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ISIJ International Vol. 49 (2009), 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. 49 (2009), No. 6

Production and Technology of Iron and Steel in Japan during 2008

The Technical Society, the Iron and Steel Institute of Japan

pp. 749-770

DOI:

10.2355/isijinternational.49.749

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Thermodynamic and Kinetic Analysis of Nitrogenization in Desulfurization of Hot Metal by Magnesium Injection

Haiping Sun, Yung-Chang Liu, Muh-Jung Lu

pp. 771-776

DOI:

10.2355/isijinternational.49.771

抄録

Literature study and thermodynamic/kinetic analysis have been carried out on the effect of carrier gas on hot metal desulfurization by magnesium injection. The literature study shows that the magnesium efficiency of the process could be deteriorated by using nitrogen as carrier gas, but the difference in magnesium efficiency for the process using argon and that using nitrogen was not clearly identified. Thermodynamic/kinetic analysis shows that when nitrogen is used as carrier gas for introducing magnesium into hot metal, the formation of magnesium nitride is possible in the regions close to the lance tip. The nitride formed at lance tip may cause lance clogging. Magnesium nitride is unstable in hot metal or in gas at high temperatures; and after leaving lance tip regions, magnesium nitride will undergo decomposition. Magnesium loss in process off gas will be increased by the decomposition of magnesium nitride that occurs too closely to bath surface or by any un-decomposed magnesium nitride at bath surface. The magnesium loss by nitrogenization and the clogging problem could be minimized by optimizing injection conditions.

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Behavior and State of Boron in CaO–SiO2 Slags during Refining of Solar Grade Silicon

Leandro Augusto Viana Teixeira, Yomei Tokuda, Toshinobu Yoko, Kazuki Morita

pp. 777-782

DOI:

10.2355/isijinternational.49.777

抄録

The thermodynamics of boron removal during the refining of solar grade silicon by slag treatment was investigated using CaO–SiO2 slags. The partition ratio of boron between slag and silicon phases and the state of boron in slag were investigated for a composition range of CaO/SiO2 between 0.55–1.21, and for boron concentrations varying from 50 ppm to 0.25 wt% at 1823 K. The best boron partition ratios were attained for CaO/SiO2 values of 1.21 and 0.55 (5.5 and 4.3, respectively), and it had a minimum value of 1.9 for a CaO/SiO2 value of around 0.8. The dependence of the boron distribution with content between silicon and slag phase showed that boron exists as a monomer for all the slag compositions studied in this work. A thermodynamic evaluation of the system was carried out by calculating the activity coefficient of BO1.5, revealing a decrease in the activity coefficient with an increase in the silica content when the CaO/SiO2 ratio was lower than 0.8. The decrease in the activity coefficient was attributed to the incorporation of boron oxide in the silicate network present in slags having high silica content. This assumption was confirmed by solid state 11B NMR analysis and supported by quantum chemical calculations.

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Removal of Boron from Molten Silicon Using CaO–SiO2 Based Slags

Leandro Augusto Viana Teixeira, Kazuki Morita

pp. 783-787

DOI:

10.2355/isijinternational.49.783

抄録

The global shortage of solar grade silicon for the production of photovoltaic cells has motivated many researches on the refining of silicon, especially the refining of metallurgical-grade silicon. In order to obtain better control of the removal process of boron from molten silicon using silicate slags, precise thermodynamic data are required. In the present study the partition ratio of boron (LB) between the slag and silicon phases and the activity coefficient of boron oxide in CaO–SiO2, CaO–SiO2–25%CaF2, and CaO–SiO2–40%CaF2 slags were evaluated at 1823 K. The activity coefficient of BO1.5 was investigated for slags of CaO/SiO2 ratio varying from 0.3–7.0; further, the borate capacity of the slag is defined in this study as:

[Equation]

The addition of Na2O to CaO–SiO2 slags was found to increase the partition ratio of boron between the slag and the silicon phase.

