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A 2D coupled electromagnetic-fluid-thermal analysis based on the Fluent software and the “User-Defined Functions” was performed to investigate the effects of conductive circuits on the bonding quality of a bimetallic composite roll produced by the electroslag remelting cladding (ESRC) process. Three typical conductive circuit schemes were designed and the distribution characteristics of physical fields were calculated and discussed. The results illustrated that the differences in the conductive circuits mainly affected the distributions of electric potential, current density, Joule heating, Lorentz force, flow velocity, and final temperatures in the slag pool, in turn. A high temperature in the slag pool always led to high temperatures at the bimetallic interface and slag/steel interface which determined the bonding quality of bimetals and the solidification quality of the composite layer. Finally, the conductive circuit of electrode → slag pool → total part of current supplying mold (abbreviation ESTM) was recommended, and a GCr15/45 steel composite billet with uniform bimetallic interface was produced by the ESRC process.

A bimetallic composite roll with the cladding layer of high-speed steel (HSS) and the roll core of ductile cast iron (DCI) was manufactured by the electroslag remelting cladding (ESRC) technology, ...

A numerical simulation based on the coupling of electromagnetic-fluid-thermal analysis was developed to investigate the effects of electrode immersion depth (EID) on the electrical resistance and heat generation in the electroslag remelting (ESR) process. The total electric current was obtained by integrating the current density at the slag/metal interface, and the electrical resistance is the ratio of potential to current. It indicates that the EID variation changes the shape, size, and current path of the slag pool, and, as a result, the current density, heat generation, and melting power are directly proportional to the EID, while the electrical resistance of the slag pool is inversely proportional to the EID. The distance between the electrode and the molten-metal pool and the contact areas between the electrode and the slag are the main factors affecting the distribution of voltage, current density, Joule heating, and temperature in the slag pool of the ESR process. A change in the current density affects the electrical resistance and heat generation, which has a direct effect on the ESR process.

According to the previous numerical simulation, a bimetallic composite billet has been produced by the new electroslag cladding method in the present study. Its longitudinal and circumferential mac...

Materials that combine magnetic order with other desirable physical attributes offer to revolutionize our energy landscape. Indeed, such materials could find transformative applications in spintronics, quantum sensing, low-density magnets, and gas separations. As a result, efforts to design multifunctional magnetic materials have recently moved beyond traditional solid-state materials to metal–organic solids. Among these, metal–organic frameworks in particular bear structures that offer intrinsic porosity, vast chemical and structural programmability, and tunability of electronic properties. Nevertheless, magnetic order within metal–organic frameworks has generally been limited to low temperatures, owing largely to challenges in creating strong magnetic exchange in extended metal–organic solids. Here, we employ the phenomenon of itinerant ferromagnetism to realize magnetic ordering at TC = 225 K in a mixed-valence chromium(II/III) triazolate compound, representing the highest ferromagnetic ordering temperature yet observed in a metal–organic framework. The itinerant ferromagnetism is shown to proceed via a double-exchange mechanism, the first such observation in any metal–organic material. Critically, this mechanism results in variable-temperature conductivity with barrierless charge transport below TC and a large negative magnetoresistance of 23% at 5 K. These observations suggest applications for double-exchange-based coordination solids in the emergent fields of magnetoelectrics and spintronics. Taken together, the insights gleaned from these results are expected to provide a blueprint for the design and synthesis of porous materials with synergistic high-temperature magnetic and charge transport properties.

