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No. 38 Mar. 2020
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<Feature-Ⅰ>Automotive Weight Reduction |
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Global Business Expansion of Wire Rods and Sheets |
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Takaaki MINAMIDA, Kuniyasu ARAGA
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Japanese automakers and parts manufacturers are
expanding their production outside Japan, increasing
the need for local procurement. To respond to this need,
Kobe Steel's wire rod and sheet business has established
production plants for steel and intermediate products
outside Japan to enable the supplying of products with
quality equivalent to that of products supplied in Japan.
This paper describes Kobe Steel's approach to expanding
its global business, focusing on special-steel wire rods
and high-tensile sheet products.
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Global Marketing Strategies for Automotive Aluminum Sheet, Extrusion and Forged
Suspension Businesses
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Dr. Yasuo TAKAKI, Shogo SAKAMOTO, Takashi OKA,
Narikazu HASHIMOTO
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The need to reduce the weight of automobiles has been
increasing year by year due to fuel efficiency regulations
responding to environmental issues. Since the 1980s,
there has been a gradual increase in the use of aluminum
sheets for automotive body panels, aluminum extrusions
for bumper reinforcements and door beams, and
aluminum forgings for suspension parts. Aluminum has
now become an indispensable automotive material. Kobe
Steel has been developing business outside Japan by
utilizing the material technology, production technology,
and application technology for automotive parts; these
technologies have been cultivated in response to the
requirements of Japanese automakers. This article
outlines the technological developments in each type of
business, the development of production plants outside
Japan, and the company's efforts to globally supply
products of the same quality as those supplied in Japan.
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Global Expansion of Copper Rolled Product Business for Automotive Terminals and
Connectors
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Yosuke MIWA
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It has been 40 years since Kobe Steel's copper rolled
product business first specialized in rolled-copper
products for electrical and electronics applications, and
a quarter century has passed since the company began
actively developing business outside Japan. Five years
ago, the company established a trilateral system for
supplying rolled-copper products, the system consisting
of three sites, one in Asia, another in North America and
yet another in Europe. This paper reviews the history of
the company's global business development up to date,
analyzes the current issues on the basis of comparison
with competing non-Japanese manufacturers of wrought
copper and copper alloy products and describes the
global business strategies, demand, and technical trends
in the future. In developing rolled-copper products
for electrical and electronics applications, including
copper alloys for automotive terminals, it is believed to
be important to follow the trends of automobiles, which
are expected to be reborn as new mobility, and to acquire
a high level of ability in responding quickly to rapidly
changing user needs.
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Technical Trends in Aluminum Alloy Sheets for Automotive Body Panels
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Yosuke OTA, Dr. Tetsuya MASUDA, Shinpei KIMURA
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Aluminum alloy sheets are increasingly being used
for automotive bodies to reduce their weights and are
required to have excellent mechanical properties, joining
performance and corrosion resistance. For outer panels,
Kobe Steel has been working to improve the performance
of 6000 series (Al-Mg-Si) alloys in bake hardenability,
formability, and surface quality after stamping. For
inner panels and structural members, the application of
Ti/Zr surface treatment is being promoted to meet the
requirements for the durability of adhesive bonding,
which are mainly adopted by non-Japanese automakers.
This paper introduces developments in the application
of aluminum alloy sheets to automotive bodies and
developments for overcoming technological issues.
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Technical Trends in Copper Alloys and Plating for Automotive Terminals
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Hiroshi SAKAMOTO
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Copper alloys and tin-plated strips are widely used
for automobile terminals. These terminals are being
downsized, requiring their copper alloy materials to
have higher strength and excellent stress relaxation
resistance. The tin plating is now required to have
high fretting corrosion resistance, in addition to a low
friction coefficient and low contact resistance. This paper
describes the technical trends in automobile terminals and
the properties of newly developed copper alloys and tin
plating, as well as future trends in technical development.
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Hot-dip Galvannealed Steel Sheet of 980MPa Grade Having Excellent Deformability in
Axial Crush
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Michiharu NAKAYA, Shinjiro KANETADA, Michitaka TSUNEZAWA
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Automotive parts that play the roles of energy absorbers
must not fracture upon collision. It has been reported
that the cracking behavior of a hat-shaped column
during an axial crush test correlates with the bending
properties of its material and that the conventional hot-dip
galvannealed (GA) dual-phase (DP) steel sheets
of 980MPa grade have insufficient performance. The
newly developed GA 980MPa grade steel sheet with
a homogeneous microstructure shows no cracking at
a bending angle that would have caused cracking in
conventional DP steel sheets, preventing crack
propagation in the thickness direction. In order to
evaluate the axial crash performance of a part made of
the newly developed steel sheet, hat-shaped columns with
two different cross-sectional geometries were examined
by drop weight impact testing. For both geometries,
the newly developed steel exhibited cracks with smaller
lengths and higher energy absorption compared with
conventional steel.
