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Tetsu-to-Hagané Vol. 74 (1988), No. 2

ISIJ International
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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. 2

International Collaboration in Testing Methods and Evaluation for Advanced Materials

Masao KANAO, Kazuyoshi NII, Norio SHINYA

pp. 207-214

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International Collaboration in Testing Methods and Evaluation for Advanced Materials

Recent Titanium Melting Techniques and the Effective Way to Improve Titanium Ingot Quality

Masaaki KOIZUMI

pp. 215-223

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Recent Titanium Melting Techniques and the Effective Way to Improve Titanium Ingot Quality

Solvent Extraction of Trace Metals in Steel

Tatsuya SEKINE, Yuko HASEGAWA

pp. 234-242

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Solvent Extraction of Trace Metals in Steel

An Approximate Analysis of Non-uniform Gas Flow through Layered Burdens

Mamoru KUWABARA, Eiji CHIKAMATSU, Iwao MUCHI

pp. 246-253

Abstract

An approximate analysis relevant to the gas flow through the shaft of blast furnace with layered burdens is developed for predicting the local azimuth of streamline, the ratio of gas-distribution between two adjacent layers, and the radial distribution of gas flow rate across each layer.
The effects of charging conditions on the non-uniformities of gas flow in layered burdens are investigated on the basis of a mathematical model derived from the analysis mentioned above. The predictions obtained by the model are shown to be in reasonable agreement with the numerical solutions by the finite difference method of the equation of continuity and the vectorial Ergun equation. Computational time for the approximate model can be considerably abridged in comparison with that for the rigorous numerical method.
The zigzag patterns of gas-streamlines were visualized in a two-dimensional packed bed composed of alternate layers of silicagel particles. Availability of the present model was verified from the close agree ment between observed and predicted streamlines.

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An Approximate Analysis of Non-uniform Gas Flow through Layered Burdens

Bath Movement of Molten Iron in a Coal Gasification Vessel

Tsutomu TANAKA, Yutaka ARIAKE

pp. 254-261

Abstract

Bath movement in two kinds of coal gasifier filled with molten iron was studied by a tracer response method. One is an LD converter type and the other is a cylinder placed in horizontal.
Bath movement in a cylindrical vessel placed in horizontal was more irregular than that of LD converter. Two kinds of time averaged recirculations were observed in a region of larger amount of liquid for the lance placed at the position of 3 : 1 division of the length of a vessel. This phenomenon was dependent on the ratio of diameter to length of a vessel.
The relation between mixing time and energy density of agitation was described byτ∝ε-O.52, which was different from the conventional behavior observed in LD converter, where τ is mixing time and ε is energy density of agitation. The difference of the mechanism of energy dissipation was considered from dimensional analysis.
An addition of liquid paraffin as pseudo slag in LD converter resulted in the remarkable decrease in the flow velocity near the wall. Beyond a critical thickness of pseudo slag, the direction of flow near the wall has reversed from the bottom of the vessel to the surface. With an increase in the thickness of pseudo slag, a considerable prolongation of mixing time was observed. The phenomenon agreed well with a mathe matical simulation under the presence of pseudo slag.

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Bath Movement of Molten Iron in a Coal Gasification Vessel

Smelting Reduction Mechanism of Chromium Ore Sinter by Solid Carbon

Shin FUKAGAWA, Teruhisa SHIMODA

pp. 262-269

Abstract

Experiments were carried out to investigate the smelting reduction mechanism of chromium are sinter bygraphite. Chromium are sinter was made from chromium are and fluxes such as lime stone, silica sand and serpentine.
The following results were obtained :
1) Chromium are particles were dispersed in molten slag until they were entirely dissolved at the terminal stage of the reduction.
2) The reduction rate is controlled by the step (ii) of the following steps :
(i) the dissolution of chromium are particles into molten slag
(ii) the reduction of chromium and iron oxide in the slag at the slag-graphite interface
3) The contents of Al2O3 and MgO in molten slag increase as the reduction proceeds with the dissolution of chromium ore particles.
4) The reduction rate seems to be decreased by this change in slag composition.

