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Tetsu-to-Hagané Vol. 74 (1988), No. 6

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ONLINE ISSN: 1883-2954
PRINT ISSN: 0021-1575
Publisher: The Iron and Steel Institute of Japan

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Tetsu-to-Hagané Vol. 74 (1988), No. 6

The Present Condition of Japanese Automobile Industry and the Progress of Iron and Steel for Automobile Used

Makoto OHSAWA

pp. 941-950

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The Present Condition of Japanese Automobile Industry and the Progress of Iron and Steel for Automobile Used

On the Yield Ratio of the Structural Steel Used for Building Frames

Ben KATO

pp. 951-961

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On the Yield Ratio of the Structural Steel Used for Building Frames

Fundamental Development of Iron Ore Briquetting Technology

Hideo KOIZUMI, Arata YAMAGUCHI, Terunobu DOI, Fumio NOMA

pp. 962-969

Abstract

A series of experiments have been conducted for the development of an iron ore briquetting technology. The following results were obtained:
(1) The drop strength of green briquettes increased with the addition of 1 wt% bentonite, 0.5-1.0 wt% rignin, 3 wt% slaked lime, and 3 wt% cement. Among these additives, bentonite was found to be the most effective.
(2) In order to examine the abrasion of briquettes in the rotary kiln induration process, tumbler tests were conducted for pre-heated briquettes. It was found that the abrasion index (-3 mm%) of briquettes improved with the above-mentioned additives especially bentonite. These results were significantly better than those for pellets.
(3) The sphere shape of pellets causes problems in the blast furnace, such as low reposed angle, susceptibility of layersliding, and pellets sinking. These problems were remarkably improved with briquetting. Additional briquette characteristics, such as compression strength and reducibility were nearly equal to those of pellets.

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Fundamental Development of Iron Ore Briquetting Technology

The Development and Operation of Coke Dry Quenching with Double Flues

Ryuichi NAKAJIMA, Nobuaki KONISHI, Fukio KUWADA, Kazutoshi MATSUMOTO, Yoshio TANI, Takaaki KIMURA, Toshiharu MATSUDA

pp. 970-977

Abstract

A latest CDQ has been installed at No. 4 coke oven in Fukuyama Works.
CDQ in Fukuyama has been designed on the basis of the operational experience gained over the years at Keihin Works. It is an effective facility which has a production rate of 110 t per h and incorporates with developed equipments such as a multi-stage flue, a rotating coke bucket and a multi-function turbine. The commercial operation was started in February, 1986. Since then, this CDQ facility has been operating successfully and contributing to energy savings in Fukuyama Works.

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The Development and Operation of Coke Dry Quenching with Double Flues

Size Segregation of Sinter in Top Bunker of a Bell-less Type Blast Furnace

Yoshimasa KAJIWARA, Yoichi AMINAGA, Takanobu INADA, Tsutomu TANAKA, Ken-ichi SATO

pp. 978-984

Abstract

The size segregation of sinter in a top bunker of a bell-less type blast furnace was experimentally investigated by the use of a full scale model as well as a 1/10scale model. The following results were obtained.
The size variation during discharging from the bunker was significantly reduced by the installation of a simple stone box of suitable size at the suitable vertical position in the bunker for the restraint of the size segregation during charging of burden into the bunker. On the other hand, the installation of an insert to regulate solid flow in the bunker during discharging resulted in the meager reduction of the size variation during discharging. Accordingly, it was proved that the restraint of the size segregation in the bunker was of prime importance for the reduction of the size variation during discharging.
The increase of the charging rate of burden into the bunker decreased the size segregation in the bunker and, as a result, the size variation during discharging was reduced.
In case of two bunkers in series, the size variation during discharging from the lower bunker significantly depended on the re-segregation of burden in the lower bunker during discharging from the upper bunker.

