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ISIJ International Vol. 54 (2014), No. 6

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

03 Dec. (Last 30 Days)

ISIJ International Vol. 54 (2014), No. 6

Production and Technology of Iron and Steel in Japan during 2013

The Technology Society, The Iron and Steel Institute of Japan

pp. 1177-1184

DOI:

10.2355/isijinternational.54.1177

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Effects of Interfacial Properties between Molten Iron and Alumina on Neck Growth of Alumina Balls at Sintering in Molten Iron

Masashi Nakamoto, Toshihiro Tanaka, Masanori Suzuki, Kenji Taguchi, Yuichi Tsukaguchi, Takaiku Yamamoto

pp. 1195-1203

DOI:

10.2355/isijinternational.54.1195

抄録

The effects of interfacial properties such as interfacial tension and wettability on the adhesion, agglomeration, and coalescence of inclusions on the immersion nozzle in a continuous casting process have not yet been evaluated quantitatively. In the present work, we focused on the neck growth of alumina balls at sintering because the adhesion, agglomeration, and coalescence of inclusions are regarded as being the consequence of sintering of oxides. We compared the neck growth of alumina balls at sintering in molten iron with that under an Ar gas atmosphere in order to clarify the effects of interfacial properties between alumina balls and molten iron on the sintering of alumina balls in molten iron. We found that neck growth in molten iron proceeds much faster than that under an Ar gas atmosphere. In addition, an equation for the neck growth of alumina balls in molten iron was formulated by evaluating the interfacial properties, i.e., the interfacial tension and wettability, between alumina balls and molten iron. The calculated results derived by considering the capillary phenomena of molten iron at the gap between alumina balls as the effect of wettability were in reasonable agreement with the experimental results in molten iron. These findings show that the non-wetting by molten iron of alumina balls promotes neck growth of alumina balls at sintering in molten iron.

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CO Reactivity and Porosity of Manganese Materials

Kira Turkova, Dmitry Slizovskiy, Merete Tangstad

pp. 1204-1208

DOI:

10.2355/isijinternational.54.1204

抄録

In the production of manganese alloys there is a continuing effort to utilize all raw materials. As ore fines cannot be directly added to the furnace, the fines must be agglomerated to sinter, pellets or briquettes. However, as the materials changes properties during agglomeration, there is a need to know how the effect the agglomerated material affects the furnace performance, compared to lumpy material. In this paper the CO reactivity and porosity of 3 ores and their agglomerates of sinter and pellets is studied.
In the furnaces, the higher manganese oxides (MnO2, Mn2O3, Mn3O4) are reduced to MnO with CO gas, producing CO2. If the CO reactivity is low, the CO2 may be produced above 800°C triggering the Boudouard reaction, which increases the total carbon and energy consumption. Hence, a high CO reactivity is beneficial for the process.
The present work combines the study of CO reactivity and porosity of eight different manganese materials. It is shown that manganese materials with high initial porosity have high CO reactivity. This means that Gabonese ore and CVRD ore will have a higher CO reactivity compared to their sinter and pellets. For Assmang ore, which has a low initial porosity, making an agglomerate with higher porosity, will increase the CO reactivity. The additional carbon consumption per ton of produced metal was also calculated for the materials investigated.

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Interfacial Reactions at Early Stages of Mn Addition to Liquid Fe

Pengcheng Yan, Lieven Pandelaers, Muxing Guo, Bart Blanpain

pp. 1209-1217

DOI:

10.2355/isijinternational.54.1209

抄録

Mn is an important alloying agent in steelmaking. Its interaction with liquid Fe during the alloying/deoxidation influences Mn recovery yield and steel cleanliness. We have experimentally studied the interfacial reactions at the early stages of Mn addition to liquid Fe containing various amounts of dissolved oxygen and sulphur. Diffusion couples were obtained by bringing liquid Fe into contact with solid Mn for various durations. After quenching these diffusion couples, the interdiffusion of Fe/Mn and the formation of a reaction zone at the Fe/Mn interface were investigated. The measured Mn concentration profile at the interface was fitted with a theoretical model based on Fick’s second law. The magnitude of the fitted apparent diffusion coefficient suggested that a layer of Fe solidified around the cold Mn. While enclosed by this Fe shell, the Mn was partially molten due to its low melting temperature. The formation of oxysulphide inclusions was observed at the Mn-rich side of the interface, while an inclusion free zone was detected in the Fe-rich side close to the interface. Based on these experimental findings and theoretical calculations, the mechanisms governing the Fe/Mn interdiffusion and the inclusion free zone formation were proposed.

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Dissolution Behavior of MgO and Al2O3 in FeS–Na2S Fluxes

Yun Lei, Yu-ichi Uchida, Takeshi Yoshikawa, Charles Q. Jia, Kazuki Morita

pp. 1218-1221

DOI:

10.2355/isijinternational.54.1218

抄録

In order to ascertain the optimal ladle lining to suppress erosion during the removal of Cu from molten iron using FeS–NaS0.5 fluxes, the dissolution behavior of MgO and Al2O3 in FeS–Na2S fluxes was investigated under different experimental conditions (temperatures, atmospheres and crucibles). The results obtained show that carbon saturation, lower CO partial pressure, higher temperature and higher Na2S content in the fluxes lead to higher dissolved Mg and Al contents in the final fluxes. As the degree of MgO dissolution in the fluxes was much greater than that of Al2O3, an Al2O3-based ladle lining is considered to be superior for Cu removal considering the erosion induced by FeS–Na2S fluxes. Finally, the dissolution mechanisms of MgO and Al2O3 in FeS–Na2S fluxes were discussed with regard to the experimental results.

