Continuous casting, initially introduced in 1840, is an attractive method in mass producing semi-finished metal shapes (slabs, blooms, and billets) from molten metal. More than 50% of current world’s steel production is produced by continuous casting. Today, annually 750 million tons of steel in the steelmaking operation, 20 million tons of aluminum and many tons of other alloys are directly cast from molten metal by continuously casting method [1]. This paper presents a short review over the processes in consciously cast steel.

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The microstructure of steel is responsible for the macro-behavior of steel or in other words steel’s material properties. Surface microcracks and internal flaws can be introduced to steel microstructure during solidification. The soundness of the steel is altered by formation of flaws and microcracks in casting production line. Additive elements to molten steel and chemical element and alloys in the iron slag may produce indigenous and exogenous inclusions in the microstructure. The presence of the inclusions in the microstructure changes the cleanliness of the steel and affects the material properties of the steel products. This paper is a review of literatures on the sources of formation of inclusions and flaws in the as-cast steel and the effect of these defects on the microstructure properties.

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The influence of solution annealing heat treatment on the microstructure and hardness of Hadfield steel containing up to 3.16% chromium and 0.15% nitrogen was investigated.
Furthermore, the effects of chromium additions on the hardness and microstructure of austenitic manganese steels in the as-cast and heat-treated conditions have been studied. The true stress-true strain response of nitrogen alloyed austenitic manganese steel with chromium additions in the as-cast and heat treated conditions under compression loading was also studied. The microstructural observations on the as-cast and heat-treated steels with chromium additions revealed the stability of austenite phase in the as-cast state deformation with precipitation of carbides and carbonitrides on the grain boundaries. These precipitates increase by increasing true strain and chromium content.
2² factorial design was used to investigate the contribution effect of chromium additions and true strain on hardness of austentic manganese steel as cast and after heat treatment. The contribution of both chromium additions up to 3.16%, true strain rate up to 0.4, and the interaction combination effect of them were determined of cast and heat treated austenitic manganese steel. The regression models were built up to identify the hardness as function in chromium additions and true strain rate of both cast and heat treated austenitic manganese steel.

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The effect of direct reduced iron (DRI) addition in metallic charge on the different steel making parameters and consumption figures have been studied. Data obtained from industrial heats carried out in 185-ton electric arc furnace (EAF) were used to study. The present study carried out in a wide range of DRI percentage, 0 - 50% of metallic charge, and the results have been statistically analyzed to correlate the percentage of DRI with the different consumption figures of electric energy, oxygen, coke and fluxing materials. In addition, the influence of DRI percentage on contents of tramp and detrimental elements affecting on steel quality has been also investigated.
The results reveal improving the steel quality by increasing DRI percentage, as the tramp elements (Cu, Sn, Ni, Cr) and detrimental elements (P, S) and also nitrogen, all decrease by increasing the percentage of DRI in the metallic charge. On the other hand, the increase in DRI percentage leads to increase in the consumptions (per ton of liquid steel) of electric energy, oxygen, coke and fluxing materials. Furthermore, the metallic yield decreases and the power on time and hence the tap-to-tap time increase as DRI percentage increases. With using higher DRI percentage in the charge, the yield strength and ultimate tensile strength of produced hot rolled bars of low carbon steel slightly decrease whereas elongation increases.

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Factorial design was used to investigate the contribution effect of cooling rate of stage between rolling and coiling and cooling rate after coiling on grain size, pearlite lamellar spacing, mechanical properties and hardness of hot rolled narrow 65Mn strip. The contribution of both cooling rates before and after coiling process, and the interaction combination effect of both rates were determined for each measured property. The regression models were built up to identify grain size, pearlite lamellar spacing, mechanical properties and hardness as a function in cooling rates before and after coiling process.
It was found that the contribution effect of cooling rate before coiling on grain size growth, enlargement of pearlite lamellar spacing, Ultimate Tensile Strength (UTS) and elongation is negative with different magnitude and it has positive effect on Yield Strength (YS) and hardness. Cooling rate after coiling has negative effect on grain size growth, enlargement of pealite lamellar spacing and elongation while it has positive contribution on UTS, YS, and hardness. The interaction combination effect of both two rates has very small positive contribution on YS and elongation, it has small positive effect on grain size growth, enlargement pearlite lamellar spacing, and it has large negative contribution on UTS and hardness. Factorial design technique is a successful technique to analysis the effecting parameters.