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Size Segregation of Sinter in Top Bunker of a Bell-less Type Blast Furnace

Reduction Rate of TiO2 in Slag by Carbon Saturated Iron Melts

Haiping SUN, Nobuya SHINOZAKI, Katsumi MORI, Yasuji KAWAI

pp. 985-990

Abstract

The reduction rate of TiO2 in CaO-Al2O3-TiO3 slag by Fe-C or Fe-Si-C melts in a graphite crucible was measured at 1 420600°C under argon atmosphere. The mechanism of transport of titanium from slag to metal was discussed.
The reduction rate of TiO2 was strongly dependent upon temperature. It was concluded that the rate-determining step of the transport rate of titanium from slag to metal was chemical reaction at slagmetal interface.
It has been turned out that, when Fe-Si-C melt was used, TiO2 in the slag was reduced by carbon and silicon in the metal phase simultaneously. With increasing initial content of silicon in the metal, the transport rate of titanium from slag to metal, as well as the ratio of amount of TiO2 reduced by silicon to overall TiO2 reduced, was increased greatly. The transport rate of titanium in this case, however, was controlled by chemical reaction rate at interface and mass transport rate in the diffusion boundary layer in the slag. The contribution of the latter would become more important at higher silicon content in the metal.

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Reduction Rate of TiO2 in Slag by Carbon Saturated Iron Melts

Operation Controlling Technique in Hot Metal Pretreatment Furnace

Kiyoshi SHIWAKU, Syozo KAWASAKI, Akimitsu KAMIMORI, Matsuhide AOKI, Kiminori HAJIKA

pp. 991-998

Abstract

A new technology for hot metal pretreatment with the modified BOF has been developed at Kobe Works. This technology has been successfully applied to mass production of high-grade steel since November 1983. The furnace for hot metal pretreatment has an 80t capacity and is equipped with two lances for flux injection and oxygen top blowing. Hot metal is desiliconized and dephosphorized with oxygen and lime-iron oxide based flux in the first stage of refining, and desulphurization with soda ash injection is followed without deslagging.
This report describes the operational control technology of this process. This operational control consists of the following items,
(1) Calculation of the optimum amount of submaterials
(2) Control of the temperature after treatment
(3) Optimization of operational pattern and gives good results in stabilization of BOF operation, decrease of refining cost, and increase of productivity.

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Operation Controlling Technique in Hot Metal Pretreatment Furnace

The Solubility of MgO-Cr2O3 in MgO-Al2O3-SiO2-CaO Slag at 1600°C under Reducing Conditions

Kazuki MORITA, Akihiko INOUE, Naoki TAKAYAMA, Nobuo SANO

pp. 999-1005

Abstract

The Solubility of MgO-Cr2O3 in MgO-Al2O3-SiO2-CaO Slag and the activilies of chromium oxide in the slags were measiredat 1 600°C under Reducing conditions. For MgO-SiO2 melts which were saturated with 2MgO·SiO2, the solubility of MgO·Cr2O3 increased with decreasing oxygen partial pressure, because of decrease in γCrO1.5.When CaO is added to the melts mentioned above, soluble total chromium content decreased because γCrO1.5 and γCrO increased with increasing CaO content in the melts.
Under a fixed oxygen partial pressure, activities of chromium oxides in the chromite MgO·(CrxAl1-x)2O3 were also measured by equilibrating them with Ni-Cr alloys for which the activity coefficient γ°Cr(at 1 600°C) was determined as 0.421 in this study. It was found that the free energy change of the reaction : MgO(s)+Cr2O3(s) = MgO·Cr2O3(s) is expressed by-126 800+47.3 T (J/mol) and that MgO·Cr2O3 and MgO·Al2O3 form a solid solution which exhibits negative deviation from ideal behavior at 1600°C.

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The Solubility of MgO-Cr2O3 in MgO-Al2O3-SiO2-CaO Slag at 1600°C under Reducing Conditions

Formation of CO Macroblowholes during Solidification of Iron-Carbon Alloys Containing below 0.03% Carbon

Masashi HASHIURA, Kazumi MORI

pp. 1006-1012

Abstract

Observations have been made on the formation of CO macroblowholes in Fe-C alloys cast in a mold containing below 0.03% carbon. Critical compositions for macroblowhole formation were determined exaimining four types of macroblowhole formation. Critical oxygen concentration for macroblowhole formation decreases with increasing carbon content from 0.0025 to 0.005%, while it is 0.01% at carbon content from 0.005 to 0.03%. No CO macroblowhole forms below 0.0025% carbon. Critical compositions for macroblowhole formation are found to be related with microstructures. Macroblowhole diameters of Fe-C alloys obtained from present study are smaller than those obtained from previous studies.