Hydrogen holds promise as a clean alternative automobile fuel, but its on-board storage presents significant challenges due to the low temperatures and/or high pressures required to achieve a sufficient energy density. The opportunity to significantly reduce the required pressure for high density H(2) storage persists for metal–organic frameworks due to their modular structures and large internal surface areas. The measurement of H(2) adsorption in such materials under conditions most relevant to on-board storage is crucial to understanding how these materials would perform in actual applications, although such data have to date been lacking. In the present work, the metal–organic frameworks M(2)(m-dobdc) (M = Co, Ni; m-dobdc(4−) = 4,6-dioxido-1,3-benzenedicarboxylate) and the isomeric frameworks M(2)(dobdc) (M = Co, Ni; dobdc(4−) = 1,4-dioxido-1,3-benzenedicarboxylate), which are known to have open metal cation sites that strongly interact with H(2), were evaluated for their usable volumetric H(2) storage capacities over a range of near-ambient temperatures relevant to on-board storage. Based upon adsorption isotherm data, Ni(2)(m-dobdc) was found to be the top-performing physisorptive storage material with a usable volumetric capacity between 100 and 5 bar of 11.0 g/L at 25 °C and 23.0 g/L with a temperature swing between −75 and 25 °C. Additional neutron diffraction and infrared spectroscopy experiments performed with in situ dosing of D(2) or H(2) were used to probe the hydrogen storage properties of these materials under the relevant conditions. The results provide benchmark characteristics for comparison with future attempts to achieve improved adsorbents for mobile hydrogen storage applications.

To meet the high cleanliness requirements of bearing steel used in high-speed railway trains, a new production process combining vacuum induction melting and electroslag remelting (ESR) was used to produce G20CrNi2Mo bearing steel. To investigate the effect of remelting on the cleanliness of the steel, two kinds of G20CrNi2Mo steels were prepared using an ESR furnace with and without high-purity argon protection. The results show that the G20CrNi2Mo electrodes smelted using a vacuum induction furnace have very high cleanliness 0.010[P%]–0.004[S%]–0.0012[O%]–0.0041[N%]). Unprotected ESR leads to an increased oxygen content, while protected ESR prevents any increase in oxygen content. Both protected and unprotected ESR results in significant desulphurisation, with desulphurisation rates reaching over 50%. The protected ESR process removes Al2O3–SiO2–MnO inclusions, and the remaining inclusions in the steel can be divided into two categories, Al2O3 and Al2O3–MnS.

The advantages of the electroslag remelting (ESR) process as to cleanness and homogeneity of the ingot structure are well known. As to homogeneity of composition, the control of titanium in stainless steel with high titanium and low aluminium contents during the ESR process has not been resolved well so far. The current work focuses on designing appropriate slag for controlling titanium content during 1Cr21Ni5Ti remelting based on the interaction of the slag/metal interface. Several kinds of slag containing different CaO contents combined with steel samples of 1Cr21Ni5Ti were employed to investigate the effect of slag on titanium content in an electrical resistance furnace, and metal samples were taken at different times for investigating the change of titanium and aluminium contents in steel. The results show that slag with low CaO content at low temperature has excellent capacity for avoiding loss of titanium content caused by its reaction with the alumina in slag, especially in case of remelting of sta...

A comprehensive mathematical model of the solidification structure during the process of electroslag remelting casting (ESRC) of low carbon martensite stainless steel ZG06Cr13Ni4Mo has been established. The change of metal pool profile and grain growth and the microstructure evolution process from the beginning to the steady stage of the ESRC process were investigated by using the moving boundary method and the coupled technology CAFE method (cellular automaton – finite element method). The transition from equiaxed grains at the lateral wall of the mould to columnar grains has been revealed. In addition, casting of this steel has been carried out and the microstructure of the ingot obtained after grinding and acid leaching. According to the comparison of the metal pool profile, morphology and growth direction of the dendrite and the secondary dendrite arm spacing (SDAS) between the experimental results and the simulation results, the validity of the model has been demonstrated, which can provide a favoura...

Mo macrosegregation was studied through the comparison of numerical simulation of the ingot pouring process and experiment on as-cast 500 kg high-Mo austenitic stainless steel ingot. The simulated results showed the evolution of temperature, melt velocity and the patterns of Mo macrosegregation, and revealed the effects of pouring temperature and cooling rate on macrosegregation. The predicted variation of Mo macrosegregation was compared with measurement values from an industrial ingot along the vertical centreline and horizontal direction. Severe normal and gravity segregation were observed. Although a basic agreement was obtained, the lack of a sufficiently fine numerical grid and the neglect of sedimentation for free equiaxed grains in the prediction brought about the absence of A-segregation and V-segregation. Further investigation would be needed to perform this investigation. The predicted results also confirmed that Mo macrosegregation in the ingot could be effectively diminished by improving cool...