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Quantitative Analysis of Mineral Composition of Iron Ore Sinter Based on Comprehensive Image Processing Techniques

Hong-wei Guo, Bu-xin Su, Zhen-long Bai, Jian-liang Zhang, Xin-yu Li, Feng Liu

pp. 1222-1227

DOI:

10.2355/isijinternational.54.1222

抄録

To acquire the mineral composition of iron ore sinter, the research work until now mainly focuses on two aspects which are traditional manual method often called Point Counting Method and Image Processing Method respectively. Point Counting Method is of high labor intensity and of low efficiency compared with Image Processing Method. Meanwhile, existing Image Processing Method always encounters low accuracy when it is applied to analyze the sinter with special microstructure such as large pores. This paper presents an improved method based on modified gray-level images and extracted texture images with knowledge base rules, producing the final images more suitable for computer to deal with. The experimental results demonstrate that this improved technique is valid for quantifying the mineral composition of sinter and it has a higher-level accuracy of recognition than existing image processing methods do.

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Effect of Coal Size Segregation in Coal Bin on Discharging Coke Cake

Yusuke Dohi, Koji Hanaoka, Tetsuya Yamamoto, Manabu Yokoyama, Kiyoshi Fukada, Takashi Matsui

pp. 1228-1234

DOI:

10.2355/isijinternational.54.1228

抄録

For improving the performance of discharging coke cake from oven chambers, the way to increase clearance between coke cake and oven wall near coke side was investigated. To avoid a pushing trouble is needed because this trouble, which has increased gradually with the aging of coke ovens, negatively affects the stable coke production and service life of coke ovens. One of the effective approaches to improve the discharging conditions is to maintain the sufficient clearance especially near coke side because the oven walls around there have been most damaged in aging coke ovens. Therefore enlarging the clearance near coke side was studied.
For this objective, it was focused on the way to decrease coal size and bulk density locally by controlling the coal size segregation in coal bin. Firstly, the effects of coal size and bulk density on the clearance were examined at laboratory. Then the effects of the charging conditions of coal blend on the size segregation and the clearance were investigated. As a result, the clearance increased with decreasing the coal size and bulk density. Moreover, the clearance was capable of variation by size segregation.
Based on the laboratory-scale study, a commercial plant trial was conducted. Consequently, it was clarified that the discharging behavior was improved by size segregation although the variation of the coal size was smaller than we initially envisioned.

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Re-Oxidation Kinetics of Flash Reduced Iron Particles in O2–N2 Gas Mixtures Relevant to a Novel Flash Ironmaking Process

Zhixue Yuan, Hong Yong Sohn

pp. 1235-1243

DOI:

10.2355/isijinternational.54.1235

抄録

A novel flash ironmaking process based on hydrogen-containing reduction gases is under development at the University of Utah. This process will directly reduce fine iron oxide concentrate particles in suspension in a flash reactor. During handling and transportation, product iron particles may come into contact with air. Since direct reduced iron is usually prone to oxidation, re-oxidation kinetics is of concern. The goal of this work was to determine the re-oxidation kinetics of flash reduced iron particles in O2–N2 gas mixtures. The effects of temperature (673 – 873 K) and O2 partial pressure (4 – 18 kPa) were studied and the nucleation and growth model was found to describe the initial period of oxidation before the rate decreased precipitously at certain conversion. The pressure dependence of the rate was first order with respect to oxygen partial pressure, and the activation energy was 14.4 kJ/mol. A complete rate equation that adequately represents the experimental data was developed.

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Effect of Powder–Liquid Interaction on Their Accumulation Behavior in Packed Bed

Shin Kikuchi, Shigeru Ueda, Tatsuya Kon, Ryo Inoue, Shungo Natsui, Hiroshi Nogami

pp. 1244-1250

DOI:

10.2355/isijinternational.54.1244

抄録

In ironmaking high temperature processes, solid, liquid, and gas phases coexist and interact one another. The gas flow in a packed bed containing liquid and powder depends on their distributions, and the packing structure. Some parts of the liquid and powder phases passing through of the packed bed accumulate. Excessive accumulation may clog the gas flow in the packed bed. The flow and accumulations behaviors of powder and liquid phases coexisting in a packed bed have yet to be clarified.
Thus the phenomena of liquid and powder accumulation and clogging were experimentally investigated in the present study. The effect of the wettability and powder diameter on their accumulation was mainly studied. The results revealed that the wettability of packed material with liquid had significant effect on the accumulation of powder through the form of the liquid holdup.