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Formation of CO Macroblowholes during Solidification of Iron-Carbon Alloys Containing below 0.03% Carbon

Activity of Sulfur in Solid Fe-Cr Alloys and Their Equilibrium Relations with Sulfides at 1 573K

Toshiharu FUJISAWA, Masayuki ASANO, Takao SUZUKI, Chikabumi YAMAUCHI, Hiroshi SAKAO

pp. 1013-1020

Abstract

Equilibrium between solid iron-chromium alloys and H2-H2S gas mixture was measured using a gas circulating method, to determine the activity of sulfur in the alloys at 1 573K.
An isothermal section of the Fe-Cr-S system at 1 573 K was experimentally determined over the metal/sulfide equilibrium region using a conventional silica capsule technique. The thermodynamic evaluation procedure based on a modified GIBBS-DUHEM integration was applied to the experimentally obtained tie-line distribution and phase relations, and a stability diagram was obtained. This revealed the existence of stable fields of the metal and sulfide phases as a function of the partial pressure of sulfur and the metal ratio. The solubility of sulfur in the Fe-Cr alloy was also determined.

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Activity of Sulfur in Solid Fe-Cr Alloys and Their Equilibrium Relations with Sulfides at 1 573K

Vacuum Arc Remelting of Titanium with Rectangular Mold

Akihiro YAMANAKA, Hiroyuki ICHIHASI

pp. 1021-1027

Abstract

Vacuum arc remelting with rectangular mold was tried in order to reduce the cost of producing titanium sheet and plate. Compact electrodes and solid ones were melted with a mold designed to have the proportion of wide side length to the narrow of 1.5 and the round inner corners. The conditions of melting and the quality of ingots were investigated, and the following results were obtained.
(1) Melting aspects are the same as those with round mold, and there is no problem in melting compact electrode.
(2) There is no difference between heat fluxes at the wide side, the short side and the corners of mold, and those are the same as the heat flux at the round mold too. As the result, the thickness of solidified shell is uniformed.
(3) Distributions of [Fe] and [O] in the ingot are as homogeneous as those in round ingot.
(4) Surface quality of the ingot from a solid electrode is good enough, even in hot rolled plate from the ingot without conditioning, however only a few sharrow defects within 0.3 mm depth are detected.

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Vacuum Arc Remelting of Titanium with Rectangular Mold

Morphological Study of Formation Mechanism and Effect of Surface Characteristics of Original Hot Rolling Sheet on Scale Like Defect "Gold Dust" Formed on Cold Rolling Sheet of Stainless Steels

Akio YAMAMOTO

pp. 1028-1035

Abstract

A study was made of mechanism and causes of minute scale-like defects on bright annealed stainless steel sheets named as gold dust defects which frequently became to be initiating points of rust corrosion. The gold dust defects were microscopical overlapped surface with peeled foil like as scale, originated from the convex sites on the material uneven surface being pushed over into neighbor concave valley by cold rolling. Sheets having coarse surface or intergranular corroded surface were given for example as the uneven surface. It was considered that the gold dust defects were formed by overlapping mainly to tail direction during cold rolling where the elongation length was smaller than the thickness reduction by cold rolling. It was found that the gold dust defects were not detected practically on the surface of material sheet having roughness under 25.0 μm in Hmax and having the corroded grain-boundary of line, step or V-groove shaped type. Brushing of material surface with crushing the convex sites without elongation, and heavy grinding or polishing were also found to be causes of gold dust defects.

