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ISIJ International Vol. 63 (2023), No. 4

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ONLINE ISSN: 1347-5460
PRINT ISSN: 0915-1559
Publisher: The Iron and Steel Institute of Japan

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ISIJ International Vol. 63 (2023), No. 4

Iron Ore Granulation for Sinter Production: Developments, Progress, and Challenges

Lele Niu, Jianliang Zhang, Yaozu Wang, Jian Kang, Sida Li, Changdong Shan, Zhen Li, Zhengjian Liu

pp. 601-612

Abstract

Iron ore granulation is an indispensable process in the production of sinter that can influence and regulate the yield, efficiency and quality. Although a great deal of research has been done on the granulation process over the past decades, we still need to think about the current and future development of this process, as sinter is still an essential raw material for ironmaking blast furnace today. This paper begins with a review of particle agglomeration theory development for sintering granulation, followed by a summary of existing granulation evaluation methods and indexes. The roles of iron ore, fuel, fluxes, and moisture in sintering granulation are also analyzed, and finally advanced granulation equipment and processes for industrial production, as well as their applications, are summarized. Correspondingly, the challenges in sintering granulation field are proposed to include: (1) Development of iron ore sintering industry; (2) Ore blending optimization based on synergistic coupling of granulation and sintering; (3) Optimization of granulation process and equipment; (4) Methods and tools for granulation scientific research. These issues will be tackled and overcome in the future by both steel enterprises and academic researchers, generating suggestions for future development in the field of sintering granulation.

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Iron Ore Granulation for Sinter Production: Developments, Progress, and Challenges

Influence of Slag Chemistry on the Dissolution of FeCr2O4 in CaO–SiO2–Al2O3–MgO Slag with Graphite Crucible

Yiyu Xiao, Kangji Wei, Lijun Wang, Shiyuan Liu, Xiaobo He, Kuochih Chou

pp. 613-621

Abstract

The effect of Al2O3 and SiO2 content and basicity (w(CaO) + w(MgO)/w(SiO2) + w(Al2O3)) on the chromite ore dissolution in CaO–SiO2–Al2O3–MgO slag system was studied under the condition of 1550°C. The results show that the increase of basicity (R = 0.54, 0.67, 0.82) results in the reduction of the dissolved amount and dissolution rate of chromite ore in the slag. The dissolved amount of Cr in lower basicity slag (R = 0.54) is about 1.5 to 2 times higher than that in higher basicity slag (R = 0.67, R = 0.82). The dissolved amount of Cr tends to increase when the Al2O3 mass content decreases from 20% to 15%. While as the Al2O3 mass fraction continues to decrease from 15% to 10%, the dissolved amount begins to decrease. This may be related to the viscosity of the slag. The spinel phase tends to form on the surface of the unreacted FeCr2O4, thus hindering the further dissolution of FeCr2O4. After starting to dissolve, the FeCr2O4 decomposes into FeO and Cr2O3 dissolving in the slag. The FeO in the slag is preferentially reduced to metal iron attached to the surface of the FeCr2O4. The main forms of Cr element in the slag are CrO and Cr2O3, and the proportion of these two depends on the composition of the slag and the experimental environment. The proportion of CrO in the slag with lower basicity is larger. In the experiment, the maximum solubility of FeCr2O4 in 60 min was obtained in the slag system with 45% SiO2, 15% CaO, 20% Al2O3 and 20% MgO.

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Influence of Slag Chemistry on the Dissolution of FeCr2O4 in CaO–SiO2–Al2O3–MgO Slag with Graphite Crucible

Inclusion Control of 15-5 PH High-strength Stainless Steel through Aluminum Deoxidation

Zhonghua Zhan, Guanbo Wang, Ruxing Shi, Weifeng Zhang, Yanling Zhang, Guoguang Cheng

pp. 622-630

Abstract

15-5PH high-strength stainless steel is an important alloy used for numerous critical components. Ultra-low oxygen content and inclusion control have become urgent problems that need to be addressed for the broad application of this steel. In this study, we investigate the thermodynamic equilibrium of Al–O and inclusion morphology of 15-5PH stainless steel to understand the basic mechanism behind the results obtained after commercial production of the alloy. The deoxidation behavior of 15-5PH stainless steel depends on the dissolved Al content ([Al%]). When [Al%] <0.001%, mixed Al–Si deoxidation occurs and the deoxidation product is Al2O3–SiO2–MnO–CrOx. When [Al%] ≥0.001%, simple Al deoxidation equilibrium is dominant and the deoxidation product is MgO·Al2O3. The formation of Al2O3–SiO2–MnO–CrOx, low melting point inclusions, and a MgO·Al2O3 interface layer reduces the activity of Al2O3, which is why the calculated results of Al–O thermodynamic equilibrium are higher than the experimental results. The measured results for the Al–O equilibrium demonstrate a relatively good agreement with the calculated values. This proved that the phases formed on the crucible surfaces were in equilibrium with the Al and O contents in the molten steels after holding for 120 min.

