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78 巻, 4 号
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溶融還元法の変化と発展を中心とした下村 泰人1992 年 78 巻 4 号 p. 509-519
発行日: 1992/04/01
公開日: 2009/05/29
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梅沢 一誠1992 年 78 巻 4 号 p. 520-526
発行日: 1992/04/01
公開日: 2009/05/29
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谷口 尚司, 菊池 淳1992 年 78 巻 4 号 p. 527-535
発行日: 1992/04/01
公開日: 2009/05/29
ジャーナル フリー本稿では近年の鉄鋼業に解決の迫られている介在物問題に関わりの深い凝集現象に注目し,いろいろな分野における凝集の研究例とその解析手法を紹介した.膨大な研究の中から紹介できた研究は一部にすぎないが,本稿が介在物問題の解決にわずかでも役立つことを切望する.
なお,固-液系混相流に関する都田と今野のレビュー,気-固系混相流に関する松本のレビュー,浮遊選鉱過程における気泡と液間の相互作用を扱った野中の総説およびコロイド凝集に対する種々の粒子間相互作用に関する奥山と臼井の解説も是非参照されたい.抄録全体を表示PDF形式でダウンロード (1416K) -
肖 興国, 清水 正賢, 稲葉 晉一1992 年 78 巻 4 号 p. 536-543
発行日: 1992/04/01
公開日: 2009/05/29
ジャーナル フリーIn order to clarify the thermal decomposition behavior of fine iron ore which is injected into the raceway of a blast furnace, thermal analyses of fine iron ore have been made under various atmospheric conditions (N2, CO2, air, O2 and N2+O2 with different oxygen concentrations from 1% to 25%), particle size (average dia.: 55, 155 and 325 μm) and heating rate (0.033, 0.167 and 0.33 K/s). A kinetic analysis of the reaction (3Fe2O3=2Fe3O4+1/2O2) has been made based on measured thermalgravimetric curves by the Coats' method. Its results show that the reaction rate could be described by a second order reaction rate equation with relation to unreacted degree.
dα/dt=k(1-α)2
k=exp(A-E/RT)
Furthermore it was found that the starting temperature (TD1) and the kinetic behavior of the reaction were independent of the particle size in the range from 55 to 325 μm. However, they were strongly affected by the oxygen potential of the gas atmosphere. Empirical equations to estimate TD1, E and A were obtained as a function of PO2 in the gas atmosphere as follows:
TD1=75560/{44.56-ln[PO2/(1.013*105)]}
E=20730/{6.543-ln[PO2/(1.013*105)]}
A={14.43+ln[PO2/(1.013*105)]}/102/6.9306
Using these equations, the thermal decomposition processes of iron ore were analyzed under various conditions and the results coincided well with our experimental results. Under heating conditions simulating raceway in a blast furnace, it was predicted that the injected fine iron ore could be almost decomposed from Fe2O3 to Fe3O4 in the raceway.抄録全体を表示PDF形式でダウンロード (1128K) -
片山 裕之, 桑原 正年, 大野 剛正, 山内 雅夫, 平田 浩1992 年 78 巻 4 号 p. 544-550
発行日: 1992/04/01
公開日: 2009/05/29
ジャーナル フリー粉鉱石を上投入しても飛散を抑制できる条件を見いだすために,コールドモデル実験と大型転炉を用いた溶融還元試験を行い,次の諸点を明らかにした.
(1)上昇ガス流の中に粉体流を落下させた時の粉体飛散量は,粉体流の表面積に比例する.粉体流の比表面積を小さくすることによって,粉体粒度,比重,上昇ガス流速によらずに飛散を飛散率を抑制することが可能である.
(2)溶融還元大型試験で,粉鉱石流を短くするように,炉壁に設けた孔からスラグが多い状態の炉内に流し込む方式で,微粉鉱石についても飛散を無視できてる程度に抑制できることを確認した.したがって,粉鉱石添加に関しては塊成化は省略可能である.しかし,同じ方法で粉炭材を添加した場合には,飛散率は30%以上と高かった.
なお,本論文中「3.溶融還元炉の試験」は日本鉄鋼連盟溶融還元研究開発委員会の共同研究において得られたものである.抄録全体を表示PDF形式でダウンロード (2561K) -
原 茂太, 床並 徹二, 荻野 和己1992 年 78 巻 4 号 p. 551-556
発行日: 1992/04/01
公開日: 2009/05/29
ジャーナル フリー高焼成の石灰るつぼを用いて1550~1700℃の範囲で溶鉄とFetO-CaOsat. 2元系スラグとの平衡実験を行った.その結果は以下に要約される.
