Search

Mold corner structures will influence the multiphase flow, heat transfer and inclusion motion behaviors in the mold, which have significant impacts on the quality of strands. Herein, a three-dimensional fluid flow and heat transfer mold model was employed to investigate the effect of four different corner structures (right-angle, big-chamfered, multi-chamfered and fillet) on the multiphase flow, heat transfer and inclusion motion behaviors in the mold. The Volume of Fluid model was used to describe the molten steel and slag, while the Discrete Phase Model was employed to track the motion of non-metallic inclusions. The dynamic mesh was applied to simulate the mold oscillation. Results show that the chamfered structures can obviously increase the flow velocity around the strand corner, especially for the big-chamfered mold. The chamfered molds can remarkably improve the corner temperature of strands at the mold exit, and the fillet mold is the most effective. The temperature on the narrow and chamfered faces of the copper plate in the chamfered molds is lower than that in the right-angle mold. The maximum amplitude of temperature fluctuation of the meniscus reaches 4.6 K. The shell thickness around the strand corner in the chamfered molds is obviously thinner than that in the right-angle mold. In addition, the chamfered structures will increase the number of inclusion particles around the strand corner.

The accurate prediction of mechanical properties and phase microstructures is of great significance to the design and development of the ultra-high strength hot stamping steel (UHSHSS). Based on the prediction of JMatPro and the experimental measurement, an accurate modified prediction model of JMatPro for the tensile strength of UHSHSS was proposed in the study, considering the influence of austenitizing temperature. At the same time, the prediction model of phase transition in quenching process of UHSHSS was established. The tensile strength and phase transition models of UHSHSS under different conditions were studied using the prediction models. Results showed that the tensile strength of UHSHSS increased with the increase of C content and decreased with the increase of Si content. For every 0.01 wt% increase in C content, the tensile strength increased by around 30 MPa. For the hot stamping process used in this study, the carbon content of hot stamping steel should be more than 0.35 wt% to achieve 2000 MPa in tensile strength. The volume fraction of the residual austenite in UHSHSS increased with the increase of C and Si content. During the quenching process, the phase transition in UHSHSS was the fastest between 4 s and 8 s, and the average decomposition rate of the austenite reached 17.8% per second. The average volume fraction of residual austenite and martensite in UHSHSS was 3.3% and 96.7%, respectively, when the quenching die temperature was 150 °C. With the increase of the die temperature, the volume fraction of residual austenite in steel increased.

Ultra-high casting speed is an important development feature for efficient continuous casting of billet. A mathematical model which addresses the high flow rate of molten steel in the billet mold is presented, coupling slag flow with heat flux and solidification. The model is then applied to investigate the correlation between transient steel flow, slag infiltration and heat transfer in the mold-shell gap during ultra-high casting speed. The results show that the meniscus level experiences a hump near the mold wall and a valley near the nozzle as a result of the recirculating flow in the upper mold. The liquid slag around the mold wall infiltrates preferentially into the gap to be consumed quickly, whereas those near the SEN flows to the mold with a low speed. Severe fluctuations in meniscus level will disturb the slag infiltration, which in turn causes the formation of uneven slag films, leading to intensified heat flux fluctuations in the mold-shell gap, especially in the area of 20−60 mm from the mold corner.

A modified coupling model, considering microsegregation, precipitation and growth of inclusion, and variable solute partition coefficient (ki), was established to investigate the precipitation and coarsening of TiN inclusion for the 0.053 wt% Ti-microalloyed steel. The influence of TiN inclusion on the steel impact toughness was revealed. Results show that the effect of phase composition on both the kTi and kN is greater than the effect of temperature, and the kTi and kN are in the range from 0.20 to 0.30 and from 0.28 to 0.45 during solidification, respectively. The change of the ki in different crystalline phases significantly affects the microsegregation and TiN precipitation. The TiN precipitation is promoted by segregation and the TiN starts to precipitate around 1754 K (corresponding to fs = 0.82) in the mushy zone. The predicted size of TiN inclusion is between 7.57 and 16.68 μm at a conventional cooling rate (1–5 K/s), which is consistent with the measured results in the slab. The square or triangle TiN inclusions with large size are harmful to the impact toughness. Many TiN inclusions can be found at the junction of the cleavage cracks. To control the TiN size and ensure the impact toughness, the cooling rate for the Ti-0.053 wt% steel solidification should be enhanced and greater than 10 K/s. Furthermore, reducing the Ti content to 0.03 wt% is a more effective way to control the TiN size.

