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ISIJ International Vol. 54 (2014), No. 4

ISIJ International
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Grid List Abstracts
オンライン版ISSN: 1347-5460
冊子版ISSN: 0915-1559
発行機関: The Iron and Steel Institute of Japan

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キーワードランキング

21 Nov. (Last 30 Days)

ISIJ International Vol. 54 (2014), No. 4

Estimation of Oxidized Pellets of a Brazilian Hematite Concentrate by Adding Serpentine

Daijun Wang, Shengli Wu

pp. 715-720

DOI:

10.2355/isijinternational.54.715

抄録

Serpentine was applied as a magnesium additive upon preparing oxidized pellets of a Brazilian hematite concentrate, the effects of ballability, preheating and roasting performance were studied in this work. The results showed that with the increasing dosage of serpentine, the green ball moisture content was increased, the compressive strength was improved too, but drop strength and burst temperature were reduced. In terms of the preheated pellets, the compressive strength were increased first and then decreased, and last leveled off. The compressive strength of roasted pellets were all improved, especially the improvement was obvious when the roasting was conducted at the temperature of 1280°C. When the serpentine ratio was constant, with the preheated temperature increasing, the compressive strength of preheated and roasted pellets were all improved. Mechanism analysis showed that the solid phase reaction could be promoted with addition of serpentine, and the consolidation strength of pellets would be increased also. Although the iron grade and reduction of pellets were reduced, the reducing swelling was decreased, but the softening begin temperature was risen, the softening range was narrowed, and the metallurgical performance of pellets was improved at the same time.

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Structural Study of Glassy CaO–SiO2–CaF2–TiO2 Slags by Raman Spectroscopy and MAS-NMR

Jiangling Li, Qifeng Shu, Kuochih Chou

pp. 721-727

DOI:

10.2355/isijinternational.54.721

抄録

During the production of titanium stabilized stainless steel, as titanium in steel has a tendency to reacting with SiO2 in mould fluxes to generate TiO2 into mould fluxes and mould powder can inevitably pick up Ti-bearing inclusions floating up from steel, TiO2 content in the molten mould fluxes gradually increases so that physiochemical properties of the fluxes change. To evaluate the effect of TiO2 increase in mould fluxes on the structure of the mould flux, the glassy slag system CaO–SiO2–CaF2–TiO2 for stainless steel casting fluxes was studied by combining Raman spectroscopy with 29Si and 19F Magic Angular spinning Nuclear Magnetic resonance (MAS-NMR) to obtain the structure information. Both Raman and 29Si MAS-NMR investigation results have shown that Q2 is predominant silicate species in structures of all samples. Ti4+ mainly exists in the form of [TiO4] in slag, and forms TiO2-like clusters with Ti4+ in tetrahedral coordination, which cannot change the degree of polymerization of the silicate network. A small amount of Ti enters into the silicate network as the role of network formation, which slightly enhances the degree of polymerization of the silicate network. According to 19F MAS-NMR spectra, most of the fluorine is exclusively coordinated by Ca2+ corresponding to F–Ca(n) site and only a few Si–F bonds were observed in samples. Increase of TiO2 content has no significant effects on the F- bonds.

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Dissolution Behavior of Al2O3 in Refining Slags Containing Ce2O3

Yan Qiang Liu, Li Jun Wang, Kuo Chih Chou

pp. 728-733

DOI:

10.2355/isijinternational.54.728

抄録

The effects of rotating speed, temperature and slag composition on the dissolution rate of alumina rod in molten CaO–SiO2–Al2O3–MgO and CaO–SiO2–Al2O3–MgO–Ce2O3 slag were investigated by the rotating cylinder method in the temperature range of 1793 K to 1853 K. It was indicated that faster rotating speed and higher temperature would result in an increasing of dissolution rate of alumina. The concentration profiles of Al, Ca, Ce etc. in the boundary layer as well as slag were determined by EDS analysis. Based on these results, the mechanism of dissolution of Al2O3 rod in Ce2O3 containing slag was discussed, and the apparent activation energy in the dissolving process were obtained in the range of 233–418 kJ/mol. The addition of Ce2O3 initially increased the dissolution rate of Al2O3, while hindered afterwards, which is explained from the view point of mass transfer coefficient.

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Structure Analysis of CaO–SiO2–Al2O3–TiO2 Slag by Molecular Dynamics Simulation and FT-IR Spectroscopy

Shengfu Zhang, Xi Zhang, Haijun Peng, Liangying Wen, Guibao Qiu, Meilong Hu, Chenguang Bai

pp. 734-742

DOI:

10.2355/isijinternational.54.734

抄録

The structure information in the CaO-SiO2-14 mass% Al2O3–TiO2 slag was investigated by the molecular dynamics simulation and the FT-IR spectroscopy at 1773 K. The influence of different additions of TiO2 and varying CaO/TiO2 ratios on the structure was studied to clarify the role of TiO2 in the slag. The results show that there exist three stable units, [SiO4] tetrahedron and [AlO4] tetrahedron as well as [TiO6] octahedron in the CaO-SiO2-14 mass% Al2O3–TiO2 slag. The average coordination numbers, CNSi–Al and CNAl–Al, are all approximately equal to 1 and are barely influenced by additions of TiO2 and varying CaO/TiO2 ratios, which indicates that both the [SiO4] and [AlO4] tetrahedrons are surrounded by only one [AlO4] tetrahedron and some other units. Nevertheless, [AlO4] can be linked by more than one [SiO4] tetrahedron but [SiO4] can only be surrounded by one [AlO4] tetrahedron. The bridging oxygen, classified into Si–O–Si, Al–O–Al and Si–O–Al, is preferentially localized in Si–O–Al. However, it is found a little violation of the so-called Al avoidance principle which states that the Al–O–Al linkage is absent have been obtained with about (less than) 5% Al–O–Al, and the bond of Al–O–Al is hardly affected by TiO2 additions. Replacement of CaO by TiO2 can only result in a slight change of the degree of polymerization, indicating TiO2 has the similar role as CaO to be a basic oxide.

