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To investigate the solute transport and redistribution in the slab continuous casting processes of high sulfur steel, a three-dimensional model coupling turbulent flow, heat and solute transportation was developed. And then a thermodynamic model for MnS precipitation was established to study the MnS precipitation and distribution in strand on a macroscale and its effect on solute macrosegregation was also explored. The results showed that the temperature and solutes concentration were the main factors for the precipitation of MnS. The effect of temperature was significant when the solid fraction was greater than 0.8. Due to the precipitation of MnS, the segregation ratio of solutes Mn and S on the center line declined from 1.05–1.15 to 0.97–1.01 and from 1.2–1.45 to 1.00–1.08, respectively. And the solute concentration of Mn and S declined and distributed more uniformly in the strand, and the macrosegregation of Mn and S was also suppressed greatly.

To quantitatively study the effects of partition coefficients, diffusion coefficients, and solidification paths on solute microsegregation, an analytical model was developed combined with the calculation of thermodynamic software FactSage. This model, applied with variational partition coefficients and temperature-dependent diffusion coefficients, is based on the Voller–Beckermann model and is extended to take into account the effects of multiple components and the peritectic phase transformation using FactSage. The predictions agree well with a range of measured data and the results of other numerical solutions. As the results indicate, the partition coefficients of solutes are functions of temperature and phase fraction during the solidification process, and the solute microsegregation increases significantly with decreasing partition coefficients. The calculations of solute microsegregation ratio (C L/C 0) in the interdendritic region are related to solidification paths. The microsegregation ratios of P and S increase as the initial C concentration increases, while they reduce with increasing initial C contents for solutes C and Si. Parameter sensitivity analysis was performed, and the results indicate that the solute microsegregation shows larger variation with partition coefficients and solidification paths than diffusion coefficients.

To investigate the variation of true density and the sulfur removal forms during the ultrahigh-thermal desulfurization process, two types of delayed petroleum cokes with different sulfur contents were calcined at temperatures up to 2500 °C at two distinct heating rates. The influence of the desulfurization coefficient on the true density growth was quantitatively discussed. Additionally, the removal forms of sulfur in petroleum cokes during thermal desulfurization were also investigated through a series of thermodynamic calculations. The results revealed a continuous increase in the true density with the uninterrupted release of sulfur during thermal desulfurization, and a maximum true density of 2.3 g/cm3 was obtained at a temperature of 2500 °C. The growth rate of the true density was dependent on the desulfurization coefficient of the petroleum cokes. The relationship between the true density growth rate and the desulfurization coefficient during thermal desulfurization was an exponential function, whi...

A new process of producing synthetic rutile from molten titanium slag with the addition B2O3 is proposed. The process includes a molten modification process and a leaching process. The molten modification process was conducted by adding B2O3 into molten slag. The leaching process was conducted by adding hydrochloric acid and subsequent NaOH. The results show that CaO and MgO are leached out by hydrochloric acid and that synthetic rutile is further improved by NaOH. The optimized conditions are 2% B2O3 amount, 5% hydrochloric concentration, 80°C leaching temperature, and 30 min leaching time. The synthetic rutile with 86.77% TiO2 and 1.23% (CaO + MgO) was prepared. From x-ray diffraction results, thermodynamic calculation and the theory of bond parameter function, with the addition of B2O3, calcium silicate is transformed into calcium borate and anosovite is transformed into magnesium borate. Calcium borate and magnesium borate are leached out by hydrochloric acid, leading to the enrichment of rutile.

The crystallographic texture, micro-hardness and magnetic property have been investigated in Cu-57 at.% Ni, Cu-53 at.% Ni, and Cu-49 at.% Ni alloy used as substrates for coated conductors. In this work, a similar rolling texture was observed in the cold rolled condition for the three alloys. For each material, annealing at higher temperature results in a much stronger cube texture but the fraction of annealing twin boundary was quiet low. When annealing at 700 °C and 800 °C, it was presumed that the increase of Cu element increased grain boundary mobility, which then lead to the enhancement of twin boundary and weakened the cube texture. In addition, magnetization measurements indicate that the increase of Cu content can effectively reduce the saturation magnetization in Cu-Ni alloys. The comparatively low ferromagnetism for both Cu-53 at.% Ni and Cu-49 at.% Ni alloys suggests that substrates produced using these materials will benefit from decreasing hysteresis losses for alternating current applications.

Slab continuous casting internal cracking is a common quality defect in the production process. The ability to predict the quality of each continuous casting product and assess whether it is suitable for hot delivery or needs to be cleaned down will greatly increase the rolled product rate and reduce the scrap rate and production management cost. According to the quality defects of internal cracks during slab continuous casting and based on the solidification and heat transfer simulations, stress and strain calculations and theoretical analysis of metallurgical processes related to continuous casting combined with an abnormal casting event expert system, the internal crack generation index of the slice unit is used to predict the crack occurrence rating of each sized slab. Moreover, the internal crack prediction model for the slab is successfully developed and applied in a domestic steel mill. The accuracy of the model prediction reached 86.85%. This method achieved the organic combination of theoretical analysis and an expert system and provides an important theoretical tool for the prediction of crack quality defects in slab continuous casting, the method can be applied in slab continuous casting production.

