The calcium treatment was the most popular and effective method to modify inclusions in the molten steel. For the modification of oxide inclusions, the partial liquid inclusion was suggested to avoid the nozzle clogging caused by solid inclusions, as well as the formation of hardly removed large liquid inclusions in the Al-killed Ca-treated steel. During the calcium treatment process, the added Ca firstly modified Al₂O₃ inclusions to liquid CaO–Al₂O₃ for T.Ca<T.O in steel, while the composition of liquid CaO–Al₂O₃ was little influenced by the T.Ca/T.O ratio for T.Ca>T.O in steel. Meanwhile, the CaS/(CaO+Al₂O₃) in inclusions increased with a higher (T.Ca-T.O)/T.S ratio in steel. For the sulfide inclusion modification, the calcium treatment retarded the precipitation of linear sulfides along the grain boundary of the steel matrix and lower the deformability of CaS during the rolling process due to the higher hardness of CaS. The length of sulfides increased with a higher T.Ca content, while it decreased with lower T.O and T.S contents in steel. Influence factors of the calcium yield of the calcium treatment were summarized to steadily increase the calcium yield, including steel composition, temperature, feeding speed, etc. An empirical equation between the [Ca], T.Ca, T.O, T.S, and [Al] was fitted to predict the [Ca] content in steel. During solidification and cooling processes of Al-killed Ca-treated steels, inclusions transformed from liquid CaO–Al₂O₃–MgO in the molten steel to Al₂O₃–MgO–CaS in the solid steel due to the equilibrium change. Moreover, the focus on the calcium treatment in the future was proposed.

Steel used for wind power must have high fatigue resistant properties because of its strict service conditions. The large-size (≥20 µm) CaO–MgO–Al₂O₃ (CMA) inclusions can lead to stress concentration and significantly reduce the service life. However, the occurrence of large-size inclusions is occasional and closely related to many factors, making it difficult to trace and control such inclusions. Herein, taking 42CrMo steel as the research object, we clarified the formation mechanism of CMA inclusions and determined its correlation with the steelmaking process. It was found that nearly all the large-size CMA inclusions in the bloom are located in the liquid region (<1873 K) of CaO–MgO–Al₂O₃ phase diagram. The results of inclusions automatic scanning showed that the low-melting-point CMA inclusions mainly form during VD treatment. Thermodynamic calculation revealed that the Al in molten steel reacts with CaO in slag under high vacuum condition, resulting in continuous diffusion of Ca from slag to steel. Then the dissolved Ca reacts with the existing solid or solid-liquid two-phase inclusions, leading to the increase of CaO in inclusions. The modified inclusions have good wettability with molten steel, and finally inherit to round bloom. Furthermore, the control policy to decrease the reaction extent between Al and CaO under vacuum condition was put forward in light of thermodynamic calculation. Under the same ratio of CaO/SiO₂, with Al content increases, the corresponding Al₂O₃ content should be increased. Under the same Al₂O₃ content, with Al content increases, the ratio of CaO/SiO₂ should be decreased.

Self-healing function in the ceramic-based composites is one of unique characteristics to improve the strength reliability by oxidation of dispersoids. Metallic iron particles are one of base metal and easy to oxidize at air atmosphere. The objective of this study is to investigate the crack disappearance behavior of Fe-dispersed alumina composite ceramics by high-temperature oxidation.

Surface cracks were introduced on Fe/Al₂O₃ samples. The samples were heat treated at 700–900°C for 1–24 h in air. Crack lengths were measured before/after heat treatment and the crack disappearance rates were calculated. The introduced cracks disappear by the formation of Fe₂O₃. The formed oxides appear to have a spider-web shape. The mesh diameter of spider-web is approximately 1–2 µm, which corresponds to the Al₂O₃ grain size of sintered body. The crack disappearance rate increases with increasing heat treatment temperature and time. From the temperature dependence of the crack disappearance rate, the apparent activation energy for the crack disappearance is found to be Q = 160 kJ/mol. The value of activation energy in this study is lower than the values of volume diffusion of Fe ions through Al₂O₃. It implies that grain boundary diffusion of Fe ions contributes to the crack disappearance.