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Isothermal Enriching Perovskite Phase from CaO–TiO2–SiO2–Al2O3–MgO Melt by Super Gravity

Juncheng Li, Zhancheng Guo, Jintao Gao

pp. 743-749

DOI:

10.2355/isijinternational.54.743

抄録

A new approach to enriching perovskite phase from CaO–TiO2–SiO2–Al2O3–MgO melt by super gravity was investigated. The samples obtained by the gravity coefficient G≥600, time t≥20 min and temperature T≥1578 K appear significant layers and perovskite phase present gradient size distribution in the sample along the super gravity. The layered sample was central cut and characterized by metallographic microscopy, and it is hardly to find any perovskite particles in the upper area of the sample and the perovskite phase gathers at the middle and bottom areas of the sample. The mechanism of moving speed of perovskite particles in super gravity field was also discussed, and the conclusion indicates that the moving speed of perovskite particles is proportional to the square of the perovskite particle size. As a result, large size perovskite particles move a farther distance than the small ones and gather at the bottom of the sample, while small size perovskite particles accumulate in the middle of the sample. Under the hypothesis that the titanium exists in the slag in terms of TiO2, with the gravity coefficient G=600, time t=20 min and temperature T=1578 K, the mass fraction of TiO2 in the concentrate is up to 34.97%, while that of the tailing is just 11.16%. Considering that the mass fraction of TiO2 is 22.34% in the parallel sample, the recovery ratio of Ti in the concentrate is up to 74.16% by centrifugal enrichment.

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Thermodynamic Assessment of Liquid Fe–Si–C System by Unified Interaction Parameter Model

Seung Hwan Ahn, Yang Hong Kim, Joong-Pil Shin, Young Eun Lee

pp. 750-755

DOI:

10.2355/isijinternational.54.750

抄録

The solution behaviors of Fe–Si–C system are characterized by the formation of SiC, and the properties are defined by the value of the standard Gibbs free energy of formation of SiC, . However, a review shows that reported values of do not agree among the investigators and are shown a significant discrepancy among them as high as 16 kJ/molSiC. In order to resolve this uncertainty, new value of is assessed by reproducing experimentally determined two-fold saturation data with the UIP modeling Fe–Si–C melt. The proposed value of is given by following equation.



With the proposed , the UIP model for Fe–Si–C system was developed from the experimentally determined solubility of C and two-fold saturations of C and SiC taken from the literature reported. The resulting activity coefficients are expressed as follows:









where =–2.004+2718/T, =2.107–15803/T, εCC=9.052+4064/T, εCSi=5.101–9647/T, εSiSi=9.254+3380/T, εCCSi=–7.482+67622/T, εCSiSi=–39.72+185440/T, εSiSiSi=–35.966+98468/T, εCSiSiSi=34.05–160482/T, and εSiSiSiSi=20.921–74752/T.The model reproduces well the experimentally determined C solubility as well as the two-fold saturation of C and SiC. It also describes well the solution behaviors in a wide range of compositions and temperatures, permitting its use for various applications such as ironmaking, steelmaking, cast-iron, Si-based ferroalloys, and the low temperature liquid phase growth of electronic grade silicon carbide.

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Retraction: A Prediction Model of Phosphorus Distribution between CaO–SiO2–MgO–FeO–Fe2O3–P2O5 Slags and Liquid Iron

Peng-cheng Li, Jian-liang Zhang

pp. 756-765

DOI:

10.2355/isijinternational.54.756

抄録

This article was retracted.

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Effect of Na2O and B2O3 on the Distribution of P2O5 between Solid Solution and Liquid Phases Slag

Senlin Xie, Wanlin Wang, Yongzhen Liu, Hiroyuki Matsuura

pp. 766-773

DOI:

10.2355/isijinternational.54.766

抄録

With the development of multiphase slag system for hot-metal treatment to achieve better dephosphorization efficiency, it is very important to improve the distribution ratio of P2O5 between the solid solution (2CaO·SiO2–3CaO·P2O5) and liquid phase slag. This study was carried out to investigate the effects of Na2O and B2O3 on P2O5 distribution ratio and morphologies of corresponding solid solutions in CaO–SiO2–Fe2O3–P2O5 slag system. The results indicated that the distribution ratio of P2O5 would be improved with the increase of Na2O content due to the formation of (2CaO·SiO2–Na2O·2CaO·P2O5) solid solution with a similar morphology as that of reference solid solution (2CaO·SiO2–3CaO·P2O5) in the reference slag. While B2O3 plays an opposite role, it would not only reduce the phosphorus distribution ratio, but also change the morphology of its corresponding solid solution due to the formation of complex solid solution (2CaO·SiO2–Ca9.93(P5.84B0.16O24) (B0.67O1.79)). Besides, the effect of cooling rate on the size of the solid solution was also studied. It would provide an instructive way for the design of multiphase slag for hot metal treatment.

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Magnus Effect on Arc Driven by Alternating Magnetic Field in Swirling Plasma Gas

Ryota Akiho, Koichi Takeda, Masaya Sugimoto, Yosuke Noguchi

pp. 774-780

DOI:

10.2355/isijinternational.54.774

抄録

An arc driven by an alternating magnetic field was investigated theoretically and experimentally in swirling plasma gas flow. The governing equation to ascertain the arc motion was assumed to include not only an electromagnetic force term but also a Magnus force one. The electromagnetic force term derives from interaction between the arc current and the imposed magnetic field. The Magnus force is produced when the rotating gas travels in the surrounding gas. The obtained equation was solved numerically using commercial software (Mathematica). Numerical calculation revealed that the movement of the magnetically driven arc is twisted by the Magnus force. The twist direction depends on that of the swirling motion of the plasma gas. Clockwise-swirling plasma gas produces clockwise twisted arc movement. The amplitude of the oscillatory arc motion decreases concomitantly with increasing swirling strength.
The experiment was performed to examine the theoretical predictions. Results from experimental observations showed that the theoretical modeling was reasonable.

