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No. 30 DEC. 2011
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<Feature-1> Material Processing Technologies
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| 1 |
High-quality Work Roll Manufacturing Technology Using New Electro
Slag Remelting (ESR)
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Jun SATO, Kouji IWANAGA, Atsushi TOMIOKA, Katsushige NISHIGUCHI,
Hiroki NAKASHIMA, Hitoshi ISHIDA
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Because cold rolling requires work rolls of high quality in their surfaces and interiors, the rolls are generally made from electro-slag-remelting (ESR) ingots which ensure a stable outcome. In order to produce rolls with excellent dendrite pattern, a fine and uniform dendrite structure with no flow pattern is required. Segregation lines, which may appear as "freckles" on the roll surface, are sometimes generated in the ingots. Such segregation lines should not exist within the use depth of the rolls. In recent years, Kobe Steel has upgraded its ESR apparatus and achieved a significant improvement in the quality of the surface and interior.
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| 7 |
Predicting Effect of Cold Rolling on Fatigue Strength under Combined Loading
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Mariko MATSUDA, Eiji OOTSUKI, Shuhei KAJIHARA, Yoji HANAWA,
Takeshi HAMADA
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The cold rolling method is adopted to improve the fatigue strength of crankpin fillet for marine diesel engines. Under working conditions, combined bending and torsional loading occurs in crankpin fillet; therefore, combined axial and torsional fatigue tests under tensile or compressive mean stress were conducted to distinguish among the three methods of fatigue strength evaluation. Modified IACS and Findley criteria were confirmed to be methods that are on the safe side. By evaluating fatigue strength by these criteria, it was confirmed that compressive residual stresses from the cold rolling method improve fatigue strength on the pin fillet surface of semi-built crankshafts under working conditions.
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| 13 |
Effect of Alloying Elements on Machinability and Hot Workability of α-β Titanium Alloy Containing Fe and C
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Shogo MURAKAMI, Dr. Katsuhiko OZAKI, Kousuke ONO, Yoshio ITSUMI
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Many studies have been conducted on titanium alloys to improve their machinability and hot workability. They are inferior in machinability and hot workability when compared with other structural materials, such as steel and aluminum alloys. The KS EL-F (Ti-4.5Al-4Cr-0.5Fe-0.15C) that has been developed has mechanical properties equivalent to those of Ti-6Al-4V at room temperature and has superior hot workability. It was found that increasing Fe and decreasing Cr concentration in the chemical composition of KS EL-F improves both machinability and hot workability. The modified alloys (Cr: 1 to 2.5%, Fe: 1.25 to 2%) were found to decrease tool tip wear by almost 30% and the hot deformation stress by about 10%. Furthermore, decreasing Cr suppressed aging embrittlement caused by the precipitation of TiCr2.
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| 19 |
Pre-coated Titanium Sheet with Excellent Press Formability
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Akihisa FUJITA, Yoshio ITSUMI, Tadashige NAKAMOTO,
Kayo YAMAMOTO
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Plate type Heat Exchangers (PHEs) are one of the main applications for commercially pure titanium. The plates, each consisting of a titanium sheet press-formed into a complex corrugated pattern, are directly linked to high performance such as that seen in the thermal conductivity of the PHE. Now Kobe Steel has newly developed a pre-coated titanium sheet with excellent press-formability, whose design includes a lubricant coating that is easily removed by alkaline cleansing.
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| 24 |
Newly Developed Iron-based Powder Mixture, High-density SEGLESS®, for High Density Compaction
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Hironori SUZUKI, Satoshi NISHIDA, Takayasu FUJIURA
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The newly-developed lubricant Kobelco Polyhydroxyl Amide (KPA) consists of two different functional materials. Based on this feature, an iron powder mixture with KPA lubricant has better powder flow at the powder stage and better ejection performance at the green stage. Since KPA lubricity is superior to that of conventional lubricants, it is possible to reduce lubricant content without increasing the ejection pressure. By utilizing this process, high-density powder metallurgical parts can be made at a production cost relatively lower than that of conventional methods.