Ultrahigh casting speed is an important tendency to improve the efficiency of continuous casting. A three-dimensional mathematical model and a hydraulic physical model on the billet mold with 160 × 160 mm cross section were established to investigate the flow behavior of molten steel with different SEN conditions and optimize the parameters of SEN at the casting speed of 6.0 m/min. Results indicate that when the immersion depth and the inner diameter of the SEN are 180 and 50 mm, respectively, the flow field and the surface velocity distribution in the mold are the most appropriate that the penetration depth of the stream is about 700 mm and the maximum surface velocity is 0.05 m/s. With the optimum parameters of SEN, the slag covers uniformly and keeps appropriately active, and no slag entrainment happens. Moreover, the differences are very slight between the results of the numerical and physical simulation, which can verify each other.

A 3D mathematical model was developed to simulate the electromagnetic field in &Phi, 600 mm round bloom continuous casting with final electromagnetic stirring (F-EMS), and the model was verified using measured data for the magnetic flux density in the stirrer centre. The distribution of electromagnetic force and the influence of current intensity and frequency were investigated. The results show that the Joule heat generated by F-EMS is very small and its influence on secondary cooling heat transfer in the stirring zone can be ignored. With an increase in current frequency, the electromagnetic force density at R/2 and R/3 of the &Phi, 600 mm round bloom first increases and then decreases, reaching a maximum at 10 Hz.

The structural and transport properties of molten titanium slag have intuitive and important effects on the reaction efficiency of the smelting process, separation efficiency of slag and metal, and quality of titanium slag. Molecular dynamics simulations were carried out to characterize the structural and transport properties of titanium slag with various contents of alkaline earth oxide. The average CNTi-O (Coordination Number) increased from 5.99 to 6.04 while the average CNSi-O increased from 4.57 to 4.93 when the content of alkaline earth oxide increased from 3.5% to 31.5%. The Ti-O-Ti bond angle in the edge-sharing [TiO6] octahedron remained at 100.00°, while the Ti-O-Ti bond angle in the vertex-sharing [TiO6] octahedron increased from 125.25° to 127.04° with an increase in the content of alkaline earth oxide from 3.5% to 31.5%. A part of the Ti-O bond in the oxygen connection was replaced with the Mg-O bond as the content of alkaline earth oxide increased from 3.5% to 31.5%. The transformation in the oxygen connection reduced the structural strength of the system. The self-diffusion coefficients followed the order: Mg2+>Ca2+>Ti4+>O2−>Si4+. The viscosity of the system decreased from 0.098 Pa·s to 0.064 Pa·s as the content of alkaline earth oxide increased from 3.5% to 31.5%, which is in good accordance with the measured results. The results will contribute to predicting and controlling the transport properties of molten titanium slag and will lay the foundation for the efficient production of high-quality titanium slag.

This paper systematically investigates the site preference and mechanical and electronic properties of L10 CoNi alloys doped with transition metal elements by first-principles calculations. The goal is to determine the elements that can improve the properties of nickel–cobalt alloys. The results of the formation enthalpy Δ H f and substitution enthalpy E site illustrate that a large portion of the doping elements tends to substitute at the Co sites and form Co7MNi8, except Cr, Os, Ir and Pt. According to the mechanical properties results, only the Cr, Os and Ir additions form Co8Ni7Cr, Co8Ni7Os and Co8Ni7Ir, respectively, which remarkably improve the mechanical properties. The anisotropy of the directional Young’s modulus and acoustic velocities predict that these alloys are all anisotropic materials. In addition, the thermal properties are studied, and the Debye temperature Θ D and minimum thermal conductivity k min reveal that only the Cr doping results in the formation of Co8Ni7Cr and improves the thermal conductivity in all directions. The density of states (DOS), crystal orbital Hamilton population (COHP) and electron location function (ELF) are calculated to elucidate the origin of the mechanical properties of the CoNi alloys. The results indicate that the strengthening effects of doping elements, such as Cr, are attributed to the enhanced covalent characteristic between the Co (or Ni) and Cr atoms. In summary, it is found that Cr, Os and Ir have good solid solution effects in the CoNi alloys, which is worthy of further study.

This paper studies the site preference and mechanical, thermal, and electronic properties of L12 Ni3Co alloys doped with Cr, Os, Ir, and Y elements based on first-principles calculations. The formation and substitution formation enthalpy results illustrate that the doping elements Cr, Os, and Ir tend to occupy the Ni site and form Ni23MCo8. According to the results of the mechanical properties, we find that except Y, the element doping in the alloys will improve the elastic modulus and hardness, especially Cr. The direction dependence of Young's modulus and acoustic velocities shows that these alloys are all anisotropic in nature but not of great quality. The thermal properties of Debye temperature and minimum thermal conductivity reveal that only Cr doping that forms Ni23CrCo8 can improve thermal conductivity. The electronic structures are analyzed to elucidate the origin of the mechanical properties of alloys, and the results indicate that the strengthening effects of doping elements like Cr are attributed to the enhanced covalent characteristic between Co or Ni and Cr atoms. In summary, it was predicted that Cr, Os, and Ir have a good solid solution strengthening effect in Ni3Co alloys, which is worth further study.

The influence of preferential orientation (namely cube texture) on annealing twins in a cold rolled (95% thickness reduction) pure nickel has been investigated during isothermal annealing at low temperature. The results reveal that the cube oriented grains in cube related twinning (CT) regions have larger average boundary migration rate in comparison with grains in non-cube related twinning (NCT) regions. However, the twin density is always lower in CT regions than that in NCT regions. This is contrary to the growth accident model that suggests that twin density was proportional to the grain boundary velocity and grain boundary distance. It can be interpreted by the fact of the selective nucleation and growth mechanism for cube oriented grains which are less dependent on annealing twinning during recrystallization. Furthermore, during grain growth the average length of annealing twin boundary segments has a significant increment, which is probably attributed to lengthening of low energy twin boundaries along with the migration of other neighboring boundaries.