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Thermogravimetry and Reaction Gas Analysis of the Carbothermic Reduction of Titanomagnetite Ores with Char

Sung-Mo Jung

pp. 781-790

DOI:

10.2355/isijinternational.54.781

抄録

The carbothermic reduction of titanomagnetite (TTM) was investigated from a kinetic viewpoint in the temperature range of 1000 to 1150°C employing thermogravimetric analysis (TGA) and quadruple mass spectrometry (QMS). The method of evaluating the fractional reduction in the carbothermic reduction of TTM by TGA was validated. The carbon in char consumed for the reduction of TTM was fully gasified into CO and CO2, which indicates that the TGA can be coupled to QMS from the viewpoint of mass balance of carbon. The carbon gasification reaction was activated when the Fe3O4 in TTM, wustite and Fe coexist at the fractional reduction of 0.21, indicating that Fe-catalyzed nature of Fe was confirmed for the carbon gasification. The activation energy for the reduction in TTM to wustite was evaluated to be 241 kJ/mol and the initial reduction stage is believed to be limited by carbon gasification. In the current study, it was considered that the changeover in reaction mechanism might be carried out from carbon gasification to the reduction in wustite to Fe by CO during the isothermal reduction of TTM with char.

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Evaluation of Sinter Quality for Improvement in Gas Permeability of Blast Furnace

Naoyuki Takeuchi, Yuji Iwami, Takahide Higuchi, Koichi Nushiro, Nobuyuki Oyama, Michitaka Sato

pp. 791-800

DOI:

10.2355/isijinternational.54.791

抄録

In the recent operation of blast furnace, it is supposed that high gas permeability of burden is important for low RAR and high PCR operation. In this work, sinter quality for improvement in gas permeability of blast furnace was investigated with reduction degradation and under-load-reduction tests. As the results, the reduction degradation of sinter is deteriorated by increasing H2 concentration in the reduction gas under the condition of below 3.8 vol% H2. However, over 3.8 vol% H2, increase of H2 has no effect on the reduction degradation because the diffusion of reduction gas in the sinter is limited. On the other hand, from the under-load-reduction test, there is possibility that increase in H2 concentration of reduction gas and decrease in slag ratio in sinter are effective to improve gas permeability of lower part of blast furnace rather than reducibility of sinter. Due to adoption of these experimental results to a 2-dimentional mathematical simulation model, the precision of pressure drop calculation of blast furnace was improved. It is considered from the evaluation by this model calculation that the RDI, a slag ratio and the slag viscosity as the sinter properties are greatly influence on the permeability of blast furnace.

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Water-gas Shift Reaction in an Olivine Pellet Layer in the Upper Part of Blast Furnace Shaft

Antti Kemppainen, Tuomas Alatarvas, Mikko Iljana, Juho Haapakangas, Olli Mattila, Timo Paananen, Timo Fabritius

pp. 801-809

DOI:

10.2355/isijinternational.54.801

抄録

In order to reduce CO2 emissions in the iron and steel industry, the utilization of H2 gas as a reducing agent is a feasible option. The use of hydrogen bearing injectants in the lower blast furnace (BF) area increases H2O concentration in the upper part of the BF shaft and the charging of moist burden has a similar effect as well. For efficient BF operation, it is important to investigate the effect of high H2 and therefore high H2O concentrations in the reducing gas. This study focuses on the upper BF shaft area where hematite to magnetite reduction takes place and temperature is in the range of the forward water-gas shift reaction (WGSR). The effect of the WGSR on the composition of the reducing gas was estimated by experimental methods. A layer furnace (LF) was used to determine the temperature for the occurrence of the WGSR under simulated BF shaft conditions. The feed gas conversion was investigated in an olivine pellet layer. The WGSR was observed in an empty LF with CO–H2O–N2 gas at 500°C. With CO–CO2–H2O–N2 gas the WGSR was observed in an olivine pellet layer at 400–450°C and in a pre-reduced magnetite pellet layer at 300–400°C indicating the catalyzing effect of magnetite on the WGSR. The results offer additional information about the effect of high H2O concentration on the composition of the reducing gas through the WGSR. The occurrence of the WGSR in the actual BF and its effects were discussed.

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Reactivity of Coke Ash on Aluminosilicate Blast Furnace Hearth Refractories

Brian Joseph Monaghan, Phillip Brian Drain, Michael Wallace Chapman, Robert John Nightingale

pp. 810-819

DOI:

10.2355/isijinternational.54.810

抄録

Blast furnace hearth refractories are a key component in achieving long furnace lives. These refractories can be degraded by among other things reactions with coke ash products. Recent studies have shown that these coke ash products could be calcium aluminate based. To understand and characterize the effects of these calcium aluminates on hearth refractories a study has been carried out that investigates the reaction kinetics of CaO.Al2O3, CaO.2Al2O3 and CaO.6Al2O3 in contact with an aluminosilicate blast furnace hearth refractory. The experimental program covered the temperature range 1450° to 1550°C. The temperatures were chosen to represent the hot face temperatures of the hearth refractories.
From this study it was found that the rate of reaction with the aluminosilicate refractory and CaO.6Al2O3 was much slower than that of CaO.Al2O3 and CaO.2Al2O3. The prevailing kinetics of the aluminosilicate refractory with CaO.Al2O3 and CaO.2Al2O3 was found to be consistent with the linear rate law. The slow rate of reaction of the refractory with CaO.6Al2O3 prohibited identification of the prevailing kinetic regime.
In characterizing the reaction interface between the aluminosilicate and the calcium aluminates it was found that there was significant reaction between the refractory and CaO.Al2O3 and CaO.2Al2O3 but little reaction with the CaO.6Al2O3. The reaction layers formed at the interface between the couples were found to consist of CaO.2Al2O3, CaO.6Al2O3, corundum (Al2O3), plagioclase (CaO.Al2O3.2SiO2) and melilite (2CaO.Al2O3.SiO2). The formation of a layer with these phases could result in spalling/wear of the hearth refractory.