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This work aims at studying the change in constituent phases of High Manganese High Aluminum content steel through isothermal ageing and their effect on the plastic behavior of the produced steels. Optical and scanning electron microscope were employed for observing the significant change in microstructure at different heat treatment regime. XRD was applied to detect the major phases after isothermal process. Three samples with different phase consitituents were subjected to compression test. The results refer to the decomposition of γ-austenite into β-phase (B2, DO3), β-Mn, K-carbide is widely changed as a result of isothermal ageing process. The plastic behavior and strain-hardening property are improved linearly with k-carbide fraction. A bit enhancement of hardness has been observed with increasing k-carbide fraction after isothermal ageing process.

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In virtual design of hot stamping, the reliable description of the material flow behaviour is an important input to ensure accurate estimations of the final shapes of parts. Currently, to characterise the hot stamping material’s flow behaviour at elevated temperatures, tensile and upsetting tests are available. The focus of this article is on the determination of the flow curves of manganese-boron steel at elevated temperatures based on upsetting tests. The measurement of material flow properties directly out of the upsetting tests still remains a complex task due to its non-uniaxial nature. Therefore, traditional methods to calculate flow curves out of such measurements are not necessarily appropriate. It requires a method which considers multi-axial stress states as well as non-uniform strain evolution. In that way the calculation of the flow curves is appropriate and it can provide reliable input for simulations of hot stamping. In order to interpret measurements and deduce flow properties more precisely, simulations using Finite Element Method (FEM) of the tests themselves are executed. Indeed in FE-models it is possible to account for complex boundary conditions such as non-uniform temperature fields, non-uniaxial stress states and friction between upsetting die and the specimen during the deformation. With use of inverse optimisation, based on the final geometry of the deformed specimen, Coulomb’s friction coefficient is estimated. It is demonstrated that an almost constant value of the friction coefficient is achieved, even after using many different types of strain hardening to describe the material behaviour in the FE-models. Finally, it is demonstrated that the deduced material flow curves with use of inverse optimisation are more accurate than that of the directly calculated out of experimental results.

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The H2/CO ratio in the reducing gas is one of the most important factors that affect the reduction rate of iron ore pellets in the direct reduction processes. The present study is focusing on the effect of H2/CO gas ratio on kinetics of direct reduction of iron ore pellets. The H2/CO ratio was in the range of 1.0-2.6 which simulates the reducing gas composition in different direct reduction technologies (Midrex, HyL, and Syngas based direct reduction). The reaction rate constants and the apparent activation energy of the reduction process were calculated for both of the experimental and mathematical regression model. The unreacted core shrinkage mathematical formulations are applied to determine the rate controlling mechanism. The highest regressions and the lowest deviations from straight lines were obtained by the application of the mathematical formulations that corresponded to the interfacial chemical reaction mechanism and mixed control of chemical reaction with gaseous diffusion mechanism. The comparison between the calculated apparent activation energy and the standard ranges indicated that the rate controlling mechanism is mixed of the interfacial chemical reaction and gaseous diffusion. The contribution of chemical reaction in the rate controlling mechanism increased as the H2/CO ratio increased. The reaction rate constants and the apparent activation energy values were found to increase as H2/CO ratio increased due to the higher diffusivity of H2 compared to that of CO gas.

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High strength medium carbon austenitic stainless steels have been developed through partial and total replacement of nickel by nitrogen. Stainless steels containing 0.4% carbon with different combinations of nickel and nitrogen were produced in 10kg induction furnace under different nitrogen pressures. The produced stainless steels were cast and hot forged and the total nitrogen was determined. Furthermore, the produced forged steels were subjected to either only solution treatment or solution treatment followed by ageing process.