The fracture toughness test is carried out at high temperatures (800–1200 °C) to study the critical value of J -integral ( J IC ) for the as-cast steel slab. Extended finite element method (XFEM) is used in an Abaqus model to study the dynamic extension of transverse surface cracks during the straightening and bending process of the as-cast steel slab. Results show that the ductile fracture toughness decreases from 26.75 to 3.46 N/mm as the temperature increases from 800 to 1200 °C. Transverse surface cracks (vertical to the casting direction) on the outer and inner arc surface of the slab extend 27.3 mm and 23.4 mm for the maximum when the slab is bending and straightening, respectively. The extended length is analysed corresponding to the position where the slab passes through bending and straightening rollers. The results show that the extended length increases largely at the end of the bending or straightening process, which indicates the stress distribution at the bending roller 15#, and the straightening roller 59#, 60# are overlarge and should be optimized.

The effect of pre-aging and peak-aging treatments prior to cryorolling on the microstructure and mechanical properties of 6016 Al alloys were investigated by hardness measurements, tensile tests, differential scanning calorimetry (DSC) and transmission electron microscopy (TEM). The results showed that high density of dislocation was induced by cryorolling with 80% thickness reduction. The pre-aging treatment enabled the alloy to have stronger work hardening effect during cryorolling and higher precipitation potential during subsequent aging than the peak-aging treatment. This was due to that the pre-aging enhanced the dislocations accumulating in the cryorolling of pre-aged specimen, and promoted the secondary precipitation during subsequent aging after cryorolling. Meanwhile, the yield strength and ultimate tensile strength of the pre-aged specimen subjected to cryorolling and subsequent aging significantly increased by 72% and 50%, respectively, while the ductility remained similar, as compared to the conventional peak-aged specimen.

A concise model is applied to compute the microstructure evolution of austenite transformation by using the dilation curve of continuously cast steels. The model is verified by thermodynamic calculations and microstructure examinations. When applying the model, the phase fractions and the corresponding transforming rates during austenite transformation are investigated at various cooling rates and chemical compositions. In addition, ab initio calculations are performed for paramagnetic body-centered-cubic Fe to understand the thermal expansion behavior of steels at an atomic scale. Results indicate that by increasing the cooling rate, the final volume fraction of ferrite/pearlite will gradually increase/decrease with a greater transforming rate of ferrite. The ferrite fraction increases after austenite transformation with lowering of the carbon content and increasing of the substitutional alloying fractions. In the austenite transformation, the thermal expansion coefficient is sequentially determined by the forming rate of ferrite and pearlite. According to the ab initio theoretical calculations for the single phase of ferrite, thermal expansion emerges from magnetic evolution and lattice vibration, the latter playing the dominant role. The theoretical predictions for volume and thermal expansion coefficient are in good agreement with the experimental data.

An open-loop dynamic spray cooling control strategy is explained in details. The strand was divided into many slices of a certain length and the midpoint of each cooling zone was set as a control point. The casting speed and temperature of each slice were tracked by using a control algorithm. Compared with the steady-state control model, the maximum temperature fluctuation values of cooling zone I–IV dropped from 70 °C, 61 °C, 51 °C and 35 °C to 17 °C, 16 °C, 12 °C and 10 °C, respectively, when using the dynamic control strategy in theoretical case. This dynamic control strategy has been applied to an actual billet continuous casting machine. The results of field trials showed that the surface temperature of the billets was well stabilized at the target temperature, and the number of strand defects, such as mid-way cracks, was reduced significantly.

To control steel quality during continuous casting and subsequent heat treatment, an understanding of the evolution laws of mechanical properties during the austenite transition and the underlying ...

The properties of nickel–cobalt alloys depend greatly on their composition. In this study, we investigated the crystal structure and mechanical properties (elastic properties and hardness) of nickel–cobalt alloys with different compositions based on first-principles calculations. The formation enthalpy (ΔH) values were calculated and the results showed that as the cobalt content increased in the alloys, the crystal structure of the alloys changed from face centered cubic (fcc) to hexagonal close-packed (hcp), and a coexistence zone with both the fcc and hcp phases existed when the cobalt content was 50–80 at.%. The formation enthalpy values for the fcc-phase and hcp-phase were equal when the cobalt content was 65.5 at.%. The results were in good agreement with the experimental results. Calculations of the elastic properties showed that increasing the cobalt content of the alloys could increase the stiffness as well as improving the compression and shear resistance, but the ductility was reduced. The hardness increased for the fcc and hcp phases as the cobalt content increased. When the cobalt content was 50 at.%, the hardness reached the maximum value of 1032 HV. Further analyses of the electron localization function demonstrated that the increases in the compression and shear resistance, stiffness, and hardness of the nickel–cobalt alloys as the cobalt increased could be attributed to the enhanced covalent bonds between Ni–Co and Co–Co atoms.