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Wetting of Solid Iron, Nickel and Platinum by Liquid MnO–SiO2 and CaO–Al2O3–SiO2

Gavin Parry, Oleg Ostrovski

pp. 788-795

DOI:

10.2355/isijinternational.49.788

抄録

Wetting of solid metals—iron, nickel and platinum, by molten MnO–SiO2 (MS) and CaO–Al2O3–SiO2 (CAS) oxide systems was studied by the sessile drop method at 1350–1450°C in reducing atmosphere. Terminal contact angles (after 240 min) for MS system were: for iron substrates—5±2 deg at 1350°C, 9±2 deg at 1390°C, 6±2 deg at 1450°C; platinum—15±2 deg at 1350°C and 1390°C, and 12±2 deg at 1450°C. Contact angle for the Ni–MS system was close to zero—3±2 deg at 1350°C and 1390°C. Contact angles with CAS system were: iron—55±2 deg (1350°C), 60±2 deg (1390°C), 44±2 deg (1450°C); nickel—59±2 deg (1350°C), 60±2 deg (1390°C); and platinum—15±2 deg (1350°C, 1390°C and 1450°C). Work of adhesion for all substrates with MS system was 910 to 930 mJ/m2. Interfacial tension with MS system was 1480 mN/m for Ni at 1350 to 1390°C, and 1880 to 1890 mN/m for Pt in the temperature range 1350 to 1450°C. For iron, interfacial tension was 1720 mN/m at 1350°C; 1580 mN/m at 1390°C and 1450°C. Lower work of adhesion and higher interfacial tension were found for metals with CAS system. Reduction of MnO from MS system was observed, leading to Mn dissolution in metal substrates. Degree of silica reduction from MS system was much smaller in comparison with MnO reduction (negligible for Pt); it was very minor from CAS system. Reduction of oxides and adsorption of oxygen modify the metal–oxide interface, making wetting dynamic and profoundly affecting interfacial properties.

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Mathematical Modeling of High Intensity Electric Arcs Burning in Different Atmospheres

Marco A. Ramírez-Argáez, Carlos González-Rivera, Gerardo Trápaga

pp. 796-803

DOI:

10.2355/isijinternational.49.796

抄録

Previous works attempting to simulate DC arcs have assumed the plasma gas to be composed by 100% air, consequently, the arc region has been represented by solving the equations that govern the process, i.e. heat and mass conservation equations coupled to the turbulent Navier–Stokes equations. A real plasma gas is composed by a complex mixture of several gases, such as air (from environment), CO and CO2 (coming from decarburization and post combustion), H2O and H2 (from humidity) as well as metallic and non-metallic vapors coming from scrap melting. The real plasma composition is unknown, however, if air does not represent the atmosphere in which a DC arc burns, the following question arises: How is the arc being affected by burning in different atmospheres? To answer this question, in this work a mathematical model was developed to represent a DC arc burning in different gases such as nitrogen, argon, hydrogen, oxygen, CO2 and CO. The model was used to study the effect of the gas composition on the electrical characteristics of the arc. It was found that air followed by CO and CO2 are the most efficient gases to melt and heat up the bath. Argon is a special case since has the highest conductivity and lowest heat capacity that would be very useful for long arc length applications.

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Ti Deoxidation Equilibrium in Molten Fe–Ni Alloys at Temperatures between 1823 to 1923 K

Seong-Ho Seok, Takahiro Miki, Mitsutaka Hino

pp. 804-808

DOI:

10.2355/isijinternational.49.804

抄録

Equilibrium relation between Ti and O in molten Fe–Ni alloy has been investigated at 1873 to 1923 K. Ti oxide equilibrated with molten Fe–Ni alloy has been determined by EBSD (Electron Backscatter Diffraction) pattern analysis using FE-SEM (Field Emission Scanning Electron Microscope). The present results have been numerically analyzed by the excess Gibbs free energy change of mixing for the Fe–Ni–Ti–O system with Redlich–Kister type polynomial. Redlich–Kister type polynomial parameters concerning Ni and Ti were determined as follows,
0ΩNi–Ti = 424280−270.40T J/mol (XTi<0.003, 1823 K≤T≤1923 K),
1ΩNi–Ti = −663380+313.15T J/mol (XTi<0.003, 1823 K≤T≤1923 K).