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Inclusion Control of 15-5 PH High-strength Stainless Steel through Aluminum Deoxidation

Solubility and Activity of Iron Oxide in Solid Solutions between Ca2SiO4 and Ca3P2O8 at 1573 K

Keijiro Saito, Yoshiaki Kashiwaya, Masakatsu Hasegawa

pp. 631-638

Abstract

Towards better understanding of fundamental dephosphorization slags of the FeO-CaO-SiO2-P2O5 quaternary system, this study aimed at clarifying the thermochemical properties of iron oxide in Ca2SiO4-Ca3P2O8 solid solutions. The solubility and activity of FeO in the solid solutions coexisting with CaSiO3 at 1573 K were determined by SEM-EDX analysis and a gas equilibrium method, respectively. Based on the present experimental results, the phase relationships could be explained that the solid solution of high FeO solubility coexists with CaSiO3 and liquid slag of low FeO content, while the solid solution of low FeO solubility coexists with CaO and liquid slag of high FeO content.

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Solubility and Activity of Iron Oxide in Solid Solutions between Ca2SiO4 and Ca3P2O8 at 1573 K

Influence of the Slag Rim on the Heat Transfer Behavior of a Mold

Wang Xingjuan, Guo Yinxing, Xiao Pengcheng, Zhu Liguang, Di Tiancheng

pp. 639-648

Abstract

To explore the influence of the slag rim on the heat transfer behavior of a mold, a slag rim was extracted from a stainless steel production factory for high-temperature continuous casting simulation experiments. The 2DIHCP (Two-Dimensional Inverse Heat Conduction Problem) two-dimensional inverse problem calculation model was used to analyze the heat transfer characteristics in the mold, and the temperature and heat flux distribution of the hot surface of the mold copper wall under different working conditions were investigated. The results showed that under a casting speed of 0.5 Â m/min, vibration frequency of 2 Hz, and amplitude of 10 mm, the seepage flow of the mold flux was 9.314 and 6.326 g with and without the slag rim, respectively, the thickness of the slag film was 2.1 and 1.3 mm, respectively, the temperature of the mold hot surface was 118.24 and 134.83°C, respectively, and the maximum heat flux density of the mold was 0.98 and 1.95 MW/m2, respectively. Through data comparison, when there is a slag rim, the amount of slag infiltration decreased by 32%, the thickness of the slag film decreased by 38%, the temperature of the hot surface of the mold increased by 14%, the heat flux density increased by 99%, and the internal crystal morphology of the slag film was complete. This indicates that the slag rim affects the heat transfer behavior in the mold by restricting the inflow of the mold flux and affecting the formation of the slag film.

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Influence of the Slag Rim on the Heat Transfer Behavior of a Mold

Comprehensive Evaluation Method for Cooling Effect on Process Thermal Dissipation Rate during Continuous Casting Mold

Kai-tian Zhang, Zhong Zheng, Jian-hua Liu, Liu Zhang, Da-li You

pp. 649-659

Abstract

Cooling in the continuous casting mold is the essential process of the molten steel solidifying into a slab shell. The synergistic relationship of casting state, process operation, continuous casting equipment, and other factors is complex and has a significant influence on thermal transfer in the mold. Therefore, a concept of “process thermal dissipation rate” defined by mold system thermal input and output was proposed in this work. The thermal input of molten steel was calculated through the casting temperature, and the slab residual thermal at the outlet of the mold was calculated by the solidification heat transfer model. Consequently, the thermal dissipation rate was calculated to quantify the multi-factor cooperative relationship of mold. The industrial case reflected that the thermal dissipation rates of three stable castings were 12.5%, 14.3%, and 18.8%, respectively, and all of them were obviously abnormal in unsteady casting such as start casting, changing tundish, and end casting. The results above indicated that the thermal dissipation rate could characterize the mold cooling target under the cooperation of complex factors and provide a new method for the dynamic evaluation of the mold system cooling effect with different casting states. Accordingly, the correlation analysis between superheat, casting speed, cooling water flow, and thermal dissipation rate revealed the synergistic influence law of multi-operation on mold cooling effect, which provided a new idea for the precise control of multi-process collaboration in continuous casting.