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Static Holdup of Liquid Slag in Carbonaceous Beds

Dongik Jang, Minsoo Shin, Joon Seok Oh, Hyun-Soo Kim, Sang Ho Yi, Joonho Lee

pp. 1251-1255

DOI:

10.2355/isijinternational.54.1251

抄録

The static holdup of liquid slag in carbonaceous beds at high temperatures was studied using lab-scale experiments. The effects of particle size, type of carbonaceous materials, and slag composition on the static holdup of liquid slag were investigated. The particle diameter was found to be the most important factor determining the static holdup. From the experimental results, the empirical dimensionless correlation for the static holdup of liquid slag (Hs) in the carbonaceous beds was derived in terms of the modified capillary number (Cpm).

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Reduction Behavior of Carbon Composite Pellets Including Alumina and Silica at 1273 K and 1373 K

Hyunsik Park, Veena Sahajwalla

pp. 1256-1265

DOI:

10.2355/isijinternational.54.1256

抄録

The effect of alumina and silica on the reaction behavior of carbon composite pellet was investigated by thermogravimetric analysis at 1273 K (1000°C) and 1373 K (1100°C). X-ray diffraction was used for the phase analysis of iron oxide changing from hematite to reduced iron. The overall reaction was divided into three stages according to phase transformation of iron oxide. CO and CO2 from off-gas data was used for kinetic analysis and for understanding reaction mechanism. The Boudouard reaction was largely influenced by alumina and silica that changed CO gas concentration resulting in different reduction behavior of the pellets. Alumina increased the reaction rate of carbon composite pellet while silica decreased the overall reaction rate.

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Three Dimensional Evaluations of REM Clusters in Stainless Steel

Yanyan Bi, Andrey Vladimirovich Karasev, Pär Göran Jönsson

pp. 1266-1273

DOI:

10.2355/isijinternational.54.1266

抄録

It is known that clusters in liquid steel have a harmful effect on the casting process and the quality of the final steel product. In this study, clusters of rare earth metals (REM) were investigated in steel samples of a S30185 stainless steel grade from a pilot trial (PT, 250 kg) and from an industrial heat (IH, 100 t). Samples were taken from the liquid steel at different holding times after the addition of mischmetal. Thereafter, REM clusters collected on film filters after electrolytic extraction and filtration were investigated in three dimensions (3D) by SEM in combination with EDS. The morphology, composition, number and size of clusters in PT and IH steel samples were analyzed and compared as a function of holding time. It was found that typical clusters with regular and irregular inclusions were the main type of clusters (69%–98%) in all PT and IH steel samples. The composition of inclusions in clusters corresponded mostly to REM-oxides. The size of clusters that were observed in different samples varied mainly from 2 to 23 μm. In addition, the size and number of most clusters in PT are larger than those in IH samples. Furthermore, the formation mechanisms and evolution of different type of REM clusters were discussed in both PT and IH heats.

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Computation of Phase Transformation Paths in Steels by a Combination of the Partial- and Para-equilibrium Thermodynamic Approximations

Takao Koshikawa, Charles-André Gandin, Michel Bellet, Hideaki Yamamura, Manuel Bobadilla

pp. 1274-1282

DOI:

10.2355/isijinternational.54.1274

抄録

A model combining the partial‑equilibrium and para‑equilibrium thermodynamic approximations is presented. It accounts for fast diffusion of interstitial elements, such as carbon, and low diffusion of substitutional elements in the solid phases, while complete mixing is assumed for all elements in the liquid phase. These considerations are turned into classical mathematical expressions for the chemical potentials and the u‑fractions, to which mass conservation equations are added. The combination of the two models permits application to steels, dealing with partial‑equilibrium for solidification and para‑equilibrium for both the δ‑BCC to γ‑FCC peritectic transformation and the γ‑FCC to α‑BCC solid state transformation. The numerical scheme makes use of calls to Thermo‑Calc and the TQ‑interface for calculating thermodynamic equilibrium and accessing data from the TCFE6 database. Applications are given for a commercial steel. The results are discussed based on comparison with classical microsegregation models and experimental data.

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Influence of a Slow Rotating Magnetic Field in Thermoelectric Magnetohydrodynamic Processing of Alloys

Andrew Kao, Peter David Lee, Koulis Pericleous

pp. 1283-1287

DOI:

10.2355/isijinternational.54.1283

抄録

The effects of a slow rotating magnetic field on Thermoelectric Magnetohydrodynamics during alloy solidification were investigated using a micro-scale numerical model. For conventional directional solidification it was shown that in general the time-dependent acceleration force on the fluid flow is negligible. Using an undercooled growth model with directional solidification approximations the effect on dendritic morphology is predicted, suggesting thermoelectric induced flows will create a significant increase in secondary branching and preferential growth directions on one side of the primary trunk. The extent of macro-segregation under these conditions was also estimated.