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Smelting Reduction Mechanism of Chromium Ore Sinter by Solid Carbon

Industrialization of a New Steelmaking Process Utilizing Hot Metal Pretreatment and Smelting Reduction

Osamu YAMASE, Masahumi IKEDA, Junichi FUKUMI, Chihiro TAKI, Kenzo YAMADA, Katsuhiro IWASAKI

pp. 270-277

Abstract

Low phosphorus hot metal is mass-produced by use of cast floor desiliconization and ladle dephosphorization, and less slag converter practice is established. Efficient manganese are smelting reduction in the converter has been realized, and high manganese yield, i.e., 65 to 70% is attained at high manganese i.e., [Mn]=1% level.
It is essential for the efficient recovery of manganese to obtain low phosphorus hot metal to the level of [P] 0.013% and to attain the highly accurate decarburization control, reduction ot (FeO), and slag basicity and a uantitv control in the converter.
By use of this new technology, it has become possible to reduce the expensive ferromanganese alloy consumption, and the cost of converter steelmaking.

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Industrialization of a New Steelmaking Process Utilizing Hot Metal Pretreatment and Smelting Reduction

Plasma Electron Beam Melting of 9 Titanium Alloys

Junji TAKAHASHI, Mitsutane FUJITA, Yoshikuni KAWABE

pp. 278-285

Abstract

The small-scale plasma electron beam melting method for β titanium alloys was investigated. The melting process was evaluated from the viewpoint of the yield of alloying elements in Ti-15Mo-2Fe-3Al and Ti-15V-3Cr-3Sn-3Al alloys and the segregation of the elements in the ingots.
The process consists of double meltings. Through the primary melting, a bar ingot was produced on a hearth. In the secondary melting of the bar ingot, solidified metal was continuously withdrawn downwards at a speed corresponding to the melting rate of the bar ingot.
The yield of alloying elements after secondary melting was from 86 to 90% in Al, 86% in Cr and 100% in the other elements such as Fe, Sn and V. The segregation in the bar ingot was recognized, but the segregation in the secondary ingot was not detectable except in the small zone finally solidified. The amounts of impurities such as C, N, O except H were the same as those in commercial alloys. The weight-loss of 14% was observed after the secondary melting. In conclusion, this process is convenient and available for melting of small-scale ingots of titanium alloy.

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Plasma Electron Beam Melting of 9 Titanium Alloys

Oxidation Dephosphorising Method of Molten Steel Containing Chromium

Yoshimasa MIZUKAMI, Naoto TSUTSUMI, Hiroshi SHIMA, Toshio HORI, Tadanobu KOMAI, Shogo TAKAISHI

pp. 286-293

Abstract

Conventional oxidation dephosphorising process has a shortcoming that when applies to chromium-containing molten steel it oxidizes the chromium as well. This study is aimed at developing a technique to produce low-phosphorus steel while preventing the chromium oxidation.
It has been found that the desired dephosphorization can be achieved while inhibiting the oxidation of chromium if the oxygen potential in the molten steel is controlled using chromium oxide, rather than iron oxide as an oxidizing source. The preferential oxidation of phosphorus depends on the equilibrium relation between chromium, phosphorus and oxygen. It has also been made clear that the slagging of flux is important from the viewpoint of kinetics.
Another study made on the mechanism of dephosphorization by the slag particles in molten steel has revealed that a film of chromium oxide is formed over the surface of slag particles to inhibit dephosphorization when iron oxide is used. Also, it has been confirmed that the addition of calcium fluoride and calcium chloride to dephosphorizing flux is conducive to the acceleration of the dephosphorizing reaction.
On applying the above finding to the dephosphorization of molten steel with an initial chromium concentration of 1 to 2 percent, as high a dephosphorization ratio as 80 percent was obtained while preventing the oxidation of chromium using a flux comprising 40% CaO, 20% CaF2, 20% CaCl2 and 20% Cr2O3.