The complexity of thermal and mechanical stresses during bending and straightening processes may cause cracks around strand corners. To analyze the thermal and mechanical behaviors around a strand corner in the secondary cooling zone, a three-dimensional thermo-elastoplastic finite element model that couples the slab and rollers with different corner structures (right-angle, big-chamfered, multi-chamfered and fillet) is established. The temperature variation is indirectly coupled through a combined three- and two-dimensional hybrid heat transfer slab model. The results indicate that all three types of chamfered structures can maintain the corner temperature of strands, avoiding the formation of a low-temperature ductility zone at the straightening segment. The stress concentration is very significant around the strand corner. During the bending and straightening processes, the stress of the strand continues to accumulate. Although all three types of chamfered structures can reduce the stress concentration, the big-chamfered structure cannot effectively decrease the peak stress at the strand corner. The effects of the multi-chamfered and fillet structure are more remarkable.

Segregation and inclusion precipitation are the common behaviours of steel solidification, which are resulted from the redistribution and diffusion of the solute elements at the solid-liquid interface. The effect of the phase transition of high-sulfur free-cutting steel is quantified in the present work for the solute partition coefficient (ki), inclusion precipitation, and microsegregation by establishing a coupling model of microsegregation and inclusion precipitation, wherein the quantified dependencies of ki in terms of temperature, phase and carbon (C) content were applied. Results showed that the solidification temperature range and phase transition of high-sulfur steel that under different solidification paths and C contents were quite different, leading to differences in ki and eventually in microsegregation. kC, kP, and kS were mainly affected by phase composition and kSi was primarily by temperature, while kMn depended on both phase composition and temperature during solidification. Increasing the C content within the interval 0.07-0.48 wt%, the ‘proportion of the δ phase maintained temperature region during solidification’ (Pδ), k P a v e and k S a v e ( k i a v e , the average value of the ki across the whole stages of solidification) decreased monotonically, whereas k C a v e increased linearly. The peritectic reaction impacted on the phase composition and ki, leading to the change in microsegregation. Such effect of the peritectic reaction was more significant at the last stage of solidification. When the Pδ was between 75% and 100% (corresponding to 0.07-0.16 wt% C), the solidification path resulted in a greater effect on the microsegregation of solutes C, P, and S because of the peritectic reaction. The microsegregation of solutes Mn and S were comprehensively influenced by kMn, kS and MnS precipitation as well. The studies would help reveal the solute redistribution at the solid-liquid interface, and improve the segregation of high-sulfur steel by controlling the solidification and precipitation in practice.

The friction behavior between strands and molds plays a significant role in the surface quality of strands, especially around the strand corner. Herein, the friction behavior in slab molds with different corner structures (right-angle, big-chamfer, multi-chamfer, and fillet) was investigated. The temperature distribution of the slab was calculated through a three-dimensional mold model that couples the fluid flow and heat transfer. Then, the friction behavior was analyzed using a friction model, which was modified via a solid slag fracture model. The results show that an air gap is formed around the slab corner because of the disappearance of the liquid slag and the fracture of the solid slag. The slab friction stress on the wide face exponentially increases from the meniscus to the mold exit, while that on the narrow face is much lower. The friction stress distribution around the slab corner in the chamfered mold is more uniform than that in the right-angle mold, especially in the fillet mold. Employing a chamfered mold allows reducing the friction stress around the slab corner. The mold friction stress on the wide face increases quasi-linearly from the meniscus to the mold exit while that on the narrow face is similar to that of the slab friction stress. In addition, the oscillation parameters have a great effect on the friction behavior.