(1)溶鉄中の酸素量は次式で示され,温度の増加により減少することが分かった.
log[%O]=-5240/T+1.743
(1848<T/K<1973)
(2)FetO-CaOsat.2元系融体はほぼ正則融体として取り扱えることが示唆された.
(3)溶鉄と平衡するFetO-CaO-CaF23元系スラグの1600℃におけるCaOの飽和溶解度曲線を定めた.
(4)CaO飽和のFetO-CaO-CaF23元系スラグと平衡する溶鉄の1600℃での酸素溶解度はCaF2濃度の増加と共に減少するが,それに伴うFetO濃度の減少に見合うほどは大きくない.これはCaF2濃度が増加するとFetOとCaF2との相互作用の増加によるスラグ中のFetOの活量係数の増加に起因すると結論された.抄録全体を表示PDF形式でダウンロード (885K) -
原 茂太, 床並 徹二, 荻野 和己1992 年 78 巻 4 号 p. 557-563
発行日: 1992/04/01
公開日: 2009/05/29
ジャーナル フリーEquilibrium phosphorus distribution between FetO-CaO-P2O5-CaF2 slags and liquid iron has been studied at 1600°C under a CaO-saturated condition. The results are summarized as follows,
(1) Increase of P2O5 content in CaO-saturated FetO-CaO-P2O5 slags contributes to an increase of the activity coefficient of iron oxide, γFetO and also a slight increase of the ratio (Fe3+/Fe2+), but decreases the activity coefficient, γP2O5.
(2) For slags containing approximately 10 mass% P2O5, an addition of CaF2 contributes to a decrease of the γP2O5 as follows, logγP2O5=2.52NFetO-1.32NCaF2-19.4
The addition of CaF2 also increases the γFetO and the ratio (Fe3+/Fe2+). It suggests that CaF2 in molten slags behaves as a basic component.
(3) For slags having 10 mass% P2O5, most suitable slags for the dephosphorization are those containing 40-50 mass% CaF2.抄録全体を表示PDF形式でダウンロード (1037K) -
井上 亮, 井上 肇, 水渡 英昭1992 年 78 巻 4 号 p. 564-571
発行日: 1992/04/01
公開日: 2009/05/29
ジャーナル フリーNitrogen and sulfur distribution ratios between CaO-Al2O3 slag and Fe-0.000133 mass% Al alloys were measured in the temperature range of 1823 to 1923 K, using Al2O3 and CaO crucibles. The distribution ratios under a CaO crucible were higher than those under an Al2O3 crucible, and increased with an increase of Al content. Nitride and sulfide capacities defined by CN3-=(mass% N)·PO23/4/PN21/2 and CS2-=(mass% S)·PO21/2/PS21/2, respectively, which were obtained by using the reported values for activity of Al2O3, agreed well those directly measured in a gas-slag experiment under an Al2O3 curcible, but disagreed with those under a CaO crucible. Activities of Al2O3 in the CaO-Al2O3 melts saturated with CaO were evaluated based on the results in the gas-slag experiments.抄録全体を表示PDF形式でダウンロード (1290K) -
田中 努, 栗田 興一, 黒田 篤彦1992 年 78 巻 4 号 p. 572-579
発行日: 1992/04/01
公開日: 2009/05/29
ジャーナル フリーAn advanced mathematical model of a cold crucible capable of describing the fluid flow coupled with heat transfer limited by the free boundaries of free surface and a solidification front has been developed. Validity of the model was confirmed through measurements of a solidification front, surface velocity of the melt and surface temperature.
Effect of parameters during operation, such as coil current, dome height and casting velocity on the fields of velocity and temperature has been investigated.
Generally, two kinds of recirculation are expected to appear in the melt. They make a collision slightly above the contact point between the melt and the crucible wall. Appropriate geometrical relation between the dome height and the position of a coil exists to promote melting of scraps fed onto the dome.