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Flow of Molten Slag through a Coke Packed Bed

Hazem Labib George, Raymond James Longbottom, Sheng Jason Chew, Brian Joseph Monaghan

pp. 820-826

DOI:

10.2355/isijinternational.54.820

抄録

The productivity and performance of the ironmaking blast furnace is significantly affected by the flow behaviour in the lower zone. The flow of reducing gas and liquids (iron and slag) through coke particles is often characterised as flow through a packed bed. To improve understanding of the flow in the lower zone of the blast furnace, an investigation has been carried out, where the primary aim was to obtain a physical description of the high temperature flow phenomena of liquid slag through a coke packed bed, based on characterisation of laboratory scale packed bed systems.
A synthetic slag in the CaO–SiO2–MgO–Al2O3 system was fed at a controlled rate to pass through a coke packed bed heated to 1500–1600°C. The mass of slag passing through the bed was logged. The bed was packed using synthetic coke to minimise the experimental uncertainty associated with the heterogeneity of industrial coke. Slag supply-drain curves, liquid holdup and residence time have been characterised. The effects of bed packing density, temperature and mineral content of the coke were tested.
Increasing the packing density or decreasing the temperature of the packed coke bed was found to increase the total liquid holdup and residence time of the slag. Increasing coke mineral content from 4.4% to 12% resulted in a decrease in the total holdup and the residence time. Mathematical models from the literature based on cold packed beds were used to predict the liquid holdup for the experiments, but were found to not adequately describe the results.

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Interfacial Reaction between Al2O3–SiO2–C Refractory and Al/Ti-Killed Steels

Young Seok Lee, Sung-Mo Jung, Dong-Joon Min

pp. 827-835

DOI:

10.2355/isijinternational.54.827

抄録

In the current investigation, the thin film method was employed to clarify the formation mechanism of the oxide layers at the interface between the Al2O3–SiO2–C refractory and liquid Fe. A reacted layer was formed in such a way that initially FeO-enriched liquid layers are widely distributed on the Fe surface and FeO and SiO2 in the liquid layer are reduced by Al in liquid Fe to develop solid Al2O3-enriched layer of inclusions. Some inclusions in liquid Fe might be produced by the remaining oxygen in Ar gas being supplied through the nozzle to prevent the adherence of inclusions onto it. The oxide layers at the interface estimated by thermodynamic calculation are in good accordance with the experimental results of the reaction between Al2O3–SiO2–C refractory and Al-killed/Al-Ti-killed steels previously reported.

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Splashing in Oxygen Steelmaking

Shabnam Sabah, Geoffrey Brooks

pp. 836-844

DOI:

10.2355/isijinternational.54.836

抄録

In oxygen steelmaking, splashing from the injection of oxygen plays an important role in the kinetics of the process. Though waves inside the cavity and formation of various modes (i.e. dimpling, splashing, and penetrating) have been investigated in the past, it is not clearly understood how these wave behaviour affects splashing. Therefore, in the present work, a cold model experimental study has been carried to establish if it was possible to quantitatively identify various modes of cavity. Fast Fourier Transform (FFT) on cavity depth oscillation showed that amplitude and frequency of cavity oscillation is highest in penetrating mode. Important aspects of the droplet generation process were identified from high speed imaging. Formation of sheet structure was identified and the height of these structures above the bath surface were found to decline as the cavity mode changed from splashing to penetrating. Existence of the splash sheets emphasizes that the sampling position can be a crucial issue in interpreting plant studies.

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Transient Fluid Flow during Steady Continuous Casting of Steel Slabs: Part I. Measurements and Modeling of Two-phase Flow

Seong-Mook Cho, Seon-Hyo Kim, Brian G. Thomas

pp. 845-854

DOI:

10.2355/isijinternational.54.845

抄録

Unstable mold flow could induce surface velocity and level fluctuations, and entrain slag, leading to surface defects during continuous casting of steel. Both argon gas injection and Electro-Magnetic Braking (EMBr) greatly affect transient mold flow and stability. Part I of this two-part article investigates transient flow of steel and argon in the nozzle and mold during nominally steady-state casting using both plant measurements and computational modeling. Nail board dipping measurements are employed to quantify transient surface level, surface velocity, flow direction, and slag depth. Transient flow in the nozzle and strand is modeled using Large Eddy Simulation (LES) coupled with the Lagrangian Discrete Phase Model (DPM) for argon gas injection. The surface level of the molten steel fluctuates due to sloshing and shows greater fluctuations near the nozzle. The slag level fluctuates with time according to the lifting force of the molten steel motion below. Surface flow shows a classic double roll pattern with transient cross-flow between the Inside Radius (IR) and the Outside Radius (OR), and varies with fluctuations up to ~50% of the average velocity magnitude. The LES results suggest that these transient phenomena at the surface are induced by up-and-down jet wobbling caused by transient swirl in the slide-gate nozzle. The jet wobbling influences transient argon gas distribution and the location of jet impingement on the Narrow Face (NF), resulting in variations of surface level and velocity. A power-spectrum analysis of the predicted jet velocity revealed strong peaks at several characteristic frequencies from 0.5–2 Hz (0.5–2 sec).