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Morphological Study of Formation Mechanism and Effect of Surface Characteristics of Original Hot Rolling Sheet on Scale Like Defect "Gold Dust" Formed on Cold Rolling Sheet of Stainless Steels

Development of Rotating Transformer with Flat Coil of Air Core for Eddy Current Flaw Detectors

Masashi MIZUNO, Katsuhiro KOJIMA

pp. 1036-1043

Abstract

A new rotating transformer with flat coils of air core has been developed for eddy current flaw detector of rotating probe type. This type of transformer provides following features in comparison with conventional one with the coils of ferrite core.
(1) Readiness to design and manufacture larger transformers with excellent homogeneity
(2) Light weight
(3) Low cost
Sufficient transmission efficiency was obtained with 20 turns for the air core coil of 200mm in inner diameter when the exciting frequency was 32kHz.
In this case the voltage transmission efficiencies were about 50% at the exciting side and 67% at the receiving side and the overall efficiency was about 34%. These values are large enough to guarantee the S-N ratio for the flaw detection. The test run of flaw detection on a reference block showed that the S-N ratio in the case of using these transformers were equivalent to that of the direct wire connection without transformer.

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Development of Rotating Transformer with Flat Coil of Air Core for Eddy Current Flaw Detectors

Surface Energy Controlled Abnormal Grain Growth in Melt-quenched 6.6% Silicon Iron Ribbons

Toshiro TOMIDA, Atsuki OKAMOTO, Masashi TAKAHASHI

pp. 1044-1051

Abstract

In order to understand the mechanism of abnormal grain growth in melt-quenched Fe-6.6%Si ribbons the recrystallization process during high temperature annealing has been investigated. Abnormal grain growth occurs at temperatures between 1 273 and 1 473 K in vacuum, dry hydrogen or dry argon atmosphere. The preferred orientation of the abnormal grain growth depends on annealing temperature and atmosphere sensitively. In the vacuum of total pressure from 6×10-3 to 10 Pa, highly oriented {111}(uuw)and {100}(0vw) textures form under the conditions of higher temperature-lower pressure and lower temperature-higher pressure respectively. In the hydrogen and the argon atmospheres with dew point of 228 K, strong {110}(uuw)and {100}(0vw)oriented textures are also observed respectively. Such an abnormal grain growth can be explained in terms of the surface energy differences between the crystallographic planes, and the surface energy itself is also affected by the oxidation.

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Surface Energy Controlled Abnormal Grain Growth in Melt-quenched 6.6% Silicon Iron Ribbons

Optimal Chemical Composition in Fe-Cr-Ni Alloys for Ultra Grain Refining by Reversion of Deformation Induced Martensite

Setsuo TAKAKI, Seiji TANIMOTO, Kouki TOMIMURA, Youichi TOKUNAGA

pp. 1052-1057

Abstract

A thermo-mechanical treatment using reversion from deformation induced martensite to austenite was suggessted to obtain ultra fine grain structure in metastable austenitic stainless steels. And, in order to determine steel composition suitable for the thermo-mechanical treatment, influence of Cr and Ni content on deformation induced transformation from metastable austenite to martensite and successive reversion to austenite was investigated for low carbon Fe-Cr-Ni ternary alloys by means of magnetic analysis. The results are as follows :
(1) An amount of martensite induced by 90% cold rolling can be estimated by the Ni equivalent of (Ni+0.35Cr), where Ni and Cr represent mass% of these elements in the alloy. In case the Ni equivalent of (Ni+0.35Cr) is smaller than 16.0%, austenite almost transforms to martensite by 90% cold rolling. An amount of austenite retained in specimens is less than 10vol%.
(2) In case the Cr equivalent of (Cr-1.2Ni) is smaller than 4.0%, martensite induced by 90% cold rolling almost reverses to austenite by 873K-0.6 ks annealing. An amount of martensite retained in specimens is less than 10vol%.
(3) On alloys whose Ni equivalent of (Ni+0.65Cr) is larger than 19.7%, Ms temperature of reversed austenite is below the room temperature, if specimens are annealed 0.6ks at 873K after 90% cold rolling.
For the Fe-Cr-Ni ternary alloys which satisfy the three conditions of (1)-(3) for composition, therefore, we can obtain almost single structure of reversed austenite by the above thermo-mechanical treatment.

