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ISIJ International
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ONLINE ISSN: 1347-5460
PRINT ISSN: 0915-1559

ISIJ International Advance Publication

  • Effect of Pearlite Volume Fraction on Two-step Ductile to Brittle Transition in Ferrite + Pearlite Structure Steel Sheets

    Hiroyuki Kawata, Osamu Umezawa

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    DOI:10.2355/isijinternational.ISIJINT-2018-764

    Abstract

    Multi structural steels exhibit high strength and good formability; however, their performance depends on the volume fraction of the secondary phase. In our previous study, ferrite + pearlite structural steel sheet showed the characteristic two-step ductile-to-brittle transition (DBT) with decreasing temperature, and the absorbed energy curve exhibited a distinct middle shelf. In this study, we evaluated the effect of pearlite volume fraction (VP) on the DBT behavior by the Charpy impact test with sub-size specimens. For specimens without pearlite, the absorbed energy directly dropped from the upper shelf to the lower shelf with decreasing temperature. For samples with 2–3% pearlite, the absorbed energy corresponding to the transition temperature range was dispersed between the two shelves, and the transition behavior seemed to be the typical DBT behavior. When VP was increased to 21%, the absorbed energy just above the transition-finish temperature became stable at a middle level between the two shelves; thus, the existence of a distinct middle shelf was confirmed. Although the transition-start temperature increased with increasing VP, VP did not affect the transition-finish temperature and the absorbed energy at the middle shelf. These results were analyzed with a simple model based on the Yoffee diagram.

  • An in situ Study of the Formation of Rare Earth Inclusions in Arsenic High Carbon Steels

    Hongpo Wang, Bin Bai, Silu Jiang, Lifeng Sun, Yu Wang

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    DOI:10.2355/isijinternational.ISIJINT-2018-853

    Abstract

    The application of rare earths is an effective way to stabilize residual elements in steel, such as As and P, so as to improve the performances of steel products. In situ methods were used to investigate the formation of inclusions and their stability at high temperatures in arsenic high carbon steels with additions of lanthanum. The results show that La2O3 and La2O2S started generating in molten steel and had significant difference of appearances and growth behaviors. La2O3 started with triangular particles and rapidly grew up like crystals; by contrast, La2O2S particles were always spherical or near-spherical and didn't significantly grow up. Arsenic existed as LaAsO4 that turned out to be unstable under high temperatures. LaAsO4 decomposed and As dissolved into the matrix when the temperature was higher than 1200°C. The formation of LaAsO4 during solidification and the dissolution of As into the matrix during heat treatment can effectively avoid the local enrichment of As. Therefore, it is possible to control As distributed uniformly in steel by appropriate heat treatment process.

  • Numerical Simulation of Multiphase Flow and Mixing Behavior in an Industrial Single Snorkel Refining Furnace (SSRF): The Effect of Gas Injection Position and Snorkel Diameter

    Weixing Dai, Guoguang Cheng, Shijian Li, Yu Huang, Guolei Zhang, Yunlong Qiu, Weifei Zhu

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    DOI:10.2355/isijinternational.ISIJINT-2018-826

    Abstract

    A three-dimensional mathematical model of an industrial Single Snorkel Refining Furnace (SSRF) was implemented in designed experiments to investigate the influence of injection position and snorkel diameter on mixing efficiency and circulation rate. The discrete phase model–volume of fluid coupled model was employed to describe the argon/steel/slag/air multiphase flow. The expansion behavior of argon bubbles was considered. The results indicated that eccentric injection is greatly beneficial for increasing circulation rate and decreasing mixing time. The effect of snorkel diameter was investigated in light of eccentric plug position. It was found that the oversized and undersized snorkel diameter are not desirable, as it contributes poor mixing at ladle bottom and periphery of snorkel, respectively. An optimum diameter was recommended according to a principle that the stirring energy of plume should be distributed reasonably for achieving homogeneous flow in the whole bath.