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Transient Fluid Flow during Steady Continuous Casting of Steel Slabs: Part II. Effect of Double-Ruler Electro-Magnetic Braking

Seong-Mook Cho, Seon-Hyo Kim, Brian G. Thomas

pp. 855-864

DOI:

10.2355/isijinternational.54.855

抄録

Plant measurements and computational models of transient flow with and without electromagnetic fields are applied to investigate transient phenomena in the nozzle and mold region during nominally steady steel slab casting. In Part II of this two-part article, the effect of applying a static magnetic field on stabilizing the transient flow is investigated by modeling a double-ruler Electro-Magnetic Braking (EMBr) system, under conditions where measurements were obtained. A Reynolds Averaged Navier-Stokes (RANS) computational model using the standard k–ε model is employed with a magnetic field distribution extrapolated from measurements. The magnetic field decreases velocity fluctuations and deflects the jet flow downward in the mold, resulting in a flatter surface level and slower surface flow with slightly better stability. The effect of EMBr on surface level and surface velocity, including the effect of the real conducting steel shell, falls between the cases assuming perfectly-conducting and insulating walls. Measurements using an eddy current sensor and nail boards were performed to quantify the effect of EMBr on level and velocity at the mold surface. Power spectrum analysis of the surface level variations measured by the sensor revealed a frequency peak at ~0.03 Hz (~35 seconds) both with and without the EMBr. With EMBr, the surface level is more stable, with lower amplitude fluctuations, and higher frequency sloshing. The EMBr also produced ~20% lower surface velocity, with ~60% less velocity variations. Finally, the motion of the slag-steel interface level causes mainly lifting rather than displacement of the molten slag layer, especially near the SEN.

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Development of New Mold Flux for Continuous Casting Based on Non-Newtonian Fluid Properties

Keiji Watanabe, Koichi Tsutsumi, Makoto Suzuki, Hiroki Fujita, Satoshi Hatori, Takayuki Suzuki, Tomoaki Omoto

pp. 865-871

DOI:

10.2355/isijinternational.54.865

抄録

Due to the importance of the physical and chemical properties of the mold flux used in the production of high-quality steel, in particular the suppression of surface defects on steel sheets, steelmaking engineers have attempted to develop new types of mold flux. This paper presents the results of research on entrapment of mold flux and on heat transfer between the mold and the solidified shell. The authors have been developing a mold flux with non-Newtonian fluid properties using nitrogen. That is, the viscosity of the molten mold flux is low at a high shear rate to reduce the friction between the mold and the solidified shell, but is high at a low shear rate to prevent mold flux entrapment. In order to approximate the properties of mold flux as a non-Newtonian fluid, nitride is added to the conventional flux to adjust the silicate network structure through the reaction between nitrogen and calcium. The contact angle of the non-Newtonian mold flux, which represents the wettability between the mold and the solidified shell, is low in comparison with that of the normal mold flux without nitrogen. It is suggested that the non-Newtonian mold flux increases the heat transfer between the mold and the solidified shell. A casting test was carried out using this non-Newtonian mold flux, and the results showed that entrapment of mold flux decreased and heat transfer increased, as assumed.

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Artificial Neural Network Modeling of Flow Stress in Hot Rolling

Parya Aghasafari, Hamid Abdi, Mahmoud Salimi

pp. 872-879

DOI:

10.2355/isijinternational.54.872

抄録

In this study, an artificial neural network model is proposed to predict the flow stress variations during the hot rolling process. Optimization of the proposed neural network with respect to number of neurons within the hidden layer, different training methods and transfer functions of the neural network is performed. The results of the optimal network were compared with those of the conventional analytic method and it is shown that using an optimal neural network the mean calculated error is drastically reduced.

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Determination of Micro-alloyed Elements Containing in the Solid Solution Phase in High Tensile Steel

Satoshi Kinoshiro, Tomoharu Ishida, Masao Inose, Kyoko Fujimoto

pp. 880-884

DOI:

10.2355/isijinternational.54.880

抄録

For the steel making control with micro-alloyed elements, it is essential to accurately analyze the distribution of those elements between different metallurgical phases in steel. The micro-alloyed elements contained in precipitates have been analyzed by conventional chemical or electrochemical procedures, selectively dissolving the Fe matrix by electrolysis, and separating precipitates as insoluble particles from the matrix by filtration. But this method has become inadequate to analyze the fine precipitates because some of the fine precipitates extracted are unavoidably uncollected. Hence, we have developed a quantitative analysis for micro-alloyed elements containing in the solid solution phase of steel, named solute elements, by using of analyzing a portion of the electrolytic solution. By electrolysis, solute elements are dissolved into the electrolyte, and the precipitates remain on the surface of the sample as insoluble particles. So, the analysis of the electrolytic solution during or after electrolysis enables the determination of solute elements directly. For certified reference materials, the sum total of concentration of solute element analyzed by this method and the precipitate analyzed by conventional method suits a certified value substantially on the micro-alloyed element. However, for the samples that contain fine precipitates, they are not in agreement with the total content obtained by the spark-OES. It is estimated that the precipitates not collected by filtration in the conventional method cause the disagreement. It shows the proposed method, which analyzes solute elements directly, is useful for estimating the distribution of the micro-alloyed elements between different metallurgical phases.

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Characterization of the Inhomogeneous Distribution of Light Elements in Ferritic Heat-Resistant Steels by Secondary Ion Mass Spectrometry

Shigeru Suzuki, Rie Shishido, Tomohito Tanaka, Fujio Abe

pp. 885-892

DOI:

10.2355/isijinternational.54.885

抄録

The addition of a small amount of boron and nitrogen is known to improve the creep strength and life of ferritic heat-resistant steels. These light elements are thought to be distributed in the microstructures in a complicated manner during the heat treatment and creep of these steels. In order to understand the influence of the light elements on the mechanical properties of ferritic heat-resistant steels, a microscopic distribution analysis of the light elements is of importance. In this study, two types of secondary ion mass spectrometry (SIMS) methods were used to investigate the measurement conditions for analyzing secondary ions derived from boron and nitrogen in steels. In dynamic SIMS with a quadrupole analyzer, boron in the samples was effectively detected as BO2– ions under irradiation with primary O2+ ions. From the time-of-flight (ToF) SIMS using a focused primary Bi32+ ion beam coupled with the exposure of the sample to a low partial pressure of oxygen, it was suggested that boron is enriched in M23C6 carbides in the steels and it may be, more or less, segregated at prior austenite grain boundaries with a moderate amount of nitrogen during normalizing. It was also demonstrated that nitrogen is precipitated as boron nitride in steels containing an excess amount of boron and nitrogen. The characteristics of the distribution of boron and nitrogen in the steels are discussed on the basis of the thermodynamic properties of these elements in the steels.