First-principles calculations were performed to investigate the influence of Mn content on the intrinsic energy barriers (IEBs) of paramagnetic FeMn alloys with face-centered cubic (fcc) structure. The IEBs were derived from the free energies accounting for longitudinal spin fluctuations (LSFs). LSFs are demonstrated to be important for the quantitative description of IEBs and their alloying dependencies at finite temperature. The unstable stacking and unstable twinning fault energies of the fcc phase slightly decrease with Mn content, whereas the intrinsic stacking fault energy ( γ i s f fcc ) is predicted to monotonically increase. This latter finding contradicts the experimentally reported, local minimum of γ i s f in the fcc/hexagonal close-packed (hcp) coexistence region. The partitioning of Mn during the fcc/hcp phase transition is proposed to reconcile theory and experiment. Both temperature and impurities ([C] and Cr) hardly influence the monotonic concentration dependence of γ i s f fcc but considerably alter the magnitude. The fcc/hcp interfacial energy is nearly independent of Mn concentration in contrast to the parabolic dependence predicted in thermodynamic modeling. In contrast to the fcc phase, the estimated intrinsic stacking fault energy of the ideal hcp structure monotonically decreases with Mn content and temperature. A high twinnability is predicted at 450 K within the stability field of the paramagnetic fcc Fe Mn alloys.

To investigate the coupling effects of reflection and absorptive gas mixture on surface temperature determined by single color pyrometer, an analytical radiation thermometry model combined with a mathematical radiative heat transfer model, which simultaneously considering both the reflected ambient radiation and the gas absorption and emission of radiation, was established in this paper. The temperature errors caused by the combination of intervening gas mixture and reflected ambient radiation were quantitatively analyzed under three practicable measurement strategies depending on the relative target and gas temperatures. As the results indicate, the investigated wavelength ranges can be roughly divided into three parts depending on the relative importance of reflection and gas mixture. Correcting for the hot/cool gas mixture effect through use of a low/high temperature reflector is usually effective because these two effects will cancel each other out. The selection methodology of spectral pass-band of radiation thermometer to minimize the influences of reflection and gas mixture absorption and emission under different conditions was presented. Sensitivity analysis of the derived temperature error to the variations in ambient temperature, target surface emissivity, gas mixture temperature and concentration, and viewing path length was investigated. Considering the case T1 = 1200 K, T2 = 1400 K, Tg = 2000 K, e1 = 0.85, L = 100 cm, X H 2 O = 0.2, X C O 2 = 0.1, p = 1 atm, the most influential factor is gas mixture temperature for wavelength longer than 1.33 µm, followed by other factors. For wavelength shorter than 1.33 µm, the high ambient temperature is the main contributor to the imprecision in the proposed model output. The analyses in the paper may provide the necessary theoretical supports for the design and application of a radiation thermometer in the presence of intervening gas.

The surface temperature of continuous casting slab in water spraying zone is a key parameter of production control. However, the accuracy of radiation temperature measurement is greatly affected by water vapor at high temperature. In this paper, a mathematical radiative heat transfer model combined with an analytical radiation thermometry model was developed. The hot water vapor absorption coefficient at a spectral resolution of 25 cm−1 as an input parameter to the radiative heat transfer model is obtained by employing the statistical narrow-band model along with gray-band approximation on the basis of the updated database HITEMP 2010. The proposed model was applied to quantitatively calculate the surface temperature, obtained by ratio and single waveband thermometer for infrared waveband from 50 cm−1 to 11250 cm−1, of assumed gray strand covered by hot water vapor. Detailed simulation studies were performed considering the following parameters: concentration of the hot water vapor, reflectivity of the target surface, background temperature of the surrounding surfaces and distance between target and thermometer. A sensitivity analysis was put forward trying to ascertain how the proposed model depends on those parameters. As the results indicate, both hot water vapor and reflected ambient radiation greatly affect the measurement accuracy of the radiation thermometry. The temperature errors caused by hot water vapor are spectrally selective. The most suitable spectral regions for ratio and single waveband thermometer operating and a criterion for choosing the optimal wavelength pairs for ratio thermometry were put forward. The analyses in the paper may provide necessary theoretical supports for the design and application of a radiation thermometer in the presence of hot water vapor.