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  • Effect of Low-temperature Nitridation on Sulfide Stress Corrosion of 321 Austenitic Stainless Steel in H2S-Containing Environments

    Shaoqiang Yu, Jun Wang, Hongyuan Fan, Xiangfeng Zhang, Guang Chen, Jing Yan, Hanshan Dong, Xiaoying Li

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    DOI:10.2355/isijinternational.ISIJINT-2018-515

    Abstract

    The effect of low-temperature nitridation on corrosion resistance and sulfide stress corrosion (SSC) behavior of 321 austenitic stainless steel in H2S-containing environments was investigated. Varying four-point bend loading of 80 pct yield stress, 100 pct yield stress, 120 pct yield stress were respectively applied to nitrided 321 austenitic stainless steels. Although no macroscopic corrosion cracking is observed, pits are formed on the alloy surfaces. As the bending stress increases, the numbers and depths of pitting corrosion on the surface of the nitrided samples are getting more and more serious. Under 100 pct YS, the surface of unnitrided sample is completely destroyed and a series of jagged corrosion pits appear. The corrosion degree of the tension side is more serious than that of the compression side for a same sample. The result demonstrates that the low-temperature liquid nitridation can effectively improve the stress corrosion resistance and SSC behavior. The low-temperature nitrided sample has better stress corrosion resistance than the unnitrided sample in H2S-containing environments and the SSC resistance of 321 austenitic stainless steel can be apparently improved by low-temperature nitridation.

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  • Non-Isothermal Melt Crystallization Kinetics for CaO–Al2O3–B2O3 F-Free Mould Fluxes

    Qifeng Shu, Jeferson Leandro Klug, Qiangqi Li

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    DOI:10.2355/isijinternational.ISIJINT-2018-677

    Abstract

    Efforts have been made to develop fluorine-free mould fluxes for the continuous casting of steel process. In this work the crystallization behaviour of fluorine-free mould slags based on the CaO–Al2O3–B2O3 system was investigated by differential scanning calorimeter (DSC) and scanning electron microscopy equipped with energy dispersive spectroscopy(SEM-EDS). The crystallization kinetics for Ca3Al2O6 primary crystals was analysed by combining modified Avrami analysis with Friedman isoconversional method. Avrami parameter n is close to 4 for samples with the ratios w(CaO)/w(Al2O3)=1 and w(CaO)/w(Al2O3)=1.2, indicating a crystallization mechanism of continuous bulk nucleation and 3D crystal growth. The Avrami parameter n for samples with w(CaO)/w(Al2O3)=0.9 is close to 3, indicating instantaneous bulk nucleation and 3D crystal growth. The crystallization rate constant is the highest and half crystallization time is the lowest for the samples with w(CaO)/w(Al2O3)=0.9, indicating the fastest crystallization. In the initial stage, effective activation energies were mainly determined by the undercooling values. In the final stage, kinetic barrier for crystallization could have some influence on crystallization; for the investigated mould fluxes crystallization in the final stage is retarded by increasing w(CaO)/w(Al2O3) ratio. Thus crystallization mechanisms were elucidated and effective activation energy of crystallization for the first crystal which precipitates from melt was determined.

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    1. Effect of V2O5 Addition on Oxidation Induration and Swelling Behavior of Chromium-Bearing Vanadium Titanomagnetite Pellets with Simulated Coke Oven Gas Injection into Blast Furnace ISIJ International Advance Publication
    2. Design and Discrete Element Analysis of Accumulated Material-type Distributing Chute on Blast Furnace ISIJ International Advance Publication
    3. Optimization of Flocculation Process to Selectively Separate Iron Minerals from Rejected Iron Ultra Fines of Indian Mines and Minimize Environmental Issue ISIJ International Advance Publication

  • Structure Based Viscosity Model for Aluminosilicate Slag

    Zhiming Yan, Ramana G. Reddy, Xuewei Lv

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    DOI:10.2355/isijinternational.ISIJINT-2018-724

    Abstract

    Based on the structure of slag, the revised structure based viscosity model was improved for viscosity prediction of the fully liquid slag in the Al2O3–CaO–MgO–SiO2 quaternary system and its subsystems. Experimental procedures and available data in the literature have been critically reviewed. In this modified model, the oxygen ions bonded with non-compensated Al3+ ions were defined as excess bridge oxygens. The concentration of different types of oxygen ions are calculated and used to express the activation energy. The present model is capable of predicting the viscosities in the Al2O3–CaO–MgO–SiO2 quaternary system and its subsystems over the wide composition and temperature ranges above liquidus within experimental uncertainties; the average of relative errors for this model was found to be 17.97%. CaO has a greater ability to decrease the viscosity than that of MgO in the system without Al2O3 because of the weaker bond strength of CaO. A viscosity maximum occurs for MO–Al2O3–SiO2 (M=Ca or Mg) slag with a fixed SiO2 content. The estimated viscosities decrease with the increase of MgO content, decrease with increasing of the Al2O3/SiO2 ratio at 5 mass% of MgO, and keep almost constant or even slightly increase with the increase of the Al2O3/SiO2 ratio at 10 mass% MgO.