Hot stamping process is widely used in the manufacture of the high strength automotive steel, mainly including the stamping and quenching process of the hot-formed steel. In the hot stamping process, the steel is heated above the critical austenitizing temperature, and then it is rapidly stamped in the mold and the quenching phase transition occurs at the same time. The quenching operation in the hot stamping process has a significant influence on the phase transition and mechanical properties of the hot-stamping steel. A proper quenching technique is quite important to control the microstructure and properties of an ultra-high strength hot-stamping steel. In this paper, considering the factors of the austenitizing temperature, the austenitizing time and the cooling rate, a coupled model on the thermal homogenization and phase transition from austenite to martensite in quenching process was established for production of ultra-high strength hot-stamping steel. The temperature variation, the austenite decomposition and martensite formation during quenching process was simulated. At the same time, the microstructure and the properties of the ultra-high strength hot-stamping steel after quenching at different austenitizing temperature were experimental studied. The results show that under the conditions of low cooling rate, the final quenching microstructure of the ultra-high strength hot-stamping steel includes martensite, residual austenite, bainite and ferrite. With the increase of the cooling rate, bainite and ferrite gradually disappear. While austenitizing at 930 &deg, C, the tensile strength, yield strength, elongation and strength-ductility product of the hot-stamping steel are 1770.1 MPa, 1128.2 MPa, 6.72% and 11.9 GPa%, respectively.

A combined hybrid 3-D/2-D simulation model was developed to investigate the flow and solidification phenomena in turbulent flow and laminar flow regions during slab continuous casting (CC). The 3-D coupling model and 2-D slicing model were applied to the turbulent flow and laminar flow regions, respectively. In the simulation model, the uneven distribution of cooling water in the width direction of the strand was taken into account according to the nozzle collocation of secondary cooling zones. The results from the 3-D turbulent flow region show that the impact effect of the molten steel jet on the formation of a solidification shell is significant. The impact point is 457 mm below the meniscus, and the plug flow is formed 2442 mm below the meniscus. In the laminar flow region, grid independence tests indicate that the grids with a cell size of 10 × 10 mm2 are sufficient in simulations to attain the precise temperature distribution and solidification profile. The liquid core of the strand is not entirely uniform, and the solidification profile agrees well with the integrated distribution of cooling water in secondary cooling zones. The final solidification points are at a position of 400–500 mm in the width direction and are 17.66 m away from the meniscus.

Transverse cracks in continuous cast steel may easily form if the hot ductility of the continuous cast steel is poor at the straightening stage. In this paper, the hot ductility of X70 pipeline steel was studied at various temperature from 600 to 1300 °C. The results show that the steel has a good hot ductility (RA above 70%) at 800–1000 and 600–650 °C. And the steel exhibits a hot ductility trough (RA below 80%) at 650–800 °C, which is mainly contributed to the austenite–ferrite transformation. For further understanding the low ductility, the fracture surface was examined by scanning electron microscope, and the second phase particles was examined by energy spectrum analysis. The results indicate that the low ductility of the steel is affected by the equiaxed (Fe, Mn)S precipitate as well as austenite transformation at the third brittle zone.

The coarse TiN inclusions can act as potential fracture initiation sites and deteriorate the impact toughness of steels. The experimental observation results indicated that CaS and TiN inclusions precipitated in solidification mushy zone. Meanwhile, it was found that CaS inclusions could act effectively a heterogeneous nucleation substrate for the precipitation of TiN inclusions, and the size of TiN inclusions with CaS core was obviously larger than those TiN inclusions without CaS core. Additionally, the thermodynamic calculation result showed that TiN inclusions began to precipitate at the end of solidification from the dendrites front; moreover, the preexisted CaS inclusions promoted the formation of TiN inclusions. Decreasing sulfur and nitrogen content could significantly reduce precipitation temperature and growth time of CaS and TiN inclusions in mushy zone. Furthermore, TiN inclusions could be prevented from precipitation at the surface of CaS inclusions when the S content of molten steel was below 0.0008 wt%.

The equilibrium partition coefficient (k) affected by chemical component, phase constitution and temperature is a critical parameter related to solutes distribution during steel solidification. In this study, the effect of Mn on equilibrium partition coefficient and phase transformation was quantitatively analysed. A technique according to the relative amount of δ-Fe and γ-Fe to determine the equilibrium partition coefficients of solutes in L, δ-Fe, and γ-Fe three-phases coexistence zone was proposed. Results showed that Mn promotes the generation of γ-Fe and its effect on peritectic reaction zone is significant. The equilibrium partition coefficients were determined based on the phase change and relative amount of δ-Fe and γ-Fe according to the solidification paths which undergo difference phase coexistence zone. All of \( k_{C}^{\delta } \), \( k_{Si}^{\delta } \), \( k_{Si}^{\delta + \gamma } \), \( k_{P}^{\delta } \), \( k_{P}^{\delta + \gamma } \), \( k_{S}^{\delta } \), and \( k_{S}^{\delta + \gamma } \) decrease with Mn increasing, while \( k_{C}^{\delta + \gamma } \) increases due to solute Mn promote the generation of γ-Fe forming from peritectic reaction.

In this paper, the critical value of J -integral ( J IC ) of as-cast steel is measured at elevated temperatures by using a Gleeble 1500D thermomechanical simulator. The J IC value and plastic deformation power U pl decrease with temperature increases. Specifically, with measured temperature at 700 °C, 800 °C and 900 °C, the respective values of J IC are 37.13 N/mm, 27.94 N/mm and 15.05 N/mm. Moreover, the detailed analyses of fracture surface show ductile fracture at elevated temperatures. The large tear dimples appear at crack initiation stage and the dimples are shallow in the early stage of crack stable propagation, and deeper later in the stage. The dimple size increases according to the load time.