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Effect of the Quality of Furan Moulding Sand on the Skin Layer of Ductile Iron Castings

Rafal Dańko, Marcin Górny, Mariusz Holtzer, Sylwia Żymankowska-Kumon

pp. 1288-1293

DOI:

10.2355/isijinternational.54.1288

抄録

The paper presents the results of investigations of the influence of the quality of moulding sand with furfuryl resin hardened by paratoluenosulphonic acid, on the formation of microstructure and surface quality of ductile iron castings. Within the studies different moulding sands were used: moulding sand prepared with fresh sand and moulding sands prepared with reclaimed sands of a different purification degree, determined by the ignition loss value. Various concentrations of sulphur and nitrogen in the sand moulds as a function of the ignition loss were shown in the paper as well as the gas emission and gas evaporation rate from the moulding sands. A series of experimental melts of ductile iron in moulds made of moulding sand characterized by different levels of surface-active elements (e.g. sulphur) and different gas evolution rates were performed. It was shown that there exist a significant effect of the quality of the sand on the formation of the graphite degeneration layer.

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Numerical Modeling of Carbide Redistribution during Centrifugal Casting of HSS Shell Rolls

Laurentiu Nastac

pp. 1294-1303

DOI:

10.2355/isijinternational.54.1294

抄録

A numerical model was further developed and applied in this work to understand and optimize the carbide redistribution during centrifugal casting process used in manufacturing of high speed steel (HSS) shell rolls. This model will help to further understand the complex solidification behavior of the HSS roll. Performance of the HSS roll requires proper formation and distribution of the VC, (V, Mo)C, and Mo2C carbides as well as the eutectic carbides, which is shown by dimensional analysis to be dominated by centrifugal buoyancy effects and solidification and carbide kinetics. The model includes a rheology-viscosity sub-model to address the interference between different moving particles or classes of particles of different sizes. The carbide redistribution model was successfully validated against experimental work. A parametric study was performed to determine the key variables that influence the distribution of the VC, (V, Mo)C, and Mo2C carbides and refine the HSS microstructure including the wash (coating) material, superheat, C content of the shell material and mold temperature.

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Numerical Study of Internal SEN Design Effects on Jet Oscillations in a Funnel Thin Slab Caster

Hugo Arcos-Gutierrez, Gerardo Barrera-Cardiel, Jose de Jesus Barreto, Saul Garcia-Hernandez

pp. 1304-1313

DOI:

10.2355/isijinternational.54.1304

抄録

The understanding of the jets oscillations inside the funnel thin slab mould is essential to ensure constant molten steel delivery, better flow patterns control and consequently increase the shop productivity and quality of the final product. To achieve this, a particular numerical study of the internal nozzle design effects on the mould fluidynamics is carried out trying to determinate the origin of the jets oscillations; for this, a mathematical model was developed including the fundamental equations, the RSM turbulence model and the VOF multiphase model. The governing equations are discretised and solved thought the implicit segregated-iterative method embedded in FLUENT®. The results show that even for SEN designs with stable operational behaviour, the jet oscillations remain present and became more intense for higher casting speeds and deeper immersions. The nozzle analysis shows that the internal geometry promotes flow perturbations at the zone where the internal transversal areas start changing, generating high and low dynamic pressures encouraging a tendency for the molten steel to leave in preference for one of the ports. In addition, a delicate micro-scale force balance was found on the internal bifurcation tip of the nozzle; this balance is related to the fluctuant velocities and the ferrostatic pressure. If this balance is broken the oscillations are more intense, promoting permanent variations of the mass flow rate from one port to the other. Consequently, it is concluded that the jets oscillations have their origin inside the SEN.

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Euler-Euler-Lagrangian Modeling for Two-Phase Flow and Particle Transport in Continuous Casting Mold

Zhong-qiu Liu, Bao-kuan Li, Mao-fa Jiang, Fumitaka Tsukihashi

pp. 1314-1323

DOI:

10.2355/isijinternational.54.1314

抄録

A mathematical model based on the Euler-Euler-Lagrangian approach has been developed to study the influence of argon gas injection on the molten steel flow and particle transport behaviors in continuous casting mold. The modified k-ε model with extra source term to account for the bubble-induced turbulence is adopted to model the turbulence in this system. The transport of particle is simulated using a Lagrangian approach based on the computed two-phase flow fields. A 1/4th scale water model has been developed to investigate the bubble behavior and fluid flow pattern. Air is injected into the submerged entry nozzle (SEN) through a circumferential inlet chamber which is made using specially-coated samples of mullite porous brick. The predictions of gas bubble distribution and fluid flow pattern are in good agreement with the water model experimental observations. Argon bubbles can change the flow pattern in the upper recirculation zone of the mold, increase the fluctuation of the top surface, and shift the impingement point on the narrow wall. The effect increases with increasing argon gas flow rate, and decreasing casting speed and bubble size. Argon gas injection enhances the removal of particles. The optimum argon gas flow rate between 5 and 10 L/min, casting speed between 0.7 and 0.8 m/min, and argon bubble size around 2.5 mm are obtained using this model to improve the removal of particles.

