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No. 35 JUN. 2017
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<Feature-Ⅰ>Material Processing Technologies |
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| 1 |
Development of Steel Castings and Forgings for Vessels
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Nobuyuki FUJITSUNA
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KOBE STEEL has been developing crankshafts, as well as other steel castings and forgings for ships, to make ships more energy efficient and reliable. This paper introduces technologies relevant to crankshafts, namely, super clean steel, technology for improving the fatigue strength of forged steel crank-throws and improved techniques of non-destructive inspection. Also introduced is the development status of highly strengthened intermediate shafts and high-strength steel for rudders.
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| 7 |
Effect of Inclusion Size on Fatigue Properties in Very
High Cycle Region of Low Alloy Steel Used for Solid
type Crankshaft
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Ryota YAKURA, Mariko MATSUDA, Dr. Tatsuo SAKAI, Dr. Akira UENO
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A study was conducted to grasp the fatigue properties, including the properties in a very highcycle fatigue region, of a low-alloy steel used for the solid type crankshaft of a 4-cycle diesel engine. Fatigue tests were conducted on specimens, some of which were taken from a solid type crankshaft and others taken from a round forged bar. The relation between the inclusion size at crack initiation sites and the fatigue property was studied on the basis of fracture mechanics. The study developed a relation equation between the fatigue life and inclusion size, as well as a relation equation between the threshold stress intensity range and inclusion size, for fracture initiated from the surface and internal inclusions. These equations show that decreasing inclusion size improves not only the fatigue strength working against surface fracture but also that attributable to internal fracture.
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| 14 |
Kobe Steel's Original Titanium Alloys Developed in the Past 20 Years
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Dr. Hideto OYAMA
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In the past 20 years, Kobe Steel has developed and commercialized various titanium alloys. AKOT is a
corrosion-resistant alloy, in which Cr has the important role of enriching Pd and Ru on the corroded surface. Ti-1.2ASN is a heat-resistant alloy that can be used at temperatures up to 800℃, in which oxidation resistance has been improved by the addition of Al and Si, and grain growth is inhibited by silicide. Ti-9 is a quasi Ti-6Al-4V alloy that is as coilable as CP-titanium. Its Al content has been suppressed to 4.5% to enhance cold rollability, and Si has been added to ensure the ductility of welds. KS EL-F is a quasi Ti-6Al-4V and is as hot-forgeable as CP-titanium, in which C is exploited to achieve high strength at temperatures up to approximately 500℃ and to reduce flow stress during hot-forging.
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| 18 |
High Heat-transfer Titanium Sheet-HEET®- for Heat Exchangers
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Keitaro TAMURA, Yoshio ITSUMI, Dr. Akio OKAMOTO,
Dr. Hideto OYAMA, Dr. Hirofumi ARIMA, Dr. Yasuyuki IKEGAMI
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A plate-type heat exchanger (PHE) that uses seawater as a cooling/heating medium is widely employed by chemical plants, power-generating facilities and large transport ships. Titanium is a common material for these heat exchangers, particularly for their primary members, including a heat exchanging plate and piping, thanks to its excellent corrosion resistance to seawater. Improving the heat-transfer performance of PHE enables the reduction in number and size of the plate used in PHE and thus enables the entire facility to be downsized. Kobe steel have developed a high heat-transfer titanium plate-HEET®-which has a heat-transfer performance that is significantly improved by fine irregularities imparted on its surface. The surface area increased by the fine irregularities, along with the promoted nucleate boiling, has improved the heat-transfer and particularly increased the evaporative heat transfer by approximately 20% or more.
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| 23 |
Dust Core with Low Core-loss for High-frequency Applications
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Hirofumi HOJO, Tomotsuna KAMIJO, Yuji TANIGUCHI,
Nobuaki AKAGI,
Hiroyuki MITANI
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Dust cores produced by compacting insulation-coated powder allow a high degree of freedom in shaping and are expected to be useful for the downsizing of parts; however, they have issues of energy loss, or core loss. A study has been conducted on reactors and choke coils, which are used at relatively high frequencies, to improve their core-loss characteristics by focusing on the particle size of the powder. As a result, "MAGMEL MH20D" powder was developed by designing powder, taking into account, not only the magnetic characteristics, but also power characteristics, and by combining Kobe Steel's conventional techniques of heat-resistant coating and grain coarsening. The newly developed powder has improved the core loss, reducing it to 30% of that achieved by conventional products, and has been adopted for the reactors of solar-power systems.