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    2. Non-Isothermal Melt Crystallization Kinetics for CaO–Al2O3–B2O3 F-Free Mould Fluxes ISIJ International Advance Publication
    3. Design and Discrete Element Analysis of Accumulated Material-type Distributing Chute on Blast Furnace ISIJ International Advance Publication

  • Temperature Field Distribution of a Dissected Blast Furnace

    Lei Zhang, Jianliang Zhang, Haibin Zuo, Kexin Jiao

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    DOI:10.2355/isijinternational.ISIJINT-2018-753

    Abstract

    The temperature field distribution of the upper part of a blast furnace (BF) is the result of the combination of charge distribution and gas flow. It is of great significance for both researchers and operators to study the thermal state and the phenomenon of the BF. The graphite box method is used in this study to obtain the temperature field distribution in the upper part of a 125 m3 BF. Graphite boxes with a variety of different melting point metals were loaded into the BF with the charge. And the temperature field distribution was obtained after the boxes were taken out with position and temperature information during the dissection process. The results illustrate that the graphite boxes are unevenly distributed in the BF, which was related to the distribution of BF materials. Furthermore, the temperature field distribution is asymmetric, and the isotherms present an irregular "W" shape, which is caused mainly by the simultaneous development of the edge airflow and the central airflow. Moreover, the shape of the softening and melting zone observed in the dissection process has a good correspondence with the temperature field. We concluded that the deflection of the temperature field and the softening and melting zone is related to the strong gas flow in the direction of No. 3 tuyere, the existence of accretion in the hearth, and the filling of refractory materials in tuyeres before blowing out.

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    3. Design and Discrete Element Analysis of Accumulated Material-type Distributing Chute on Blast Furnace ISIJ International Advance Publication

  • Optimization of Flocculation Process to Selectively Separate Iron Minerals from Rejected Iron Ultra Fines of Indian Mines and Minimize Environmental Issue

    Manindra Manna

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    DOI:10.2355/isijinternational.ISIJINT-2018-382

    Abstract

    Indian iron ore mining industry disposes large amount of ultra fines containing high gangue minerals, thereby lead to loss of iron values and environmental pollution. Selective flocculation studies have been thought of for beneficiation of ultra fines. Response of different types of starches to iron ore ultra fines generated by the hydro-cyclone in Joda Iron Ore Washing Plants, Orissa, India has been studied. The starches used are: (i) maize starch (MS), (ii) potato starch (PS) and (iii) causticized potato starch (CPS). The order of selectivity as flocculant towards iron bearing minerals is observed as MS<PS<CPS. This can be attributed to the different C-H chain morphology of the starches. MS has more amylopectin than PS. Amylopectin adsorbed strongly onto all oxides minerals as carbonyl groups attached to C-2 and C-3 atoms of starch form surface complex with surface atom of all oxide minerals whereas amylose has a more adsorption tendency to hematite only. Amylose has less number of end groups than amylopectin, thus exhibiting lesser adsorption density than amylopectin. The selective adsorption characteristics of PS to hematite further improves by modification. Iron content and the iron recovery of the concentrate depend on flocculant dosage as well as settling time. A good concentrate is obtained suitable for pellet feed with Fe content in the concentrate increased from 57.8 mass% to 66.3 mass% and with an iron recovery of 66.5% by this process using CPS as a flocculating agent under optimized conditions. The tailing generated is suitable for building materials like tiles.