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Scenario-based Modeling Approach and Scatter Search Algorithm for the Stochastic Slab Allocation Problem in Steel Industry

Yana Lv, Gongshu Wang, Lixin Tang

pp. 1324-1333

DOI:

10.2355/isijinternational.54.1324

抄録

A common problem encountered in steel companies is that of allocating the surplus slabs to customer orders so as to minimize the total cost of production and inventory. Due to many unpredictable events arising in practical manufacture environment, slab yields and customer demands are full of uncertainties. This paper focuses on such uncertainties and studies the stochastic version of the slab allocation problem that has received little attention in the literature. Using a scenario-based approach, we formulate the problem as a mixed integer linear programming (MILP) model. To make the MILP model more concision, we reformulate it with less variables and constraints by using a scenarios aggregation approach. The commercial optimization software such as IBM ILOG CPLEX can solve the model to optimality for small and medium scale instances, but fail to solve large scale instances to optimality. Thus, a scatter search algorithm with directed local search based on follow-up technique is proposed to solve the problem approximately. Moreover, we introduce a random perturbation strategy to avoid search process being tapped in local optimum. Computational results on randomly generated instances show that the proposed algorithm is effective.

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Quantitative Determination of Free Lime Amount in Steelmaking Slag by X-ray Diffraction

Jakub Vaverka, Kenji Sakurai

pp. 1334-1337

DOI:

10.2355/isijinternational.54.1334

抄録

Steelmaking slag is a by-product of steel making. It has been reused as a material for civil engineering, pavement construction etc. For such applications, it is extremely important to evaluate the amount of free lime, which has the chemical form of calcium monoxide (CaO) and can cause the failure of mechanical properties by volume expansion through absorption of water or carbon dioxide gas. So far, various chemical analyses of the free lime content have been employed that are frequently combined with ethylene glycol extraction. Unfortunately the method does not always distinguish the chemical form of calcium. In the present paper, we propose the use of X-ray diffraction. The technique can clearly show the existence of different chemical forms of calcium, such as CaO, Ca(OH)2, CaCO3, and calcium silicates such as Ca2SiO4 and other forms as different peaks. As the technique is non-destructive, one can also use other chemical analyses for the same samples. The amount of free lime can be determined by the standard addition method. In our study, the content of free lime in slag powder of under 32 micron dia was determined as 11.5 mass%. It was also found that the amount of free lime can be effectively decreased to 3–5 mass% by hot steam and/or carbonation processes.

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Heat Transfer Characteristics of a Circular Water Jet Impinging on a Moving Hot Solid

Hitoshi Fujimoto, Katsutoshi Tatebe, Yamato Shiramasa, Takayuki Hama, Hirohiko Takuda

pp. 1338-1345

DOI:

10.2355/isijinternational.54.1338

抄録

The heat transfer characteristics of a circular water jet impinging on a moving hot solid were investigated experimentally. In the experiments, distilled water at room temperature was used as the test coolant. The circular jet issued from a 5-mm-diameter pipe nozzle, fell vertically downward, and impinged on a horizontal moving sheet made of 0.3-mm-thick stainless steel. The initial temperature of the sheet, the jet velocity, and the moving sheet velocity were varied systematically. The initial temperature of the moving sheet was set to 100, 150, 200, or 250°C. The mean velocity at the nozzle exit was 0.4, 0.8, or 1.2 m/s, and the moving velocity was 0.5, 1.0, or 1.5 m/s. Observations made using flash photography and thermography showed that the location of the front edge of the liquid film formed upstream of the jet impact point depends on all of these factors. The local heat flux is very small in the dry area, increases steeply near the front edge of the liquid film, and reaches a peak. If the distance between the front edge of the liquid and the jet impact point is relatively large, a second peak appears near the jet impact point. An experimental correlation was developed for predicting peak heat fluxes near the front edge of the liquid, although it has no theoretical background. The correlation agrees moderately well with the experiments.

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Unusual Crystallographic Aspects of Microband Boundaries within {111}<110> Oriented Grains in a Cold Rolled Interstitial Free Steel

Nasima Afrin Zinnia, Md Zakaria Quadir, Paul Richard Munroe, Michael Ferry

pp. 1346-1352

DOI:

10.2355/isijinternational.54.1346

抄録

Microbands are well-known deformation features that generate in the rolling microstructures of many metals and alloys. The boundaries across two neighbouring microbands are comprised of dense dislocation walls and they accommodate a small average crystallographic rotation in the range of 1–4°. In this study, a combination of high resolution electron backscattered diffraction (EBSD) and transmission electron microscopy (TEM) was used to observe orientation differences of up to 20° across microband boundaries in the rolling substructures of {111}<110> oriented grains in steel. Despite their high angle nature, the microband interfaces maintain their well-known crystallographic characteristics, by being closely aligned with highly stressed slip planes. Rigid body rotations are argued to take place around the interface normal between adjacent microband lattices. This results in an unusual microstructure whereby alternating microband boundaries, oriented in equal and opposite relative angles, produce an array of orientation pairs in their spatial distributions.