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Reduction Behavior of Hematite Composite Containing Polyethylene and Graphite with Different Structures with Increasing Temperature

Taichi Murakami, Takumi Akiyama, Eiki Kasai

pp. 809-814

DOI:

10.2355/isijinternational.49.809

抄録

Plastic wastes can play the significant role of reductants for iron oxides by supplying reducing gases, e.g., H2 and CO, through pyrolysis. However, there is a problem that the thermal degradation temperature of plastics is significantly lower than the reduction temperature of iron oxide. If a large temperature difference can be formed within the composite granule, the reducing gases thus released can be used as reductants. Therefore, in this paper, the reduction behavior of the composites prepared by using hematite, graphite, and polyethylene regents with different compositions and structures was examined in order to understand the reduction behavior and to attain a high utilized ratio of polyethylene to reduction. Reduction experiments of the composites were carried out under an inert gas flow, and gases formed during reduction were continuously analyzed. The reduction degree of hematite was calculated using the concentration of these gases. Further, micro- and macrostructures of the reduced composite were observed. The addition of polyethylene to a hematite composite containing polyethylene and graphite led to a decrease in the final reduction degree, under the same ratio of carbon to oxygen in the composite. This indicates that the contribution of polyethylene to the reduction reaction was limited. This is because the crack formation enhanced the direct outward flow of the composite without contributing to the reduction reaction. In contrast, the double-layer composite, in which the polyethylene content in the inner layer is larger than that in the outer, shows an effective utilization of polyethylene as compared to the homogeneous composite.

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Recycling of Waste Mill Oil through Non-recovery Coke Making

S. C. Barman, P. Prachethan Kumar, B. R. Patil, A. Kinlekar, S. Reddy

pp. 815-818

DOI:

10.2355/isijinternational.49.815

抄録

A plant scale trial was conducted to recycle the mill oil waste through non recovery coke oven route. The waste mill oil was added in the coal blend as a binder before hammer mill and charged in the ovens. JSW Steel has non-recovery coke ovens synergized with vibro-compaction technology to produce coke of 1.2 Mtpa. About 300 L of the mill oil which is generated in the hot strip mill daily was used in the trial. A cake density of 1.1 t/m3 has been achieved using vibro-compaction with optimized moisture, oil addition and crushing fineness. The coke produced with and without oil of same coal blend and coking conditions, was tested and compared. It is observed that utilization of mill oil has not shown any deteriorating effect on coke quality. There is a marginal increase in flue gas as well as oven crown temperature which helped to increase the power generation. This present paper describes the effect of mill oil addition on coke quality and the oven thermal conditions and the feasibility of recycling the waste through non recovery coke ovens at JSW Steel Ltd.

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Model Study of the Effects of Coal Properties and Blast Conditions on Pulverized Coal Combustion

Yansong Shen, Baoyu Guo, Aibing Yu, Paul Zulli

pp. 819-826

DOI:

10.2355/isijinternational.49.819

抄録

High coal burnout within the raceway is important for the operation of a blast furnace. It is usually achieved by adjusting some operational parameters in practice. In this work, a three-dimensional model we developed recently is used to investigate the effects of some key operational parameters on coal burnout. The results confirm that notable improvements in final burnout can be achieved for coals with more fine particles and high volatile matter, and by higher oxygen enrichment. The use of high blast temperature can increase coal burnout, but the further increase in blast temperature over 1200°C has little effect on final burnout. The effects of these parameters on other combustion characteristics are also analysed, in terms of volatile content, temperature field and gas species distribution, aiming to understand the underlying mechanisms behind these improvements. It is demonstrated that local oxygen supply is very important for high burnout in addition to coal properties. In addition, it is necessary to consider the raceway region when investigating the effects of these variables on coal burnout. This study helps identify appropriate and cheaper coals and optimise operating conditions to maximize the benefits of pulverized coal injection.

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Reaction Model and Reduction Behavior of Carbon Iron Ore Composite in Blast Furnace

Shigeru Ueda, Kazunari Yanagiya, Kentaro Watanabe, Taichi Murakami, Ryo Inoue, Tatsuro Ariyama

pp. 827-836

DOI:

10.2355/isijinternational.49.827

抄録

Decreasing the carbon dioxide emission from steel industries is an important issue. It is considered that due to the high reactivity of carbon iron ore composite, it can control the thermal reserve zone temperature and decrease the consumption of reducing agents in blast furnace. In the present study, a reaction model of the carbon iron ore composite based on a lumped system is proposed to analyze the reduction behavior in the blast furnace. This model is composed of several reaction steps between carbon, iron ore, and gas phase. The carbon solution loss reaction rate of the small particles of reducing agents is determined by the thermogravimetric method. It is found that the gasification of reducing agents is the rate-determining step in the reduction of the carbon iron ore composite. Accordingly, the particle size and reactivity of reducing agents such as coke have an influence on the reduction rate of the carbon iron ore composite. The influence of the gas composition in the atmosphere around the composite on the reduction is analyzed by using the reaction model. Moreover, the reduction behavior of the carbon iron ore composite in the blast furnace is quantitatively examined by comparison of reduction degree and gas composition change in order to investigate the reduction mechanism of reducing agents.

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Development of Technology to Control Mg Content in Molten Nickel Alloy of NW2201

Yuichi Kanbe, Hidekazu Todoroki, Yusuke Kobayashi, Kiyoteru Shitogiden

pp. 837-842

DOI:

10.2355/isijinternational.49.837

抄録

Technology to precisely control Mg content has been developed to improve hot-workability of NW2201 Ni alloy. Relatively high standard deviation of Mg contents, 0.007, out of average Mg content of 0.02 mass% was problem among heats. This brought poor hot-workability leading to sliver-like surface defects on the strip when Mg content was relatively high or low.
Laboratory-scale experiments were performed to understand the behavior of Mg in terms of equilibrium and mass-transfer of the slag/metal reaction of 3(MgO)+2Al=(Al2O3)+3Mg. Experiments were firstly carried out to understand Mg content in molten Ni equilibrated with CaO–Al2O3–MgO–CaF2 system slags. It was found that Mg content in liquid Ni depended on Al content and C/A (CaO/Al2O3 ratio in mass%) in the slag. The measured Mg contents mostly agreed with thermodynamic calculation. Further, kinetic analysis was also undertaken experimentally by approaching from both higher and lower Mg contents to the equilibrium Mg content. As a result, mass-transfer of Mg in molten Ni is considered as the rate-determining step for the above reaction.
By applying the countermeasures, introduced from the view points of both equilibrium and kinetics, for practice, the standard deviation of Mg content was improved from 0.007 to 0.003 among heats. Consequently, the defects have been improved successfully.

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Crystallization Behaviors of Mold Fluxes Containing Li2O Using Single Hot Thermocouple Technique

Hui Liu, Guanghua Wen, Ping Tang

pp. 843-850

DOI:

10.2355/isijinternational.49.843

抄録

Minor addition of Li2O (<2 mass%) can significantly alter the melting temperature and viscosity of a mold flux. However, the crystallization tendency of mold fluxes containing Li2O more than 2 mass% hasn't been understood. In this paper, single hot thermocouple technique, X-ray diffraction, and Back Scattered Electron (BSE) were employed to investigate the crystallization behavior concerned with CCT and TTT diagrams of mold fluxes containing high content of Li2O.
The critical cooling rate and crystallization rate of samples were increased with the addition of Li2O, whether there is Na2O or not. But the incubation time was reduced obviously with Li2O more than 6 mass% in mold fluxes. The critical cooling rate and incubation time of NL1.5 sample (Na2O=8 mass%, Li2O=1.5 mass%) were close to those of L7 sample (Na2O=0 mass%, Li2O=7 mass%). Moreover, there is no difference in the crystal phase of the two samples, and the crystal phases precipitated at high temperature and low temperature were respectively Ca2(SiO4) and Ca4Si2O7F2. Li-cuspidine was promoted to precipitate when the basicity of the sample was increased. The small, dense grains of cuspidine were observed in NL1.5 sample, and the thickness of slag film was 0.4 mm more than that of L7 sample. The heat flux of NL1.5 sample measured was 10% less than that of L7 sample, as expected. Therefore, high content of Li2O can be substituted by the combination of Na2O and minor of Li2O, as is the composition in the commercial mold fluxes.