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| 30 |
Newly Developed Iron Powder for Highly Efficient Dust Cores
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Hirofumi HOJO, Nobuaki AKAGI, Tetsuya SAWAYAMA, Hiroyuki MITANI
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Dust cores are made by compacting insulated magnetic powder. One of the advantages of dust cores is magnetic isotropy, which enables three-dimensional magnetic circuit designs. Such designs are expected to reduce the size and weight of magnetic parts. There is a strong demand to reduce core loss so that the cores can be used more for magnetic parts, such as motor cores. This paper reports on methods for reducing iron loss in dust cores and on the magnetic properties of the dust cores consisting of improved powder made by a new method. A dust core with an iron loss of 28.6W/kg was produced. This core is comparable with ones made of laminated steel sheets.
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<Feature-2> Steel Wire Rod and Bar
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| 36 |
Overseas Deployment of Wire Rod & Bar Manufacturing and Wire Rod Secondary Processing
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Goro AKAISHI, Noriaki HIRAGA
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The demand for special steel wire rods and bars has been increasing as Japanese auto makers continually expand their overseas operations, increasing the local procurement of automotive parts. Kobe Steel now has a technical tie-up with two special steel mills in Europe and North America so that high quality wire rod and bar can be supplied to auto makers and parts makers. Kobe Steel has also constructed a system to provide for the secondary processing of wire rod products for Japanese parts makers, mainly by establishing secondary processing companies in Asia and North America.
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| 41 |
Development History of Wire Rods for Valve Springs
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Nao YOSHIHARA
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To reduce fuel consumption, automotive valve springs need to be made lighter. Kobe Steel has developed high strength steel for valve springs to meet this requirement. Furthermore, by continuously developing technology for the control of internal defects, such as non-metallic inclusions, high strength valve spring steels with good robust quality have been provided. This paper describes the development history of wire rods for valve springs with high fatigue strength.
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| 46 |
Development Trends of Soft Magnetic Iron
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Dr. Masamichi CHIBA
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Driven by advances in electronically controlled systems for automobiles, the demand is growing for soft magnetic steels that can generate a large electromagnetic force with low electric power. New steels with very low carbon content have been developed in consideration of their DC electromagnetic properties, their cold forgeability, and machinability. This paper describes the recent development trends of soft magnetic steel and the advantages of our developed steel (ELCH2 series).
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| 52 |
Influence of Ti Precipitate in Carburizing Steel Containing Boron
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Dr. Nariaki OKAMOTO, Yosuke SHINDO, Mutsuhisa NAGAHAMA
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When cold forged gear steel is carburized, fine precipitates of TiC prevent austenite grain from coarsening. While preventing grain from coarsening, these precipitates increase the deformation resistance against cold forging due to precipitation hardening. This study evaluates the influence of TiC precipitates on the deformation resistance, as well as their characteristics that work to prevent grain coarsening during the carburization of a steel containing boron.
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| 57 |
Low Alloy Steel for Fracture Splitting Connecting Rod
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Akihiro MATSUGASAKO
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To reduce vanadium content in the steel for fracture splitting connecting rods, the effect of titanium addition on the splitting property was investigated. The results indicate that Ti addition effectively reduces the impact value of the steel. This is considered to be attributable to the decrease in the volume fraction of ferrite and in the precipitation strengthening of the ferrite. Furthermore, Ti was also found to have no adverse effect on machinability. Based on these results, a new steel was developed for fracture splitting connecting rods.
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| 62 |
Production Technology of Wire Rod for High Tensile Strength Steel Cord
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Kazuhiko KIRIHARA
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The wire rod for steel cord is designed for high tensile strength. The steel cord is typically used to reduce tire weight. For several years, such steel cord has also been used as saw wire to cut silicon ingots. The saw wire is more highly tensile and has a smaller diameter. Therefore, an appropriate wire rod is required for manufacturing such saw wire. This report describes the technology to control non-metallic inclusions and the wire rod with superior drawingability needed for manufacturing the high strength wire used for steel cord and saw wire.
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<Feature-3> Steel Plate and Sheet
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| 66 |
Characteristics of Brittle Crack Arrest Steel Plate for Large Heat-input Welding for Large Container Ships
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Masahito KANEKO, Dr. Tokutaka TANI
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Once it happens, brittle fracture in the hatch coaming parts around the deck openings of container ships causes serious structural damage that could potentially result in both fatalities and environmental damage. With this in mind, ships are designed and constructed so as to ensure that brittle crack does not occur. Further, if by chance it does occur, having a back-up function for arresting brittle crack included in the steel plate is essential. This report describes the characteristics of KE36 class brittle crack arrest plates. Improvement in brittle crack arrestability was achieved by the refinement of crystal grains, which is a result of strictly temperature-controlled TMCP (Thermo Mechanical Control Process).
