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The electroslag casting with liquid metal (ESC LM) is a new technology for producing composite roll of high quality based on electroslag metallurgy. In the present work, a two-dimensional quasi-steady state mathematical model of just one half of the ESC LM facility is developed due to the axial symmetry. Influences of operating voltage and pouring temperature on the heat transfer of the composite roll system have been studied. The Lorentz forces and Joule heat are combined with the turbulent flow and energy equations via additional source terms in these equations by the user-defined functions (UDF) based on Fluent software. Simulation results indicate that the distributions of electric potential, current density, Lorentz forces, and Joule heat are concentrated on the upper area of slag bath and a much shallower molten steel pool is obtained. By using the current carrying mold, the heat transfer from slag bath and superheat of the molten steel pool are lower than the conventional ESR process, which is beneficial to a vertical crystallization and an excellent bonding interface between the roll core and working layer of the composite roll. The study of this paper gives us a better understanding of the ESC LM process.

The uniform and intergranular corrosion behavior of two kinds of nickel-free and manganese alloyed high nitrogen stainless steels (HNSSs) were investigated. A type of 316L stainless steel (316L SS) was also included for comparison purpose. Both solution annealed (SA) and sensitization treated (ST) steels were examined. It was found that the SA HNSSs had much weaker resistance to uniform corrosion compared to the SA 316L SS. The addition of molybdenum, to some extent, improved the uniform corrosion resistance of the HNSSs. The sensitization treatment had little influence on the uniform corrosion resistance of all the steels. The HNSSs showed an obvious susceptibility to intergranular corrosion, in particular the ST HNSSs. The intergranular corrosion rates of the sensitized HNSSs were much higher than that of the sensitized 316L SS. The degree of interganular attack for the ST HNSSs was much more serious than that for the 316L SS. The addition of molybdenum obviously improved the resistance of the ST HNSSs to intergranular corrosion. The double loop electrochemical potentiokinetic reactivation tests also proved that the HNSSs were rather susceptible to the sensitization treatment compared to the 3 16L SS. The relatively weak resistance of the HNSSs to uniform and intergranular corrosion may be due to high manganese promoted anodic dissolution. The improvement of uniform and intergranular corrosion resistance caused by the addition of molybdenum could be attributed to the synergistic effects of molybdenum and nitrogen in the HNSSs on the fort-nation and stability of passive film.

The thermophysical properties of premelted slag and synthetic slag were measured under laboratory conditions. The tests of liquid steel desulfurization using CaO-Al2O3-SiO2-MgO series premelted slag and a synthetic slag have been carried out with a MoSi2 electric resistance furnace. It was shown that the former had better desulfurization capacity than the latter. Thus, the premelted slag was chosen to be the desulfurizer for RH-KTB refining. A plant trial at a 250 ton RH-KTB unit used the premelted slag as desulfurizer and the average initial sulfur content in steel was 41.9 × 10−6. The results showed that the mean sulfur content in steel at the end of RH-KTB refining had decreased to 30 × 10−6, the lowest sulfur content was 22 × 10−6, and the mean desulfurization efficiency was 28.1%.

The effect of the refining slag composition on the inclusions in molten steel was studied in MgO crucible by using MoSi2 furnace. The experimental steel was heavy rail steel and Si-Ca-Ba alloy was used as the deoxidizer. The results showed that the total oxygen content of steel, and the total quantities, total areas and average radius of inclusions decreased with the increased basicity of refining slag. The total quantities and total areas of inclusions were the least when Al2O3 content in refining slag was between 13% and 20%, while the proportion of small inclusions increased when Al2O3 content was higher than 20%. The contents of SiO2 and Al2O3 in inclusions were affected directly by the SiO2 and Al2O3 contents in refining slag, and it was very remarkble when the slag composition was CaOAl2O32SiO2. Therefore, it's feasible to control the composition of inclusions by controlling the composition of refining slag.

Nitrogen solubility in the austenitic stainless steel melts was measured in the laboratory by bubbling nitrogen gas under different partial pressures of nitrogen and temperatures. A new thermodynamic model for the calculation of nitrogen solubility in molten stainless steel in a wide range of alloy concentrations, temperatures, and pressures has been successfully established by introducing a new term for the effect of pressure on the nitrogen activity coefficient. The calculation results were in good agreement with the measured values. The influences of temperature, nitrogen partial pressure and chemical composition on the nitrogen solubility in molten stainless steel are discussed based on the calculated results. It is possible to produce high nitrogen steels at normal pressure by optimizing the design of the alloy composition and controlling the lowest melting temperature from a thermodynamic point of view.

Hot deformation behavior of high nitrogen martensitic stainless steel 30Cr15Mo1N is investigated by isothermal compression tests at the temperature range of 900–1250 °C and the strain rate range of 0.01–10 s−1. The results indicate that the activation energy of this alloy (503.5 kJ mol−1) is higher than that of conventional martensitic stainless steels. The developed Arrhenius-type constitutive equation considering strain compensation can predict flow stress of 30Cr15Mo1N with good consistency. The critical conditions for initiation of dynamic recrystallization (DRX) are determined based on the strain hardening rate versus flow stress curves. The DRX is inhibited and grain size decrease with increasing strain rate from 0.01 to 1 s−1. However, the fraction of DRX increased and grain size coarsened when strain rate is further increased to 10 s−1. Cr-rich M23C6 and M2N precipitated at grain boundaries at lower temperatures, which can effectively pin grain boundaries and, thereby retard or even inhibit the process of DRX. In addition, dislocations tangled and piled up around precipitates, thereby hindering dislocation movement. The influence of precipitates on DRX can be eliminated due to their dissolution at higher temperatures.

The cellular automaton-finite element (CAFE) model is used to simulate solidification structures of 19Cr14Mn0.9N high nitrogen steel under different solidification pressures. The effect of solidification pressure on model parameters is firstly investigated. After validation, this model is used to clarify the effect of solidification pressure on compactness degree with number of grains and primary dendrite arm spacing (λ1). The results show that increasing solidification pressure from 0.5 to 1.2 MPa exhibits a significant increment (200 W m2 K−1)) on heat transfer coefficient and slight change for other model parameters. The model validation indicates CAFE model can accurately simulate solidification structure under higher solidification pressure. Under higher solidification pressure, the primary dendrite arm spacing (λ1) of central equiaxed grain becomes smaller and the number of grains of the whole ingot increases obviously, revealing a further improvement on the compactness degree of ingot. At a given pressure, the decrement in the number of grains is obvious away from the edge of ingot. With increasing solidification pressure, a more significant increment in the number of grains exists at columnar grain zone than that at central equiaxed grain zone, suggesting a greater increasing tendency of compactness degree at columnar grain zone.

Electroslag casting with liquid metal (ESC LM) using current conductive ring has been developed. This technology is different from classical electroslag remelting (ESR) process. No consumable electrode is needed in the process. Liquid metal after refining is introduced into the mold directly. Current conductive ring instead of consumable electrode is the conductive unit for heating slag pool for the first time. Short collar mold and continuous withdrawal mechanism like continuous casting process are employed in the process. Conductive path of ESC LM process using current conductive ring is transformer current conductive ring liquid slag molten steel solid ingot base plate transformer. A mathematical model of electroslag casting process with liquid metal is developed for understanding the technology. Thermal field, voltage, and current density distributions in the system have been simulated, which are similar but different from conventional ESR process. Results of industrial trial indicate that there is no obvious macrosegregation and cracks in the industrial ingots produced by these methods. Ingot quality is equivalent to the conventional electroslag ingot. In addition, the production efficiency of ESC LM process is obvious higher than conventional ESR operation.