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Effect of C and Mn Variations Upon the Solidification Mode and Surface Cracking Susceptibility of Peritectic Steels

Eddy Alfaro López, Martín Herrera Trejo, José Jorge Ruíz Mondragón, Manuel de Jesús Castro Román, Hugo Solís Tovar

pp. 851-858

DOI:

10.2355/isijinternational.49.851

抄録

This work studies the effect of chemical composition, C and Mn contents, and cooling rate on both the solidification mode and the evolution of phases during the solidification of three steels; two of hypo-peritectic and one of hyper-peritectic composition. Furthermore, the cracking susceptibility associated to both the differences in mechanical behavior of δ and γ phases, and contraction during solidification, was inferred.
Slight variation of C or Mn, in the order of 0.04%, promoted significant changes in the evolution of phases during solidification. It was observed that for the hypo-peritectic steel closer to the peritectic point, the Mn microsegregation observed for high cooling rates promoted at the end of solidification a hyper-peritectic solidification mode. On the other hand, independently of the solidification mode and chemical composition of the studied steels, the differences in the mechanical behavior of δ and γ phases led to a cracking susceptibility in two solid fraction zones.
Furthermore, for the steel exhibiting hypo-peritectic solidification mode the peritectic transformation occurred at higher solid fraction compared with the steels showing hyper-peritectic solidification mode. Therefore, the remaining liquid ability to feed the contraction in the solid–liquid shell associated to the peritectic transformation resulted adversely affected. Hence, the cracking susceptibility observed in the hypo-peritectic steel is not only generated by differences in the mechanical behavior of δ and γ phases, but also by the liquid inability to compensate the contraction associated to the peritectic transformation.

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A Shape Decision and Control Scheme for the Stainless Steel at the Skin Pass Mill

Yone-Gi Hur, Young-Kiu Choi

pp. 859-867

DOI:

10.2355/isijinternational.49.859

抄録

The objective of this paper is to build a shape decision and control system for the stainless steel and to ensure reducibility of workload for the next rolling process. The criterion of the shape quality is derived from the customer needs, and a shape decision system is implemented at the skin pass mill (SPM). The methods of shape decision are based on curve fitting and frequency analysis, and so on. A shape control system is also implemented with a programmable logic controller (PLC) using fuzzy logic. It receives process data from sensors such as shape meters, load cells, and pressure transducers. The field test with concerned customers is successful in the shape decision and control. The rate of the right decision is almost 99% and the claims from the customer have been largely reduced by annual 102 tons. The productivity of the rolling process is increased up to 38%.

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Influence of Lubricant Factors on Coefficient of Friction and Clarification of Lubrication Mechanism in Hot Rolling

Akira Azushima, WeiDong Xue, Yoshiaki Yoshida

pp. 868-873

DOI:

10.2355/isijinternational.49.868

抄録

In order to reduce the rolling force and the roll wear, the lubricants have been used in hot sheet rolling of steel, but the lubrication behavior at the interface between roll and workpiece in hot steel rolling have never been well understood. On the other hand, hot rolling process with high reduction in thickness have been developed to produce the ultra-fine grained steels. The high reduction in hot rolling causes some troubles such as the increase of the rolling force, the occurrence of friction pick up and so on. To solve these problems, the lubrication behavior at the interface between roll and workpiece in hot steel rolling must be quantitatively understood. In this paper, the coefficients of friction were measured by using the newly developed simulation testing machine for hot rolling. The effects of lubricant factors such as the compositions and the viscosity of the base oil and the additive agents on the coefficient of friction were investigated. From these experimental results, the lubrication behavior at the interface between roll and workpiece was investigated and the lubrication mechanism was proposed.

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The Effect of Lubricant on Microwear of Dull Rolls in Temper Rolling by 4 Hi Rolling Mill

Naoki Nagase, Seiichi Shido, Ikuo Yarita

pp. 874-880

DOI:

10.2355/isijinternational.49.874

抄録

The surface roughness of a roll is imprinted on a carbon steel sheet by temper rolling. It is important to reduce roll microwear; since the roll surface causes microwear, the roughness of the rolled sheet could not be controlled. In most cases, temper rolling is performed using lubricants or under a dry condition. However, the influence of lubricant on roll microwear has not been clarified. In this study, roll microwear has been evaluated under three lubrication states, using a 4-high rolling mill. Temper rolling experiments for as-annealed low-carbon steel strips and as-annealed high-carbon steel strips have been conducted in the reduction range of 1 to 3%. The experiments were performed under three lubrication states: a dry condition, with a water-soluble lubricant, and with a mineral oil. A shot-dull roll (SD roll) and an electric-discharged dull roll (ED roll) were employed. Surface textures of the rolls have been observed directly with a laser microscope by identifying the exact locations using markers to acquire three-dimensional microgeometry before and after rolling. Surface textures in terms of the mean surface roughness (Ra), three-dimensional texture, cross-sectional profile and material ratio curve were applied to compare the microwear of dull rolls. As a result, roll microwear was found to occur when a total contact length between roll and strip reaches 80 m. The ED roll shows greater roll microwear than the SD roll under the dry condition. The use of the water-soluble lubricant and the mineral oil decreases the roll microwear of the ED roll.