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    2. Effect of V2O5 Addition on Oxidation Induration and Swelling Behavior of Chromium-Bearing Vanadium Titanomagnetite Pellets with Simulated Coke Oven Gas Injection into Blast Furnace ISIJ International Advance Publication
    3. Non-Isothermal Melt Crystallization Kinetics for CaO–Al2O3–B2O3 F-Free Mould Fluxes ISIJ International Advance Publication

  • Dependence of Carbon Concentration and Alloying Elements on the Stability of Iron Carbides

    Hideaki Sawada, Naoki Maruyama, Shinichiro Tabata, Kazuto Kawakami

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    DOI:10.2355/isijinternational.ISIJINT-2018-695

    Abstract

    The precipitation of iron carbides is a crucial factor that determines the properties of tempered martensite. However, the effect of alloying elements on the carbon concentration of ε carbide has not yet been clarified. In this work, we studied the effect of alloying elements on the carbon concentration of ε carbide using first-principles calculations and a three-dimensional atom probe. The first-principles calculations showed that ε carbide with a lower carbon concentration tends to form by the inclusion of Si. The carbon concentration in ε carbide measured by the three-dimensional atom probe was consistent with the first-principles calculations.

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    3. Non-Isothermal Melt Crystallization Kinetics for CaO–Al2O3–B2O3 F-Free Mould Fluxes ISIJ International Advance Publication

  • Design and Discrete Element Analysis of Accumulated Material-type Distributing Chute on Blast Furnace

    Lingling Li, Zhenghai Liu, Jiaye Xu, Jialian Shi

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    DOI:10.2355/isijinternational.ISIJINT-2018-678

    Abstract

    A new accumulated material-type distributing chute on blast furnace (BF) is designed to prolong the service life of distributing chute on BF according to powder mechanics theory, and a Comparative simulations study between the accumulated material-type distributing chute and smooth-plate straight chute is conducted using discrete element method. Additionally, the influence of shape of transverse ribs in accumulated area and particle size on the impact of chute are discussed. Results show that this type of distributing chute on BF has formed a stable material accumulation under the impact zone of material flow and its material cushion forms a certain thickness, which greatly reduces the impact and abrasion of material flow. The impact force of the material flow on the chute is reduced to 10.1%–17.2%, and the sliding velocity of particles near the bottom plate is reduced to 29.1%–33.4% compared with the smooth-plate straight chute. Therefore, the new accumulated material-type distributing chute has good anti-impact ability and abrasion resistance. Shape of transverse ribs in accumulated area and particle size have a relatively small effect on the impact of chute after discussing.

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  • Effect of V2O5 Addition on Oxidation Induration and Swelling Behavior of Chromium-Bearing Vanadium Titanomagnetite Pellets with Simulated Coke Oven Gas Injection into Blast Furnace

    Wei Dong Tang, Song Tao Yang, Xiang Xin Xue

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    DOI:10.2355/isijinternational.ISIJINT-2018-681

    Abstract

    The study discusses the oxidation induration and swelling behavior of chromium-bearing vanadium titanomagnetite pellets (CVTP) with V2O5 additions, and the reduction swelling index (RSI) and compressive strength (CS) of reduced CVTP were investigated with simulated coke oven gas (COG) injection into the blast furnace (BF). The results show that the CS of CVTP decreases and the porosity of CVTP increases with increasing V2O5 additions. The proportion of microsize pore size distribution of CVTP between 0 to 5 µm decreases notably while the pore size distribution between 5 to 30 µm increases with increasing V2O5 additions. The V2O5 mainly exists in the form of V2Ti3O9 and V1.93Cr0.07O3 in CVTP and V2TiO5 in reduced CVTP. The V-bearing spinels on the grain boundaries with fragmentized and prismatic structure restrain the CS of CVTP. The CS of reduced CVTP decreases and RSI increases with increasing V2O5 additions. The V2O5 addition facilitates the aggregation and diffusion of metallic iron particles, and the shape of the metallic iron whiskers transform round dot to prismatic. The pores and intervals enlarge, and thickness of lamellar crystals thickens gradually with increasing V2O5 additions. The study could supply the theoretical and technical basis for the utilization of CVTP and other V-bearing ores with COG recyclable technology.

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    3. Optimization of Flocculation Process to Selectively Separate Iron Minerals from Rejected Iron Ultra Fines of Indian Mines and Minimize Environmental Issue ISIJ International Advance Publication

  • Comprehensive Optimization Control Technology of Rolling Energy and Oil Consumption in Double Cold Rolling

    Ya-ya Cui, Xiao-lei Wang, Hang-zhe Dong, Zhen-hua Bai

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    DOI:10.2355/isijinternational.ISIJINT-2018-723