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Optimal Chemical Composition in Fe-Cr-Ni Alloys for Ultra Grain Refining by Reversion of Deformation Induced Martensite

Strengthening of Metastable 16-10 Austenitic Stainless Steel by Ultra Grain Refining

Setsuo TAKAKI, Seiji TANIMOTO, Kouki TOMIMURA, Youichi TOKUNAGA

pp. 1058-1064

Abstract

The behavior of reversion from deformation induced martensite to austenite and the mechanical properties of specimens containing reversed austenite were investigated using a 15.6%Cr-9.8%Ni steel by means of transmission electron microscopy, magnetic analysis and tensile testing. Martensite content of specimens was controlled by cold rolling, and salt bath was used for reversion treatment. The results are as follows :
(1) In case of 0.6ks isochronic annealing, martensite content of specimens decreases abruptly in the temperature range from 800K to 900K as the result of reversion to austenite and the temperature range where reversion occurs is not affected by the cold working before annealing.
(2) The 0.2% proof stress of specimens containing work hardened austenite and reversed austenite is dependent on the volume fraction and the strength of each phase.
(3) Additional cold rolling of deformation induced martensite is very effective for grain refining of reversed austenite formed by the following 873K-0.6ks annealing, resulting in increase of 0.2% proof stress. A specimen, for example, with 93% cold rolling prior to the reversion treatment has an ultra fine austenitic structure with the mean grain size of 0.5lm giving a high 0.2% proof stress of about 0.7GPa.

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Strengthening of Metastable 16-10 Austenitic Stainless Steel by Ultra Grain Refining

Effects of Austenitizing Conditions on Creep Rupture Properties of a 12Cr Heat Resisting Steel

Xing-yang LIU, Toshio FUJITA

pp. 1065-1072

Abstract

The effect of austenitizing conditions on creep rupture properties has been investigated for a 12%Cr heat resisting steel.
1) The creep rupture strength at 600°C was improved considerably by increasing austenitizing temperature from 950°C to 1100°C. Increasing austenitizing temperature further from 1100°C to 1150°C or higher has no distinct improving effect on creep rupture strength, but causes a drastic reduction in creep rupture ductility. Therefore, the optimum austenitizing temperature for the steel would be around 1050°C to 1100°C.
2) The increase in austenitizing temperature resulted in a decrease in the amount of undissolved carbides such as M23C6 and NbC. M23C6 dissolves completely at about 1 100°C and NbC does at about 1150°C for 1/2 h. For the decrease in the amount of undissolved carbides gives solution hardening effect and fine-precipitation hardening effect after tempering, it is considered that the change in the amount of residues with the change in austenitizing temperature is the most important factor affecting creep rupture strength.
3) The increase of prior austenite grain size with the increasing austenitizing temperature also contributes some what to the improvement of creep rupture strength, but may bring about higher concentration of S at the grain boundaries and thus, reduces creep rupture ductilities drastically.
4) Varying austenitizing time from 30min to 2 h at 1050°C and 1100°C has no distinct effect on creep rupture properties.

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Effects of Austenitizing Conditions on Creep Rupture Properties of a 12Cr Heat Resisting Steel

New Empirical Formula for Estimation of Hardenability from Chemical Compositions

Masakatsu UENO, Kametarou ITOH

pp. 1073-1080

Abstract

The accuracy of GROSSMANN'S equation, which has been widely used for calculation of the hardenability of a steel, is not always satisfactory in paticular in the case of B-added steels. We found out that this problem arose from the fact that the GROSSMANN'S equation was not always formulated rationally. In this work, an investigation has been made to obtain the new empirical formula for estimating the hardenability in place of GROSSMANN'S equation.
The results are as follows :
The hardenability of a steel can be predicted acculately by the following equations.
(1) In the case of a B-added steel (free-B≥5 ppm)
log Vc-90=2.94-0.75β
β(%)=2.7C+0.4Si+Mn+0.45Ni+0.8Cr+2Mo where, Vc-90 is the critical cooling velocity (°C/s) at which 90% martensite structure can be obtained.
(2) In the case of a B-free steel.
log Vc-90=3.69-0.75β'
β'(%)=2.7C+0.4Si+Mn+0.45Ni+0.8Cr+Mo
Those results show that the effect of Mo in B-free steels is a half of that in B-added steels and the effect of B itself is equivalent to 1%Mn addition.