Unraveling the critical granular size in various chemical processes involving granular materials, such as blast furnace ironmaking process, holds significant importance in optimizing production efficiency. This study focuses on investigating the critical granular size by employing six mono-sized sinter packed beds, which are reduced at elevated temperature up to 1400°C. Quantitative analysis reveals two distinct behaviors, inconsistent shrinkages between 1200–1350°C and size-dependent rates of pressure drops approaching their maximum values. These results highlight the presence of a critical granular size between 2 mm and 4 mm under present experimental conditions. To elucidate these findings, a hypothesis based on the competition between the active role of liquid generation and the passive role of liquid holdup is proposed, and the strategies for utilizing the small particles below the critical size in binary-sized beds are given full discussions. This work aims to provide laboratory-scale experimental insights into the critical granular size effect and will shed light on exploring the critical granular size in industrial-scale processes involving granular materials in the future.

Recently, there has been a rapid increase in the discovery of ancient iron smelting furnaces on the Korean peninsula, which are assumed to have been in operation for a long period of time from the Proto Three Kingdoms Period to the Three Kingdoms Period. The iron smelting furnaces are concentrated in the central and southeastern regions of the peninsula, which has led to discussions regarding their timing and regional characteristics. In this study, we focused on the deep circular pit (Furnace pit), which corresponds to the underground structure of the furnace, and various types of pits (Forepit) for collecting pig iron and slags that flowed out from the furnace. We examined the regional and chronological characteristics of the iron smelting furnaces by reconstructing the three-dimensional structure of the furnaces. As a result, it was confirmed that the iron smelting furnaces changed from a semi-underground type, in which the furnace floor was located below the ground surface, to an above-ground type, in which the floor was located at the same level as the ground surface, and that the forepits changed from a horizontal to a vertical structure. These changes were the result of technological transformation and the ingenuity of the craftsmen who carried out the iron-making operations, in response to the higher quality and quantity of the iron produced.

Utilization of biomass, which is regarded as a carbon neutral fuel, has been discussed to decrease in the carbon dioxide emission from the ironmaking processes. Previous reports insisted the volatile matters in the uncarbonized biomass contributed to the reduction of iron ore at low temperature. However, its mechanism has not been explained by the pyrolysis reaction of biomass components. In this study, the low temperature reduction behavior of the carbon-iron ore composite using uncarbonized biomass was compared with that using its components such as cellulose and lignin. Furthermore, the effect of volatile matters in the biomass on the reduction of iron ores was examined.

The composite using uncarbonized biomass was started to be reduced at 400–450°C by CO produced by pyrolysis of cellulose. As the temperature was further increased, iron ore was reduced to metallic iron at approximately 800°C by hydrogen produced by the interaction between cellulose and lignin. The metallic iron may contribute to the gasification of biomass char and fast reduction reaction as the catalyst.

In order to explore the formation process of brittle layer, the dissection investigation of actual BF was analyzed, the penetration experiments were carried out, the cause of brittle layer formation in carbon brick was summarized. The mechanism of dendritic penetration of molten iron was clarified, the kinetic model of penetration was established combined with the penetration mechanism. The results show that: The brittle layer is observed on the hot face of carbon brick, there are a lot of striated gaps in the brittle layer near the hot face. The penetration depth of molten iron increases with the increase of temperature and penetration time, the penetration velocity is relatively high at the beginning, then gradually decreases. The dendritic penetration of molten iron is a key common problem in carbon brick, it is easier to form at the junction of two phases in carbon brick. There are three paths for each branch of dendritic penetration, the penetration of the third path is extremely destructive to carbon brick owing to the elongation of penetration in this path is relatively large. The essence of the meniscus is the confrontation between the cohesion of molten iron itself and the adhesion between molten iron and carbon brick. The model calculation indicates that the adhesion force is relatively small, the key to prevent the penetration is to control the adhesion force between molten iron and carbon brick. The maximum penetration depth of molten iron can be evaluated through the penetration model.