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The Effect of Soluble Lubricant on Surface Imprinting in Temper Rolling by 4 Hi Rolling Mill

Naoki Nagase, Seiichi Shido, Ikuo Yarita

pp. 881-889

DOI:

10.2355/isijinternational.49.881

抄録

The surface roughness of carbon steel sheets is controlled by dull roll surface imprinting by temper rolling. In most cases, temper rolling is performed using a lubricant or under a dry condition. However, the oil film of the lubricant and its lubricating ability have not been clarified. In this study, the effect of a lubricant on surface imprinting by temper rolling was investigated under the following three lubrication states: a dry condition (no lubricant), with a water-soluble lubricant and with a mineral oil. Temper rolling experiments for as-annealed low-carbon steel strips and as-annealed high-carbon steel strips were conducted in the reduction range of 1 to 3%, using the 4-high rolling mill. A shot-dull roll and an electric-discharged dull roll were employed as work rolls. The surface texture of temper rolled strips was observed directly, and surface textures in terms of the mean roughness (Ra), three-dimensional texture, cross-sectional profile, material ratio curve and probability density in order to compare the effect of the lubrication states. As a result, for high-carbon steel, the use of the water-soluble lubricant leads to better surface imprinting than the dry condition and the use of the mineral oil. The use of the mineral oil results in the least surface imprinting. For the low-carbon steel, the use of the water-soluble lubricant and the dry condition lead to better surface imprinting than the use of the mineral oil.

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Texture Development and Formability of Strip Cast 17% Cr Ferritic Stainless Steel

Haitao Liu, Zhenyu Liu, Guodong Wang

pp. 890-896

DOI:

10.2355/isijinternational.49.890

抄録

In order to optimize the formability of ferritic stainless steel (FSS), control of the crystallographic texture is essential. In the present work, texture development of cast strips with different initial solidification structure during rolling and subsequent annealing and the formability of final sheets were investigated. Fully equi-axed and columnar grained cast strips of Fe17%Cr FSS were fabricated by a pilot twin-roll strip caster. The equi-axed and columnar grained bars cut from a conventional continuous cast slab were used as comparable specimens. It was shown that in the cold rolled and annealed sheet of fully equi-axed cast strip, uniform and strong γ-fiber recrystallization texture was formed and {001}‹110› component was almost eliminated. By contrast, the recrystallization texture in the conventional sheets with equi-axed and columnar initial solidification structures exhibited typical shift towards high-index {334}‹483›, which led to a reduced r-value as compared to that of the equi-axed cast strip. The final annealed sheet of fully columnar cast strip, however, showed weaker γ-fiber recrystallization texture and lower r-value than those of conventional sheets. It is, therefore, believed that twin-roll strip casting can improve the formability of 17% Cr FSS only under the pre-condition that appropriate solidification structure is obtained.

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High Speed–High Quality Friction Stir Welding of Austenitic Stainless Steel

Takeshi Ishikawa, Hidetoshi Fujii, Kazuo Genchi, Shunichi Iwaki, Shigeki Matsuoka, Kiyoshi Nogi

pp. 897-901

DOI:

10.2355/isijinternational.49.897

抄録

Although several studies on the friction stir welding of high temperature materials have recently been reported, their practical use has not yet occurred due to some problems to be solved such as decreases in the corrosion resistance and joint efficiency during a high-speed joining. In this study, the effect of the welding speed on the joint efficiency was investigated in detail. As a result, it has been clarified that at a rotational speed of 600 rpm, the friction stir welding of 304 austenitic stainless steel is possible up to the joining speed of 1200 mm/min, and the tensile strength of the joint exceeds that of the parent material up to the joining speed of 1150 mm/min. In addition, the corrosion resistance is significantly improved at the higher welding speeds. No rust was observed during the salt spray testing of the 1000 mm/min joint. Thus, an increase in the welding speed can improve productivity and the product quality by decreasing corroded region. These results are expected to extend to an actual application to products by further improving the technology.