A titanium ingot consisting of completely melted scraps was continuously cast aided by the proposed operation condition obtained through the numerical calculation.抄録全体を表示PDF形式でダウンロード (2436K) -
水上 英夫, 鈴木 俊夫, 梅田 高照1992 年 78 巻 4 号 p. 580-586
発行日: 1992/04/01
公開日: 2009/05/29
ジャーナル フリーThe effects of casting conditions as surface roughness and surface materials of the substrate, and pouring temperature on the solidification behavior and the structure of rapidly solidified 18Cr-8Ni stainless steel droplet samples have been studied. On the onset of the solidification, undercooling phenomena is observed. The undercooling linearly depends on the cooling rate, but does not on the casting conditions. Initial solidification length increases, and primary arm spacing and surface grain size decreases with increasing cooling rate. With very small cooling rate, solidification morphlogy changes from cell to dendrite. It presumably shows the change in the primary phase in the initial solidification.抄録全体を表示PDF形式でダウンロード (5460K) -
申 健, 梶谷 敏之, 鈴木 俊夫, 梅田 高照1992 年 78 巻 4 号 p. 587-593
発行日: 1992/04/01
公開日: 2009/05/29
ジャーナル フリーA technique for tensile tests has been developed for the investigation of mechanical properties of carbon steels during solidification. The equipment enables the test piece to melt and solidify without a crucible at a predetermined cooling rate. The tensile strength and ductility of Fe-C-1 mass% Mn samples have been measured during and after solidification. Temperature Range of Strength Generation (TRSG) during solidification is determined. It has been verified that ZST (Zero Strength Temperature), the maximum temperature showing the strength of sample by the tensile loading is different from ZDT (Zero Ductivity Temperature), the temperature showing the brittle-ductile transition. These mechanical properties of steels have been examined in relation with solid fraction which is evaluated from numerical analysis for micro-segregation during solidification, TRSG is the temperature range where solid fraction is 0.6-0.8, ZST is the temperature at which the solid fraction 0.6-0.7, and ZDT is about 1. The influence of carbon contents on the tensile strength of sample has also been studied.抄録全体を表示PDF形式でダウンロード (4410K) -
九津見 啓之, 千野 淳, 石橋 耀一1992 年 78 巻 4 号 p. 594-600
発行日: 1992/04/01
公開日: 2009/05/29
ジャーナル フリーA method for quantitaive analysis of Laves phase and M23C6 type carbide in high Cr heat resistance ferritic steel has been estab lished, and precipitation behavior of the Laves phase and carbide in these steels were investigated. The results obtained are as follows.
(1) The Laves phase and carbide are quantitatively extracted by potentiostatic electrolysis in 10% AA-1% TMAC-methanol electrolyte or in 10 %HCl-methanol electrolyte.
(2) Only the Laves phase in the residues extracted by above electrolysis can be dissolved in 0.5% Br2-methanol solution at 20°C for over 90 minutes. Consequently, the amount and chemical composition of the Laves phase and carbide can he determined by analysis of this treatment solution and the residues respectively.
(3) The amount of the Laves phase increased with an increasing of aging time, while the amount of carbide remained constant.
(4) The chemical composition of the Laves phase and carbide were independent of aging time, and approxiamately constant.抄録全体を表示PDF形式でダウンロード (3229K) -
林 公隆, 三吉 康彦1992 年 78 巻 4 号 p. 601-607
発行日: 1992/04/01
公開日: 2010/05/07
ジャーナル フリー塩化物溶液中において,Znのアノード溶解機構を検討した結果,以下の知見が得られた.
(1) 中性(pH=5～8)条件下においてZnのアノード溶解反応速度は塩化物イオン濃度に対し3次,水酸イオンに0次で正比例する.この場合の電流電位曲線(i-φ曲線)のTafel勾配は≅17mV/decadeとなることが判明した.
これは中性近傍の溶液条件下においてZnのアノード溶解反応はCl-イオン濃度に大きく影響をうけることを意味するものである.
この時の反応律速となる素反応はZnCl2・ZnOHads.+H++Cl-〓ZnCl3-+Zn2++H2O+e-と推定される.
(2) アルカリ性(pH=12.5～13.5)条件下においてZnのアノード溶解反応速度は塩化物イオン濃度に対し0次,水酸イオンに3次で正比例する.この場合の電流電位曲線のTafel勾配は≅40mV/deczdeとなることが判明した.
これはアルカリ性の溶液条件下においてZnのアノード溶解反応がCl-イオン濃度の影響をほとんどうけないが,OH-イオン濃度に高い依存性を示すことを意味するものである.
この時の反応律速となる素反応はZnOHads.+2OH-〓ZnO22-+H++H2O+e-と推定される.抄録全体を表示PDF形式でダウンロード (785K) -
富田 友樹, 高谷 泰之, 小林 圭史, 原田 良夫, 中平 宏1992 年 78 巻 4 号 p. 608-615
発行日: 1992/04/01
公開日: 2009/05/29
ジャーナル フリーIn order to develop protective contings for sink rolls used in a coatinuous hot-dip galvanizing, sprayed cermet coatings were formed on a mild steel by High Velocity Flame Spraying system using two commercially produced WC-12 mass% Co powders and their durability in molten pure zinc(703783 K) have been studied by SEM, XRD, EDX and hardness tester.