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Characterization of Compound Particles Formed during Thin Slab Direct Rolling of Ti-added Nb HSLA Steel

Youryeol Lee, Bruno Charles De Cooman

pp. 893-899

DOI:

10.2355/isijinternational.54.893

抄録

The absence of a reheating stage in thin slab direct rolling of Ti-added Nb HSLA steel results in the formation of compound two-phase particles prior to and during rough rolling in an in-line strip processing line. The compound two-phase particles are composed of a cuboid Ti-rich (TixNb1–x)N (0.76≥x>0.72) core and a Nb-rich cap-shaped epitaxial deposit of (TixNb1–x)C (0.29≥x>0.09) or NbC formed on one of the {100}-type faces of the cuboid (TixNb1–x)N (0.76≥x>0.72) core. At the interface between the cuboid core and the cap-shaped deposit, the Ti/(Nb+Ti) atomic ratio was found to increase gradually from a low value of Ti/(Nb+Ti)≈0, on the cap-side of the particles, to a high value of Ti/(Nb+Ti)≈0.6, on the cuboid core side of the precipitate. The fact that the compound two-phase particles are present at 1200°C indicates that they have a greater thermodynamic stability compared to NbN or NbC. A kinetic precipitation model was used to evaluate three possible mechanisms for the formation of the compound particles: a low cap/cuboid interfacial energy and a high matrix/cuboid interfacial dislocation density.

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Characterization of Microstructure and Mechanical Properties of Inconel 625 and AISI 304 Dissimilar Weldments

Kasinath Devendranath Ramkumar, Parvateneni Mithilesh, Digumarthi Varun, Ajay Reddy Gopi Reddy, Natarajan Arivazhagan, Sockalingam Narayanan, Kesavan Gokul Kumar

pp. 900-908

DOI:

10.2355/isijinternational.54.900

抄録

This investigation has been performed to characterize the microstructure and mechanical properties of the GTA and PCGTA welded dissimilar combinations of Inconel 625 superalloy and AISI 304 austenitic stainless steel. These welds were obtained by employing ERNiCrMo-3 filler metal. The weldments were characterized by the combined techniques of optical microscopy and SEM/EDAX analysis. Hardness and tensile studies were conducted to assess the mechanical properties of the weldments. Tensile studies showed that the fracture had occurred at the parent metal of AISI 304 side in both the cases.

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Atmospheric Corrosion Behavior of Weathering Steel in Periodically Changed Environment

Xu Zhang, Shanwu Yang, Hui Guo, Xinlai He

pp. 909-915

DOI:

10.2355/isijinternational.54.909

抄録

The service environments of weathering steel are periodically various. However, the general accelerated corrosion test cannot effectively simulate the periodic change. In order to investigate the influence of periodic changed environments on corrosion, a low alloy weathering steel was exposed to an indoor air with NaCl and NaHSO3 aqueous solutions spraying the steel in turns. It was found that both atmospheric corrosion rate and the degree of alloy element enrichment in the inner rust layer were higher when the samples were sprayed with NaCl aqueous solution. Meanwhile, more compact rust layers were formed when the samples were sprayed with NaHSO3 aqueous solution. Rust layer would stabilize more rapidly by spraying NaCl and NaHSO3 aqueous solutions in turns than by spraying a single corrosion solution, which can be attributed to a combined advantage of alloy element enrichment and slow corrosion. Stabilization of rust layer is not necessarily derived from enrichment of alloy elements and stabilization of rust layer can produce stronger effect against further corrosion than enrichment of alloy elements.

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Effect of Screen Open Area on Active Screen Plasma Nitriding of Austenitic Stainless Steel

Akio Nishimoto, Tatsuya Matsukawa, Hiroaki Nii

pp. 916-919

DOI:

10.2355/isijinternational.54.916

抄録

Austenitic stainless steel SUS 316L was nitrided by active screen plasma nitriding (ASPN) using screens with various open areas to investigate the effect of the screen’s open area ratio on the nitriding response. The sample was placed on the sample stage in a floating potential and isolated from the cathodic screen and anode. The screen, which was SUS 316L expanded metal mesh with 38%, 48%, or 63% open area ratio, was mounted on the cathodic stage around the sample stage. Nitriding was performed in a nitrogen–hydrogen atmosphere with 25% N2 + 75% H2 for 18 ks at 693 K under 600 Pa by the ASPN process. After nitriding, the nitrided microstructure was examined using a scanning electron microscope and an electron probe microanalyzer. The phase structures on the nitrided surface were determined by X-ray diffraction. In addition, the surface hardness and cross section of the nitrided samples were measured by the use of a Vickers microhardness tester. The thickness of the nitrided layer of the S-phase decreased with increasing open area ratio of the screen.

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Formation of Nano/ultrafine Grain Structure in a Ti-modified 201L Stainless Steel through Martensite Thermomechanical Treatment

Saeed Sadeghpour, Ahmad Kermanpur, Abbas Najafizadeh

pp. 920-925

DOI:

10.2355/isijinternational.54.920

抄録

The formation of nano/ultrafine grain structure in a Ti-modified 201L austenitic stainless steel using the martensite thermomechanical treatment was investigated. Effects of Ti micro-alloy addition on the formation of strain-induced martensite (SIM) during cold rolling and austenite reversion during subsequent annealing were studied. The results showed that the nano-grained Ti-modified 201L steel with the average grain size of 45 nm possessed the yield strength of 1000 MPa, ultimate tensile strength of 1330 MPa and total elongation of 42%. Such improvement in mechanical properties of the thermomechanically processed steel is believed to be due to the formation of SIM supplemented with precipitation of Ti carbides.