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Comprehensive Evaluation Method for Cooling Effect on Process Thermal Dissipation Rate during Continuous Casting Mold

Application of Variable Gauge Rolling Technology for Plate to Reduce the Head Impact

Zhijie Jiao, Chunyu He, Shiwen Gao, Xu Wang, Yongxiang Zhang, Lei Hao

pp. 660-669

Abstract

The Variable Gauge Rolling (VGR) technology is adopted for plate rolling. Two passes are treated as a group, with reducing the head reduction, increasing the tail reduction, to reduce the peak impact torque of the head, and give full play to the equipment capacity in the stable rolling stage to increase the pass reduction. The prediction models of plate width and length, rolling force and torque in VGR process are established. The using strategy of VGR are determined, and two methods for increasing reduction are put forward. The main body and head and tail sections of the rolled plate are calculated separated. The reduction corresponding to the target rolling torque is calculated by Newton iterative method, and pass schedule distribution of VGR process is shown. The VGR technology is applied for plate rolling process. The practical application shows that the influence of head impact in the plate rolling process can be reduced by using VGR. The torque amplification coefficient decreases linearly with the increase of gauge variation, and rolling passes number can be reduced through reasonable pass schedule distribution. The practical application shows that VGR can reduce the influence of head impact in the plate rolling process.

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Application of Variable Gauge Rolling Technology for Plate to Reduce the Head Impact

Optimum Water Content Estimation for Wet Granulation of Iron Ore Powders with Quicklime Binder

Shota Yokokawa, Hideya Nakamura, Tomotaka Otsu, Shuji Ohsaki, Satoru Watano, Shohei Fujiwara, Takahide Higuchi

pp. 670-677

Abstract

Wet granulation plays an important role in the processing of fine ore powder. Water content is a critical process parameter that determines the granule properties during wet granulation. However, in the ironmaking industry, various types of iron ore powder imported from different regions are blended, quicklime powder is added as a binder, and used as raw materials. Therefore, the physicochemical properties of the raw powders are not always consistent, which makes it difficult to determine the optimum water content. In this study, we present a method to determine the optimum water content using the agitation torque of wet ore powder blended with quicklime. First, we investigated the agitation torque for blending of various types and ratios of ore powders and quicklime. Two types of torque profiles were observed: a unimodal torque profile (Type I) and a torque profile with a plateau region (Type II). From the agitation torque profile, the characteristic water content (Wtorque) for estimating the optimum water content () was individually defined for the types I and II. The Wtorque was well correlated with the , regardless of the type and blending ratio of the original ore powders and quicklime. Finally, the optimum water content was estimated using the Wtorque. The estimated water content was confirmed to be in good agreement with the experimental results, demonstrating that the optimum water content for the wet granulation of fine ore powder with quicklime can be determined using agitation torque.

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Optimum Water Content Estimation for Wet Granulation of Iron Ore Powders with Quicklime Binder

Measurement of Exothermic Values of Casting-sleeve Materials Using an Ice Calorimeter

Hoang Nhu Ngo, Tsuyoshi Nishi, Hiromichi Ohta

pp. 678-686

Abstract

Defects, which are a major problem in casting, can affect the integrity of products. The processes used to reduce defects are often complex and increase manufacturing cost. Simulations are used to predict casting defects by analyzing the flow and solidification of the metal. However, simulation results often differ from actual casting results because appropriate values for the physical properties have not yet been experimentally obtained. Thus, in this study, an ice calorimeter was developed to measure the exothermic value of sleeve materials under rapid heating conditions. In the case where a thermocouple or radiation thermometer is used to determine the heater temperature, heat loss due to the lead wires or hole for temperature measurement cannot be avoided. Therefore, in this study, the heater resistance was obtained using current and voltage, and the temperature was determined using the resistance value. Although some variations were observed, the average measured exothermic values of all exothermic sleeve materials (1.2 kJ/g) matched approximately with those predicted by computer simulation using known thermophysical properties and experimentally obtained distributions of shrinkage cavities. Therefore, the exothermic values obtained in this study are considered valid.