It was found that the durability of WC/Co sprayed coatings in molten pure zinc depended on the binding phases, which varied according to a powder-preparation process. Namely, the binding phase in WC/Co sprayed coatings made of powders prepared by a Spray-dried process ( SD-coating) mainly consisted of β-Co phase, but that prepared by a Sintered & Crushed process (SC-coating) mainly consisted of η-phase (Co3W3C and Co6W6C). In case of SD-coating, the binding phase, β-Co, dissolved into molten pure zinc so that the thickness has decreased in a short time. Though, in case of SC-coating, a Zn-rich and Co-poor layer was build up under the surface and the hardness dropped to HV 5001000 just below the surface, no changes of the thickness and microstructures have been observed for a long time.
The appearant activation energy for the growth of Zn-invaded layer in SC-coating was 170 kJ/mol, which was nearly equal to that for dissolution of β-Co. It was suggested that a small amount of β-Co was also contained in SC-coating and such a excellent durability must have been obtained due to the different distribution manner of β-Co.抄録全体を表示PDF形式でダウンロード (8998K) -
井上 毅1992 年 78 巻 4 号 p. 616-623
発行日: 1992/04/01
公開日: 2009/05/29
ジャーナル フリーHardenability of Fe-C-Mo alloys varies to a larger extent with carbon and molybdenum contents, and with quenching temperature, and this is attributed to the variation in effective molybdenum and carbon due to insoluble carbides. For this reason, it is important for molybdenum hardenability to be evaluated by net amount of effective molybdenum with a correction of insoluble carbide.
In this study, basing on the previously reported data, multiplying factor of molybdenum is derived as a function of effective molybdenum, [Mo]( % ), for Fe-C-Mo alloys containing molybdenum up to 2%:
fMo=-0.512×[Mo]2+2.86×[Mo]+1
Furthermore, prediction formulae calculating the amount of insoluble carbide remained on quenching as well as molybdenum and carbon fixed as carbide are proposed by a kinetic consideration of carbide dissolution at quenching temperature. Combining these formulae, hardenability of Fe-C-Mo alloys are calculated directly from chemical compositions and quenching conditions.抄録全体を表示PDF形式でダウンロード (1048K) -
須藤 正俊, 大木 継秋, 柴田 善一1992 年 78 巻 4 号 p. 624-631
発行日: 1992/04/01
公開日: 2009/05/29
ジャーナル フリー1) The cleavage fracture can occur along the deep drawing axis of a cup which is deep drawn from a hot-rolled or cold-rolled steel blank. This cleavage fracture can be principally explained to be brought about with the increase in (200) pole density on the fracture surface. The work hardening and circumferential tensile residual stress can cause brittle fracture, but can not explain the whole fracture behavior.
2) The reduction in the brittle fracture due to the increase in r value of blank sheet and additional ironing process can be caused by decreasing the (200) pole density on the fracture surfaces.
3) The decrease in cleavage fracture unit (dc) which is closely related to the toughness, is in linear relationship with the decrease in the (200) pole density and grain size on the fracture surfaces.抄録全体を表示PDF形式でダウンロード (1169K) -
植松 美博, 山崎 浩一1992 年 78 巻 4 号 p. 632-639
発行日: 1992/04/01
公開日: 2009/05/29
ジャーナル フリーEffects of rolling temperature and inter-pass annealing on the microstructures of hot rolled and annealed strips and the ridging property of cold rolled and annealed sheet have been investigated of continuously cast slab of Nb added 17% Cr stainless steel which had a near {100}//N. D orientation.
In such a case of no inter-pass annealing where no recrystallization during hot rolling occures, decrease in the rolling temperature increases deformation bands, and these banding makes recrystallized structures of hot rolled strip fine. When recrystallization occures by inter-pass annealing, microstructures of hot rolled strip become finer and uniform recrystallization occures after hot strip annealing.
