Showing papers in "Tetsu To Hagane-journal of The Iron and Steel Institute of Japan in 2006"

Subjects for Achievement of Blast Furnace Operation with Low Reducing Agent Rate

Abstract: The technology which reduces the reducing agent rate by the improvement in the reaction efficiency of blast furnace leads to reduction of hot metal manufacturing cost, but also solution of recent CO2 emission reduction. The subjects for achievement of the blast furnace operation with low reducing agent rate were described on reduction measures of the carbon consumption and problem of the measures referring to the example of reducing agent rate of the present state blast furnace concerning blast operation and reactive improvement. And, carried out concrete measures were introduced in order to aim at the low reducing agent rate operation.The following results were obtained.1) Since it has reached the already high reaction efficiency in present state blast furnace, it is not easy to attempt further reduction of the reducing agent rate.2) The blast furnace use of high reactivity coke or reduced iron is equal level or over it in comparison with the reduction effect by the assumed blast operation in this paper.3) The promotion of coke reaction load with the gasification is worried, when it aims at the low reducing agent rate operation by the high reactivity coke use.4) It is estimated that the threshold also exists for the reducibility of competing ore, when it aims at the low reducing agent rate operation using the high reactivity coke.5) The use of the low SiO2 sinter is effective for the improvement on the permeability in the blast furnace, when it aims at the low fuel rate operation. However, the new technology of the permeability improvement is desired, since there is some a limit for low SiO2 of the sintered ore, when future raw material supply and demand is considered.

Identification and Formation Mechanism of a Deformation Process Determining Microstructure of Type IV Creep Damage of the Advanced High Cr Containing Ferritic Heat Resistant Steel

Abstract: grain HAZ and dual phase HAZ, according to the temperature acceleration creep test at 700•Ž. The tensile strength at room temperature was the lowest at around Ac1 transformation point, determined by rapid heating diratometry. Therefore, the Type IV damage did not coincident the conventional HAZ softening phenomenon often observed in low carbon steels. Dislocation substructure of the fine grain zone is composed of the globular sub-grain microstructure and the coarsened carbide through the Transmission Electron Microscope observation of thin foils. They were possibly explained to be formed through the thermal cycle of HAZ and Post Weld Heat Treatment as follows: a base metal with lath martensite microstructure is warmed above Ac3 point once, and immediately cooled and transformed. Such \"weak\" lath martensite structure, apparent ambiguous lath martensite, was easily recovered to the globular

Some Fundamental Aspects of Highly Reactive Iron Coke Production

Abstract: It is important to develop the production and utilization technology of highly reactive coke in order to improve the efficiency of blast furnace reactions. In this study, some fundamental aspects of highly reactive iron coke produced in a coke oven chamber were investigated. First, the effects of catalytic Fe powder addition to coal before carbonization on coke strength were investigated. The addition of Fe powder decreased the coal caking property and hence the resultant coke drum index (DI15015). On the other hand it increased coke reactivity (JIS coke reactivity index and CRI) to a great extent. This means that the caking property of blended coals needs to be adjusted higher to produce iron coke with proper strength and high reactivity. Secondly, it was shown that the iron ore reacts with silica brick at 1200°C in a condition similar to that in a coke oven chamber. The iron ore and silica reacted to produce fayalite (2FeO·SiO2) and the brick was damaged. On the other hand, it was proven that the iron ore does not react with silica brick at 1100°C in the above condition. Based on this fundamental study, iron coke with proper strength and high reactivity was successfully produced in a coke oven chamber on a commercial scale by adjusting the coal blend composition and the coke oven temperature. Furthermore it was revealed that about 70% of iron in iron ore powder added to coal was reduced to metallic iron during carbonization.