Nonmetallic inclusions such as carbides and nitrides were separated by electrolytic dissolution. Nitrogen as nitrides was determined and soluble nitrogen was calculated. XRD technique was used to investigate the types of nonmetallic inclusions. The microstructure of produced stainless steels was observed and the grain size was measured. The tensile properties at room temperature were determined. The influence of grain size, total nitrogen, insoluble and soluble nitrogen on tensile strength was investigated. All produced stainless steels as-quenched were aged at temperatures range from 450°C to 950°C for different times. Hardness test was carried out for aged stainless steels and the optimum ageing conditions were determined.

After solution treatment of the investigated stainless steels at 1050°C, a great portion of alloy carbides and nitrides is observed to be taken into solution. Nitrogen in solid solution increases both yield and tensile strengths. At optimum ageing temperature, this portion in solution precipitates, mainly as Cr2N, was causing higher precipitation strengthening. The yield strength and ultimate tensile strength of the aged stainless steels were found to increase at average rates of 706 MPa/1 mass % nitrogen and 723 MPa/1 mass % nitrogen, respectively. On the other hand, the increase of nitrogen content deteriorates the steel ductility.

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The factorial design approach can be used to precisely estimate the effect of different parameters on the reduction process of iron oxide. In the current study, a 24 factorial design was used to significantly calculate the magnitude impact of manganese oxide and silica on the reduction yield of iron oxide which was reduced with H2 at 900-1100°C. A regression model was built on the experimental reduction results of pure iron oxide and iron oxide doped with either MnO2 (mass content of 6%) and/or SiO2 (mass content of 7.5%) at 900°C and 1100°C. The developed mathematical model was used to predict the reduction yield as a function of four parameters including MnO2 (mass content of 0-6%), SiO2 (mass content of 0-7.5%), reduction time (1.0-10 min) and temperature (900-1100°C). In addition, the effect of the interaction combination of different parameters (MnO2, SiO2, time, and temperature) on the reduction yield was estimated. The results showed that the reduction time has the highest positive effect on the reduction yield of iron oxide sinter followed by the applied temperature and then SiO2 addition. On the other hand, MnO2 exhibited the highest negative effect on the reduction yield of iron oxide followed by the combination effect of SiO2 with time and temperature. The interaction combination effect of MnO2 with temperature or MnO2-SiO2 with time and temperature on the reduction yield was very small. The regression model was applied to theoretically estimate the reduction yield of pure and doped iron oxide at 900-1100°C. The obtained values of the derived model are in a good agreement with the experimental results under different conditions.

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In the last two decades, the significant market demands for microalloyed steels have led to enormous efforts as regards the optimization of their properties. Following a national research program, the present work was scheduled to deal with a special grade of V-microalloyed steel. This grade was examined after a series of successive isothermal heat treatment to produce a variety of phase combinations (e.g., ferritic-martensitic, ferritic-martensitic-bainitic and ferritic-bainitic microstructures). Tensile and impact tests were performed to gain knowledge about the mechanical properties. The resulting microstructures were evaluated by means of SEM and optical microscopy. The results indicated that the corresponding tensile behaviour of the steels was strongly affected by microstructure and heat treatment parameters. Furthermore, the related ultimate tensile strength and impact values were broadly varied (750 to 1200 MPa and 5 J to 40 J, respectively) by the steels´ microstructure and chemical composition. The corresponding fracture surfaces were found to vary with the steel´s microstructure.

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The influence of accelerated cooling and coiling temperature is studied in a microalloyed steel grade in order to investigate the strengthening owing to phase transformation in the presence of microalloying elements. A Nb-V microalloyed steel grade was deformed in the austenitic range followed by controlled quenching to simulate rolling and runout table cooling conditions. Cooling rate was varied from 100 to 150 °C/sec, while coiling temperatures were varied between 475 to 625 °C, with 25 °C step. Decrease in transformation temperature in conjunction with accelerated cooling resulted in non-equiaxed ferrite structures with array of phase morphologies. Intermediate transformation temperatures produced increase in strength concurrent with observed peak broadening in X-ray diffraction. In addition, microstructural modelling is done using Quench properties module of JMatPro under experimental conditions.

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