The ridging property of cold rolled and annealed sheet corresponds to the condition of recrystallization of hot rolled and annealed strip. When coarse unrecrystallized domaines remain in the center layer of annealed hot strip, it causes severe ridging in final annealed sheet. These results suggest that the unrecrystallized center layer of hot rolled and annealed strip retains strong {100} //N. D orientation and thereby deteriorates ridging properties of final annealed sheet. The suggestion is supported by another experiment of one pass hot rolling.抄録全体を表示PDF形式でダウンロード (7119K) -
丸山 典夫, 角田 方衛1992 年 78 巻 4 号 p. 640-646
発行日: 1992/04/01
公開日: 2009/05/29
ジャーナル フリーThe effect of varying stress on fatigue life under cathodic protection by a zinc sacrificial anode and freely corroding condition in synthetic sea water and in air was investigated using 800 MPa grade high strength steel notched specimens ( Kt= 3.5 ).
The main results obtained are as follows:
1) Under a constant stress amplitude (CSA), fatigue lives in sea water under cathodic protection are shorter than those in air. However, under two step stress amplitude (TSSA ), fatigue lives under cathodic protection are rather longer than those in air.
2) In a low stress amplitude region, fatigue lives under TSSA are shorter than those under CSA in air and under cathodic protection.
3) Even when the higher stress amplitude in TSSA is much lower than the values shown by the S-N curves under CSA, the failure of notched specimens occurs.
4) Under the free corrosion potential, there is no difference in fatigue lives between under TSSA and under CSA, and Miners rule exists between them.
5) Under TSSA, macroscopic crack growth rate is retarded in air and under cathodic protection, and the effect of TSSA on macroscopic crack growth is in reverse to that on crack initiation and microscopic crack growth.抄録全体を表示PDF形式でダウンロード (1037K) -
宮原 一哉, 伊藤 彰, 茅野 秀夫, 細井 祐三1992 年 78 巻 4 号 p. 647-649
発行日: 1992/04/01
公開日: 2009/05/29
ジャーナル フリーPDF形式でダウンロード (2418K) -
草開 清志, 新家 伸一, 大岡 耕之1992 年 78 巻 4 号 p. 650-657
発行日: 1992/04/01
公開日: 2010/01/15
ジャーナル フリーThe nucleation and growth behavior of disc-shaped ordered γ''-phase and spherical ordered γ'-phase in Ni-base superalloys, modified Inconel X-750 type alloy (X-750M) and Inconel X-750 type alloy (X-750), has been investigated mainly by micro-Vickers hardness test and transmission electron microscopy. The hardness of X-750M aged in various conditions closely related to the size and the quantity of γ'' and δ-phases. Increasing the Nb content while decreasing the (Al+Ti) content in the alloys promoted the formations of γ'' and δ-phases. The growth kinetics of γ''precipitates in the region free of δ-phase followed the prediction of Lifshitz-Slyozov-Wagner theory of diffusion controlled growth at all aging temperatures. The activation energy of the growth of γ'' precipitates in X-750M was estimated to be 397 kJ/mol.抄録全体を表示PDF形式でダウンロード (8944K) -
松木 一弘, 宮崎 省吾, 村田 純教, 森永 正彦, 湯川 夏夫1992 年 78 巻 4 号 p. 658-665
発行日: 1992/04/01
公開日: 2010/05/07
ジャーナル フリーReを含む高性能単結晶超合金の組成の最適化指針を得るため,Ni-10Cr-12Al-1.2Ti-2.6Ta-2.0W-0.7Mo(mol%)の7元系合金に0～1.00mol%Reを添加した一連の合金について,その相安定性を調べると共に,各合金元素のγ相およびγ'相への分配比の検討を行った.また,すでに著者らが設計したRe添加の高性能合金(Ni-1OCr-12Al-1.5Ti-2.1Ta-2.3W-0.8Mo-0.25Re,mol%)に0, 4.5, 9.0mol%Coを添加した合金についても,その相安定性を調べると共に各合金元素の分配比を調べ,Re添加合金の組成の最適化という観点からCoの効果を検討した.
(1)Ni-10Cr-12Al-1.2Ti-2.6Ta-2.0W-0.7Mo(mol%)合金のNiとReをそれぞれ0, 0.25, 0.40, 0.50,1.00mol%ずつ置換した合金における相安定性は,(a)0.25mol%Reが共晶γ'相の抑制限界,(b)0.40mol%Reがαおよびσ相の抑制限界,として整理できる.
(2)Ni-10Cr-12Al-1.2Ti-2.6Ta-2.0W-0.7Mo-0/0.25/0.40/0.50Re(mol%)合金において,Reはほとんどγ相中に固溶した.さらに,本合金系に0.25mol%より多くReを添加した際,合金組成の最適化を図るためには,Ni-10Cr-12Al-1.2Ti-2.6Ta-2.0W-0.7Mo-0.25Re(mol%)合金に比べ,Cr,W,Mo,Ta量の減少,Al量の増加を考えなければならない.