An unequal interval arrangement of nozzles (UIAN) in the casting direction of the secondary cooling process for round billet continuous casting has been presented. The cooling coefficient, spray width in the casting direction and water flow density distribution around the round billet circumference of the nozzles have been accurately determined. The effects of transverse nozzle arrangement, inter-zone distance, number of segments, and length of cooling zone on the temperature and stress fields of round billets were analyzed with a thermal-mechanical finite-element model. Alternating the maximum and minimum water flux by rotating 22.5° between the odd and even rows nozzles can prevent the cooling intensity from being too strong at the same position along the casting direction of a round billet, and enhance the quality of the strand. Decreasing the inter-zone distance can help to even out the surface temperature and stress distribution of a round billet. Careful design of the number of segments number and length of the cooling zone can avoid sharp fluctuations in temperature at the spray cooling end position. An optimized secondary cooling system for achieving even secondary cooling has been designed and applied to an actual round billet casting machine, and the surface temperature of the round billets was very even, with mid-way cracks being completely eliminated.

A hot compression bonding process was developed to prepare a novel laminated composite consisting of high-Cr cast iron (HCCI) as the inner layer and low carbon steel (LCS) as the outer layers on a Gleeble 3500 thermomechanical simulator at a temperature of 950 °C and a strain rate of 0.001 S-1. Interfacial bond quality and hot deformation behaviour of the laminate were studied by microstructural characterisation and mechanical tests. Experimental results show that the metallurgical bond between the constituent metals was achieved under the proposed bonding conditions without discernible defects and the formation of interlayer or intermetallic layer along the interface. The interfacial bond quality is excellent since no deterioration occurred around the interface which was deformed by Vickers indentation and compression test at room temperature with parallel loading to the interface. After well cladding by the LCS, the brittle HCCI can be severely deformed (about 57 % of reduction) at high temperature with crack-free. This significant improvement should be attributed to the decrease of crack sensitivity due to stress relief by soft claddings and enhanced flow property of the HCCI by simultaneous deformation with the LCS.

The influence of temperature reversion in secondary cooling and its reversion rate on hot ductility and flow stress–strain curve of C-Mn steel has been investigated. Tensile specimens were cooled at various regimes. One cooling regime involved cooling at a constant rate of 100 °C min−1 to the test temperature, while the others involved temperature reversion processes at three different reversion rates before deformation. After hot tensile test, the evolution of mechanical properties of steel was analyzed at various scales by means of microstructure observation, ab initio prediction, and thermodynamic calculation. Results indicated that the temperature reversion in secondary cooling led to hot ductility trough occurring at higher temperature with greater depth. With increasing temperature reversion rate, the low temperature end of ductility trough extended toward lower temperature, leading to wider hot ductility trough with slightly reducing depth. Microstructure examinations indicated that the intergranular fracture related to the thin film-like ferrite and (Fe,Mn)S particles did not changed with varying cooling regimes; however, the Widmanstatten ferrite surrounding austenite grains resulted from the temperature reversion process seriously deteriorated the ductility. In addition, after the temperature reversion in secondary cooling, the peak stress on the flow curve slightly declined and the peak of strain to peak stress occurred at higher temperature. With increasing temperature reversion rate, the strain to peak stress slightly increased, while the peak stress showed little variation. The evolution of plastic modulus and strain to peak stress of austenite with varying temperature was in line with the theoretical prediction on Fe.

Mould electromagnetic stirrers (M-EMS) have played an increasingly important role in improving inner quality of special steel billet. A coupled three-dimensional numerical simulation of the electromagnetic field, flow field and temperature distribution in the mold with M-EMS for billet continuous casting was carried out based on the finite element method. The influence of the current and frequency of M-EMS on the flow field and temperature distribution was discussed. According to the simulation results, with the increase of the current, the steady flow became unstable accompanying with the bias flow, and the temperature distribution was unsymmetrical. However, the effect of the frequency on flow field was exactly opposite compared with the current. The significant swirl flow with M-EMS prevented the superheated jet moving downward and weakened the invasion depth of the jet, and thus the location of the hot zone in the mould moved up evidently.

The objective of this study is to develop a hot diffusion-compression bonding process for cladding low carbon steel (LCS) to high chromium cast iron (HCCI) in solid-state. The influence of temperature (950–1150 °C) and strain rate (0.001–1 s −1 ) on microstructure, hardness and bond strength of the HCCI/LCS bimetal were investigated. The interface microstructure reveals that the unbonded region can only be found for 950 °C due to lack of diffusion, while the intergrowth between the constituent metals occurred at and above 1100 °C. When bonding temperature increases to 1150 °C, a carbide-free zone was observed near the interface on the HCCI layer, and the thickness of the zone decreases with an increase of bonding strain rate. These evolutions indicate that the bond quality was improved by raising temperature and reducing strain rate due to the increase of element diffusion. The hot compression process of the bonding treatment not only changes the carbide orientation of the HCCI, but also increases the volume fraction of Cr–carbide. Based on the microstructural examinations and mechanical tests, the optimum bonding temperature and bonding strain rate are determined to be 1150 °C and 0.001 s −1 , respectively.

Using an efficient first-principles computational scheme for paramagnetic body-centered cubic (bcc) and face-centered cubic (fcc) Fe, we investigate the impact of thermal longitudinal spin fluctuat ...