    Abstract

    In double cold rolling process, rolling energy and oil consumption is normally controlled separately, thereby causing a high comprehensive cost. This study investigated a calculation model of plate-out oil film thickness on strip surface, oil film thickness in deformation zone, friction coefficient, bite angle, forward slip, rolling force, rolling power, rolling energy consumption, and rolling oil consumption. Subsequently, the effect of emulsion flow and concentration on rolling energy and oil consumption comprehensive cost was quantitatively analyzed. On this basis, an objective function of rolling energy and oil consumption comprehensive cost was proposed, and the corresponding comprehensive optimization control technology for rolling energy and oil consumption was developed. Through a field application of this technology, the reduction of rolling energy and oil comprehensive consumption cost was achieved by optimizing emulsion flow and concentration comprehensively. Thus, a significant economic benefit was created with further popularization and application values.

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  • Effect of Nut Coke Addition on Physicochemical Behaviour of Pellet Bed in Ironmaking Blast Furnace

    Dharm Jeet Gavel, Allert Adema, Jan Van Der Stel, Jilt Sietsma, Rob Boom, Yongxiang Yang

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    DOI:10.2355/isijinternational.ISIJINT-2018-580

    Abstract

    One of the primary causes that limit the blast furnace productivity is the resistance exerted to the gas flow in the cohesive zone by the ferrous burden. Use of nut coke (10–40 mm) together with ferrous burden proves beneficial for decreasing this resistance. In present study, effect of nut coke addition on the olivine fluxed iron ore pellet bed is investigated under simulated blast furnace conditions. Nut coke mixing degree (replacement ratio of regular coke) was varied from 0 to 40 wt% to investigate the physicochemical characteristics of the pellet bed. Three distinct stages of bed contraction are observed and the principal phenomena governing these stages are indirect reduction, softening and melting. It is observed that nut coke mixing enhances the reduction kinetics, lowers softening, limits sintering and promotes iron carburisation to affects all three stages. In the second stage, the temperature and displacement range is reduced by 60°C and 24%, respectively upon 40 wt% nut coke mixing. Addition of nut coke exponentially increases the gas permeability (represented by pressure drop and S-value). A higher degree of carburisation achieved on the pellet shell (iron) is suggested to be the principal reason for decrease in the pellet melting temperature. The pellets softening temperature increases by approximately 4°C, melting and dripping temperature drops by 11°C and 12°C, respectively, for every 10 wt% nut coke addition. Consequently, the nut coke addition shortens the softening, melting and dripping temperature ranges, which shows improved properties of the cohesive zone.

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  • Direct Reduction Recycling of Mill Scale Through Iron Powder Synthesis

    Kameswara Srikar Sista, Srinivas Dwarapudi, Virendra Prakash Nerune

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    DOI:10.2355/isijinternational.ISIJINT-2018-628

    Abstract

    Mill scale, a potential raw material for recycling from hot rolling mill operations is chosen and one step thermo-chemical reduction technique is employed to beneficiate the iron content in the form of powdered iron. Experiments are conducted at various temperature (600–1300°C) and time (1–4 h) combinations using hydrogen as reducing atmosphere. Physical and chemical properties of mill scale iron powders (MIP) are analysed using particle size analyser, gas pycnometer and wet chemical testing. MIP are also characterized for phase and morphology using X-ray diffractometer and scanning electron microscopy respectively. Effect of parameters like temperature of reduction, time of reduction, particle size of raw material, sintering and grinding on the iron powder synthesis is well studied. Mill scale iron powder with > 99% degree of metallization, 97% Fe (T), > 96% Fe (met) and 2.63 g/cc apparent density is obtained at 1200°C, 4 h and 1300°C, 4 h parameters and this material would stand promising for recycling through nutrition supplements, body warmers, water purification, sound insulators, etc applications.

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  • Numerical Investigation of Applying High-carbon Metallic Briquette in Blast Furnace Ironmaking

    Huiqing Tang, Tao Rong, Kai Fan

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    DOI:10.2355/isijinternational.ISIJINT-2018-673

    Abstract

    Application of high-carbon metallic briquette (HCMB) in the blast furnace (BF) ironmaking for coke saving was previously proposed. This paper is focused on clarifying the in-furnace phenomena and demonstrating the advantages of applying the HCMB in BF ironmaking. A mathematical model has been formulated based on the gas-solid counterflow and its validity was confirmed by the comparison of the simulation results with the averaged industrial data from a BF with a productivity of 6250 tHM/day. Afterward, BF operations under two HCMB mixing ratios (5% and 10%) were simulated. Simulation results indicate that charging HCMB in BF can suppress the coke gasification and improve the ore reduction above the CZ. Coke of approximately 12 kg could be saved for producing one-ton hot metal from the ore under an HCMB mixing ratio of 5%, and approximately 17 kg under an HCMB mixing ratio of 10%. Simulation results still indicate that the reasonable mixing ratio of HCMB is less than 5%, under which, significant changes of the BF operation conditions for HCMB charging are not required.