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Measurement of Exothermic Values of Casting-sleeve Materials Using an Ice Calorimeter

In-situ Tensile Tester for Scanning Three-Dimensional X-ray Diffraction Microscopy

Yujiro Hayashi, Daigo Setoyama, Hidehiko Kimura, Yusuke Yoneyama, Keisuke Takeuchi

pp. 687-693

Abstract

Understanding of deformation and degradation of bulk metals under loading is necessary to improve the safety and environmental performance of mechanical components such as automobile parts. One of the key parameters in mechanical characterization is strain. Large strains that affect reliability can often be measured as changes in the crystallographic orientation. Electron backscatter diffraction (EBSD) method can measure strains only on the sample surface. However, since strain distribution varies under constrained conditions, nondestructive measurement inside the material is necessary to determine the actual mechanical response of the material.

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In-situ Tensile Tester for Scanning Three-Dimensional X-ray Diffraction Microscopy

Optimization and Improvement of the Projection Welding of Nut Based on Regression Analysis

Liwei Xing, Tianjian Yu, Jie Zhang, Xiaofang Xing, Hao Lu

pp. 694-702

Abstract

Since it has the advantages of high production efficiency, no shunting effects, and the ability to arrange solder joints on narrow locations without the limitation of point distance, projection welding of nut has been widely used in the automotive industry. This paper presents a new welding quality prediction and analysis framework by using regression analysis techniques. The relationship between the welding parameters (welding time, welding current and electrode force) and the Pull-out load of the M6 welded square nut and the 1.5 mm thick pickled hot-rolled steel was obtained by multiple nonlinear regression analysis. The influence and interaction of welding parameters on the Pull-out load are discussed. Using this regression model, a better combination of process parameters can be obtained. The mechanical properties, microstructure and microhardness of welded joints were also investigated.

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Optimization and Improvement of the Projection Welding of Nut Based on Regression Analysis

Effects of Welding Parameters on Sigma Phase Precipitation in 25Cr-5Ni-1Mo-2.5Cu-1Mn-0.18N Duplex Stainless Steel

Kenta Yamada, Takahiro Osuki, Kazuhiro Ogawa, Briony Holmes, Kasra Sotoudeh, Hongbiao Dong

pp. 703-709

Abstract

Recently, a new grade of duplex stainless steel, UNS S82551 (25Cr-5Ni-1Mo-2.5Cu-0.18N), has been developed to overcome the drawbacks in super martensitic stainless steel, conventional 22Cr and 25Cr super duplex stainless steels in terms of productivity and cost. The characteristic of the alloy design of UNS S82551 is to use Cu, instead of Mo, to ensure comparable corrosion resistance and strength. In addition, due to the significant decrease in Mo content, UNS S82551 is expected to be less sensitive to sigma phase precipitation during single or multi-pass welding compared with conventional and super duplex stainless steels. There is a trade-off between achieving better properties and avoiding sigma phase precipitation when increasing alloying elements such as Mo, Cr and Cu. In order to utilize the new UNS S82551 steel in industry for welding in a similar manner to conventional and super duplex stainless steels, the prevention of sigma phase precipitation is important. This work investigated the effect of weld thermal cycling on sigma phase precipitation behaviour in UNS S82551 welds. During thermal cycling in the tests, the amount of sigma phase for UNS S31803 and UNS S32750 increased with increasing the number of thermal cycles, and lower cooling rate, but it was not observed for UNS S82551. Based on the isothermal kinetics of sigma phase precipitation, the amount of sigma phase precipitated during thermal cycle can be predicted by applying the additivity rule to the physical model. The area fractions of sigma phase calculated have a good fit to the experimental ones.