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Oxidation Dephosphorising Method of Molten Steel Containing Chromium

The Rate of Nitrogen Removal from Molten Steel by Reductive Gas

Yoshimasa MIZUKAMI, Susumu MUKAWA, Tsuyoshi SAEKI, Hiroshi SHIMA, Shuhei ONOYAMA, Tadanobu KOMAI, Shogo TAKAISHI

pp. 294-301

Abstract

The fundamental study has been made on the rate of nitrogen removal from molten steel to gas phase with reductive gas injection and flushing. A fluid flow on the surface of molten, steel is observed in hydrogen gas flushing. Hydrogen gas increases the rate of nitrogen removal. The apparent rate constant approaches to the chemical reaction rate constant. It is considered that the fluid flow on the surface of molten steel caused by Marangoni convection increases the liquid mass transfer, and thus, the nitrogen removal rate.
When CO is used as a reductive gas, partial pressure of CO, Pco, must be kept in a suitable range for each composition of molten steel, because silicon in molten steel is oxidized to silica by CO gas, and this oxide decreases the liquid-gas interface area for nitrogen removal from molten steel. The suitable CO partial pressure can be estimated by equilibrium calculation. The effects of gas flow rate on nitrogen removal with different gaseous materials in RH degassing equipment can be estimated from the results of the fundamental study.

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The Rate of Nitrogen Removal from Molten Steel by Reductive Gas

Formation of CO Macroblowholes during Solidification of Iron-Carbon Alloy Ingot

Masashi HASHIURA, Kazumi MORI

pp. 302-309

Abstract

Formation of CO macroblowholes during solidification of Fe-C alloys containing 0.03-0.3% C cast into a mold has been investigated. Critical composition for blowhole formation was determined from examining four types of formation of macroblowholes. Critical oxygen concentration decreases with increasing carbon content from 0.05% to 0.15%, while it is constant above 0.15% carbon. Below 0.05% carbon, the critical oxygen concentration tends to be almost constant. Microporosities formed in the interdendritic region grow to macroblowholes. The number of microporosities increases with increasing oxygen content. The mechanism of macroblowhole formation is explained. The critical composition for blowhole formation of 0.1% carbon is calculated theoretically using a model on the basis of experimental data of solidification rate and primary dendrite arm spacing. Good agreement is found between calculation and experiment for the critical composition.

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Formation of CO Macroblowholes during Solidification of Iron-Carbon Alloy Ingot

Formation Mechanism of Freckle in Unidirectional Solidification

Toshiki KAWAMURA, Shigeo ASAI, Iwao MUCHI

pp. 310-317

Abstract

Experimental and theoretical works have been conducted to clarify the formation mechanism of freckle in unidirectional solidification. The formation process of freckle in mushy zone and the movement of interdendritic liquid were visualized and observed by use of a cold model of NH4Cl-H2O system.
It is noted that freckle grows up against the freezing direction, i.e., from the liquid-mushy interface to the mushy-solid interface. Fingertype fluid movement is observed near the liquid-mushy interface which is presumed to trigger the channel flow inducing freckle.
A mathematical model which takes account of the freezing and remelting phenomena in the mushy zone has been developed to simulate the formation process of freckles. Methods for preventing the formation of freckle are proposed on the basis of the formation mechanism investigated in this paper.

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Formation Mechanism of Freckle in Unidirectional Solidification

Phase Transformation and Heat Transfer during Cooling of Steel

Shoji TANIGUCHI, Toshiyuki MURAKAMI, Atsushi WATANABE, Atsushi KIKUCHI

pp. 318-325

Abstract

Studies on the cooling of a carbon-steel disk were made to discuss the heat transfer accompanied with phase transformation.
Hypereutectoid steel, eutectoid steel and hypoeutectoid steel were used as the disk. Its diameter and height are both 30 mm. The disk was cooled from the bottom by a jet of water or nitrogen gas, after it was heated inductively up to about 1 200 K. Heat-transfer coefficients which are necessary for the analysis of heat transfer in the system, were obtained by analysing the cooling curve of a copper disk, under the assumption of one dimensional heat conduction in the disk. These values of heat-transfer coefficients could be successfully used for the prediction of cooling curves of stainless steel disk.
In the case of carbon steels, the heat generation by phase transformation was accounted in the one-dimensional heat conduction equation. The fractions of various phases such as austenite, martensite, bainite, ferrite and pearlite were estimated by the use of the continuous cooling transformation diagram (CCT diagram). Calculated cooling curves in carbon steels by the present model were in good agreement with the observed ones.