To reveal the characteristics of solute distribution and the formation of centerline segregation in continuous casting (CC) slab, a 3D simulation model for the prediction of centerline segregation during a slab CC process was developed. Experiments including the morphology of strand transverse section obtained by acid etch and the segregation degree of C tested by chemical analyzer were carried out to verify the accuracy of the numerical model. The maximum deviation between the calculated and experimented results reaches as low as 3.22%. In the turbulent flow region, the solute distribution in the liquid pool is relatively uniform and its distribution pattern is similar to that of flow pattern. In the final stage of solidification during a slab CC process, the solidification of molten steel in the centerline region is not simultaneous and the pattern of solute distribution is highly depended on the shape of liquid pool. The final solidification and serious segregation occur at a position roughly 595 mm from the slab center. Moreover, the quantitative relations between the position of solidification front and the solute concentration on the centerline were studied. The results show that solute redistribution and the solidification front moving continuously toward centerline lead to the formation of centerline segregation in CC slab. The central segregation degree of solutes in steel Q345 arranged in weakening order is S, C, P, Si, and Mn.

Ni-Co-B ternary coating was obtained by electrodeposition with an microhardness of 285–360 HV. After heat treatment, the hardness reaches up to 953–1100 HV, and CoB, Co2B, and Ni3B second phases were observed. The mechanical properties and electronic structures of NiCo and borides (NiB, Ni2B, Ni3B, Ni4B3, CoB, Co2B, and Co3B) were then systematically investigated by first-principles calculations. Among them, CoB possesses the highest bulk modulus (294 GPa), shear modulus (143 GPa), Young's modulus (370 GPa), and hardness (12.73 GPa), but the weakest ductility. In addition, the hardness of borides gradually increases with increasing boron content. The electronic structures indicate that B-B and Co/Ni-B covalent bonds play an important role in the mechanical properties of borides. Overall, CoB has the largest elastic modulus and hardness, which is expected to increase the rigidity of Ni-Co-B alloys.

Two-color pyrometry is well established and widely applied to surface temperature measurements. However, its accuracy degrades significantly when the transmission path between the object surface and the pyrometer is full of high concentration participating media, which attenuates the surface radiation signal to the pyrometer. To improve measurement accuracy, a theoretical optimization wavelength selection criterion for two-color pyrometry working with the interference of a participating medium is established on the basis of the Plank’s law and Wien's approximation. The closer to zero the criterion value is, the smaller the measuring error is. Therefore, the optimum choice of operating wavelengths combination for two-color pyrometer is obtained through inter-comparison of the criterion values. Evaluation of the practical applicability of the new criterion is performed by employing an analytical radiation thermometry model considering radiative attenuation and augmentation in participating media. Theoretical estimations confirm that the new criterion has good applicability and scientific quality considering two typical media ordinarily encountered in engineering applications: water vapor and water mist. This selection criterion not only provides solid reference information for the proper selection of wavelengths combination, but also helps one to better understand the fundamentals of measurement errors for two-color pyrometer interfered with participating media. The analyses in the paper provide the necessary theoretical supports for the design and application of a two-color pyrometer.

The viscosity of titanium slag has a crucial effect on the separation efficiency from metallic iron, the foaming extent of slag, and the kinetics of smelting reactions. Properties of slag depend on its microstructures essentially. Molten FeO-TiO2 system was investigated through molecular dynamics simulations to characterize its structural and transport properties at 1973 K. With FeO content increasing from 5 to 50%, CNTi-O decreases from 6.02 to 5.87, CNO-Ti decreases from 2.95 to 1.89, and the structural strength of the FeO-TiO2 system is hence reduced. [TiO6] octahedron is only one stable structural unit and is distorted in molten FeO-TiO2 system. [TiO6] octahedrons are connected by two ways: edge-sharing Ti-Ti and corner-sharing Ti-Ti. The edge-sharing Ti-Ti has stronger combining capacity than the corner-sharing Ti-Ti. The structural strength and viscosity of FeO-TiO2 system will be reduced by the transformation from Ti-O-Ti to Fe-O-Ti, which is resulted from the addition of FeO. Furthermore, the self-diffusion coefficients of Fe2+, Ti4+, and O2– follow the order: Fe2+ > Ti4+ > O2−. With FeO content increasing from 5 to 50%, the viscosity of molten FeO-TiO2 system decreases from 0.1272 to 0.0232 Pa·s. The results will contribute to understand and predict the macroscopic properties of high-temperature titanium slag.