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| 28 |
Highly Heat-Resistant Aluminum Alloy "KS2000"
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Toshiyuki TANAKA, Yasuki KAMITAKAHARA
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Rotating/sliding components that operate at elevated temperatures, such as impellers and pistons, require aluminum alloys having a heat resistance higher than that of conventional aluminum alloys. Kobe Steel has optimized the additive elements to finely disperse precipitates that improve hightemperature properties, the homogenization conditions to finely disperse crystallized products and the conditions of plastic deformation to refine grain size. The optimizing of the composition and processing conditions resulted in the development of a new aluminum alloy, "KS2000," having an excellent heat resistance compared with the conventional 2618 alloy.
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<Feature-Ⅱ> New Materials and Technologies for Automobiles
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| 34 |
Martensitic Steel Sheets of 1300 and 1500MPa Grades
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Yukihiro UTSUMI, Atsuhiro SHIRAKI,
Sae HAMAMOTO,
Junichiro KINUGASA
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Super-high strength steel sheets of a strength exceeding
980 MPa have been used in reinforcement parts for
automotive bumpers and door to meet strengthened
collision safety standards and to decrease weight for the
sake of emission reduction. A study has been conducted to
improve the bending workability, resistance weldability,
and delayed-fracture immunity required for the steel
sheets used in parts produced through cold forming,
such as bumper reinforcements. The study then led to
the development of martensitic steel sheets of 1300 MPa
and 1500 MPa grades. The newly developed steel has
enabled the production of bumpers of 1300 MPa grade
and 1500 MPa grade, the world's highest grades for cold
worked bumper reinforcements, while also enabling 10
to 15% less weight compared with conventional bumper
reinforcements.
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| 39 |
Steel Sheets for Highly Productive Hot Stamping
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Sae HAMAMOTO, Hiroyuki OMORI, Tatsuya ASAI,
Naoki MIZUTA,
Noriyuki JIMBO, Takayuki YAMANO
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Rapid progress is being made in the application of
hot-stamped, super-high strength parts to automobile
bodies. Hot stamping is a technology that can solve
the problems associated with high-strength steel sheet,
e.g., an increased forming load and deterioration of
dimensional accuracy; however, the method has suffered
from low press productivity and limitation in the shapes
of parts. In order to overcome these issues, a steel sheet
for hot stamping has been developed via compositional
design. This paper introduces the characteristics of the
newly developed steel sheet and its practical applications,
including a demonstration of the multi-step hot stamping.
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| 45 |
Characteristics of 1180MPa Grade Cold-rolled Steel Sheets with Excellent Formability
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Tadao MURATA, Sae HAMAMOTO, Yukihiro UTSUMI,
Takayuki YAMANO,
Dr. Yuichi FUTAMURA, Takayuki KIMURA
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High-strength steel sheets are being used in recent years to improve crashworthiness and to decrease weight in order to reduce automobile emissions. Higher strength is desired particularly for automotive body frame members. In response to this demand, Kobe Steel has developed a 1180 MPa grade cold-rolled steel sheet with excellent formability. This paper introduces the guidelines for the microstructural control and typical characteristics of the steel sheet. The newly developed steel exhibits favorable practical characteristics of delayed-fracture resistance, spot weldability and conversion treatability, in addition to excellent strength and formability.