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New Empirical Formula for Estimation of Hardenability from Chemical Compositions

Corrosion Resistance of High Ni Alloys in High Temperature Chloride Solutions Containing H2S

Katsumi MASAMURA, Yoshiichi ISHIZAWA, Toru INAZUMI, Shuji HASHIZUME, Iwao MATSUSHIMA

pp. 1081-1088

Abstract

Effects of environmental and material factors, such as temperature, partial pressures of hydrogen sulfide and carbon dioxide and alloy composition on corrosion resistance of Ni-Cr-Fe alloys in H2S-CO2-Cl- environments simulating sour oil and gas wells are discussed. Main factor controlling the resistance to stress corrosion cracking (SCC) of high Ni alloys in Ni content as far as the results in the present work are concerned. Higher Ni content gives higher resistance to SCC. For a certain content of Ni in an alloy, there are optimum content of Cr and Mo to improve SCC resistance. When Δ is determined by the following formula :
Δ=Ni-(Cr+1.5Mo-20)2/12
SCC was not observed in alloys that had composition range of Δ>19 in 20% NaCl solution saturated with 1 atm. H2S at 230°C. Higher Ni content gave higher critical temperature for the occurrence of SCC in H2S-CO2-Cl- environment. While the presence of hydrogen sulfide in itself does not affect corrosion re sistance of Ni-Cr-Fe alloys, hydrogen sulfide coexisting with chloride ions increases the detrimental effect of chloride ions for passivating metals. Cold working in Ni-Cr-Fe alloys increases the susceptibility to SCC in sour environment.

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Corrosion Resistance of High Ni Alloys in High Temperature Chloride Solutions Containing H2S

Improvement of Resistance to Breakage of Hot Work Roll with High Rolling Load on the Basis of Fracture Mechanics

Makoto SAITO, Sadao OTA, Hiroshi TOYODA

pp. 1089-1096

Abstract

Mechanism of breakage of hot work roll with high rolling load was analyzed on the basis of fracture mechanics. It was revealed that the process to the breakage of hot work roll could be represented as a cir cumferential fatigue crack growth from the fire crack to the critical depth, where stress intensity factor was equal to the fracture toughness of the roll material. Simulation of the circumferential fatigue crack growth was carried out on a continious billet mill roll using fatigue crack propagation properties (f.c.p.p.) of the roll material. The simulation results could explain the breakage pattern of the roll on actual rolling service, and made it clear that the life of hot work roll before breakage highly depended on the f.c.p.p. Test rolls (ultra high carbon steel roll) with superior f.c.p.p. were manufactured on the basis of the previous study made by the autors. From the performance results, it was found that resistance to breakage of the test rolls was remarkably improved and that the total rolling tonnage of the test rolls could be increased by 50% with the help of the improvement of wear due to the massive carbide which was intentionally intro duced for the improvement of f.c.p.p.

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Improvement of Resistance to Breakage of Hot Work Roll with High Rolling Load on the Basis of Fracture Mechanics

Mapping of Low Cycle Fatigue Mechanisms at Elevated Temperatures for an Austenitic Stainless Steel

Kenji KANAZAWA, Koji YAMAGUCHI, Satoshi NISHIJIMA

pp. 1097-1104

Abstract

Mapping of low cycle fatigue mechanisms at elevated temperatures was attempted for a better understanding of low cycle fatigue behavior of an austenitic stainless steel at elevated temperatures. Results of strain-controlled, uniaxial low cycle fatigue tests on solution treated stainless steel of type 310 were used in the present analysis. The experiments were performed under the conditions of 15 different temperatures from room temperature to 800°C, and 4 strain rates from 6.7 × 10-3 s-1 to 6.7 × 10-6 s -1. Modes of dislocation structure and fracture were classified according to stress amplitude and fatigue life respectively and plotted on temperature-strain rate diagram. By superposing the two maps, it becomes easy to find the principal factors which govern the fatigue life under any conditions of temperature and strain rate. The proposed idea of mapping is believed to have wide applicability, e.g. for selecting materials and predicting fatigue behavior under service conditions.