The effects of Mg on the inclusions and the as-cast microstructure of high carbon and high chromium die steel, a grade of cold working die steel with high C content of 1.4–1.6% and high Cr content of 11.0–13.0%, were systematically investigated. It is found that inclusions vary with the route as Al2O3 (No Mg) to MgO·Al2O3 + Al2O3 (5 ppm Mg), and then to MgO+MgO·Al2O3 (11 and 15 ppm Mg). The average diameter of the inclusions decreased from 1.91 μm (no Mg) to 1.29 μm (15 ppm Mg), while the number density increased from 2.69 × 104 mm− 3 (no Mg) to ∼5.62 × 104 mm− 3 (15 ppm Mg). The changes in the size and the number density were discussed in terms of the effect of inclusions on the nucleation process and the wettability of them with steel melt. The as-cast microstructures were greatly refined with Mg addition that correlated with the evenly dispersed fine Mg containing inclusions.

A new family of resource-saving ferritic stainless steels, with the composition of 17Cr–xSn (x = 0.1–0.4 wt-%) have been developed by examining the effect of Sn on high temperature ductility, the corrosion resistance properties and the passivation film structure. The results show that tin-bearing stainless steel obtains superb plasticity and there is no evidence of tin-containing precipitation in the fracture facets. High temperature brittleness at about 900°C is caused by the carbide or nitride precipitation along the grain boundary or inside. The precipitation in the grain boundary hinders the free movement of dislocation, thus increasing the strength and decreasing the toughness of steel. The polarisation curves and weight loss measurement indicate that the corrosion resistance of stainless steel is improved by adding small amount of Sn. The existence of Sn in passivation film suppresses the anodic dissolution of steels during long exposure to the aggressive solution, and the dense rust layer i...

The inclusions modification, the morphology of microstructure, the mechanical property at room temperature and the mechanical property at high temperature of tin bearing stainless steel were studied under the experimental condition. The effect of tin on the microstructure of steel matrix and the composition evolution of deoxidisation were analysed. Under experimental conditions, because of the lower defect in ultra-pure ferritic lattice, the well distribution of tin in lattice overcame the problem of hot brittleness happened in low carbon steel by the segregation of tin. Small amount of tin increased the tensile strength, improved its plastic strain ratio and relatively high amount of tin had no adversely effect on the workability. With the increase in temperature, the addition of tin improved the plasticity on the contrary.

The effects of Sn on the corrosion resistance and the passivation film structure were investigated. The relation between the corrosion resistance and the microstructure was established. The results from X-ray photoelectron spectroscopy analysis indicate that tin exists in the outer layer of passivation film mainly in the form of SnO2, and there is a tin rich region in the inner layer. The enrichment of tin in the metal/oxide interface will improve the stability of the passivation film, raise the pitting potential and reduce the corrosion current density. The enrichment of tin around the sulphide inclusions will help form tin rich layer and release the pitting corrosion caused by sulphide.

Electroslag remelting (ESR) hollow ingot process with T-shape current supplying mould is a new metallurgical technology. A mathematical model was developed to describe the interaction of multiple physical fields of this process for studying the process technology. Maxwell, Navier-Stokes and heat transfer equations have been adopted in the model to analyse the electromagnetic field, magnetic driven fluid flow, buoyancy driven flow and heat transfer using finite element software ANSYS. Moreover, the model has been verified through the metal pool depth measurements, which were obtained during remelting of 10 electrodes into Φ900/500 mm hollow ingots of P91 steel, with a slag composition of 50–60 wt-% CaF2, 10–20 wt-% CaO, 20–30 wt-% Al2O3, ≤8 wt-% SiO2. There was a good agreement between the calculated results and the measured results. The calculated results show that the distribution of current density, magnetic induction intensity, electromagnetic force, Joule heating, fluid flow and temperature ar...