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Hot Ductility of Incoloy 901 Produced by Vacuum Arc Remelting

Fatemeh Mohammadi Shore, Maryam Morakabati, Seyed Mehdi Abbasi, Amir Momeni, Rashid Mahdavi

pp. 1353-1360

DOI:

10.2355/isijinternational.54.1353

抄録

Hot tensile testing was adopted over the temperature range of 850°C–1150°C and at strain rates of 0.001 s–1–1 s–1 to study the hot ductility of Incoloy 901. Hot ductility of the material was optimized in range of 950°C–1050°C and descended at either higher or lower temperatures. Dynamic recrystallization was the reason for the improvement of ductility at high temperatures. At lower temperatures, e.g. 850°C, dynamic precipitation of intermetallic phases could effectively inhibit dynamic recrystallization and resulted in poor hot ductility.
At very high temperatures, e.g. 1150°C, the hot ductility drop was due to the decohesion of particles/matrix interfaces. The insensitivity of material to flow localization was understood from the monotonic increase of the strain rate sensitivity over the studied temperature range. The peak strain of the material unexpectedly increased with increasing temperature up to 1050°C and then decreased at higher temperatures. These results accounted for the possibility of dynamic precipitation of intermetallics at temperatures below 1050°C and thereby delaying dynamic recrystallization. The hyperbolic sine constitutive equation was used to describe the dependence of tensile stress on deformation temperature and strain rate and the corresponding material constants were determined. The average apparent activation energy for the initiation of dynamic recrystallization was determined as 359 kJ mol–1.

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Welding Behaviour of Low Nickel Chrome-Manganese Stainless Steel

Himanshu Vashishtha, Ravindra Vasantrao Taiwade, Rajesh Kisni Khatirkar, Avinash Vijay Ingle, Ravin Kumar Dayal

pp. 1361-1367

DOI:

10.2355/isijinternational.54.1361

抄録

Chrome-Manganese steel is relatively new steel as compared to its counterpart 304 series stainless steels. There are relatively few studies on the welding behaviour of low nickel Cr–Mn stainless steel (in particular, on the effect of heat input on the microstructural developments). In the present investigation, a low nickel chrome-manganese stainless steel was welded (shielded metal arc welding process) to see the effect of heat input on the microstructural evolution and mechanical properties. At higher heat inputs (404.2 J/mm and 528.1 J/mm), tensile strength and hardness are lower compared to low heat input (316.6 J/mm). Fractographic investigation of the tensile tested specimen revealed dimple-like ductile fracture. An attempt was also made to evaluate the phases incorporated in the investigated steel using Schaeffler diagram.

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Bonding and Separation between Ti-15 mol% Sn Alloy and Iron Materials

Yasuhiro Morizono, Seiichiro Nakatsukasa

pp. 1368-1373

DOI:

10.2355/isijinternational.54.1368

抄録

Diffusion bonding of Ti-15 mol% Sn alloy to various iron materials was carried out in the temperature range of 1073–1273 K for 0.9–14.4 ks in a vacuum to verify interface separation, a phenomenon that has been observed between Ti-20 mol% Al alloy and high-carbon steel after bonding treatment at 1273 K for 3.6 ks. Four types of carbon steel and one type of cast iron were used as an opposite material for the Ti-15 mol% Sn alloy. In the case of steel having a relatively low carbon content, a sound joint without defects like a gap at the interface was obtained through bonding treatment at 1273 K for 3.6 ks. However, the joints with high-carbon steel and cast iron, which were fabricated at 1273 K for 3.6 ks, had gaps at the interfaces, and several specimens separated near the interface promptly after bonding treatment. The separated surfaces of the high-carbon steel and cast iron were relatively smooth. A microstructure corresponding to the grain boundary and pearlite was observed in the surfaces. It was found that this phenomenon depended on the heating temperature and the holding time. These features were consistent with those of interface separation previously reported in the case of Ti-20 mol% Al alloy. Therefore, it is concluded that the separation phenomenon was caused by interdiffusion across the interface between the titanium alloy and the iron material.

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Elastic Limit of Fe–Pd Alloys Exhibiting Lattice Softening

Fei Xiao, Takashi Fukuda, Tomoyuki Kakeshita

pp. 1374-1378

DOI:

10.2355/isijinternational.54.1374

抄録

The elastic limit (maximum elastic strain) of Fe–Pd alloys exhibiting a second-order-like martensitic transformation from the face centered cubic structure to the face centered tetragonal structure was investigated by varying the test conditions. The elastic limit decreased from 7.3% to 4.6% as temperature was increased from 240 K to 300 K, a phenomenon that can probably be attributed to the strong temperature dependence of the elastic constant C′. The elastic limit also significantly decreased upon changing the compression direction from [001] to [011] because of the large elastic anisotropy. However, the critical resolved shear stress was only slightly influenced by temperature and the compression direction. The elastic limit of a polycrystalline specimen of the alloy was one order in magnitude smaller than that of its corresponding single crystal.

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High-temperature Oxidation Behavior of 9Cr Ferritic-steel in Carbon Dioxide

Keitarou Kaya, Shigenari Hayashi, Shigeharu Ukai

pp. 1379-1385

DOI:

10.2355/isijinternational.54.1379

抄録

Commercial STBA26, 9Cr-1Mo ferritic steel, was exposed to CO2 gas and air at 700°C in order to understand the oxidation behavior of a 9Cr-steel in CO2 atmosphere. Oxidation of STBA26 was significantly accelerated in CO2 compared to that in air. In CO2 thick iron rich oxide nodules were formed on the steel and chromium rich carbides were found to form below the oxide scale.
The carbon activity at the scale/alloy interface was sufficiently high to maintain parabolic internal continuous carbon supply to the interface is considered to be a reason to cause a breakaway of protective oxide scale.