We propose a first-principles framework for longitudinal spin fluctuations (LSFs) in disordered paramagnetic (PM) multicomponent alloy systems and apply it to investigate the influence of LSFs on the temperature dependence of two elastic constants of PM austenitic stainless steel Fe15Cr15Ni. The magnetic model considers individual fluctuating moments in a static PM medium with first-principles-derived LSF energetics in conjunction with describing chemical disorder and randomness of the transverse magnetic component in the single-site alloy formalism and disordered local moment (DLM) picture. A temperature-sensitive mean magnetic moment is adopted to accurately represent the LSF state in the elastic-constant calculations. We make evident that magnetic interactions between an LSF impurity and the PM medium are weak in the present steel alloy. This allows gaining accurate LSF energetics and mean magnetic moments already through a perturbation from the static DLM moments instead of a tedious self-consistent procedure. We find that LSFs systematically lower the cubic shear elastic constants c' and c(44) by similar to 6 GPa in the temperature interval 300-1600 K, whereas the predominant mechanism for the softening of both elastic constants with temperature is the magneto-volume coupling due to thermal lattice expansion. We find that non-negligible local magnetic moments of Cr and Ni are thermally induced by LSFs, but they exert only a small influence on the elastic properties. The proposed framework exhibits high flexibility in accurately accounting for finite-temperature magnetism and its impact on the mechanical properties of PM multicomponent alloys.

Mold corner structure will influence the strand corner temperature by changing fluid flow and heat transfer of liquid steel at mold corner. A three-dimensional model coupling fluid flow and heat transfer in the mold and a two-dimensional moving-slice heat transfer model in secondary cooling zone was established to investigate slab corner temperature under different mold corner structure: right-angle, big-chamfer, multi-chamfer and fillet. Results show that strand corner temperature increases obviously at mold exit through using chamfered mold. Compared with the corner temperature of right-angle strand, corner temperature of big-chamfered, multi-chamfered and fillet strand are promoted during the straightening process, which will avoid the low ductility temperature zone. When mold corner structure changed from right-angle to big-chamfer, the rise of corner temperature is much higher than that changed from big-chamfer to multi-chamfer or fillet.

The heat transfer in mold copper plays an important role in the solidification behavior of steel. In this study, a three-dimensional heat transfer model coupled with flow behavior of the cooling water was established to analyze the temperature field of the copper and water slots. And this model was verified by the measured temperature rise of cooling water at the inlet and outlet of slots. The advantages of this model were obtained by comparing it with Dittus–Boelter model and the Sleicher–Rouse model, which did not consider the flow of water. The results show that the Dittus–Boelter model has the highest temperature and that the coupled model has the lowest temperature. Moreover, the coupled model includes calculation of the temperature and velocity field of the cooling water inside the slots. This temperature information is very helpful for predicting the water boiling in the slots. In addition, the coupled model shows that the temperature, heat flux, and heat transfer coefficient around the water slot wall are different from the conventional models.

Based on the thermodynamic calculations, the universal secondary cooling structure, and the specific water rate for round blooms continuous casting in various diameters were investigated with a 2D heat transfer model. Results indicated that extension of the secondary cooling zone along casting direction significantly lowered the surface temperature recovery after the water cooling, though little influence on the recovering rate. The universal secondary cooling structure for the continuous casting of round blooms in diameters from 280 to 350 mm was optimized by appropriately extending the length of secondary cooling zone. The target unbending temperature was 908 °C for steel 16MnNb due to the thermodynamic calculation. To the optimized universal secondary cooling structure, the optimal specific water rates were 0.35 and 0.25 L kg−1 for the continuous casting of round blooms 280 and 350 mm in diameter, respectively. The present study had been applied to real production, resulting in round blooms in good quality, and contributing to the efficiency and flexibility of round blooms continuous casting process.

To understand the high temperature flow behaviour of a novel pearlitic steel (PS) and low carbon steel (LCS) bimetal, hot compression tests in a wide range of temperature and strain rate were conducted on a Gleeble 3500 thermo mechanical simulator, and the constitutive model was developed based on the experimental data. The measured true stress–strain curves exhibited three types of variation patterns, which are (i) a plateau type, (ii) single peak type and (iii) multi peaks type. These patterns well displayed the effects of the deformation temperature, strain rate and plastic strain on the flow behaviour of the bimetal. By incorporating the Zener–Hollomon parameter and material parameter functions of α ( e ), n ( e ), Q ( e ) and A ( e ) into Arrhenius-type constitutive equation, the flow stress values predicted by the proposed model show a good agreement with experimental results by the evidence of reproducing true stress–strain curves accurately, high value of correlation coefficient ( R =0.9873) and low value of average absolute relative error ( AARE =4.81%). The proposed constitutive equation can be used to realise numerical simulation and determine processing parameters during hot-working of the PS/LCS bimetal.

The present work focuses on the peritectic reaction and transformation in a commercial hypo-peritectic steel. This multiple phase transformation was studied by means of the high temperature confocal scanning laser microscopy (HTCSLM) and the differential scanning calorimetry (DSC) analysis. The results indicate that the technique of combining HTCSLM and DSC can effectively distinguish and characterize the peritectic reaction and transformation. The results of these two methods verify and complement each other in interpreting the peritectic reaction and transformation. In situ observation of HTCSLM reveals that the austenite → δ-ferrite transformation during the continuous heating firstly occurred around the inclusion and at austenite grain boundary. The emerging δ/γ interfaces travel through previous γ grains by a finger-like morphology. With further heating, the unstable liquid phase formed by the peritectic reaction transforms into the δ-ferrite phases again. These stable δ-ferrite phases subsequently melt into liquid phase. During the peritectic solidification, in situ observation reveals that the peritectic reaction is firstly observed to occur at the junction interface of the liquid phase and δ-ferrite phase. The γ intermediate phase propagates and thickens toward the liquid phase side and the δ-ferrite phase side in the subsequent peritectic transformation. The δ-ferrite and γ phases were observed to coexist in solid phase when the peritectic transformation finishes. Based on the linear regression of DSC results, it is found that the activation energy of the peritectic reaction is larger than that of the other phase transformations during heating, but it is on the contrary during cooling.