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Development of Ultrahigh Strength Low Alloy Steel through Electroslag Refining Process

S. K. Maity, N. B. Ballal, G. Goldhahn, R. Kawalla

pp. 902-910

DOI:

10.2355/isijinternational.49.902

抄録

In this investigation, attempts are made to develop special steel by electroslag refining (ESR) process. The base alloy is prepared with a chemical composition of 0.28% C, 1.0% Mn, 1.0% Mo, 0.35% V, 4.2% Cr with trace amount of S and P. This alloy displays yield strength of about 1450 MPa in quenched-and-tempered condition. It is further attempted to increase the strength and toughness of the base alloy by addition of 1 to 3% of nickel. As a result there is a substantial improvement of mechanical properties. 3% nickel steel displays tensile strength of 1758 MPa and yield strength of 1542 MPa. The austenite grains are marginally reduced in nickel alloys. With the chemical composition of nickel alloys when about 0.07% titanium is inoculated during ESR process, there is a deterioration of the tensile properties. In 3% nickel alloy the effect is more prominent, which displays yield strength of 1455 MPa along with the lowest value of elongation. Scanning electron microscopy (SEM), transmission electron microscopy (TEM) and electron probe microanalysis (EPMA) studies indicate that the microstructures of un-inoculated nickel steel predominantly consist of tempered lath martensites. In titanium inoculated alloys the microstructures are mixture of retain austenite, bainite and martensites. Strengths are deteriorated possibly due to the inhomogenous distribution of carbon because of the formation of different phases and depletion of nickel due to the precipitation of the corresponding intermetallics of (Ni, Ti).

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Austenite Recrystallization–Precipitation Interaction in Niobium Microalloyed Steels

Stephanie Vervynckt, Kim Verbeken, Philippe Thibaux, Martin Liebeherr, Yvan Houbaert

pp. 911-920

DOI:

10.2355/isijinternational.49.911

抄録

A good combination of strength and toughness in HSLA steels can be achieved by the addition of microalloying elements such as Nb. Nb can retard the static recrystallization of austenite at lower temperatures by solute drag or by precipitation pinning. In this study, the recrystallization behavior of four Nb-microalloyed model alloys which were designed to show either extensive or almost no precipitation, was compared by multi-hit torsion tests and double hit compression tests. A good consistency between the different types of tests was found and the results were verified by optical micrographs. Further, by construction of softening–time–temperature diagrams the recrystallization behavior was linked to the precipitation state of the material which was investigated by thermodynamical equilibrium calculations and by experimental observations from TEM-EDX, Inductively Coupled Plasma Mass Spectroscopy and X-ray Diffraction. Quantitative agreement between the experimental measurements and the calculations for precipitated mass fraction and precipitate composition as a function of temperature and steel composition is demonstrated.

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Interlamellar Spacing of Pearlite in a Near-eutectoid Fe–C Alloy Measured by Serial Sectioning

Guohong Zhang, Masato Enomoto

pp. 921-927

DOI:

10.2355/isijinternational.49.921

抄録

The interlamellar spacings of pearlite formed isothermally at 700 and 680°C in a near-eutectoid Fe–0.82mass%C alloy were measured by serial sectioning coupled with scanning electron and atomic force microscopy. The intersection angle of cememtite lamellae with the metallographic surface was determined from the variation of horizontal displacement of cementite lamellae with removal depth. The true lamellar spacing was then calculated from the apparent lamellar spacing on the surface. When the angle was small, i.e. less than ~20°, it was measured directly by atomic force microscope. The minimum and mean true lamellar spacings are in good agreement with those measured by other methods. The distribution of interlamellar spacings on the specimen surface back calculated from the spectra of true interlamellar spacing assuming the random orientation of cementite lamellae was in fair agreement with the measured one. It is likely that the distribution of true lamellar spacings is primarily due to recalescence and the minimum true spacings rather than the mean value may be relevant to the thermodynamic theory of pearlite transformation.

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