Efforts to Save Nickel in Austenitic Stainless Steels

Abstract: The price of nickel is maintaining high level due to the demand continuing to outstrip supply, therefore the stainless steel, which is the largest consumer of nickel, has been maintaining a high-price. In this review, the way of nickel saving by more than half and the comparison of properties between the nickel saving stainless steels and Type 304 were reviewed, and the problem caused by the use of the nickel saving stainless steels were discussed. Nickel saving stainless steels have the following 4 types; martensitic stainless steels, ferritic stainless steels, duplex stainless steels and Cr-Mn-Ni austenitic stainless steels. Nickel saving stainless steels have both superior and inferior points as compared to Type 304, however they have a large possibility of substitution for Type 304. Further expansion of the use of nickel saving stainless steels is expected if the properties required for the stainless steel are reconsidered for proper demands.

Effect of High Al2O3 Slag on the Blast Furnace Operations

Abstract: Increasing the Al2O3 content in the blast furnace slag, the blast furnace operations tend to make troubles such as excess accumulation of molten slag in the blast furnace hearth and increasing pressure drop at the lower part of the blast furnace. So, it will be important to keep good slag fluidity at the blast furnace operations such as, drainage of tapping and keeping good permeability.In order to clarify the effect of high Al2O3 slag fluidity on the blast furnace, high Al2O3 slag (20%) test operations of experimental blast furnace have been carried out. Investigation results of the test operation are as follows;1) Slag MgO improves the hearth drainage rate at high Al2O3 slag operation.2) Permeability of the dripping zone is improved by decreasing slag CaO/SiO2, at high Al2O3 slag operation of the blast furnace.3) It was verified that the slag drainage phenomena were able to described by the fluid model.4) The optimum composition of high Al2O3 slag of the blast furnace is high MgO and low CaO/SiO2.

Evaluation of mechanical property in matrix of metallurgical coke by nano-indentation method

Abstract: 高炉法は還元ガスを炉内に通気することで鉄鉱石を還元 し,銑 鉄を得るプロセスである。高炉内においてコークス が果たす役割は主に,熱 源供給,還 元剤であるCOの 発生 源,炉 内の通気 ・通液性を確保するためのスペーサ,溶 銑 生成のための浸炭源の4つ である。その中で も特に,炉 内 の還元ガスの通気および溶融物の通液性 を確保す るための スペーサと しての役割が,高 炉の安定操業において,最 も 重要であると されている1)。そのため,コ ークスは高強度 なものほど高品質であると されている。 コークスの強度に影響 を与える因子 としては,乾 留温度 や乾留時間などの熱処理条件や劣質な非微粘結炭の配合量 など原料に関するもの等,様 々なものが考 えられる。 近年,石 炭価格は高騰 しており,コ ークス製造に主に使 用 される強粘結炭にいたっては,2005年 度における価格 は前年度の2倍 程度にまで達 している2)。それゆえ,コ ー クスの安定供給および生産コス ト削減の点から,強 粘結炭 に安価な非微粘結炭を多量に配合す ることが望 まれてい る。 しか し,非 微粘結炭の配合量 を増加 させ ること は, コークスの品質低下につながってしまう。そこで品質を保 持 しつつ,配 合比 を増加 させる技術の開発が行われており, 事前または事後処理等の工夫 を施す こと で配合比 は60% 程度とす ることが可能と なっているが3),配 合比の さらな る増加が望まれる。 この問題 を解 決 し,高 炉操業 を効率化す るためには, コークス生成過程において,粘 結炭および非微粘結炭がど のように変化し,強 度が発現するのかを明確にすることが 重要である。そのためには,コ ークスの微視構造を考慮 し た強度評価が不可欠である。しか し,従 来のコークス強度 評価は,経 験則に基づく巨視的評価が主なものであり,気 孔や基質の微視構造が強度因子に及ぼす影響 を明確に示す ことが困難である。近年,均 質化法や重合メッシュ法 を用 いてコークスの微視構造を考慮 した強度評価がなされてい る4)。このような微視構造を考慮 した強度評価にはコーク ス基質の機械的性質,特 に弾性係数 を測定することが必要 不可欠である。しかし,コ ークスは気孔率 が大きいため, 弾性係数の測定において,気 孔の影響を排除する必要があ る。 近年,サ ブミクロンオーダーの微小領域の機械的性質を