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Three-dimensional Frontal Cellular Automata Model of Microstructure Evolution – Phase Transformation Module

Dmytro Svetozarovich Svyetlichnyy, Aleksandr Ilich Mikhalyov

pp. 1386-1395

DOI:

10.2355/isijinternational.54.1386

抄録

The paper presents three-dimensional frontal cellular automata (FCA) based model for modeling of microstructure evolution during technological processes. It is hierarchical system. The first level is FCA, the second level is modules of microstuctural phenomena; and the third level is models of technological processes. The phase transformation module (PTM) is one of the components of the second level. PTM will contain several models of phase transformation; one of them presents transformation of austenite into ferrite and perlite. This phase transformation controlled by diffusion is considered as the nucleation and the growth of grains of other phases. The nucleation algorithm is presented in the paper. An effect of nucleation sites on final microstructure was studied on three extreme nucleation variants: nucleation on the boundaries, on the edges and in the grain corners. Simulations have been carried out for low cooling rate and relatively long time of the holding at appropriate temperature. The simulation results of the microstructure evolution studies are presented in the paper.

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Numerical Simulation with Thorough Experimental Validation to Predict the Build-up of Residual Stresses during Quenching of Carbon and Low-Alloy Steels

Edwan Anderson Ariza, Marcelo Aquino Martorano, Nelson Batista de Lima, André Paulo Tschiptschin

pp. 1396-1405

DOI:

10.2355/isijinternational.54.1396

抄録

A mathematical model to calculate the build-up of residual stresses during quenching of carbon (AISI 1045) and low-alloy (AISI 4140 and 4340) cylindrical steel bars is proposed. The model is implemented as a combination of the commercial software AC3®, to simulate the microstructure evolution, and Abaqus®, to model the heat transfer and the elastic, plastic, thermal, and phase transformation strains/stresses by the finite element method. All steel properties required in the model are calculated as an average of the properties of individual microconstituents (austenite, pearlite, bainite, or martensite) weighted by their local volume fractions, enabling the model application to any type of carbon or low-alloy steel. To thoroughly verify the simulation results, experimental measurements were carried out in cylindrical bars quenched in stirred water and these measurements were compared with model results. The heat transfer coefficient between the bar and the water was calculated by an inverse solution technique, resulting in the constant value of 7200 W m–2 K–1 for the whole quenching period. For the low-alloy steels, measured and calculated volume fractions of martensite in the bar cross sections are in very good agreement, but for the carbon steel, large discrepancies are observed in the fractions of most constituents. Tangential and axial residual stresses were measured on the lateral surface of the quenched bars using the X-ray diffraction method. These stresses, which are compressive, agree well with those calculated by the present model, showing discrepancies generally lower than 10%.

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Microstructural and Texture Development during Multi-Pass Hot Deformation of a Stabilized High-Chromium Ferritic Stainless Steel

Saara Mehtonen, Eric Palmiere, Devesh Misra, Pentti Karjalainen, David Porter

pp. 1406-1415

DOI:

10.2355/isijinternational.54.1406

抄録

With the ultimate target of improving the deep drawability of a dual-stabilized 21%Cr ferritic stainless steel, the evolution of the flow stress, microstructure, texture, dislocation structures and precipitation during multi-pass hot deformation were studied. Plane strain compression in three passes with 0.4 – 0.5 pass strains and 20 s inter-pass times was employed together with scanning electron microscopy combined with electron backscatter diffraction (SEM-EBSD) and transmission electron microscopy (TEM). The temperature of the final pass was varied between 1223 K and 923 K and the final cooling took place either by water quenching to room temperature or water cooling to 923 K followed by cooling at 0.33 K/s to room temperature. At 1223 K, static recrystallization was almost complete during the 20 s inter-pass times and this randomized the texture. When the deformation temperature was lowered to 1073 K or 923 K, in-grain shear bands were formed in the grains belonging to the γ fibre. The deformation temperature of the third pass had only a minor effect on the deformation texture intensity maxima. The final dislocation structure was not changed by the cooling rate from 923 K, but slow cooling enabled precipitation to occur. The results indicate that although the deformation conditions affect the deformed microstructures and dislocation structures, the effect of the deformation temperature on the texture was insignificant.

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Influence of Sheared Edge on Hydrogen Embrittlement Resistance in an Ultra-high Strength Steel Sheet

Masataka Yoshino, Yuki Toji, Shusaku Takagi, Kohei Hasegawa

pp. 1416-1425

DOI:

10.2355/isijinternational.54.1416

抄録

Automotive parts made from steel sheets normally have sheared edges, which have been reported to decrease the hydrogen embrittlement (HE) resistance of ultra-high strength steel (UHSS) sheets. However, the mechanism on the detrimental effect of the sheared edge on HE resistance is not yet clearly understood. In this study, the influence of the edge condition in UHSS sheets on the HE property was investigated using a 1180 MPa grade steel sheet. The HE resistance of specimens with the edges ground or as-sheared was evaluated by the U-bend method. Two types of as-sheared specimens, which had been bent so that either the burnished surface or the fracture surface was the outer side, were prepared. The specimens with the ground edges did not fracture under any conditions. The fracture stress of the fracture surface specimens was significantly lower than that of the burnished surface specimens. Microcracks were observed at the edge of the specimens except for the ground specimens, and larger microcracks were observed in the fracture surface specimens. Fracture stress drastically decreased as the microcrack length increased. The threshold of the stress intensity factor K decreased with increasing diffusible hydrogen content. When the threshold stress intensity factor at each diffusible hydrogen content was defined as KH, the fracture condition was described as K > KH. The reason why the fracture stress in the as-sheared specimen decreased was considered to be that K increased due to the microcracks introduced by bending.