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Effect of Tempering Temperature on the Microstructure and Hardness of a Super-bainitic Steel Containing Co and Al

Feng Hu, Kaiming Wu, Tingping Hou, Amir Abbas Shirzadi

pp. 926-931

DOI:

10.2355/isijinternational.54.926

抄録

The effect of tempering temperature, within the range of 400 to 700°C, on the microstructure and hardness of two super-bainitic steels, one as the control parent sample and the other with added Co & Al was investigated. Post-tempering examinations of the super-bainitic samples showed that low temperature tempering cycles (400–500°C) resulted in carbides formation, and some increases in the hardness possibly due to precipitation strengthening in the Co & Al contained steel. Once the tempering temperature increased to 600°C, the hardness plummeted in both steels due to the concurrent coarsening of the bainitic ferrite plates and more precipitation of carbides. At the higher tempering temperature of 700°C, further reduction in the hardness occurred because of the accelerated recovery of ferrite and spheroidization of carbides. This work clearly showed that the super-bainitic steel containing Co & Al had a superior tempering resistance particularly at low tempering temperatures (<500°C) due to reduced carbide precipitation in the presence of Co & Al.

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Effect of High Heat Input on Toughness and Microstructure of Coarse Grain Heat Affected Zone in Zr Bearing Low Carbon Steel

Minghao Shi, Pengyan Zhang, Chao Wang, Fuxian Zhu

pp. 932-937

DOI:

10.2355/isijinternational.54.932

抄録

Microstructure evolution and impact toughness of simulated coarse grained heat affected zone (CGHAZ) in Zr bearing low carbon steel have been investigated in this study. Thermal simulator was used to simulate microstructure evolution of CGHAZ with high heat input welding thermal cycle at 1400°C peak temperature. Microstructure of CGHAZ consisted of high volume fraction of AF inside grain and GBF at prior austenite grain boundaries. Prior austenite grain size of CGHAZ increases with heat input increasing. Excellent impact toughness (more than 100 J) of CGHAZ with heat input of 1000 kJ/cm was obtained in this experiment. Impact toughness of CGHAZ with 400 kJ/cm (230 J) is the highest, because austenite grain size of CGHAZ with 400 kJ/cm favors the development of AF inside grain. Impact toughness is not only related with high angle boundaries but also with effective grain size. High supercooling of CGHAZ provided driving force for the AF transformation during welding thermal cycle, increasing the number of AF.

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Effect of Martensite Volume Fraction on Void Formation Leading to Ductile Fracture in Dual Phase Steels

Takashi Matsuno, Daisuke Maeda, Hiroshi Shutoh, Akihiro Uenishi, Masayoshi Suehiro

pp. 938-944

DOI:

10.2355/isijinternational.54.938

抄録

This study examines the ductile fracture of three dual-phase steels that contain low volume fractions of martensite (3.2%, 6.2% and 10%) and are composed of nearly the same quality of ferrite and martensite. The strains to rupture of the DP steel with 3.2% martensite are considerably higher than those of the DP steels with 6.2% and 10% martensite. The evolution of voids with respect to equivalent plastic strain, which is transformed from the thickness reduction of the specimen, was analyzed by SEM observation in fractured tensile specimens. The observation clarified the fact that the evolution of void size saturates at the specific strain in the DP steel with 3.2% martensite, whereas the void size in the DP steels with 6.2% and 10% martensite grows exponentially with strain. This significant favorable behavior of the DP steel with 3.2% martensite is probably caused by the relatively low heterogeneity of the stress and strain partitioning between the two phases, which allows attaining a significant higher ductility of this steel.

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Creep Deformation of Type 2205 Duplex Stainless Steel and its Constituent Phases

Heeyong Park, Bruno Charles De Cooman

pp. 945-954

DOI:

10.2355/isijinternational.54.945

抄録

The creep deformation of type 2205 duplex stainless steel in industrial continuous annealing conditions was analyzed and compared with the creep behavior of its constituent phases, ferrite and austenite. The bulk ferrite phase deformed by viscous glide. The deformation of the bulk austenite phase was by lattice diffusional creep at low applied stress and by dislocation climb at higher applied stress. Grain boundary sliding was the rate controlling mechanism of creep deformation of duplex stainless steel. The value of the stress exponent and the grain size exponent of the creep rate equation both strongly support the possibility that cold rolled type 2205 duplex stainless steel deforms superplastically during recrystallization annealing in industrial continuous annealing furnaces.

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Fracture Toughness of an Advanced Ultrahigh-strength TRIP-aided Steel

Junya Kobayashi, Daiki Ina, Asahiko Futamura, Koh-ichi Sugimoto

pp. 955-962

DOI:

10.2355/isijinternational.54.955

抄録

The fracture toughness of an advanced ultrahigh-strength 0.2%C-1.5%Si-1.5%Mn-1.0%Cr-0.05%Nb (in mass%) transformation-induced plasticity (TRIP)-aided steel with a bainitic ferrite and/or martensite structure matrix was investigated for applications in automobiles, construction machines, and pressure vessels. After the steel was austenitized and isothermally transformed via heat treatment at temperatures between 200°C and 350°C below the martensite-finish temperature, it exhibited a good combination of tensile strength (1.4 GPa) and total elongation (15%). In addition, the steel achieved a much higher plane-strain fracture toughness (KIC = 129–154 MPa m1/2) than conventional structural steel such as SCM420 steel (KIC = 57–63 MPa m1/2). Surprisingly, the fracture toughness was nearly the same as that of a maraging steel. Our results indicate that the high fracture toughness was associated with (1) a softened wide lath-martensite matrix with a low carbide content and carbon concentration and (2) effective plastic relaxation of localized stress concentration by the strain-induced transformation of fine metastable retained austenite in the narrow lath-martensite and retained austenite mixture, which suppresses void formation and cleavage crack initiation at the pre-crack tip.