Creep Deformation Process Determining Microstructure of Type IV Creep Damage of the Advanced Ferritic Heat Resistant Steel with High Cr Content

Abstract: 高効率発電プラン トの蒸気条件の向上に不可欠の部材を 構成する高Crフ ェライ ト系耐熱鋼 には,環 境負荷低減の 観点から高いクリープ強度が必要であり1),こ れまでに9~ 11%Cr鋼 の クリープ特性向上研究 が精 力的に進められ2), 一部 には600°C ,10万 時間の クリープ破断強度が100MPa を凌駕する材料が実用化 されている3)。しかし,ほ ぼ全て のフェライ ト系耐熱鋼 には溶接熱影響部(Heat Affected Zone,以 降HAZと 略記す る)外 縁 の細粒域 に発生 する, Type IV損 傷 と称 され る低延性破壊型のク リープ寿命低下 現象が見 られ,設 計による応力負荷の軽減対策などで,あ る程度の緩和が可能ではあるが,発 生機構が明確でないこ とから根本的な解決策は提案 されていない。著者 らは機構 解明のために必要な,Type IV損 傷が発生する溶接継手の 部位 とミクロ組織を特定 し,同 転位組織の生成機構につい ての仮説を提案 している4)。すなわち,以 下の事実 を実験 的に再現 し,明 らかにした。 (1)HAZ外 縁に相当す る部位 は母材の焼戻 しラスマルテ ンサイ ト構造が急熱 ・急冷 される場合に一度Ac3点 直上に 再加熱 され,フ ェライ ト相(α)がオーステナイ ト相(γ)へ 逆変態す るが,最 高加熱温度 はたかだか1000°C 近傍で あって,γ 粒は短時間の内に冷却 され,成 長することなく 細粒域 と呼ばれ る組織 を形成する。 (2)細粒域ではクリープ破断寿命が他の溶接継手部位に比 較 して短 く,ク リープ変形抵抗が低下 していると考 えられ る。 (3)細粒域の転位組織は,短 時間HAZ熱 サイクルで生 じ る炭化物の不完全固溶に起因す る基材の固溶炭素低下とγ 粒径の微細化により,冷 却時に生成するラスマルテンサイ ト構造の焼入れ性が低下 して,続 く溶接後熱処理(Post Weld Heat Treatment,以 降PWHTと 表記する)に よって回 復サブグレイン組織化する。 (4)不完全固溶炭化物上 には炭化物が再析 出して,HAZ 熱サ イクル とPWHTに 起 因す る析 出物,主 に(Fe,Cr)23C6 (以降M23C6と 呼称する)と(Nb,V)(C,N)(以 降MXと 呼称 する)の 粗大化が生 じる。 以上のType IV損 傷発生組織の特定 と組織生成機構の推 定によ り,Type IV損 傷 を生成する組織が有する特徴はほ ぼ金属組織学的に説明することが可能となる。 しかし,根

The Characteristics of Catalyst-coated Highly Reactive Coke

Abstract: It is important to develop the production and utilization technology of highly reactive coke in order to improve the efficiency of blast furnace reactions. In this study, the characteristics of catalyst-coated highly reactive coke produced by the ‘post-addition of catalyst to coke’ method were investigated. First, the catalytic effect of Fe and Ca on graphite and deashed coke during the C–CO2 reaction was investigated. Fe and Ca addition increased the reaction rate and decreased the reaction beginning temperature. Second, the reaction rate of Fe or Ca coated coke was kept high until the weight loss reached 10%. This means that a high catalytic effect is maintained in the thermal reserve zone of the blast furnace. Furthermore, it was found that 70% of the catalyst coated on the coke surface remains after drop impacts. It is expected that the loss of catalyst during coke handling and transportation is small. Catalyst-coated highly reactive coke is promising for improving the efficiency of blast furnace reactions.