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Mapping of Low Cycle Fatigue Mechanisms at Elevated Temperatures for an Austenitic Stainless Steel

Influence of the Local Brittle Zone on Critical CTOD of Weld HAZ in 50kgf/mm2 Tensile Strength Steels

Toshiaki HAZE, Shuji AIHARA, Yukito HAGIWARA, Yokimi KAWASHIMA, Kouichi UCHINO, Sachio TOMITA, Rikio CHIJIIWA

pp. 1105-1112

Abstract

An investigation was made to clarify the influence of Local Brittle Zone (LBZ) on critical CTOD (δC) of multi-pass weld Heat-Affected Zone (HAZ) and metallurgical factors controlling the toughness of the LBZ by using four HT50 structural steels of various chemical compositions. The multi-pass welded joint exhibited low δCin case the fatigue-crack front of a COD specimen reached LBZ. The LBZ was identified to be a grain-coarsened zone reheated between AC1 and AC3 by the subsequent welding pass. Simulated HAZ with double thermal cycle reproduced the main microstructure of the LBZ. In the simulated HAZ COD test, cleavage fracture was initiated from a high carbon-martensite-island formed by the reheat-thermal cycle. By temper-thermal cycle due to further welding pass, the martensite-islands were decomposed into cementite-ferrite aggregates to various degree, depending on the chemical compositions of the steels. The higher degree of the decomposition resulted in the greater increase in δC. Close correlation was found between the minimum value of the measured δC in the welded joints and δC of the simulated HAZ with triple thermal cycle.

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Influence of the Local Brittle Zone on Critical CTOD of Weld HAZ in 50kgf/mm2 Tensile Strength Steels

Fatigue Strength of Annealed 0.45%C Pb-Free-Cutting Steel

Yukitaka MURAKAMI, Kimio MINE, Hisafumi USUKI

pp. 1113-1118

Abstract

According to the conventional hypothesis, the high machinability of free cutting steels is attributed to both the easy cutting due to stress concentration at inclusions such as Pb and S (MnS) and their lubricating effects between cutting tool and chips. However, previous studies have not necessarily made clear the rela tionship between the strength characteristics and the cutting mechanism from the viewpoint of fracture caused by the crack nucleation due to the stress concentration at inclusions. If these inclusions behave as fracture origins, we cannot expect high fatigue strength of free cutting steels.
In the present paper, the effects of Pb and MnS on fatigue strength were studied by comparing the fatigue behavior of annealed 0.45%C Pb-free-cutting steel (SAE10L45) and 0.46%C steel (S45C). The effects of small fatigue cracks and small artificial holes(diameter: 40-500μm, depth: 40-500μm) on fatigue strength were also investigated by microscopic observations.
Experimental results showed no evident difference in both static and fatigue strengths between SAE10L45 and S45C; no evident decrease in strength of SAE10L45 due to the existence of inclusions of Pb and S (MnS) was confirmed. This result should be considered to explain the high machinability of SAE10L45, because the stress concentration at inclusions of Pb and MnS may not be the main factor for the high machinability.

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Article Title

Fatigue Strength of Annealed 0.45%C Pb-Free-Cutting Steel

Fully Automatic Analysis System of Steel Works

Shigeomi SATOU, Yutaka YOSHIOKA, Youichi ISHIBASHI

pp. 1119-1125

Abstract

The analysis of steel composition for production control has been requiring time and labor-saving, in the case of the continuous casting process. A fully automatic emission spectrochemical analyzing system has been developed consisting of an automatic sampling system, a sample transfering system, an automatic analyzing system and a transmission system of analytical values. The procedure was fully automatic from sampling of molten steel, reception of samples at the laboratory to transmission of analytical values. The most suitable condition for automatic analysis was established.

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Article Title

Fully Automatic Analysis System of Steel Works

「温故知新」のミニ版となるか/留学生ローカル事情

浅井 滋生, 佐野 信雄

pp. 1195-1196

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Article Title

「温故知新」のミニ版となるか/留学生ローカル事情

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