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Effects of Welding Parameters on Sigma Phase Precipitation in 25Cr-5Ni-1Mo-2.5Cu-1Mn-0.18N Duplex Stainless Steel

Improved Cross-tension Strength of a Friction-element-welding Joint by Tempering Treatment Using Electric Heating

Sho Matsui, Kohsaku Ushioda, Hidetoshi Fujii

pp. 710-718

Abstract

Resistance spot welding is widely used in automobile assembly, but reduction of the cross-tension strength (CTS) is inevitable when using high-strength steel sheets. Therefore, we focused on joining high-strength steel sheets using friction element welding (FEW), which is mainly used to join steel sheets and aluminum alloy sheets, to improve the CTS. However, even when using FEW, the CTS decreases at the joint, when a high-carbon-content steel sheet is used as the lower sheet. This CTS decrease is presumed to be due to the low local ductility caused by the large hardness difference (ΔHn) between martensite (M) and ferrite (α) in the inter-critically annealed and quenched area during joining. The local ductility of the material having complex structure with hard and soft phases is affected by the structural morphology and ΔHn. Therefore, we attempted to improve the CTS by creating joints whose α of the inter-critically annealed and quenched area was equiaxed or acicular, and performed tempering treatment using electric heating to reduce ΔHn of this part. The results showed that ΔHn decreased at the annealed joint and the CTS improved. Furthermore, the highest CTS was observed at the joint having acicular α when tempering was performed. It was inferred that the reduction of ΔHn using electric heating improved the local ductility and CTS of the area. Furthermore, it was considered that the local ductility and CTS are also influenced by the α morphology.

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Improved Cross-tension Strength of a Friction-element-welding Joint by Tempering Treatment Using Electric Heating

Microstructure Characterization of Al–Si Coatings on Hot Stamping Steel under Different Heat Treatment Processes

Guibin Cui, Yang Meng, Xinhua Ju, Chunlian Yan

pp. 719-726

Abstract

The microstructures of Al–Si coatings under different heat treatment processes were characterized by scanning electron microscopy and transmission electron microscopy. The research shows that with the increase of heat treatment temperature, the Fe element in the matrix continuously diffuses into the Al–Si coating, the higher the heat treatment temperature, the more sufficient the diffusion, which promotes the evolution of the intermetallic compounds in the Al–Si coating. The EBSD Kikuchi pattern calibration and the transmission electron microscope multi-band axis calibration method can accurately determine the various phases of the Al–Si coating at different heat treatment temperatures, especially the phases with the same or similar crystal structure. The phases of Al–Si coating without heat treatment are Al, Si, Al13Fe4(θ) and Al167.8Fe44.9Si23.9(τ5); when the heat treatment temperature increased to 500°C, the phase of the Al–Si coating remained basically unchanged, and only part of Al167.8Fe44.9Si23.9(τ5) evolved into Al9Fe2Si2(τ6); when the heat treatment temperature increased to 600°C, Al5Fe2(η) was newly formed in the Al–Si coating and Al2Fe3Si3(τ1) was precipitated on its edge; when the heat treatment temperature increased to 700°C, the Al2Fe3Si3(τ1) precipitated evolved into AlFe in the Al–Si coating; when the heat treatment temperature increased to 800°C, the diffusion layer (α-Fe) is formed in the Al–Si coating next to the iron substrate; When the heat treatment temperature increased to 900°C, the phase of the Al–Si coating is basically the same as the former, but its morphology changes significantly, the diffusion layer is significantly thicker, and the band-shaped AlFe phase is obviously discretized.

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Microstructure Characterization of Al–Si Coatings on Hot Stamping Steel under Different Heat Treatment Processes

Effects of Normalizing Temperature on the Precipitation of Fine Particles and Austenite Grain Growth during Carburization of Al- and Nb-Microalloyed Case-Hardening Steel

Genki Saito, Norihito Sakaguchi, Kiyotaka Matsuura, Taichi Sano, Takuya Yamaoka

pp. 727-736

Abstract

This paper deals with the precipitation behaviors of AlN and Nb(C, N) particles during normalizing of hot-forged Al- and Nb-microalloyed case-hardening steel, and investigates the effects of the number density and volume fraction of these particles on the grain growth behavior of austenite (γ) during the subsequent high-temperature carburization. When the sample was cooled from the hot forging temperature at 16°C/min, AlN did not precipitate at all and was completely supersaturated in the matrix, although fine Nb(C, N) particles precipitated during cooling. When reheated to the normalizing temperature, AlN particles started precipitation at approximately 620–640°C on the grain boundaries of the bainitic ferrite matrix and the interfaces between the cementite particles and the matrix, and the AlN particles contained Cr and Mn, and had an NaCl structure and Bain orientation relationship with the matrix. The AlN structure changed from NaCl type into wurtzite type at approximately 800°C. AlN particles grew during reheating to the normalizing temperature and holding at the temperature. Both the number density and volume fraction of the AlN particles were dramatically increased by reducing the normalizing temperature from 1070 to 900°C. The distribution of these particles strongly affected the γ grain structure formed during carburization. As the normalizing temperature was reduced from 1070 to 950 and 900°C, the γ grain structure became finer. Some abnormally large grains were formed near the carburized surface, when normalized at 1070°C. However, no abnormal grain was found when normalized below 950°C.