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| 50 |
Influence of Type of Loading on Fracture Behavior of High Strength Steel
with Very High-Cycle Fatigue
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Yusuke SANDAIJI
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Fatigue fractures initiating in internal inclusions occurs in high-strength steel in the very high-cycle fatigue region; however, the fracture behavior under cyclic shear stress has yet to have been elucidated. This study involves ultrasonic torsional fatigue tests and ultrasonic axial fatigue tests being performed on the same bearing steel to compare the fracture behavior. The influence of the
type of loading on very high-cycle fatigue characteristics is also examined. Both torsional and axial fatigue tests resulted in fractures originating in inclusions and Optically Dark Areas (ODA) were observed in the vicinity of the origins of all the fractures. However, no difference with the type of loading was recognized in the relationship between the ⊿K value, obtained from the inclusion and ODA sizes, and the number of cycles. Nevertheless, there are differences in the type of inclusions that cause fractures. It has been found that in the case of the torsional fatigue test, inclusions elongated in the rolling direction tend to be the originating points of fractures.
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| 55 |
Mechanical and Tribological Properties of DLC Films for Sliding Parts
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Dr. Hirotaka ITO, Dr. Kenji YAMAMOTO
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Diamond-like carbon (DLC) film has the advantage of having both low friction and low wear, and in recent years it has been applied to various sliding parts, such as parts for internal-combustion automotive engines. This paper presents a study on the mechanical characteristics and sliding properties of DLC films deposited by unbalanced magnetron sputtering (UBMS) equipment. It was clarified that the UBMS equipment can control the amount of hydrogen in a DLC film and as a consequence the mechanical properties of the DLC film can be changed. Furthermore, sliding tests using oil lubrication clarified that controlling the amount of hydrogen in DLC and the choice of additives in the oil are critical to achieving both low friction and low wear at the same time.
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| 61 |
Surface Treatment Technologies of Aluminum Alloy for Automobiles
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Yosuke OTA, Tetsuya KOJIMA
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Light materials, such as aluminum alloy sheets, are
increasingly being used for the purpose of reducing
weight in automotive bodies. Regarding the surface
characteristics required for such aluminum alloy
sheets, emphasis is being placed, especially in Europe,
on bonding durability to suppress the deterioration of
joints bonded using adhesive in environments such as
salt water spray conditions. Titanium/zirconium (Ti/Zr)
treatment is a surface treatment adopted by automotive
manufacturers outside Japan to improve the bonding
durability of automotive aluminum materials. In Europe,
electric discharge texturing (EDT) surfaces, as well
as dry lubricant, are being used in addition to Ti/Zr
treatment. In order to use materials that are surface
treated in accordance with European specifications, the
process conditions, including conversion coating, must be
optimized. Kobe Steel can provide Ti/Zr treatment, EDT
surfaces and dry lubrication.
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| 65 |
Highly SCC Resistant 7000-series Aluminum Alloy Extrusion |
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Dr. Takahiro SHIKAMA, Dr. Shinji YOSHIHARA
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A study was conducted to develop extrusions of highstrength 7000-series aluminum alloy with excellent stress corrosion cracking (SCC) resistance. The target proof stress was 400MPa. Normally, the SCC resistance of 7000-series alloys decreases with increasing strength. This study focused on the mechanism of SCC; namely, the anodic dissolution of a boundary precipitate, MgZn2. The electric potential of this precipitate was controlled to suppress its anodic dissolution and to improve the SCC resistance. In addition, the addition of Zr was confirmed to suppress recrystallization, and the surface recrystallization, which deteriorates SCC resistance, has been suppressed. This paper introduces the elemental technologies regarding the development of this alloy for achieving both high strength at the level. of 400MPa proof stress and SCC resistance.
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| 69 |
Application of Aluminum Extrusions to Automotive Parts
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Narikazu HASHIMOTO
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Recent automobiles have problems of increasing body weight due, for example, to enhanced structural strength for improving collision safety, an increase in the number of parts such as sensors and installation of large batteries. Meanwhile, it is also necessary to respond to the strengthening of fuel-efficiency regulations, and aluminum materials are being increasingly used for the purpose of weight reduction. In particular, aluminum extrusions, which enable complicated cross-sectional shapes to be obtained with relative freedom, are being increasingly applied to automotive parts such as automotive bumper systems and frame members. This paper reports on the current status and future trends of automobile parts adopting aluminum extrusions, with its main focus on a 7000-series alloy that is our main product.
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