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| 70 |
Effect of Steel Toughness on Brittle Crack Arrest Behavior of T-weld Joint Structure Using Thick Plates
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Dr. Eiichi TAMURA, Dr. Tomokazu NAKAGAWA, Kazuyuki TSUTSUMI,
Naohiro FURUKAWA
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Brittle crack arrest properties in ship construction have become more important as shipbuilding steel plates become thicker and stronger. There have been indications that steel toughness can have the effect of arresting brittle crack initiating in a welded joint; however the T-weld joints of an actual large structure have not been well investigated. This report describes how the brittle crack length and steel toughness were found to affect brittle crack arrest behavior. Furthermore, it was suggested that brittle crack could be arrested by using a horizontal plate of Kca that would be sufficient even for the T-weld joint of an actual large structure.
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| 76 |
Effects of Ca Addition on Formation Behavior of TiN Particles and HAZ Toughness in Large-Heat-Input Welding
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Taku KATO, Shinsuke SATO, Dr. Hiroki OHTA, Toyoaki SHIWAKU
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A new process technique, Kobe super toughness (KST), enables maintaining excellent toughness in heat affected zones (HAZs) formed by large heat input welding. In order to improve the KST treatment, the effect of Ca addition on HAZ toughness was studied with focus on TiN particles. It was found that Ca addition inhibits the crystallization of coarse TiN particles and increases the number of fine TiN particles precipitated. Consequently, a fine-grained microstructure of HAZ was achieved and HAZ toughness was improved significantly.
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| 80 |
Characteristics of Highly Formable 590-980MPa Grade Hot-dip Galvannealed Steel Sheets for Automobiles
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Dr. Yuichi FUTAMURA, Masaaki MIURA, Michitaka TSUNEZAWA
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A series of 590-980MPa grade hot-dip galvannealed steel sheets has been developed in order to improve the formability of automotive body frame parts, such as lower pillars. These are either DP or TRIP-aided steel sheets, designed 1) to have homogeneous microstructures, 2) to inhibit the precipitation of carbide, 3) to maintain ferrite as much as possible, 4) to harden the ferrite to prevent degradation of local deformability, and in TRIPaided steel sheet, additionally, 5) to obtain a large amount of retained austenite. The above microstructural controls are mainly accomplished by the addition of silicon, which can be adopted through a special surface preparation technology. The developed steel sheets have not only excellent formability, but also meet practical performance requirements, including good spot weldability and high coating.
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| 85 |
Formability of TRIP Type Banitic Ferrite Steel Sheet
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Takayuki KIMURA
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In recent years, cold rolled steel sheets of 980MPa grade have been increasingly used for automotive parts to improve collision safety (crashworthiness) and to reduce body weight. Kobe Steel has developed a new 980MPa cold rolled steel sheet with elongation properties that are an improvement over conventional dual-phase (DP) steel sheets. This article focuses on the press formability of the newly developed steel sheet. Press formability testing was performed using a smallsized model die and a large-sized actual part die. The result clearly indicates that the developed steel sheet has a significantly improved press formability when compared with conventional DP steel sheets.
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| 90 |
Integrated Application Method for KOBEHONETSU™ Steel Sheet
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Dr. Yasuo HIRANO, Tetsuya IGARASHI, Haruyuki MATSUDA,
Makoto NISHIMURA
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KOBEHONETSU is the trade name for a steel sheet having heat-radiation ability. A method was developed for applying this steel sheet to dissipate heat in highperformance electronic equipment. By applying KOBEHONETSU to both the heat sink and housing simultaneously, the amount of heat transferred out of an electronic device was significantly increased to a level comparable with that achieved by a cooling fan. This cooling effect is enhanced by increasing the heat sink area, which makes KOBEHONETSU more applicable to heat sources such as CPUs. For example, this steel sheet can be machined into heat sinks, while maintaining its area and heat dissipation capability, for cases where heat sinks may interfere with other parts.
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