somewhat neglected by most researchers. The effects of primary martensite and alloying elements including manganese, cobalt and aluminum on the isothermal decomposition of austenite during typical Q&P process were studied by dilatometry. The transformation kinetics was studied systematically and resulting microstructures were discussed in details. The results suggested that the primary martensite decreased the incubation period of isothermal decomposition by accelerating the nucleation process owing to dislocations especially on phase and grain boundaries. This effect can be eliminated by a flash heating which recovered dislocations. Co addition significantly promoted the bainite transformation during partitioning while Al and Mn suppressed the isothermal bainite transformation. The bainite transformation played an important role in carbon distribution during partitioning, and hence the amount and stability of austenite upon final quenching. The bainite transformation during partitioning is an important factor in optimizing the microstructure in Q&P steels.
Embedding direct reduction followed by magnetic separation was conducted to fully recover iron and titanium separately from beach titanomagnetite （TTM）. The influences of reduction conditions, such as molar ratio of C to Fe, reduction time, and reduction temperature, were studied. The results showed that the TTM concentrate was reduced to iron and iron-titanium oxides, depending on the reduction time, and the reduction sequence at 1 200℃ was suggested as follows ： Fe2.75 Ti0.25O4→Fe2TiO4→FeTiO3→FeTi2O5. The reduction temperature played a considerable role in the reduction of TTM concentrates. Increasing temperature from 1 100 to 1 200℃ was beneficial to recovering titanium and iron, whereas the results deteriorated as temperature increased further. The results of X-ray diffraction and scanning electron microscopy analyses showed that low temperature （≤1100℃） was unfavorable for the gasification of reductant, resulting in insufficient reducing atmosphere in the reduction process. The molten phase was formed at high temperatures of 1250-1 300℃, which accelerated the migration rate of metallic particles and suppressed the diffusion of reduction gas, resulting in poor reduction. The optimum conditions for reducing TTM concentrate are as follows： molar ratio of C to Fe of 1.68, reduction time of 150 min, and reduction temperature of 1 200℃. Under these conditions, direct reduction iron powder, assaying 90.28 mass% TFe and 1.73 mass% TiO2 with iron recovery of 90.85%, and titanium concentrate, assaying 46.24 mass% TiO2 with TiO2 recovery of 91.15%, were obtained.
A new hot-dip galvanizing method was employed on hot-rolled low carbon steel.The effects of Al contents on microstructure,micro-hardness and corrosion resistance of Zn-Al alloy coatings were systematically investigated.Phase composition,microstructure and element distribution in Zn-Al alloy coatings were analyzed using X-ray diffraction（XRD）and electron probe micro analysis（EPMA）,respectively.It is found that Al content（0.6-6.0 wt.%）in galvanizing zinc affects surface quality and adhesion between coatings and matrix in the newly developed method.In addition,with increasing Al content,micro-hardness significantly increased due to the increase in Zn-Al eutectoid phases.Potentiodynamic polarization and electrochemical impedance spectroscopy（EIS）also revealed that increase in Al plays a noticeable role in improving the corrosion resistance of Zn-Al alloy coatings.
Chinese steel industry has made significant progress on reducing fresh water consumption and CO /SO /COD (chemical oxygen demand)/dust emissions, and improving comprehensive utilization of solid waste. Some steel companies have become topped worldwide. However, due to the large output quantity of crude steel, the whole steel industry is still a huge source of pollutants. At present, environmental protection standards are encountering challenges of lack of technical support, taxation policy and other issues. Steel industry is currently facing enormous environmental pressure. The development trends of environmental protection technologies were studied by summarizing different development stages. To realize the development targets, the industry needs to carry out its research with independent intellectual property rights, develop comprehensive management systems and establish ecological chain with other industries. This can not only raise the level of environmental protection in a broader range, but also improve the energy efficiency of iron and steel plants and increase added value of waste utilization. Finally, 23 environmental protection technologies were proposed and 4 new environmental protection practices were studied.
The process of automobile lightweight can be promoted by the application of tailor rolled blank (TRB) in the automobile industry. Therefore, research on the formability of TRB is of good practical significance and application value because of the enormous potential of TRB in the aspect of automobile lightweight. Aiming at the present condition of lack of researches on the influence of characteristic parameters on TRB drawing process, the drawing formability of TRB was studied with a combination method of simulation and experiment by taking square box as the research object. Firstly, drawing simulation and experiment of TRB were carried out. Then, effects of thickness transition zone (TTZ) position and blank size on the drawing formability of TRB were analyzed. Forming limit and TTZ movement for TRB square box during the drawing process were respectively discussed, when transition zones of TRB were located at different positions and blanks were of different sizes. The results indicate that lubrication condition exerts greater influence on TRB forming limit in comparison with TTZ movement, and the smaller blank size and TTZ being located at the blank center or slightly offset to the thinner side are preferable for acquiring greater forming limit and smaller TTZ movement.