A mathematical model was developed to simulate gas-metal-slag three-phase flow during the surging auxiliary slag skimming process. The flow in the ladle is computed using the large eddy simulation (LES). The Eulerian volume of fluid (VOF) model is used for tracking the interface of gas-metal-slag, and the Lagrangian discrete phase model (DPM) is used for describing the bubble plumes’ movement. The procedure of bubble coming out of the liquid and getting into the air is modeled using a user-defined function. Results show that when the lance position is too close to the back wall of the ladle or the injection volume is too large, it will increase the erosion of the back wall. The mean velocity of the splashing zone is much greater than that of the slag removal zone, and the velocity fluctuation is large, which is easy to cause splashing. In addition, the large injection volume will aggravate the occurrence of splashing and slag entrapment, resulting in excessive iron loss and severe liquid surface fluctuation, which is not conducive to improving the efficiency of slag removal.

In this work, the change in steel grade in a tundish of 20.3 tons with two exits employed from low to medium carbon grade steels is analyzed by numerical simulation, using multiphase flow modeling conditions in an isothermal state and non-isothermal, considering heat losses by radiation in the slag opening zone. The Tundish Volume Fraction (TVF) method determines the overlapping steel up to 10, 25, and 50% of the remaining steel. For non-isothermal cases, the temperature gradient over the incoming and old steel was 17 K. The model is validated through plant temperature measurements and steel heat losses at the tundish exits. The results indicate that heat transfer substantially modifies the fluid-dynamic behavior of steel. Likewise, the short circuit phenomenon is visible in the case of a 50% reduction of steel attributed to a non-reported elsewhere flow memory loss phenomenon once the tundish work level was recovered during the simulation under isothermal conditions. On the other hand, the intermixed steel is reduced as the amount of old steel remaining in the tundish is reduced; in addition, for the same case under isothermal conditions, the calculation of this amount is higher by a value close to 3 times that calculated under non-isothermal conditions.

The classification method of steel surface defects with high performance and easy to be embedded in the detection equipment is one of the keys to ensure the quality of hot rolled strip. However, the development of deep convolutional neural networks (CNNs) in many real-world applications is largely hindered by their high computational cost, especially in industrial production, although it has good classification accuracy compared with machine learning-based methods in image recognition. Therefore, in this work, we present a lightweight network FCCNet based on the convolutional neural network to facilitate its application in the detection system. To compensate for the accuracy loss caused by the network downsizing, a knowledge distillation (KD) method using a larger trained network (teacher network) to teach a smaller network (student network) is adopted to improve the performance of our model. As a result, our method achieves a classification accuracy of 99.44%, precision of 99.46%, recall of 99.45%, and an F1 score of 99.45% on the NEU-CLS dataset, using only 0.03 MB parameters. These results show that the FCCNet is lighter than other existing classic CNNs with good performance for surface defects classification of hot-rolled steel strip, and it has the potential to be applied in the actual production line.

The reducibility and mechanical properties of iron ore sinter in blast furnace is critical to effective plant operation. The reduction reaction of sinters progresses heterogeneously owing to microstructures with various mineral phases and pore networks. The reduction process was investigated by semi-microbeam synchrotron X-ray multimodal analysis. Heterogeneous chemical state evolution of Fe and trigger sites of crack formation were visualized using two-dimensional Fe K-edge X-ray absorption near-edge structure analysis and were discussed based on reduction gas transfer. The elemental composition map and X-ray diffraction microanalysis were also combined to reveal the microprocesses during the reduction, such as calcium ferrite decomposition and crystal grain growth.