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Lattice Defects Revealed by Hydrogen Thermal Desorption Analysis of Carbon Steel Strained with/without Hydrogen Pre-charging

Yutaka Tsuchida

pp. 963-969

DOI:

10.2355/isijinternational.54.963

抄録

Effects of cyclic straining on the development of lattice defects were studied in a medium carbon steel containing globular cementite, using thermal desorption analysis (TDA) of post-charged hydrogen that acts as a tracer. The TDA curves were statistically analyzed using Gaussian function in order to separate comprised sub-peaks. The influence of hydrogen pre-charging was further explored. TDA desorption curves were separated into dislocations, grain boundaries, vacancies and vacancy clusters assuming Gaussian distributions for making quantitative comparisons of each defect. Tensile straining of 0.04 readily forms small amount of vacancies. Cyclic straining of 0.004 strain amplitude was more effective in vacancy formation, followed by their clustering. Hydrogen pre-charging before strain cycling was effective in enhancing the formation of those kinds of lattice defects. The maximum fractions of peak areas due to vacancies and vacancy clusters attained in the present study are 21.9% and 6.5% of the total desorption respectively. It was also revealed that the amount of hydrogen in the desorption peak from dislocations increases by straining in the presence of hydrogen. Slow tensile straining was more notable than cyclic straining, while the latter was increased by intensified hydrogen pre-charging.

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Thermo-mechanical Behaviour of 23/8 Austenitic Stainless Steel

Nilamadhaba Sahu, Ashish Selokar, Ujjwal Prakash

pp. 970-978

DOI:

10.2355/isijinternational.54.970

抄録

The flow behaviour as well as initiation of dynamic recrystallization in Fe-23wt%Cr-8wt%Ni (23/8 steel) austenitic steel containing 0.28 wt% nitrogen was investigated using Gleeble 3800 thermomechanical simulator. Hot working was carried out in temperature range of 950–1100°C at strain rates ranging from 0.01 to 10 s–1. Based on experimental results a constitutive equation was predicted for peak flow stress embracing the Zener-Hollomon parameter. The deformation activation energy and stress exponent were calculated as 671.66 KJ/mole and 3.762 respectively. The critical stress for initiation of dynamic recrystallization was determined by the identification of an inflection point in the strain hardening rate versus stress plot. The average normalized critical stress for the metal was found as 0.806. The power dissipation efficiency and instability maps for the 23/8 austenitic stainless steel were developed adopting modified Dynamic material model (DMM). The power dissipation efficiency calculated using DMM was compared with that of modified DMM. The validity of power law during deformation process for the above material was analysed. The processing maps in connection with microstructures and experimental flow curves were used to interpret possible safe processing conditions of the above material during hot metal working. The peak efficiency of 35.91% at 0.6 strain was observed under 1100°C and 1 s–1 whereas the optimum processing condition was found under 1100°C and 0.1 s–1 having efficiency of 23.4%. Dominating damage mechanisms causing microstructure instability in this material are identified.

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Influence of Tempering Temperature on Low Cycle Fatigue of High Strength Steel

Hyuksun Kwon, Frédéric Barlat, Myounggyu Lee, Younil Chung, Sangho Uhm

pp. 979-984

DOI:

10.2355/isijinternational.54.979

抄録

In this study, the mechanical and low cycle fatigue properties for a heat-treatment steel subjected to quenching and tempering (QT) were evaluated. The steel had a modified chemical composition with respect to a conventional material and was subjected to tempering at various temperatures. It was shown that the material tempered at 250°C exhibited superior fatigue properties in the short life regions. Carbon atom clusters in concentration of 18 at% in martensite were observed using atom probe tomography (APT) for the steel tempered at 250°C. It is believed that these clusters contribute to the improvement of fatigue properties by hindering the motion of dislocations.

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Influence of Al2O3/TiO2 Ratio on Viscosities and Structure of CaO–MgO–Al2O3–SiO2–TiO2 Melts

Yu-Lan Zhen, Guo-Hua Zhang, Kuo-Chih Chou

pp. 985-989

DOI:

10.2355/isijinternational.54.985

抄録

The effect of Al2O3/TiO2 ratio on viscosities of CaO–MgO–Al2O3–SiO2–TiO2 melts was investigated by the rotating cylinder method in this study. In addition, structural characterizations of these quenched vitreous samples were also studied by Raman spectroscopy. It was indicated from the experimental results that viscosity increases as gradually increasing Al2O3/TiO2 ratio while keeping the contents of other components constant. The Raman spectra analyses indicated that TiO2 mainly exists in the form of [TiO4] as a network former in composition range of 3–17 mol%. With increasing the Al2O3/TiO2 ratio, the [TiO4] content decreases and the degree of polymerization of the melt increases resulted from the increase of Al2O3 which behaviors as an acidic oxide and incorporates into the SiO2 network with the charge balance of CaO. Consequently, there will be an increase of viscosity with increasing Al2O3/TiO2 ratio.

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Identification of the Major Constituents of Fused Potassium Silicate Fertilizer

Yasuko Yao, Etsuo Hamada, Kaoru Sato, Takashi Akiyama, Tadakatsu Yoneyama

pp. 990-993

DOI:

10.2355/isijinternational.54.990

抄録

The major component of fused potassium silicate (FPS) fertilizers, produced from steel-making slag, was studied. FPS compounds have received considerable attention as slow-release potassium fertilizers beneficial for crops. This major component was found to be a single phase compound, K2Ca2Si2O7, which had not been previously identified. In order to confirm the presence of the newly identified compound, we synthesized a potassium calcium silicate mixture, K2O–2CaO–2SiO2, by fusing a mixture of K2CO3, CaCO3, and SiO2. The X-ray diffraction patterns of the synthesized K2O–2CaO–2SiO2 were largely consistent with those of FPS fertilizer, and Energy Dispersive X-ray Spectroscopy indicated that this compound was a single phase with a K:Ca:Si molar ratio of 1:1:1. It is concluded that the major component of FPS fertilizer is a compound of K2O–2CaO–2SiO2, newly identified as K2Ca2Si2O7. FPS fertilizers exhibit the characteristic, controlled by their K2Ca2Si2O7 content, of slowly releasing potassium into water and soil.

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Prediction of Bainite Start Temperature in Alloy Steels with Different Grain Sizes

Singon Kang, Suchul Yoon, Seok-Jae Lee

pp. 997-999

DOI:

10.2355/isijinternational.54.997

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