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  • Phosphorus Partition and Phosphate Capacity of TiO2 Bearing Basic Oxygen Steelmaking Slags

    Phillip Brian Drain, Brian Joseph Monaghan, Raymond James Longbottom, Michael Wallace Chapman, Guangqing Zhang, Sheng Jason Chew

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    DOI:10.2355/isijinternational.ISIJINT-2018-683

    Abstract

    The phosphorus partition (LP) and phosphate capacity (CPO43-) were measured for TiO2 bearing basic oxygen steelmaking slags in the CaO–SiO2–MgO–FetO–(TiO2–MnO–Al2O3–P2O5) system at 1650°C. The effect of slag and metal additions were tested by varying the TiO2 content from 0.0 to 18.0 mass% and the [Ti] content from 0.009 to 0.301 mass%. A recently published LP model was used to assess the experimental LP data using the measured slag composition and temperature. Experimental LP data from this study and literature data were used to modify the published model to include titania.Increasing the TiO2 concentration of the slag was found to decrease the LP and CPO43- of basic oxygen steelmaking (BOS) slags. Capacity values in the range of 2.2×1016 to 1.5×1018 at 1650°C were obtained. An empirical model for determining CPO43- was developed for BOS slags using a large dataset of published slag and pO2 data for relevant slag systems, including published data for titania bearing slags. The predicted CPO43- from the empirical model was found to agree with the experimentally determined CPO43- data from this study.

  • Thermal Driving Demonstration of Li4SiO4/CO2/Zeolite Thermochemical Energy Storage System for Efficient High-Temperature Heat Utilizations

    Seon Tae Kim, Chisato Kurahashi, Hitoshi Hoshino, Chiharu Takahashi, Yoshiro Tamura, Hiroki Takasu, Shusuke Saito, Masaki Kurihara, Yukitaka Kato

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    DOI:10.2355/isijinternational.ISIJINT-2018-428

    Abstract

    Thermochemical energy storage (TcES) system using lithium orthosilicate/carbon dioxide (Li4SiO4/CO2) reaction was developed for recovery and utilization of high temperature thermal energy generated from high temperature industrial process. Li4SiO4/CO2 TcES packed bed reactor (LPR) and zeolite packed bed reactor (ZPR) were developed as thermal energy storage and CO2 reservoir. Both reactors, LPR and ZPR, were connected by flexible tube and thermal driving operation of TcES system was demonstrated. For lithium orthosilicate packed bed reactor, tablet forms of Li4SiO4 named K-tablet was developed and used in this study.Li4SiO4 carbonation (thermal energy output process) and lithium carbonate (Li2CO3) decarbonation (thermal energy storage process) were conducted sequentially with specific condition. All experimental results showed similar tendency; a middle temperature in the Li4SiO4 packed bed reactor rapidly increased and decreased at the initial time of carbonation and decarbonation respectively. From kinetic analysis, it was confirmed that the developed K-tablet reacted around 80% and a thermal energy output density of LPR was estimated 331–395 kJ/L-packed bed, 759–904 kJ/L-material. The thermal driving demonstration of Li4SiO4/CO2/Zeolite TcES system shows high possibility to utilize surplus heats in low-carbon ironmaking system efficiently.

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  • Effect of Silicon on AHSS As-Cast Microstructure Development and Properties

    Rafael Coura Giacomin, Bryan A. Webler

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    DOI:10.2355/isijinternational.ISIJINT-2018-598

    Abstract

    This work linked properties and performance in as-cast condition for 3rd generation advanced high strength steel (AHSS) by examining the effects of chemical composition and microstructure on mechanical properties. Elevated levels of carbon, manganese, and silicon in new AHSS grades lead to a complex evolution of microstructure during solidification that can lead to castability problems. Three lab cast ingots with 0.2 wt% C, 3 wt% Mn, and 0.5, 1.5, and 3 wt% Si were characterized by their microstructure and mechanical properties. Light optical microscopy (LOM) and Scanning Electron Microscopy (SEM) confirmed that the microstructure of steels was mostly granular bainite, with some proeutectoid ferrite allotriomorphs at 3 wt% Si. Tensile testing showed Si increased strength and that ductility of all samples was low. Higher silicon levels were found to promote formation of proeutectoid ferrite allotriomorphs and changed the cracking propagation behavior. Some comparisons between the observed microstructures and those expected in continuously cast slabs were also discussed.