In metal rolling processes, internal holes or cracks can result in unqualified products. This paper evaluates the possibility of cracking in three-roll planetary rolling of bismuth-containing stainless steel bar by combining experiments, finite element simulations, and theoretical modeling. Stress-strain data obtained from hot compression experiments were used to draw hot processing maps after modification. The prediction results of several standard ductile fracture criteria were compared, and it was found that the Ayada criterion could accurately predict the size and location of rolled section cracks during the rolling process. The study also investigated the effects of three key forming parameters: billet temperature, strain rate, and friction coefficient on the percentage of damaged area. Results showed that billet temperature had a significant influence on crack initiation followed by strain rate. A mathematical model with damage value as its target was established using a three-way cubic polynomial regression analysis for these parameters’ interaction effect on crack initiation and development. By calculating extreme values for this function based on optimized process parameters, a set of optimum processes with minimal risk for initiation cracking was obtained. Field rolling results confirmed no cross-sectional cracks according to these optimized process parameters.

The skidding between rolls and steel strip is more likely to occur in the cold rolling process in accordance with an increase of tensile strength of the material following the customers’ demand. This happens when the work rolls rotates faster than the longitudinal speed of the strip at the exit of the roll-bite. This phenomenon leads to not only the strip surface defection but the thickness nonuniformity and thus the aim of this study is defined to clarify the mechanism behind the phenomenon. In order to clarify the factor causing the skidding, the cold rolling experiments using two different steel grades, namely the Low Carbon Steel (LCS) and the Advanced High Strength Steel (AHSS) having respectively 270 and 980 MPa tensile strength, have been conducted, which was then assessed by the numerical analyses and the comparison of the forward slip characteristics was made between these two steel grades. It has been revealed that the forward slip is decreased under the low friction coefficient condition with an increase of the rolling reduction. In addition, the friction coefficient of the AHSS is lower than that of the LCS. The existence of the micro-plasto-hydrodynamic lubrication in the AHSS suggests a decrease in friction coefficient, which results in the exhibit of skidding, which was not observed in the LCS.

The components of the powertrain that transmits power to an engine drive have been fabricated with various welding techniques, such as laser welding and gas metal arc welding. To reduce the weight of these components and hence the energy consumption of automobiles, the authors propose ring-mash welding as a component-joining method, which works by solid-phase bonding. The specimens were raw SCM415H chromium molybdenum steel, an alloy steel provided for machine structural use. Temperature and pressure are important parameters of joining. The proposed ring-mash welding relies on Joule heat generation. The bonding area softens during heating, facilitating solid-phase bonding. To clarify the bonding mechanism of ring-mash welding, the bonding condition was investigated under different applied pressures and electric currents. Although spatter was generated during bonding under excessive heat conditions, it was suppressed by increasing the applied pressure. The bonding strength depended more on the current than on the applied pressure. A small continuous gap appeared at the bonding interface under low current, which became intermittent, and eventually disappeared as the current increased. The bonding area was quenched by the temperature rise and rapid quenching during the joining process and an altered microstructure with increased hardness was formed. The optimal bonding conditions were determined.

ISO 12135, which describes the method for the fracture toughness test, requires that the specimen temperature be held at the test temperature for 30 s per 1 mm of specimen thickness before testing to ensure a constant temperature through the full specimen thickness. However, this requirement results in an inefficient practice when testing thick specimens; e.g., a specimen with a thickness of 100 mm must be held at the test temperature for 50 min. Considering the high thermal conductivity of metals, the authors considered this requirement is excessively conservative, and therefore developed a new decision method for the temperature control time based on a heat transfer analysis. In the proposed method, the temperature control time is decided based on the material properties and temperature condition as well as the specimen thickness, and the required time is much shorter than that required by the ISO standard for general purposes. Cooling tests were conducted to investigate the effectiveness of the proposed method. The temperature history was measured at the surfaces and mid-thickness, and as a result, the proposed method showed more rational required times than the ISO requirement. The proposed required time was overestimated in most tests, however, these errors are significantly smaller than that of conventional one. Although some results were underestimated by a few seconds, this is not a problem because the values were sufficiently small. Based on these results, we concluded that the proposed method is more appropriate than the requirement in the ISO standard.