A two-dimensional heat transfer model was developed for the secondary cooling system during beam blank continuous casting. The finite element method was used to calculate the heat transfer. Accurate cooling boundary conditions in the secondary cooling zone are involved, including spray water cooling, water evaporation cooling, radiation cooling and roll contact cooling in the casting direction and non-uniform distribution of spray water flow density in the cross-section. The causes of longitudinal crack at the fillet during Q235 steel continuous casting were analysed on the basis of the simulation of the developed model, and then the spray water flow and the transverse nozzle layout were optimised. Practical results show that the surface quality of the beam blank improved after optimisations. Numerical results from the present model were validated using previous experimental measurements, which show good agreement.

A three-dimensional (3-D) cellular automata (CA) model coupled with the finite-element (FE) method has been proposed to simulate dendrite growth with various crystallographic orientations during solidification. The model introduces a new tracking neighborhood method to resolve the mesh dependency caused by the cubic lattice in the CA model for simulating 3-D dendrite growth. The migration of the solid–liquid (SL) interface is associated with the dendritic preferential orientation and the driving force for the phase transition. The latter is obtained from a thermodynamics database. The local curvature and anisotropy of the surface energy are also incorporated to describe the growth kinetics of the SL interface. The solute transfer is calculated using the FE method. A numerical simulation has been performed on a Fe-1.5 wt pct C alloy. The grain morphologies with various crystallographic orientations and the solute distribution during isothermal solidification are studied and discussed. The simulation results are compared with analytical solutions and experimental results, which are in good agreement.

The molten steel flow pattern in continuous casting tundish could be improved if the flow control devices were properly used. With reasonable application of weir and air curtain, the disturbance at injection zone of the tundish was reduced. The flow path of the molten steel was changed, and the short-circuit flow was eliminated. Therefore, the residence time was lengthened. An air curtain with bubbles floating could promote the surface flow and improve inclusions removal. The application of weir and air curtain in an ultrathick slab continuous casting tundish was investigated with hydraulics and mathematics simulation. The residence time and dead volume fraction were studied through orthogonal experiments with different positions of the flow control devices. The efficiency of three factors was analyzed, and the optimum positions of the weir and air curtain were obtained. Besides, the discrete phase model was suitable for simulation of the interaction between gas bubbles and molten steel, and the mathematics results shown the optimum one got larger inclusion flotation rate.

A three-dimensional (3D) cellular automata (CA) model has been developed for the simulation of microstructure evolution in alloy solidification. The governing rule for the CA model is associated with the phase transition driving force which is obtained via a thermodynamic database. This determines the migration rate of the non-equilibrium solid–liquid (SL) interface and is calculated according to the local temperature and chemical composition. The curvature of the interface and the anisotropic property of the surface energy are taken into consideration. A 3D finite element (FE) method is applied for the calculation of transient heat and mass transfer. Numerical calculations for the solidification of Fe–1.5 wt% C alloy have been performed. The morphological evolution of dendrites, carbon segregation and temperature distribution in both isothermal and non-isothermal conditions are studied. The parameters affecting the growth of equiaxed and columnar dendrites are discussed. The calculated results are verified using the analytical model and previous experiments. The method provides a sophisticated approach to the solidification of multi-phase and multi-component systems.

Ultrathick continuous slab casting is a growing technology, especially in developing countries due to the vast market demand of thick rolled plate. The structure of the submerged entry nozzle is regarded as the crucial factor to determine flow related phenomena in the mould. This article conducts a 0·55 scale water model and a three-dimensional numerical model to investigate the influences of submerged entry nozzle on flow behaviour, temperature field and solidified shell distribution in a 420 mm ultrathick slab mould. Physical and numerical finite volume methods with K–ϵ turbulence model simulations verify that the flow pattern in ultrathick mould is similar with that in conventional slab mould. The diffuse type nozzle fails to increase the surface velocity while easily causing slag entrainment. The four-spout nozzle gives a detrimental effect on shell distribution. The tunnel bottom nozzle is optimal, because it shows a lively surface behaviour and a favourable heat transfer between mould flux and surfa...

The flow transport of a 420 × 320 × 90 mm beam blank continuous casting mold that used open-stream pouring combined with submerged refractory funnels was studied. By considering the dynamic similarity, geometric similarity, and air entrapment quantity similarity, a full-size water model was established. Meanwhile, the 3D mathematical models that included three phases were applied. Through the combination of the water model and the mathematical model, the distribution and morphology of the phases in the mold were investigated. The results indicate that bubbles existed in the molten steel due to entrapment and the flow pattern was different from that of the full protection-poured mold. Furthermore, the effects of funnel immersion depth and funnel diameter on the bubbles’ impact depth, funnel’s inside wall shear stress, and overall area of the air/steel interface were discussed. The results provide useful information for the industrial continuous casting process.

The surface temperature of continuous casting slab in the secondary cooling zone is a key parameter of production control. However, the accuracy of radiation temperature measurement of high temperature casting slab is greatly affected by the environmental factors, such as water vapor, spray, water film and other participational medias during continuous casting process. In this paper, the radiation characteristics of water vapor and its influences to radiation temperature measurement of continuous casting slab were investigated. Based on the database HITRAN 2004 and the measuring principle of monochrome thermometer & colorimetric thermometer, the measuring errors under different operating infrared spectral wavelength were compared. Results showed that spectral region with wavelength nearby 1.0 m or 1.6 m would be the optimum for high temperature infrared thermometer used under the conditions with moist steam, water spray and water film at the secondary cooling zone in steel continuous casting.