Hydrogen bubbling is a typical corrosion morphology caused by hydrogen sulfide corrosion. In order to explore hydrogen sulfide corrosion of iron, the composition of flue gas under actual conditions was simulated in this research. Hydrogen sulfide corrosion in flue gas of four kinds of materials selection of ground process pipeline and underground pipe string was researched experimentally. The pressure and temperature of hydrogen bubbling corrosion morphology under actual flus gas conditions were obtained. The electrochemical corrosion mechanism between iron and hydrogen sulfide was investigated.

Alumina ceramic coating was prepared on Q235 carbon steel by plasma electrolytic oxidation. The discharge process was analysed according to the voltage–time curve. The microstructure of the ceramic coating was investigated by scanning electron microscopy, X-ray diffractometry and energy dispersive X-ray spectroscopy. The bonding strength, thickness, hardness, surface roughness and corrosion properties of the coatings were studied. The results indicated that coating on Q235 carbon steel mainly consisted of α-Al2O3 and γ-A12O3. The coating showed coarse and porous surface. The surface roughness of the coating was 1·8 μm, and the average diameter of the pores was 3–4 μm. The hardness of the coating was 1854 HV. The thickness of the coating was ∼28 μm, and the bonding strength was 23 MPa. The corrosion tests indicated that the corrosion current density of alumina coated Q235 in 3·5%NaCl was 8·289×10−7 A cm−2, which was decreased by two orders of magnitude compared with the uncoated one. The corrosion ...

Electroslag casting with liquid metal (ESC LM) is a new technology in electroslag metallurgy. Solid ingot, hollow ingot and bimetal composite can be produced by the ESC LM process. Using both internal and external current carrying moulds for ESC LM is a new method for manufacturing hollow ingots. Liquid metal is employed directly during the ESC LM process rather than the conventional consumable electrode. The process was simulated using infinite element software ANSYS. The results indicate that the conductive path of the ESC LM process is entirely different from the conventional electroslag remelting process. There are two conductive current paths: one conductive path is transformer→external current conductive mould→liquid slag→internal current conductive mould→transformer, and another conductive path is transformer→external current conductive mould→liquid slag→molten steel pool→liquid slag→internal current conductive mould→transformer. Current density, magnetic inductive intensity, electromagneti...

Oxide based ceramic conversion layers containing Ca and P were prepared on AZ91D Mg alloy by plasma electrolytic oxidation technique in Na2SiO3 and NaOH systems respectively. The conversion layers prepared in both systems were porous and grey white. The doping of Ca decreased the porosity of the conversion layers in Na2SiO3 system, while increasing the porosity of and the microcracks of the conversion layers in NaOH system. The conversion layer prepared in NaOH system was composed of MgO, and the one prepared in Na2SiO3 system was composed of Mg2SiO4 and MgO; P and Ca only existed in the form of amorphous state in the conversion layer. The doping of Ca decreased the relative content of P while increasing the relative content of Ca in both conversion layers. The ceramic conversion layers in both systems improved the corrosion resistance of the AZ91D Mg alloy in 0·9%NaCl solution by one or two orders of magnitude.

A new chromium free zinc–phosphate–molybdate composite conversion coating on AZ91D magnesium alloy has been developed using an acidic bath mainly containing zinc phosphate, sodium molybdate and sodium fluoride. The examinations of the microstructure and phase compositions reveal that the composite conversion coating is composed of nanocrystalline metallic Zn, Zn3(PO4)2.4H2O and MgMoO4. It has been found that the addition of molybdate in the conversion bath can refine the microstructure of the composite conversion coating and eliminate the formation of microcracks. Corrosion tests demonstrated that the zinc–phosphate–molybdate composite coating possesses a better corrosion resistance than conventional zinc–phosphate conversion coatings in 3%NaCl and NaOH (pH 13) solutions. This newly developed composite conversion coating has a low weight loss during electrocoating process and can effectively improve the adhesion and corrosion resistance of the electrocoat on AZ91D alloy.