The kinetic coefficients (μ) for the fcc Fe-(0-0.5 wt%)C alloy solidification and melting were investigated using molecular dynamics simulations. The activation energy for the diffusion of C atoms (QC) at the solid-liquid interface was calculated using the Debye-Waller factor to reveal the effect of C atoms dragging on the interface mobility. The influence of C segregation and interface roughness on interface mobility was also investigated. Simulation results show that for melting, the C content has a minor effect on the μ, and the μ is mainly ranged 18.1-19.4 cm/s•K, while for solidification, the μ linearly decreases with the increasing C content, and the μ is ranged 9.6-17.9 cm/s•K. In addition, a ‘platform’ zone was observed under low undercooling, in which the interface velocity is close to zero and suggests weak interface mobility, resulting from the segregation and dragging of C atoms at the interface. The ‘platform’ zone size linearly enlarges with the increasing C content. The QC increases with the increasing C content, which is ranged 0.71-0.91 eV for the fcc Fe-(0.1-0.4 wt%)C alloy solidification, indicating the C atomic motion is weakened and the C atoms dragging is reinforced due to C content increasing. Interface roughness and C atoms distribution analyses show that for the fcc Fe-C alloy solidification, a smooth solid-liquid interface is unfavourable for interface mobility, and the smooth interface is usually accompanied by the non-uniform distribution of C atoms. Therefore, increasing the interface roughness may be help for improving interface mobility and segregation for alloy solidification.

Molecular dynamics simulations were adopted to characterize the structural and transport properties of the FeO-TiO2-SiO2 system. The bond lengths of Si-O and Ti-O remain unchanged respectively at 1.62 A, and 1.94, as the FeO content increases from 4% to 36%. Most Ti-O-Ti bond angles remained unchanged at 100.00°, while a small proportion of Ti-O-Ti bond angles increased from 126.67° to 131.64°, as FeO content increased from 4% to 36%. The proportion of Ti-O-Ti oxygen connection decreased from 71.82% to 50.87% while the proportion of the Fe-O-Ti oxygen connection increased from 1.74% to 17.64%, as the FeO content increased from 4% to 36%. The self-diffusion coefficients of ions increased in the order: Fe2+ > Ti4+ > O2- > Si4+ and the viscosity of the system decreased from 0.1231 Pa•s to 0.0478 Pa•s, as the FeO content increased from 4% to 36%.

Through DFT calculation, the adsorption properties, geometry changes and charge transfer of CO2 molecule on pristine graphene (PG), vacancy defect graphene (VG) and doped graphene (DG) are investigated. The results show that different adsorption forms of CO2 on PG and VG are physisorption through van der Waals force with few charge transfer. On PG, it shows weak physisorption. On VG, it is strong physisorption. Therefore, the appearance of defect can increase adsorption ability for CO2. When CO2 parallel to the H-site of PG and monoatomic vacancy graphene (M-VG), the adsorption structure is the most stable, which is similar with literature. On DG, N-doped can not enhance the adsorption and charge transfer ability, and this result is consistent with co-doped system of Cu/N-DG and Ni/N-DG. While Cu or Ni-doped can increase adsorption and charge transfer ability, and decrease the adsorption distance. When CO2 on Cu-DG, Cu/N-DG, Ni-DG and Ni/N-DG, these adsorption processes are chemisorption process in which new chemical bonds are formed. Adding defects and Cu/Ni atoms to graphene can serve as an excellent adsorption material for the preparation of catalysts to activate CO2. Among them, Cu-DG has the best performance. Moreover, through electronic band structures and density of states analysis, we find that vacancy and Cu/Ni-doped can open the band gap, increase the width of the pseudo-gap, and strengthen the adsorption and activation ability of CO2 gas molecular in heterogeneous catalytic reaction based on graphene support.