The technology of nail shooting was improved and used to study the transverse shape of the solidified shell during steel continuous casting. Three locations across the slab width (1/2, 1/4 and 1/8) were measured by nail shooting and which indicated a larger solidification coefficient and longer liquid core in the slab at higher casting speeds. The solidified shell across the slab width direction was non-uniform due to uneven secondary spray cooling. The point of final solidification at locations 1/8 and 1/4 was much longer than the position between the slab centre and location 1/4, leading to a long solidification end of >2 m, which is poor for the application of dynamic soft reduction. A mathematical model was developed to simulate the growth of the solidified shell and which was in good agreement with the measurements measured by nail shooting. Based on the measurements and simulations, the water spray pattern was improved, making the solidified shell more uniform. Dynamic soft reduction was the...

In the current paper, a low-cost technology was used to prepare glass–ceramics through directly heat-treating with molten glass containing blast furnace slag and silica sand. By making use of the sensible heat of the molten slag, the energy cost was much lower than that in conventional method. The utilized ratio of slag was about 90% and the optimum heat treatment schedule for glass–ceramics was confirmed by an L9(34) orthogonal test. The effect of CaF2 on the microstructure of the glass–ceramics was studied by DSC, XRD and SEM, the bending strength of the glass–ceramics was tested by three points bending tester. The results showed that, after the optimum heat treatment schedule of nucleation at 780 °C for 0.5 h and crystallization at 960 °C for 1.5 h, the crystalline phases were akermanite and diopside, the bending strength of the glass–ceramics was about 45.8 MPa. If CaF2 was added, a remarkable reduction of crystal size was observed, the crystallization of diopside and Ca2SiO2F2 was promoted while that of akermanite was inhibited, the bending strength of glass–ceramics samples could be greatly improved to 120 MPa.

We investigate the impact of longitudinal thermal spin fluctuations on the temperature dependence of the elastic constants of paramagnetic body-centered-cubic (bcc) and face-centered-cubic (fcc) Fe. Based on a series of constrained local magnetic moment calculations, the spin fluctuation distribution is established using Boltzmann statistics and involving the Jacobian weight, and a temperature-dependent quadratic mean moment is introduced that accurately represents the spin fluctuation state as a function of temperature. We show that with increasing temperature, c' and c(44) for the fcc phase and c(44) for the bcc phase decrease at different rates due to different magnetoelastic coupling strengths. In contrast, c' in the bcc phase exhibits relatively high thermal stability. Longitudinal thermal spin fluctuations diminish the softening of both elastic constants in either phase and have comparatively large contributions in the fcc phase. In both bcc and fcc Fe, c(44) has a larger temperature factor than c'. On the other hand, c' is more sensitive to the longitudinal thermal spin fluctuations, which balance the volume-induced softening by 21.6% in fcc Fe.

A three-dimensional (3D) cellular automata (CA) model has been developed for simulation of dendrite growth during non-equilibrium solidification. The heat and mass transports are calculated using 3D finite element (FE) method. The migration of solid/liquid (SL) interface is associated with effective free energy difference incorporating solute trapping and relaxation effects. The non-equilibrium solute partition coefficient involving solute trapping and relaxation effects is used to calculate solute redistribution at SL interface. The interface curvature and anisotropy of surface energy are introduced to represent the characteristics of dendrite tip. The CA model has been applied to simulate the microstructure evolution of Fe-1.5 wt.% C alloy. The grain morphology, solute and temperature distributions, and velocity of dendrite tip are characterized during both isothermal and non-isothermal conditions. The velocity of dendrite tip and secondary dendrite arm spacing during directional solidification are validated and are in good agreements with previous experimental and mathematical results.

Based on a basic water cooling model, a novel model with closed feedback loop was developed for online temperature control system (OTCS) to control the strand surface temperature online during steel continuous casting process. The OTCS considered the temperature delay to the casting speed and water flowrate and combined the feedback control model with feed forward control model for the control of secondary cooling water. The online feed forward control with the temperature of molten steel in the tundish and the temperature of cooling water was also considered. A fine adjusting temperature region and an optimal temperature region were applied to the OTCS to avoid big temperature fluctuation during control process and to shorten the adjusting time. A single point OTCS was applied to a slab continuous caster, showing that the slab surface temperature was well stabilised at the target temperature under the control of the OTCS in continuous casting process. During tundish change or big variation of cas...

In the current paper, Methods of enlarging the area for the distribution of segregation solutes were introduced to mitigate center macro-segregation in steel billets and steel slabs during continuous casting process, which cost less and have significant effect. The location of center macro-segregation is relative to the shape of liquid-core at the solidification end during steel continuous casting. A method of dissymmetrical cooling on different surfaces, by which the area for the precipitation of segregation solutes was enlarged, was introduced to mitigate the center macro-segregation in billets during continuous casting process. Method of optimizing the uniformity of solidified shell in the transverse direction was introduced to mitigate the center macro-segregation in steel slabs. The uniform cooling intensity along the transverse direction guaranteed a regular solidification end in the continuous casting slab, which aided in the effective application of dynamic soft reduction technology. A relevant 2-D heat transfer model was developed for the optimization of uniform solidification. The current method was applied to the industrial slab continuous casting using the heat transfer model. The results indicated a better industrial slab quality with much less center macro-segregation after the use of the method.