The pressure is one of the basic parameters which greatly influences the metallurgical reaction process and solidification of steels and alloys. In this paper the history and present situation of research and application of pressurized metallurgy, especially pressurized metallurgy for special steels and alloys have been briefly reviewed. In the following part the physical chemistry of pressurized metallurgy is summarized. It is shown that pressurizing may change the conditions of chemical reaction in thermodynamics and kinetics due to the pressure effect on gas volume, solubility of gas and volatile element in metal melt, activity or activity coefficient of components, and change the physical and chemical properties of metal melt, heat transfer coefficient between mould and ingot, thus greatly influencing phase transformation during the solidification process and the solidification structure, such as increasing the solidification nucleation rate, reducing the critical nucleation radius, accelerating the solidification speed and significant macro/micro-structure refinement, and eliminating shrinkage, porosity and segregation and other casting defects. In the third part the research works of pressured metallurgy performed by the Northeastern University including establishment of pressurized induction melting (PIM) and pressurized electroslag remelting (PESR) equipments and development of high nitrogen steels under pressure are described in detail. Finally, it is considered in the paper that application of pressurized metallurgy in manufacture of high performance special steels and alloys is a relatively new research area, and its application prospects will be very broad and bright.

F− is used widely as an additive in the electrolyte solutions during the plasma electrolytic oxidation (PEO) of Mg alloys. The goal of this work was to investigate effects of sodium fluoride (NaF) on the structure and corrosion resistance of the ceramic coatings containing Ca and P on AZ91D (UNS M11916) Mg alloy using the PEO technique. The phase composition, morphology, and the element distribution of the coatings were studied using x-ray diffraction, scanning electron microscopy, and energy-dispersive spectroscopy. The corrosion resistance of the coatings in the simulated body fluid (SBF) was examined using electrochemical impedance spectroscopy (EIS) and the polarizing curve methods. The results show that the coating was composed mainly of magnesium oxide (MgO), which was increased with a dosage of NaF. Ca and P also existed in the coating. The coating had a two-layer structure: the outer layer was loose and porous and the inner layer was comparatively dense. There were many microholes on the ...

We report an intense room-temperature blue upconversion in Tm3+∕Yb+3-codoped Ga2O3–GeO2–Bi2O3–PbO(PbF2) glasses upon excitation with a convenient 980nm laser diode. Effects of PbF2 doping on the thermal stability, structure, and upconversion properties of Tm3+∕Yb3+-codoped gallate-germanium-bismuth-lead glasses have been investigated. We find that the presence of PbF2 provides two potentials: shortening the ultraviolet cutoff band and decreasing the phonon energy of host glasses. The blue-upconversion intensity has a cubelike dependence on incident pump-laser power, indicating a three-photon process. Energy-transfer process and nonradiative phonon-assisted decay could be responsible for the population of the G41 emitting level of the Tm3+. The results indicate the potential possibility towards the development of an oxide-based blue-upconversion glass-fiber laser.

Intense blue-upconversion in Tm3+∕Yb3+-codoped gallate–bismuth–lead glasses has been achieved under an excitation from a commercially available 980nm laser diode. Energy transfer processes and excited-state absorption account for the population of the G41 emitting level of the Tm3+. Although the addition of GeO2 has enhanced the glass thermal stability, the phonon mode associated with vibration of GeO2 has almost no influence on the blue-upconversion intensity and the radiative lifetime of H43 level. The dependence of the phonon energy of the host on contributions from multiphonon decay on the fluorescence has been discussed. Significant enhancement of the blue-upconversion has also been observed in gallate–bismuth–lead glasses with the incorporation of PbF2 content.