In order to clarify the microscopic characteristics and evolution rules of varying P2O5-based binary melt structures, molecular dynamics simulation (MD) was utilized to conduct a comprehensive study on its structure and performance. The investigation results demonstrated that the basic unit of P2O5-based binary melt network structure is [PO4]3−, and its structure is close to the standard tetrahedron. With the increase of P2O5 content, Q0, Q1 and Q2 will gradually shift to Q3 structure, resulting the network structure of each phosphate system more complicated. For a given P2O5 content in different systems, as the size of the metal cation decreases, the P O structure becomes more disordered and the degree of polymerization of systems increase. The order of polymerization degree of distinct binary systems is BaO P2O5＜K2O P2O5＜Na2O P2O5＜CaO P2O5. In addition, by linking the change law of the degree of polymerization of P2O5-based binary systems with macroscopic thermodynamic properties of dephosphorization, it is concluded that the dephosphorization capacity of varying binary systems is inversely proportional to their degree of polymerization.

The Cu-Ni bimetallic catalyst supported by graphene derivatives was employed to explore the reaction mechanisms of converting CO2 to methanol. Their properties were analyzed by Raman, XRD, XPS, TG-DSC, TEM and CO2-TPD. Cu or Ni catalyst supported by graphene oxide (GO) tended to combine with defects, leading to less defects of Cu-GO and Ni-GO. So does reduced graphene oxide (rGO). However, ammonia modified graphene (NGO) presented more defects compared to GO and rGO. These changes showed that the functional group and metal ion had been introduced. In addition, more active component (Cu°) could be detected in rGO supported catalyst. In GO and rGO, the addition of Ni could promote the reduction of Cu2+, while Ni showed inhibitory performance in NGO. CuNi-rGO and CuNi-NGO could chemically activate more CO2 at lower temprerature. These catalysts could lower the activation energy of CO2 by 40 %. Most of Ni and Cu dispersed uniformly on supports. In rGO, the size of Cu-Ni was less than 20 nm. In NGO, the size was 50–100 nm. Which means more activation component could been exposed to reactant gas on rGO and it was a better support. Compared with literature, the adsorption capacity of CO2 could increase 76.92 % maximally. In the catalytic test, CuNi-rGO showed a CO2 conversion of 7.87 % and the methanol selectivity of 98.7 % at 498 K and 4.0 MPa, which exhibited a competitive performance compared with other catalysts in literatures.

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.

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.

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.

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.

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.

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.

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.

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 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.

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.

In order to verify the reasonableness of off-gas pressure and wall temperature, a mathematical model for gas flow and heat transfer in ladle furnace (LF) lid is developed based on 3-D Navier–Stokes equations and k–e two equation turbulent models as well as energy conservation equation. The gas velocity vector distribution of skirt clearance between the top edge of ladle and furnace lid and electrode gaps between three graphite electrodes and furnace lid, the gas flow line distribution, pressure and temperature distribution on the furnace lid wall are simulated. Simulation results show that appropriate off-gas pressures are 200 Pa, 200 Pa and 150 Pa when electric arc emerges from molten steel surface and alloy hole is unsealed, electric arc emerges from molten steel surface and alloy hole is closure, electric arc immerges into molten steel surface and alloy hole is closure, respectively. The maximum temperature presents in the middle of LF lid in all of heating conditions, and the temperature value are 563, 603 and 343 K. Finally, the relations between gas volume and off-gas pressure are analyzed in different width of skirt clearance, and some relevant mathematical expressions are obtained. By comparing both simulation results and practical data, the advice on reducing off-gas pressure is proposed, and the maximum temperatures of furnace lid wall have good agreement with actual data.