Friction stir welding (FSW) was applied to a 10 mm-thick plate for the Fe-15Mn-10Cr-8Ni-4Si seismic damping alloy. A sound FSW joint was obtained successfully without macro-defects such as groove-like defects and tunnel holes. However, small pores with diameters of 1–5 µm were formed owing to the wear of the FSW tool during the FSW. The decrease in the heat input suppressed the tool wear. Consequently, the distribution of small pores was limited to the border of the stir zone at the advancing side under smaller heat input conditions. The stir zone of the FSW specimen produced at 125 rpm showed a higher tensile strength of 759 MPa owing to the grain refinement and the high elongation of 50% compared with the base metal. In addition, the stir zone exhibited a remarkable fatigue life of 9723 cycles. This was higher than that of the base metal (8908 cycles). Grain refinement occurred by discontinuous dynamic recrystallization (DDRX) via high-angle boundary bulging and direct nucleation in the high-dislocation area. The increase in the heat input suppressed the DDRX owing to the promotion of dynamic recovery.

The aim of this paper is to predict the deformation-induced martensitic transformation of the retained austenite in steels under various deformations, including loading-path changes, by using mesoscopic finite element analyses (FEAs). First, a TRIP steel was subjected to monotonic uniaxial tension and compression, as well as a couple of two-stage loadings to investigate the effect of loading direction and loading-path on transformation behavior experimentally. In monotonic loading, tension induced transformation at higher rate than compression did. Whereas, in two-stage loadings, the transformation progress was suspended immediately after the start of secondary loading. As the secondary tension proceeded, the transformation resumed and gradually accelerated toward the transformation rate for monotonic tension. These experimental results were analyzed by FEAs with a two-dimensional image of microstructure. The transformation rates under monotonic loading are well predicted by the simulation. It is also suggested that the difference in the transformation rate between tension and compression is mainly due to the volumetric expansion associated with martensitic transformation, and that the transformation behavior of the untransformed austenite is dominated by the distribution of the hard transformed martensite. In addition, the prediction of the transformation rate in secondary tension after pre-compression required the consideration of back stress in the austenite. The reproducibility of the transformation behavior just after the onset of secondary deformation was improved by the hypothesis that the equivalent value of back stress tensor at the transformation needs to exceed its maximum value in the past.

The ancient copper smelting was simulated to produce molten Cu–Fe alloys without Fe lump from Chile copper ore powder and limonite powder at 1300 to 1350°C. Using the same furnaces and the same conditions of operation for copper smelting, the ancient ironmaking was performed to produce molten Fe–C alloy. The atmosphere in the furnaces was controlled by the redox reaction of Fe and FeO. For the copper smelting, the oxygen partial pressure was higher than the equilibrium value of Fe and FeO, and for the ironmaking it was lower than the equilibrium value. From these aspects, the technical continuity from ancient copper smelting to ironmaking was clarified.

In this work, the effect of the slag phase on dephosphorization in BOF (basic oxygen furnace) is explored by industrial practical experiments. The research results show that the final dephosphorization rate is related to the phase of slag rather than basicity and T.Fe content in slag. The correlation between the dephosphorization ability of slag and the proportion of liquid phase (phase B) and phosphorus-containing solid solution phase (phase A) in the slag is much higher than that of RO (MgO·FeO, MnO·FeO) phase (phase C). The phosphorous partition fitting by using the minimum second-order multiplication proposed in this work is compared with the equations suggested by Healy and Ogawa. The comparison result shows that the dephosphorization ability of slag can be well predicted by analyzing the proportion of liquid phase and phosphorus-containing solid solution phase in slag, and the mechanism of the influence of the slag phase on dephosphorization is discussed.