Showing papers in "Tetsu To Hagane-journal of The Iron and Steel Institute of Japan in 2005"

Development of a Dynamic Model for Assessing Environmental Impact Associated with Cyclic Use of Steel

Abstract: Synopsis : Steels are produced in large quantities and being recycled at high rate in Japan. However, recycling of steel scraps would lead to the enhancement of contamination of undesirable tramp metals in steel scraps. So, the limitation of recycling of the steel scarps would be expected in the near future. This may increase in the production of virgin steels and environmental impacts associated with total steel production in Japan . The authors have developed a dynamic model to assess the maximum recyclable ratio of steel scraps and the total environmental impacts caused by the steel production in Japan. The model is based on population balance model (PBM) , material pinch technology in corporate with LCA. The amount of steel scraps generated in Japan and their concentration of tramp metal during 1990-2030 were estimated by PBM . The maximum recyclable ratio of steel scraps in each year was calculated by material pinch technology , in which assessed were optimal balance between the amount and quality of steel scraps and those of steel products. The total CO2 emissions caused by steel production in Japan during 1990-2030 were estimated by LCA.

Hydrogen Absorption into High Strength Bolts under Atmospheric Exposure and Delayed Fracture Susceptibility Evaluation

Abstract: Synopsis : Hydrogen absorption into high strength steel bolts and its effects on delayed fracture susceptibility have been investigated, by means of thermal hydrogen analysis on exposed bolts and hydrogen permeation tests under atmospheric exposure. Thermal hydrogen analysis on small parts of exposed bolts showed hydrogen localization near the surface of the bolts. Hydrogen permeation tests under atmospheric exposure showed intermittent hydrogen entry, and maximum instantaneous hydrogen content was bigger thanthe measured value by the thermal hydrogen analysis. Delayed fracture susceptibility of high strength bolts with tensile strength of 1521 N/mm2 depended upon the safety index defined as the ratio of the threshold hydrogen permeation coefficient (ILO and the maximum hydrogen permeation coefficient under atmospheric exposure (JL env). The results suggest that hydrogen at the surface of the bolts plays an important role on delayed fracture.

Influence of Rolling Condition on Deformation of Surface Micro-defect in Plate Rolling

Abstract: Synopsis : The shape change of surface micro-defects in plate rolling was investigated using a rigid-plastic finite element analysis . Rolling of plate with rectangular-shaped scratches or plunges, which lay perpendicular to the rolling direction , was simulated. The influence of rolling conditions, such as reduction, friction coefficient, roll diameter and pass schedule on the shape of existing defect after rolling was evaluated . From these results, the relationship between the shapes of surface defect before and after rolling was obtained , and the optimum condition to eliminate defects was discussed. The proposed prediction method of surface defect can be utilized to make defect free products in rolling and forging processes.

Functional Forms of Carbon and Chlorine in Dust Samples Formed in the Sintering Process of Iron Ores

Abstract: Synopsis : The chemical forms of the carbon and chlorine present in dust samples obtained from windboxes of the iron are sintering machine have been studied with X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The chlorine in the dust samples is present as KCl with the average crystalline size of 40-50 nm and covalent C-Cl bonds in condensed aromatic structures of unburned carbon surface. The proportion of chlorinated aromatic structures increases almost linearly with increasing that of surface oxygen complexes on unburned carbon, strongly suggesting that active surface sites of the carbon formed in the sintering process work as reaction sites with HCl and Cl2. Model ex-

Effect of Tungsten on the Ostwald Ripening of M23C6 Carbides in Martensitic Heat Resistant Steel

Abstract: Synopsis : It is well known that tungsten (W) is the key element for creep strength of the advanced martensitic heat resistant steels developed for main steam pipe in ultra-super critical power plant. W is found to suppress coarsening of M23C6 type carbide during creep at elevated temperatures, which can never be predicted according to the conventional Ostwald ripening model for a Fe-X-C system in aFe. In this study, therefore, the effect of W on the coarsening of M23C6 during aging has been analyzed in a detailed experiment and modeled using a modified Ostwald ripening equation for Fe-X1-X2-C system. It is found that W substitutes only for Cr in M23C6 lattice to form [Fe,(Cr, W)19]C6. Using the modified Ostwald ripening equation the coarsening of M23C6 is found to be controlled by the lattice-diffusion of W, resulting in the coarsening rate reduced about one order of magnitude by I% W addition. Key word Ostwald ripening; martensitic heat resistant steel; creep strength; M23C6 carbide; W containing steel; fossil fired power plant.