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Multi-material Automotive Bodies and Dissimilar Joining Technology to Realize
Multi-material
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Dr. Junya NAITO, Dr. Reiichi SUZUKI
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This paper introduces multi-material car body designs
using ultra-high strength steel and aluminum alloy to
realize an estimated weight reduction of 12 to 33% from
the base body composed of conventional steel. Also
included is an explanation of the dissimilar joining
necessary for realizing multi-material car bodies as well
as a dissimilar joining technology uniquely developed by
Kobe Steel.
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<Feature-Ⅱ> Iron and Steel Manufacturing Technology
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Outline of Steel Production System
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Tsutomu HAMADA
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While taking place of upgrading such as consolidations
and mergers in order to increase competitiveness in the
steel industry, Kobe Steel aims to enhance competitiveness
through the high added value of technology, products
and services, and further differentiation by constructing
unique business models. In order to provide competitive
technologies and products, in 2017 Kobe Steel completed
a new hot metal pretreatment plant at its Kakogawa
Works and in order to enhance cost competitiveness,
decided and implemented the consolidation of upstream
(ironmaking and steelmaking) processes of Kobe Works
with Kakogawa Works. After consolidation, Kakogawa
Works has been transformed into the cost-competitive
steelworks that manufactures a wide variety of steel
products, such as steel sheets, thick plates and wire rods.
Kobe Works could significantly improve the quality and
cost competitiveness of special steel wire rods and bars
using billets manufactured by Kakogawa's equipment
introduced the latest technology, without reducing steel
production. In the global supply system for products,
Kobe Steel has established a three-pole supply system in
Japan, US and China for special steel wire rods (steel
wire) and high formable advanced high tensile strength
steel sheet.
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Decreasing Coke Rate under All-Pellet Operation in Kobe No.3 Blast Furnace
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Hitoshi TOYOTA, Tomonori MAEDA, Nayuta MITSUOKA,
Kota TANAKA
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Having no coke plant, Kobe Works of Kobe Steel aimed
at low coke-ratio operation of its blast furnace process.
Furthermore, its sintering plant was closed in 1999,
and the process was converted to all-pellet operation in
2001. Afterward, the plant was using self-fluxed dolomite
pellets produced at and shipped from Kakogawa Works.
Kobe Works was the only site in Japan that adopted
and continued all-pellet operation and optimized the
complex control of burden distribution in accordance
with the high pellet ratio and pulverized coal combustion
in accordance with the multi-brand coal types, which
it did in the 4th blast furnace (inaugurated in 2007).
Furthermore, replacing lump ore with self-fluxed dolomite
pellets has improved the meltdown property of iron ore at
high temperature. As a result, operation at a low coke rate
of 283 kg/tonne was achieved under the severe conditions
of a high pellet ratio (80%) and raw materials that were
all stored in the yard.
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Establishment of Special Steel Production System at Kakogawa Works
-Construction of No.3 Secondary Refining Equipment and No.6 Continuous Caster-
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Yasumasa YOSHIDA, Hideya OKADA, Hiroaki SAKAI,
Hiroyuki ONODA, Dr. Takehiro NAKAOKA
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Kobe Steel shut down the operation of the ironmaking
and steelmaking process at Kobe Works in October
2017, and in November 2017, this upstream process
was consolidated at Kakogawa Works. Prior to this, by
January 2017, the Steelmaking Department of Kakogawa
Works had established a special-steel production system
for wire rods by installing No.3 secondary refining
equipment (2LF, 4RH) and a No.6 continuous caster. A
challenge in designing the new process was to produce
small lots of special steel with high productivity, high
yield and high quality at Kakogawa Works, which has
a large heat size. In order to solve this problem, cutting
edge technologies were introduced in the upstream
equipment. This has enabled small-lot production and
quality improvement while continuing stable production
under the full production system after the consolidation of
the upstream process. This paper reports the features of
newly installed equipment, the concept of quality design,
and the operational status.