Mechanical properties of a newly developed microalloyed bainitic steel were investigated after the hot forging, air cooling and tempering process. The microstructure of the as forged bainitic steel mainly consists of granular bainite and -20 vol. % martensite. The fraction of retained austenite remains unchanged until tempering at 200 ℃, above which it decreases significantly. The increase of tempering temperature leads to decreases of both ultimate tensile strength and total elongation but decreases of both yield strength and reduction of area. The maximum and mini- mum values of impact toughness were observed after tempering at around 200 and 400 ℃, respectively. These effects are mainly attributed to the decomposition of martensite/austenite con stituents and the tempering effects in martensite. The tempering of the forged bainitic steel at around 200 ℃ results in an excellent combination of strength and toughness, which is comparable to that of the conventional quenched and-tempered 40Cr steel. Therefore, low-tempering treatment coupled with post-forging residual stress relieving is a feasible method to further improve the mechanical prooerties of the bainitic foging steel.
The thermal stability of retained austenite（RA）and the mechanical properties of the quenched and intercritical annealed 0.1C-5Mn steel with the starting ultrafine lamellar duplex structure of ferrite and retained austenite during tempering within the range from 200 to 500°C were studied by X-ray diffraction（XRD）,transmission electron microscopy（TEM）and tensile testing.The results showed that there was a slight decrease in the RA volume fraction with increasing tempering temperature up to 400°C.This caused a slight increase in the ultimate tensile strength（UTS）and a slight decrease in the total elongation（TE）;thus,the product of UTS to TE（UTS×TE）as high as 31GPa·% was obtained and remained nearly unchanged.However,aportion of the RA began to decompose when tempered at 500°C and thus caused a~35% decrease of the RA fraction and a~16%decrease of the value of UTS×TE.It is concluded that the ultrafine lamellar duplex structure is rather stable and the excellent combination of strength and ductility could be retained with tempering temperature up to 400°C.Thus,thermal processes such as galvanization are feasible for the tested steel provided that their temperatures are not higher than 400°C.
304 austenitic stainless steel was cold rolled in the range of 20%–80% reductions and then annealed at 700–900 °C for 60 s to obtain nano/ultrafine-grained (NG/UFG) structure. Transmission electron microscopy, electron backscatter diffraction and X-ray diffraction were used to characterize the resulting microstructures. The results showed that with the increase of cold reduction, the content of martensite was increased. The steel performed work hardening during cold-working owing to the occurrence of strain induced martensite which nucleated in single shear bands. Further rolling broke up the lath-type martensite into dislocation-cell type martensite because of the formation of slip bands. Samples annealed at 800–960 °C for 60 s were of NG/UFG structure with different percentage of nanocrystalline (60–100 nm) and ultrafine (100–500 nm) grains, submicron size (500–1000 nm) grains and micron size (>1000 nm) grains. The value of the Gibbs free energy exhibited that the reversion mechanism of the reversion process was shear controlled by the annealing temperature. For a certain annealing time during the reversion process, austenite nucleated first on dislocation-cell type martensite and the grains grew up subsequently and eventually to be micrometer/submicrometer grains, while the nucleation of austenite on lath-type martensite occurred later resulting in nanocrystalline/ultrafine grains. The existence of the NG/UFG structure led to a higher strength and toughness during tensile test.
The morphology,microstructure and decomposition behavior of M2C carbides in high speed steels with different chemical compositions have been investigated by scanning electron microscopy,transmission electron microscopy,electron backscatter diffraction and X-ray diffraction.The results show that the morphology and substructure of M2C carbides are very sensitive to chemical compositions of high speed steels.M2C carbides present the plate-like shape in tungsten-molybdenum steel and present the polycrystal orientation in the eutectic cell.In contrast,they show the fibrous shape in molybdenum-base steel and exhibit the monocrystal orientation.Plate-like and fibrous M2C carbides are both metastable and decompose into M6 C together with MC at high temperatures.MC nucleates inside the plate-like M2C while it is formed at the fibrous M2C/matrix interface during the decomposition process.Such differences are expected to arise from different compositions of plate-like and fibrous M2C carbides.
The formation of slag eye in a gas stirred ladle was studied through cold models and industrial trials. In the cold model, water and sodium tungstate solution were employed to simulate liquid steel, and silicon oil was employed to simulate slag. The simulation results revealed that the gas flow rate and bath height had strong effects on the slag eye size. In particular, the thickness of slag layer played a strong role in the slag eye size. In addition, the slag eye could not be formed when the thickness of the top layer was more than 4 cm in water-silicone oil model. Besides, the section area of vessel had a great impact on the slag eye size. Industrial trials results showed a similar trend that the gas flow rate was very significant on the slag eye size. The predictions of the existing models showed larger predictions deviations compared with the experimental data. Moreover, a new model without fitting parameters was developed based on force balance and mathematical derivation, and verified by the experimental data. The new model provides the prediction with small deviations by comparing with the data acquired from cold models and industrial trials.