Effect of Microstructure on Deformation Behavior of Ferrite-Bainite Steels

Abstract: Synopsis : Effect of bainite volume fraction on tensile properties of ferrite-bainite steels was investigated experimentally and analytically . Ferritebainite steels with different bainite volume fractions having the similar mechanical properties for each constituent phase were prepared and the tensile properties were investigated. Lower yield ratio (YR) and higher n-value were obtained for the steels with bainite volume fraction of 16 to 35%, while the ferrite or bainite single phase steels exhibited relatively higher YR and lower n-value. In order to investigate microscopic deformation behavior of ferrite-bainite steels, an axisymmetric unit cell model based on a regular array of second-phase particles arranged on a BCC lattice was applied. Finite element analyses were carried out to investigate the macroscopic and microscopic response of unit cells with morphological features based on the actual steels. Macroscopic deformation behavior of ferrite-ainite steels calculated by the unit cell model showed good agreement with experimental results. In addition, the effect of bainite volume fraction on YR and n-value was well simulated by the unit cell model. Microscopic investigation on the unit cells revealed that significant strain concentration existed in the ferrite phase near the ferrite/bainite boundary for ferrite-16% and 35% bainite steel, which had higher experimental n-value . However, further increasing of bainite volume fraction caused plastic deformation of bainite phase and the strain concentration was decreased , resulting in lower level of n-value for ferrite-58% bainite steel. Effect of bainite morphology on strain hardening behavior of ferrite-bainite steels was also discussed based on analytical study using the unit cell model .

Dynamic Material Flow Analysis for Stainless Steels in Japan and CO2 Emissions Reduction Potential by Promotion of Closed Loop Recycling

Abstract: Synopsis : Stainless steels are corrosion resistant alloys which are widely used in consumer goods and industrial equipments. Stainless steels contain scarce and energy intensive elements such as Ni, Cr, Mo, etc. So, closed loop recycling is preferable for sustainable production of stainless steel. However, some parts of stainless steel are not separate from ordinal steel scraps in recycling processes and not recycled as \"stainless steel\". The objective of this study is to analyze the dynamic material flow of stainless steels in Japan and assess CO2 emissions reduction potentials by promotion of closed loop recycling of stainless steels in the future. First, the authors analyzed material balance of input elements, i.e. Fe, Ni and Cr, in the production of stainless steels in 2002 to figure out the material flow of stainless steel which can not be obtained from statistics. The amount of post-consumer stainless steel that would come into society in the future was estimated by PBM (Population Balance Model). It was found that only 2% of post-consumer stainless steel of Fe—Cr alloys was collected as stainless steel scraps and the rest was collected as ordinal steel scrap. On the other hand, approximately 95% of post-consumer stainless steel of Fe—Ni—Cr alloys was collected as stainless steel scraps. CO2 emissions reduction potential by the increase of 1% in closed loop recycling of stainless steel scraps of Fe—Cr alloys was estimated at 75000 t/year by using LCA.

Effect of solute copper on yield strength in dislocation-strengthened steels

Abstract: The effect of copper atoms in solid solution (solute Cu) on yield strength was investigated in dislocation-strengthened steels such as a martensitic steel and a work-hardened steel, which have high dislocation density. The yield strength of the martensitic steel increases with increasing content of the solute Cu. However, the increment of the yield strength by the solute Cu is smaller in the martensitic steel than in the ferritic steel. Dislocation density of the martensitic steel increases with increasing Cu content and the yield strength is also enhanced depending on the dislocation density. The increment of the yield strength can be reasonably explained by the dislocation strengthening mechanism based on the Bailey–Hirsch relationship. In the work-hardened ferritic steel, the solid solution strengthening by Cu is significant when the dislocation density is low, but it tends to disappear with increasing the dislocation density through cold-rolling. These are indicative of the facts that the yield strength of the dislocation-strengthened steel is determined by the dislocation strengthening and the contribution of the solute Cu on the yield strength disappears owing to high dislocation density.