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Phase Transformation and Heat Transfer during Cooling of Steel

Effect of Continuous Annealing Thermal Pattern on Strength and Ductility of Cold Rolled Dual Phase Steel

Hidenori SHIRASAWA, Yoshiki TANAKA, Kazuhiko KORIDA

pp. 326-333

Abstract

Strength and ductility of cold rolled dual phase steels produced by two types of intercritical continuous annealing were investigated on three kinds of steels different in carbon, silicon and manganese contents. Over-aging temperatures of water quench aging ( QA) type annealing and direct aging (DA) type annealing were varied from as water quenched to 500°C. Ductility of steel was evaluated by elongation and hole expanding ratio associated with stretch formability and stretch flangeability, respectively. Although the steel with the least chemistry showed no significant ductility difference, at the same strength level, between both types of annealing, the steels with the higher chemistry resulted in conspicuous difference between the two types, i.e., high elongation was given by DA type annealing and high hole expanding ratio, by the other. The increased elongation of DA type steel was explained by the high work hardening rate in the relatively wide range of tensile strain, which is due to the high hardness second phase as well as the formation of retained austenite. The increased hole expanding ratio of QA type steel mainly resulted from softening of martensite which increases the resistance for the crack initiation at the interface of ferrite and martensite by decreasing their hardness difference.

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Effect of Continuous Annealing Thermal Pattern on Strength and Ductility of Cold Rolled Dual Phase Steel

Effect of Induction Heating Tempering for Strengthening and Toughening of Spring Steel

Kazuhiro KAWASAKI, Takayo CHIBA, Takao YAMAZAKI

pp. 334-341

Abstract

It was shown in the previous paper that grain refining by Induction Heating austenitizing and Quenching (IHQ) is effective for the improvement of mechanical properties of Si-Cr spring steel (SUP12). However, it was also shown that Induction Heating Tempering (IHT) as well as grain refining by IHQ plays an important role for superior mechanical properties of Induction Heating Quenched and Induction Heating Tempered (IHQIHT) material.
So, in this report the independent effect of IHT on strengthening and toughening of SUP12 is investigated.
(1) IHT is effective for the improvement of ductility, toughness, fracture toughness, resistivity to delayed fracture, and fatigue life apart from the effect of grain refining by IHQ. In case of SUP 6, SUP 7, SWRH62B and S45C, IHT materials show toughness generally superior to that by the ordinary tempering.
(2) Shorter time and higher temperature heating as well as rapid heating in IHT are effective for strengthening and toughening.

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Effect of Induction Heating Tempering for Strengthening and Toughening of Spring Steel

Characteristics of Micro-structure of Induction Heating Tempered Spring Steel

Kazuhiro KAWASAKI, Takayo CHIBA, Takao YAMAZAKI

pp. 342-349

Abstract

It was clearly shown in the previous paper that Induction Heating Tempering (IHT) showed an independent effect on strengthening and toughening of Si-Cr spring steel (SUP12) apart from the effect of grain refining by Induction Heating austenitizing and Quenching (IHQ).
So, in order to clarify the cause of the effect of IHT on strengthening and toughening the micro-structureof IHT and Furnace Heating Tempered (FHT) materials was investigated. The results are as follows :
(1) The amount of grain boundary precipitation of carbide in IHT material is slightly less than that in FHT material. And in the case of comparatively higher hardness material such as HRC=53, carbide particle in IHT material is smaller than that in FHT material.
(2) These characteristics of micro-structure coincided with consideration about the mechanical properties, the nucleation and growth process of austenite from tempered structure, and the calculation results about carbide precipitation.
(3) Retained austenite in IHT material is also effective for strengthening and toughening, but the effect is less than that of carbide precipitation.