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| 60 |
Improving Control Accuracy of Steel Plate Temperature by Accelerated Cooling
with Columnar Water Jets
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Takahiro OHARA, Keiichi YAMASHITA, Kiichiro TASHIRO,
Kensuke UENISHI, Taketsugu OSAKA, Dr. Masahiko MITSUDA
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The amount of cooling water, which affects the heat
transfer characteristics, and the height of residual water
on the steel plate surface, the height that changes in
accordance with the steel plate size, were modeled for
the accelerated cooling of steel plates with cylindricallyarranged
multi jet. In addition, the heat transfer
characteristics associated with the height of residual
water were investigated by laboratory experiments to
model the heat transfer coefficient, which is an index
of heat transfer characteristics. Furthermore, the heat
transfer coefficient model was optimized by the actual
temperatures measured at multi-points on a steel plate
in an actual machine, which enabled the accurate
prediction of the plate temperature. A water flow rate
control function was newly developed on the basis of the
temperature prediction results and was introduced into
the actual machine, which improved the accuracy of the
plate temperature control.
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| 67 |
On-line Inter-stand Tension Monitor System for Bar Mill
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Dr. Masanori KOBAYASHI, Tomohide TAIRA, Masakazu KATO,
Hiroshi NAKAMURA, Dr. Yoshio MORIMOTO, Dr. Shusuke YANAGI
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In wire rod and bar mills, it is important to optimize
inter-stand tensions in order to prevent problems during
rolling and to prevent dimensional variations in the
longitudinal direction. The stabilization of inter-stand
tension, however, has hitherto been dependent on the
adjustment skills of operators. This paper relates to
a method that was developed to estimate inter-stand
tensions on the basis of a model for wire rod rolling.
This model uses the values of motor current, which can
easily and constantly be obtained during rolling without
relying on the skills of the operators. A tension monitor
system was newly developed to provide the rolling mill
operators with inter-stand tension estimated in real time
using the above method, and this monitor was introduced
to the bar rolling mill at the Kobe Works of Kobe Steel.
As a result, the system has facilitated the motor speed
adjustment performed by the operators. This contributes
to the stabilization of the inter-stand tension in actual
operation and to the reduction of operational troubles.
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| 72 |
Technology for Reducing Strip Meandering in Tandem Cold Mill
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Shigeto KOIZUMI, Dr. Shusuke YANAGI, Dr. Masanori KOBAYASHI
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Strip meandering in a tandem cold mill causes strip
breakage troubles and must be suppressed. The issue of
meandering has been studied for a long time, but many
of the studies focused on runout of the strip tail end
with tension released, or on the inter-stand meandering
behavior during tandem rolling. On the other hand, even
at the entry side of a tandem cold mill with a tension
lower than that of inter-stand, strips may meander due
to various disturbances and cause problems. Hence, an
analysis model of meandering behavior was constructed
while considering the restraint by bridle rolls disposed on
the entry side of a tandem cold mill. The effect of entryside
tension on meandering behavior was investigated,
and the calculation results were verified by rolling
experiments. It was found that the tension enhancement
on the entry-side was effective for the suppression of
meandering. Consequently, the entry-side tension of the
tandem cold mill of Kakogawa Works was increased, and
this has reduced the problems due to meandering.
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| 80 |
Influence of Modified Oxide Inclusions on Initiation of Rolling Contact Fatigue Cracks in
Bearing Steel
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Masaki SHIMAMOTO, Dr. Eiichi TAMURA, Akihiro OWAKI,
Akihiro MATSUGASAKO
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In order to elucidate the mechanism by which the
modification of oxide inclusions in bearing steel leads
to the improvement of rolling contact fatigue (RCF)
properties, a study was conducted with particular
attention to the difference in the crack initiation time.
Compared with normal Al-killed steel, non-Al-killed
steel with modified oxide inclusions has been confirmed
to exhibit improved rolling contact fatigue properties.
Investigations using ultrasonic testing (UT) and acoustic
emission (AE) have revealed that the non-Al-killed steel
has a smaller number of defects detected by UT and the
number of signals detected by AE, both indicating the
suppressed initiation of initial cracks. A study done on
the reasons shows that SiO2-based inclusions generated
in the non-Al-killed steel have excellent adhesion
between each inclusion and the matrix, with a smaller
difference in Young's modulus between them. Therefore,
it is conceivable that the non-Al-killed steel experiences
a decreased amount of the strain change that occurs
in the vicinity of inclusions during rolling load, which
suppresses the initiation of initial cracks and improves the
rolling contact fatigue properties.
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