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Wetting and Cooling Performance of Mineral Oils for Quench Heat Treatment of Steels

Gopalan Ramesh, Kotekar Narayan Prabhu

pp. 1426-1435

DOI:

10.2355/isijinternational.54.1426

抄録

In the present work, wetting kinetics, kinematics and heat transfer characteristics of mineral oils having varying thermo-physical properties sourced from different suppliers were investigated using contact angle, online video imaging and cooling curve analysis techniques. The relaxation behavior of mineral oils of low viscosity and surface tension on Inconel substrate indicated improved wettability and fast spreading kinetics while mineral oils of high viscosity and surface tension showed reduced wettability and slower spreading kinetics. Further, the spreading behavior of mineral oils of lower viscosity and density showed the absence of viscous regime. During rewetting, formation of double wetting fronts and more uniform nature of wetting front were observed with mineral oils of high viscosity and flash point whereas no additional wetting front was observed for mineral oils of low viscosity and flash point. Among the convectional/fast/hot mineral oils, higher wetting front velocity and cooling rate were obtained for low viscosity mineral oil. The heat extracting capability of high viscosity mineral oils was higher during vapour and nucleate boiling and lower during liquid cooling stage. Further, highly viscous mineral oils showed uniform heat transfer compared to mineral oils having low viscosity.

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Gigacycle Fatigue Properties of Double-Melted SCM440 Steel and Size Effects

Yoshiyuki Furuya

pp. 1436-1442

DOI:

10.2355/isijinternational.54.1436

抄録

Gigacycle fatigue tests were conducted on double-melted SCM440 low-alloy steel using larger and conventional specimens and comparing the results with those of single-melted steel. Although all specimens experienced internal fractures, size effects were minor in the double-melted steel, unlike in the single-melted steel: specifically, for the double-melted steel, differences in fatigue strength and inclusion size were minimal between the larger and conventional specimens. These results mean that the double-melted steel showed superior gigacycle fatigue properties to the single-melted steel when the larger specimens were used in the fatigue tests, whereas this superiority was doubtful when conventional specimens were used. When the inclusion sizes were estimated using the results for the larger specimens, the inclusion size for 150 kg of the double-melted steel was a maximum of 47 μm, one-third of that for the single-melted steel. The use of larger specimens is thus highly advisable for evaluating the gigacycle fatigue properties and the inclusion size of high-strength steels.

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Influence of Gluconic Acid on Dissolution of Si, P and Fe from Steelmaking Slag with Different Composition into Seawater

Xiaorui Zhang, Hidaka Atsumi, Hiroyuki Matsuura, Fumitaka Tsukihashi

pp. 1443-1449

DOI:

10.2355/isijinternational.54.1443

抄録

In order to continuously supply nutrient elements such as Si, P and Fe into seawater for the multiplication of phytoplankton, steelmaking slag has always been utilized at coast. Yet Fe as the obligatory micronutrient element shows an extremely low solubility under the natural seawater condition. As one kind of the broadly existing organic ligands, gluconic acid is able to form a complex with iron in alkaline aqueous solution, by which the soluble iron will be stabilized and thus the solubility of iron will be improved. In the current research, the influence of gluconic acid on the dissolution of Si, P and Fe as well as the variation of pH was investigated by using shaking experiment. Present results show that gluconic acid has little effect on the variation of pH and the increase of the dissolved Si and P concentrations, whereas gluconic acid enhances the dissolution of Fe greatly by forming the iron-gluconate complexes. However, the photo-reduction reaction of iron-gluconate complex occurred during shaking in the day time results in a slight decline of the concentration of the soluble iron.

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High Temperature Reduction of the Stiff Vacuum Extrusion Briquettes under the ITmk3 Conditions

Aitber Bizhanov, Alexander Pavlov, Olga Chadaeva, Yogesh Dalmia, Bhagiratha Mishra

pp. 1450-1452

DOI:

10.2355/isijinternational.54.1450

抄録

Stiff vacuum extrusion has been applied for the agglomeration of the iron ore concentrate and fine coal. The products of agglomeration– extrusion briquettes (BREX) were subjected to the high temperature reduction. Under the conditions similar to the ITmk3 process in general. It has been demonstrated that the iron ore and coal BREX could be considered as the alternative to the iron and coal pellets for the high temperature reduction in furnaces like Rotary Hearth Furnace (RHF).

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Improved Thermodynamic Formula for Austenite/(Austenite+Cementite) Phase Boundary in Low Alloy Steels

Suchul Yoon, Seok-Jae Lee

pp. 1453-1455

DOI:

10.2355/isijinternational.54.1453

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