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Characteristics of Micro-structure of Induction Heating Tempered Spring Steel

High Temperature Corrosion of Alloys in a Simulated Coal Gasification Atmosphere

Michiya OKADA, Ken'ichi USAMI, Tadaoki MORIMOTO

pp. 350-357

Abstract

The corrosion resistance of commercial grades stainless steels, Fe-base, Ni-base, and Co-base alloys and that of the pack coated alloys with Cr, Al, or Si were investigated in a simulated coal gasification atmosphere in the temperature range of 200 to 850°C for 100 to 500 hours. Fe- and Co-base alloys and high Cr (>20%) stainless steels exhibited good corrosion resistance to sulfur attack. Ni-base alloys were rapidly sulfurized above 600°C. Pack aluminizing of alloys with high Cr was the most effective in improving the resistance to sulfidation attack comparing with pack chromizing and pack siliconizing. In order to clarify the effects of alloying elements to sulfur attack, additional experimental heats in which the content of Cr, Ni, Co and Al was individually changed were examined in the same corrosive condition. Addition of Cr, Co or Al to Fe-Cr alloys was effective against sulfidation. It was observed that addition of 2 to 3% of aluminum to Fe-Cr or Fe-Cr-Ni alloys promoted the formation of protective oxide scale. A discussion was made on the effect of these alloying elements in Fe-base alloys on the corrosion behavior in the coal gasification atmosphere.

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High Temperature Corrosion of Alloys in a Simulated Coal Gasification Atmosphere

Corrosion Fatigue Crack Growth Characteristics of a 50 kgf/mm2 TMCP Steel in Synthetic Sea Water

Kenjiro KOMAI, Hideki OKAMOTO

pp. 358-364

Abstract

The corrosion fatigue (CF) crack growth rate of a 50 kgf/mm2 TMCP steel has been measured in ASTM synthetic sea water. The CF crack growth rate in synthetic sea water both at free corrosion and under a cathodic potential is smaller than that in air under a low ΔK level at R=0.1. The crack growth under a cathodic potential is proceeded by fatigue mechanism at a low ΔK level, while at a high ΔK level it is accelerated by hydrogen embrittlment. The CF crack growth characteristics under a cathodic potential can not be explained in terms of ΔKeff, since Ca and Mg deposits-induced wedge effect enlarges region II in load-strain hysteresis loops. A modified stress intensity factor range, ΔKcont, deduced from the load range shared by regions I and II is useful to explain the influence of cathodic potential on crack growth rate. When severe corrosive dissolution occurs at free corrosion potential, the crack growth characteristics can be uniquely explained in terms of effective crack growth rate considering the crack closure (da/dt)eff and ΔKcont.

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Corrosion Fatigue Crack Growth Characteristics of a 50 kgf/mm2 TMCP Steel in Synthetic Sea Water

An Analysis of Fatigue Crack Growth Property in Ti-6Al-4V at Low Stress Intensity Range in Air

Masae SUMITA, Norio MARUYAMA, Kozo NAKAZAWA

pp. 365-372

Abstract

Fatigue crack growth property in air in three kinds of Ti-6Al-4V was analyzed at stress intensity range less than 30 kgf/mm3/2. The following results were mainly obtained.
1) α phase shows cleavage-like fracture at low stress intensity range. The fracture mode of β phase depends on the shape of a precipitated in β phase. Fracture surface of β phase in which fine a particles precipitated is flat and featureless, and that in which lath like a plate formed is cleavage like.
2) Microstructure influences fatigue crack growth rate, which depends on the volume of a phase, shape of a particles in β phase etc.
3) ΔK threshold decreases with increase of stress ratio until more than 0.9.
4) The effective ΔK threshold is about 7.5 kgf/mm3/2 without reference to microstructures, because the mode of fracture is intergranular at ΔK close to the ΔK threshold and is same among the three kinds of specimens.