Simultaneous Determination of Trace Tramp Elements (Zn, Pb and Bi) in Steel by Anodic Stripping Voltammetry

Abstract: 発生量が著 しく増加することが予想 される市中スクラッ プを新鉄源として再利用することは,省 エネルギー,二 酸 化炭素の抑制や限りある資源を大切にリサイクル しようと いう地球環境等の観点か らますます重要 となりつつ ある。 スクラップを多量に使用して高品質の鋼材 を経済的に製造 するためには,鋼 質に有害な トランプ元素を迅速かつ精確 に高感度定量で きる分析技術の確立が必須の課題である。 これら トランプ元素の工程管理分析に利用 される技術の多 くは相対的方法であるために標準物質が不可欠であるが, 信頼性の高い トランプ元素分析用標準物質の作製 ・供給は はなはだ不十分である。 ス トリッピングボル タンメ トリー(SV)は,分 析種 を含 む電解質溶液 を撹絆 しながら一定時間,定 電位あるいは開 回路(無 電解)で 分析種を作用電極上(ま たは中)に 濃縮 した後,一 定速度で電位を走査 して析出物 を再溶解 させ, その際に得られる電流電位曲線(溶 出曲線)よ り分析種を 定量す る方法である。このように,SVに は定量操作に分 析種の選択的濃縮過程が含まれるため,(1)高 感度,(2)高 精 度,(3)操 作が簡便で,熟 練 を必要 としない,(4)迅 速,(5)有 害試薬を用いる前分離操作が不要,(6)数 元素の同時定量が 可能,(7)化 学形態別分析(ス ペシエーション)が 可能,(8) 装置が簡単で比較的安価,(9)ダ ウンサイズ化が容易,(10)分 析操作のコンピュータ化,自 動化が容易などの特長を有 し, 鉄マ トリックスや共存成分か らの妨害が抑制できればこの 方法は鉄鋼中微量成分の定量に最適である。また,試 料を 酸分解 して得 られた溶液 を複雑な化学処理や多量の試薬を 添加することな く電解液 として使用すると,分 析操作が簡 単でコンタミネーションや損失を防ぐことができる。 この特長 を生かした金属材料,環 境,生 体等の試料中微 量元素の定量に関する研究は非常に多いが,鉄 鋼分析への 応用例は少ない。著者らは,ス トリッピング分析法を鉄鋼 分析へ適用 して満足な結果が得られることを明らかに して きた12)。鉄鋼3)および鉄鉱石4)中のCu,Pb,Cd,Znを ス ト リッピング分析法を利用 して同時定量 した報告では,定 量 に先立 ちマ トリックスFe(III)の煩雑な抽出分離を必要とす る,共 存元素の妨害があるなど問題点が多い。本研究では, 鉄スクラップ中に混入し,熱間 加工性など機械的特性の劣 化に影響する微量 トランプ元素であるZn,Pbお よびBiを 直接 同時 定量 で きる簡便 な高感度 ア ノーデ ィックSV (ASV)の 開発を試み,ト ランプ元素分析用鉄鋼標準物質の

Mixing Time of Cylindrical Bath Agitated by Swirl Motion of Gas-liquid Two-phase Jet and Sludge Treatment Using Ozone

Abstract: Synopsis : Sludge treatment using a gas—liquid two-phase swirling jet and ozone was proposed. The swirl motion of a gas—liquid two-phase jet appeared in a cylindrical bath under certain injecting conditions, and the bath was strongly agitated in the presence of the swirl motion. The swirling jet brought a very excellent effect on the ozone reaction with sludge. The intensity of agitation was quantitatively evaluated by means of mixing time. An empirical equation was derived for the mixing time. Sludge was decomposed by this method and, as a result, BUDS and SS in the sludge were significantly decreased.

Water-model Experiments on Gas and Liquid Flow in the Continuous Casting Immersion Nozzle

Abstract: Synopsis : Water-model experiments were carried out to understand the behavior of argon gas introduced into the immersion nozzle from the vicinity of the sliding gate. The gas was completely lifted up into the tundish when the water flow rate was lower than a certain critical value. On the other hand, it was completely carried deep into the mold when the water flow rate was higher than another critical value. An estimation method of the two critical values was proposed. The mean diameter of bubbles for a water flow rate between the two critical values increased with an increase in the distance from the sliding gate. The relationship between the mean diameter and the characteristics of water flow in the nozzle was revealed.