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Effects of Normalizing Temperature on the Precipitation of Fine Particles and Austenite Grain Growth during Carburization of Al- and Nb-Microalloyed Case-Hardening Steel

A Novel Way Refining the Partially Reverted Globular Austenite in Reversion from Martensite

Xianguang Zhang, Huan Liu, Yingjie Ren, Wenchao Yang, Jiajun Chen, Peng Shi, Goro Miyamoto, Tadashi Furuhara

pp. 737-745

Abstract

Refining of the partially reverted globular austenite grain is of great importance to obtain high mechanical property of advanced high strength steels and a new approach for such refining, pre-tempering of initial martensite, is proposed in this study. The pre-tempering results in precipitation of the coarse and alloying-elements partitioned cementite particles in an Fe-2.5Mn-1.5Si-0.35C alloy. The cementite particles with Mn and Si partitioning enhanced the nucleation of globular austenite grains but suppressed its growth during continuous heating. The enhancement in nucleation and restriction in growth of globular austenite resulted in the refinement of partially reverted globular austenite grains and fully transformed austenite grains after reversion. This provides a new strategy to control the growth of partially reverted globular austenite by tailoring coarse and partitioned cementite particles.

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A Novel Way Refining the Partially Reverted Globular Austenite in Reversion from Martensite

Online Prediction of Mechanical Properties of the Hot Rolled Steel Plate Using Time-series Deep Neural Network

Zhao Yang, Yifan Wang, Feng Xu, Xiaoqiang Li, Kai Yang, Weihao Xia, Jiajia Cai, Qian Xie, Qiyan Xu

pp. 746-757

Abstract

The prediction of steel’s properties by the process parameters has been of great interest because they can effectively reduce production costs and improve product quality. At present, the extensively used artificial neural network (ANN) can only reveal the correlation between parameters and mechanical properties from the perspective of statistics but loses the critical information on time-series correlation in the steel production process. In this work, time-series neural networks based on long short-term memory (LSTM) were established to predict the steel plate’s yield strength (YS), ultimate tensile strength (UTS), and elongation (EL). The results verified that the proposed LSTM model exhibited sufficient accuracy and outperformed the classical algorithms (SVM, random forest, ANN), with mean squared error reduced by 30% when compared with ANN. Also, the sensitivity analysis proved that LSTM was more capable to make full use of the information contained in input parameters and achieved better generalization performance. Notably, the interpretation of the results was more consistent with the real physical metallurgical process of a hot-rolled steel plate and can provide a better understanding of the physical metallurgical process.

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Online Prediction of Mechanical Properties of the Hot Rolled Steel Plate Using Time-series Deep Neural Network

Effect of Microstructure on Mechanical Properties of Quenching & Partitioning Steel

Yuki Toji, Tatsuya Nakagaito, Hiroshi Matsuda, Kohei Hasegawa, Shinjiro Kaneko

pp. 758-765

Abstract

The microstructure and mechanical properties of a low-carbon steel produced via the quenching & partitioning (Q&P) heat treatment was investigated, with particular focus on the hole expansion ratio, which is an index of the stretch-flange-formability. 0.19mass%C-1.5mass%Si-2.9mass%Mn steel was annealed at 850°C, then cooled to 150–400°C (QT: quench temperature), followed by holding at 400°C for 1100 s. Yield strength and hole expansion ratio drastically increased when the QT was below the Ms (martensite start) temperature. The steel with QT of 300°C exhibited not only a higher elongation, which has been well documented, but also a higher hole expansion ratio, when compared to the conventional TRIP steel with QT of 400°C having equal tensile strength around 1200 MPa. The micro-void formation during deformation was suppressed in the steel with QT of 300°C due to the smaller volume fraction of large blocky martensite compared to the TRIP steel. These excellent mechanical properties are attributed to its unique microstructure consisting of a certain amount of tempered martensite, lath-shaped retained austenite and bainitic ferrite, which was generated via the Q&P heat treatment.

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Effect of Microstructure on Mechanical Properties of Quenching & Partitioning Steel

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