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An Analysis of Fatigue Crack Growth Property in Ti-6Al-4V at Low Stress Intensity Range in Air

The Effects of Carbon on Low Cycle Fatigue Softening of Austenitic Stainless Steels

Koji SHIBATA, Masahiko KOGITA, Cheng-shu CHEN, Toshio FUJITA

pp. 373-379

Abstract

Effects of carbon on low cycle fatigue behavior of 20Cr-15Ni and 15Cr-15Ni stainless steels have been investigated at room temperature. Thin foils from the cyclically deformed specimens were subjected to electron microscopy. Single crystals produced by remelting some of the steels were also tested. They were deformed by compression sliced in the predetermined directions, and their dislocation configurations were observed in electron microscope. The effects of carbon and/or silicon addition on proof strength, cyclic deformation behavior and dislocation configurations were also studied. It was shown that the carbon alloyed steels showed fatigue softening as reported previously in a 0.18C-25Cr-20Ni steel. The softening was observed even at the small number of cycles, and was enhanced by an increase in carbon content and a decrease in strain amplitude. Carbon also reduced the trend of dislocations to form cellular configurations. It was revealed that such effects of carbon were increased by Si addition and that Si increased the solid solution hardening by carbon. All these results were qualitatively consist with the concept that solid solution hardening by some complexes between carbon and chromium atoms existed in the as-solution treated condition and broke down during cyclic deformation to induce fatigue softening.

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The Effects of Carbon on Low Cycle Fatigue Softening of Austenitic Stainless Steels

Effect of Decarburizing Helium Environment on Creep Behavior of Ni-base Heat-resistant Alloys for High-temperature Gas-cooled Reactors

Yuji KURATA, Yutaka OGAWA, Hajime NAKAJIMA

pp. 380-387

Abstract

Creep tests of Ni-base heat resistant alloys (Hastelloy XR and XR-II) were conducted at 950°C in four kinds of helium environments with different impurity compositions in order to examine the effect of decarburizing environment.
Both alloys were decarburized in a helium environment with low partial pressure of oxygen and carbon activity. The decarburization induced degradation of creep properties such as lower creep rupture strength, higher creep rate and earlier start of accelerating creep. Whether the decarburization of the Hastelloy XR and XR-II might occur or not in the primary helium coolant of high temperature gas-cooled reactor (HTGR) could be predicted by using a corrosion map of a stability diagram for chromium. Controlling impurities to maintain higher partial pressure of oxygen and carbon activity in primary helium coolant of HTGR is proposed in order to prevent degradation of creep properties of the materials caused by decarburization.

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Effect of Decarburizing Helium Environment on Creep Behavior of Ni-base Heat-resistant Alloys for High-temperature Gas-cooled Reactors

Effect of Metallurgical Factors on Machinability of Steel Wool Wire

Ikuo OCHIAI, Hiroshi OHBA

pp. 388-395

Abstract

To clarify the mechanism of steel wool cutting, the effect of metallurgical factors such as strength, micro-structure, and nonmetallic inclusions, on the machinability of the steel wool wire were investigated from the viewpoint of the microscopic fracturing of the material in the vicinity of the tip of the cutting edge. The results obtained are as follows :
(1) The shear deformation of the material in the plastic deformation zone is preceded by microscopic fracturing along the grain boundaries which are elongated by cold drawing with a high total reduction of area.
(2) The metallurgical factors making the grain boundaries embrittle, such as coarse ferrite/pearlite structure, more than 80% total reduction in area by cold drawing, etc., improve the machinability of steel wool wire.
(3) Changing the composition of nonmetallic inclusions to that characterized by low melting points, andreducing the total amount of nonmetallic inclusions are effective for the improvement of the machinability of steel wool wire.

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Effect of Metallurgical Factors on Machinability of Steel Wool Wire

八つ当たり/メイク・ア・プロフィット

田中 紘一, 川上 正博

pp. 398-398,404

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八つ当たり/メイク・ア・プロフィット

第5回電気めつき鋼板シンポジウム(アメリカ)に出席して

中小路 尚匡

pp. 399-399

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第5回電気めつき鋼板シンポジウム(アメリカ)に出席して

第2回塑性加工国際会議(2nd ICTP)出席報告

池 浩

pp. 400-400

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第2回塑性加工国際会議(2nd ICTP)出席報告

第8回プラズマ化学国際シンポジウム出席報告

武田 紘一

pp. 401-401

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第8回プラズマ化学国際シンポジウム出席報告

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