(3)Ni-10Cr-12Al-1.5Ti-2.1Ta-2.3W-0.8Mo-0.25Re-0/4.5/9.0Co(mol%)合金において,Coは相安定性を良好に保ちながらNiとほぼ完全に置換して,γおよびγ'相に固溶した.なお,Coを添加しても各合金元素の分配比は変化しなかった.従って,Ni-Cr-Al-Ti-Ta-W-Mo-Re系合金にCoを添加して合金組成の最適化を図ることは,高性能合金を得るうえで有効である.抄録全体を表示PDF形式でダウンロード (5046K) -
松木 一弘, 村田 純教, 森永 正彦, 湯川 夏夫1992 年 78 巻 4 号 p. 666-672
発行日: 1992/04/01
公開日: 2009/05/29
ジャーナル フリーThe optimum Ta/W compositional ratio was searched for in Ni-10/11 mol % Cr-12/14 mol% Al -Ta-W( -5mol% Co) alloys in order to get an excellent combination of creep-rupture, phase stability and hot-corrosion resistance in a Na2SO4-NaCl salt. Solidification and precipitation temperatures were also examined as a function of the Ta/W ratio. The γ' solvus temperature and the creep-rupture life were found to increase with increasing Ta/W ratio up to 1.0. However, when the ratio exceeded 1.0, the creep-rupture life reversely decreased probably due to the increase in the residual amount of the eutectic γ' phase in alloys. On the other hand, hot-corrosion resistance increased monotonously with the Ta/W ratio. From the present study it was concluded that the Ta/W compositional ratio of 0.5 to 1.0 was most suitable for balancing the high temperature properties in this alloy system.抄録全体を表示PDF形式でダウンロード (913K) -
丹羽 直毅1992 年 78 巻 4 号 p. 673-679
発行日: 1992/04/01
公開日: 2009/05/29
ジャーナル フリーThe deformation and fracture behavior of the aged microstructure of Ti-13V-11Cr-3Al alloy was studied by SEM in-situ observation. Comparing with beta matrix, the areas where alpha phase precipitates i.e. alpha colonies and the neighborhoods of grain boundaries show higher resistance to deformation. Thus, strength becomes higher by increase of alpha precipitates with aging. In the fracture of this alloy, a main crack propagates with forming microcracks within alpha colonies and along grain boundaries ahead of the main crack and joining them. The crack propagation along grain boundaries is faster and less ductile than the transgranular crack propagation following microcracks in alpha colonies. With development of aging, the grain boundary cracking becomes prevailing as a fracture mechanism, hence, ductility reduces notably. Alpha precipitates play an important role not in strengthening but also in fracture of this alloy.抄録全体を表示PDF形式でダウンロード (13516K) -
佐久間 信夫, 三井 達郎, 倉部 兵次郎, 辻本 得蔵1992 年 78 巻 4 号 p. 680-687
発行日: 1992/04/01
公開日: 2009/05/29
ジャーナル フリーTitanium and its alloys are conventionally melted in watercooled copper hearth to avoid the chemical reaction between crucible and molten metal. However, titanium activity in TiAl is supposed to be low. This study was carried out to prove the possibility of vacuum-induction melting of TiAl alloys in high-purity CaO crucible. The following results were obtained.
(1) Oxygen contents in TiAl were always 0.110.14 wt% corresponded to thermodynamical equilibrium value when about 800 g was melted. This amount was a little larger compared with 0.04 wt% in plasma-arc melted TiAl. (2)Small amounts of 0.130.15 vol% of CaO inclusions with the sizes of 15μm were contained in TiAl, being nearly equal to killed steels. (3)New crucibles with 520 wt% CaF2 for preventing CaO-TiAl reaction, showed no effect for decreasing oxygen content, but a usefull effect for reducing inclusions due to the thermal stress relief by CaF2 film between CaO particles, resulting in long durabilities. (4) As-cast TiAl with compositions of 33.534.5 wt% Al showed elongations of 0.60.8% lower than plasma-arc melted TiAl. However, they were ameliorated to 1.1-1.4% by annealing at 900°C to 1200°C. This phenomenon can be explained from the point of veiw of the O diffusion from γ phase to α2 phase.抄録全体を表示PDF形式でダウンロード (6728K)
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