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  • Chemical Structure of Si–O in Silica Fume from Ferrosilicon Production and Its Reactivity in Alkali Dissolution

    Yiwei Zhong, Xinle Qiu, Jintao Gao, Zhancheng Guo

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    DOI:10.2355/isijinternational.ISIJINT-2018-516

    Abstract

    As an environmentally hazardous waste, silica fume was considered as a potential alternative for cement and SiO2 production. The structure of Si–O was highly relevant to the reactivity of Si conversion for efficient utilization. In this study, the characteristic and chemical structure of Si–O in silica fume were characterized by X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FTIR). Deconvolution of XPS and FTIR spectra into elementary profiles was carried out to analyze the structural components. As a result, the valence state, bonding structure and elementary unit in the Si–O network of silica fume were determined. Then, the reactivity silica fume with alkali solution was studied involving the effects of NaOH concentration and temperature. The staged kinetics behavior was associated with the structure of Si–O bonds, and the activation energies were determined. The results thus provided fundamental information for the utilization of silica fume for SiO2 production and geopolymer.

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  • Effect of Cooling Rate on the Solidification Microstructure and Characteristics of Primary Carbides in H13 Steel

    Mingtao Mao, Hanjie Guo, Fei Wang, Xiaolin Sun

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    DOI:10.2355/isijinternational.ISIJINT-2018-524

    Abstract

    The microstructure, alloying elements segregation and characteristics of primary carbides in AISI H13 steel that solidified at different cooling rate were investigated by optical microscope (OM), field emission scanning electron microscope (FE-SEM), electro-probe microanalyzer (EPMA) and automated inclusion analyzer ASPEX. The microstructure of H13 steel samples become more refined with increased cooling rate. The equation of relationship between cooling rate (RC) and secondary dendrite arm spacing (λ) for H13 steel could be expressed as λ = 175.4RC-0.322. Primary carbides are located in interdendritic region, where existed obvious Cr, Mo, V and C segregation. Higher cooling rate promoted higher alloying elements segregation and facilitated earlier precipitation of primary carbides during solidification process. The number, size, amount and mean area of primary carbides decreased significantly with the increased cooling rate, however the shape of the primary carbides were insensitive to cooling rate. Thermodynamic calculation indicated that V-rich primary carbides precipitated at solid fraction larger than 0.94, Mo-rich primary carbides precipitated at solid fraction larger than 0.99 in the cooling rate range investigated. Lower cooling rate suppressed alloying elements segregation, but the precipitation of primary carbides could not be avoided in the cooling rate range.

  • Heat Transfer Characteristic of Slit Nozzle Impingement on High-temperature Plate Surface

    Bingxing Wang, Zhixue Liu, Bo Zhang, Zhaodong Wang, Guodong Wang

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    DOI:10.2355/isijinternational.ISIJINT-2018-576

    Abstract

    Heat transfer mechanism of a slit jet impingement was thoroughly studied to improve capacity and uniformity of a hot steel strip/plate during its ultrafast cooling or quenching. The impact angle has a significant influence on the heat transfer characteristics of the stationary slit jet impinging process. Heat transfer capability and rewetting front propagation, which include such parameters as qmax, tMHF, and TMHF, differ significantly between the upstream and downstream regions. Parallel flow and intense sputtering in the downstream region are apparent for the forward-moving inclined slit jet impingement cooling process. The antiparallel flow in the upstream region is thinner, and the sputtering is reduced and is relatively stable. As the plate moves forward, the wetting front expands and forms almost a straight line with synchronized and uniform heat transfer. The inclined angle increases from 0 to 45°, which significantly increases the heat transfer intensity and shortens the time to nucleate boiling stage as well as the width of the transitional boiling region. A higher moving velocity reduces and promotes qmax moving to the downstream region.

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