Online edition:ISSN 2188-0921
Print edition:ISSN 0913-4794

No. 38  Mar. 2020

≪ All Articles ≫
<Feature-Ⅰ>Automotive Weight Reduction
1 Global Business Expansion of Wire Rods and Sheets
Takaaki MINAMIDA, Kuniyasu ARAGA 
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.
5 Global Marketing Strategies for Automotive Aluminum Sheet, Extrusion and Forged Suspension Businesses
Dr. Yasuo TAKAKI, Shogo SAKAMOTO, Takashi OKA,
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.
11 Global Expansion of Copper Rolled Product Business for Automotive Terminals and Connectors
Yosuke MIWA 
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.
16 Technical Trends in Aluminum Alloy Sheets for Automotive Body Panels
Yosuke OTA, Dr. Tetsuya MASUDA, Shinpei KIMURA 
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.
21 Technical Trends in Copper Alloys and Plating for Automotive Terminals
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.
28 Hot-dip Galvannealed Steel Sheet of 980MPa Grade Having Excellent Deformability in Axial Crush
Michiharu NAKAYA, Shinjiro KANETADA, Michitaka TSUNEZAWA 
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.
32 Multi-material Automotive Bodies and Dissimilar Joining Technology to Realize Multi-material
Dr. Junya NAITO, Dr. Reiichi SUZUKI 
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.
<Feature-Ⅱ> Iron and Steel Manufacturing Technology
38 Outline of Steel Production System
Tsutomu HAMADA 
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.
46 Decreasing Coke Rate under All-Pellet Operation in Kobe No.3 Blast Furnace
Hitoshi TOYOTA, Tomonori MAEDA, Nayuta MITSUOKA,
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.
53 Establishment of Special Steel Production System at Kakogawa Works
-Construction of No.3 Secondary Refining Equipment and No.6 Continuous Caster-
Yasumasa YOSHIDA, Hideya OKADA, Hiroaki SAKAI,
Hiroyuki ONODA, Dr. Takehiro NAKAOKA 
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.
60 Improving Control Accuracy of Steel Plate Temperature by Accelerated Cooling with Columnar Water Jets
Takahiro OHARA, Keiichi YAMASHITA, Kiichiro TASHIRO,
Kensuke UENISHI, Taketsugu OSAKA, Dr. Masahiko MITSUDA 
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.
67 On-line Inter-stand Tension Monitor System for Bar Mill
Dr. Masanori KOBAYASHI, Tomohide TAIRA, Masakazu KATO,
Hiroshi NAKAMURA, Dr. Yoshio MORIMOTO, Dr. Shusuke YANAGI 
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.
72 Technology for Reducing Strip Meandering in Tandem Cold Mill
Shigeto KOIZUMI, Dr. Shusuke YANAGI, Dr. Masanori KOBAYASHI 
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.
80 Influence of Modified Oxide Inclusions on Initiation of Rolling Contact Fatigue Cracks in Bearing Steel
Masaki SHIMAMOTO, Dr. Eiichi TAMURA, Akihiro OWAKI,
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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