Water-model Experiment on Melting Powder Trapping by Vortex in the Continuous Casting Mold

Abstract: Water-model experiments have been carried out to understand the behavior of mold powder trapping phenomena by vortex in continuous casting mold. The following findings are obtained. (1) Mold powder trapping by the vortex occurs irregularly near the immersion nozzle. It occurs only in the wake of the immersion nozzle. (2) As for the occurrence frequency ratio of the vortex, the maximum value appears in the water flow rate regime ranging from 61.4 to 70.2 L/min. This regime is supposed to have a lose relationship with water flow velocity change near the immersion nozzle. (3) An empirical equation is proposed for the length of the molten mold powder entrapped by the vortex.

Effects of the Grain Size and Volume Fraction of Second Hard Phase on Mechanical Properties of Dual Phase Steel

Abstract: Synopsis : The reduction in car weight has led to demand for higher strength steels. However, increasing strength generally has a negative effect on formability. The high strength steels being developed are divided broadly into two types: steels characterized by high uniform elongation such as DP and TRIP steels having a heterogeneous microstructure, and steels characterized by high local elongation such as bainite steel having a homogeneous microstructure. High strength steels with both high uniform elongation and local elongation are under investigation. In this study, various levels of carbon content and hot-rolling reduction in DP steel containing Si, Mn, Cr, and Mo were examined. The effects of grain size and volume fraction of martensite on the mechanical properties of DP steel were studied. It was found that increasing reduction, i.e., decreasing the diameter of the dispersed martensite, improved the balance between strength and total elongation. The authors investigated the total elongation in terms of both uniform elongation and local elongation. Reduction increased the balance of strength and uniform elongation as well as the balance of strength and local elongation. The balance of strength and uniform elongation increased markedly with increasing carbon content when the reduction was large. The reason for these results is explained in terms of work-hardening theory and SEM observation of deformed DP steels. An ideal microstructure for uniform and local elongation in high strength steels is concluded to be macroscopically homogeneous and microscopically heterogeneous.

Improvement in Blast Furnace Reaction Efficiency through the Use of Highly Reactive Calcium Rich Coke

Abstract: A method to produce coke in ‘lump’ form with high strength and reactivity through the addition of a catalyst was investigated in order to improve blast furnace reaction efficiency. The addition of Ca compounds to coal before carbonization was found to considerably increase the reactivity of the coke at a low temperature range in the thermal reserve zone of a blast furnace. Furthermore it was proved that strong, highly reactive ‘lump’ form coke could be produced by adding a Ca-rich non-caking coal and adjusting the coal blend composition. Based on this fundamental study, the Ca-rich coke was successfully produced in coke ovens on a commercial scale, both at Kimitsu and Muroran works. The use of the Ca-rich coke in the Muroran No. 2 blast furnace was found to cause a decrease in the reducing agent rate by 10 kg/t-p. This technology, producing coke of high reactivity and strength through catalyst addition, is promising as a means of improving the reaction efficiency of a blast furnace.

Prediction of Carbon Profiles in Vacuum-carburized Steels Based on Carburizing Mechanism

Abstract: Synopsis : In order to develop effective ways to estimate carbon distribution in vacuum carburized steel, the surface interaction during vacuum carburizing was investigated. 0.1 mm thick specimens were vacuum carburized for sufficiently long time. The carbon content and carbide area fraction of specimens proved to be the value in equilibrium with graphite. This result shows that the graphite exists while vacuum carburizing on the surface of specimens, and that the local equilibrium between specimens and graphite is dominant factor. Carbon profile of carburized round bar was calculated on the basis of diffusion equation, on the assumption that surface carbon content is as much as the value in equilibrium with graphite. The calculatuied carbon profiles correspond to measured ones for some materials and carburizing conditions.