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<FEATURE>Steel Plate and Sheet |
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| 1 |
Research and Development of Steel Plate and Sheet in Kobe Steel |
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Shinya MIYAWAKI
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| 2 |
Characteristic 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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A brittle fracture, when it once occurs in the hatch coaming around the deck opening of a container ship, can
cause serious structural damage that potentially result in both fatalities and environmental damages. With
this in mind, ships are designed and constructed to ensure that no brittle crack will occur. However, in the
unlikely event of a brittle fracture occurring, a back-up function of arresting the brittle crack should be
included in the steel plate. This report describes the characteristics of KE36 class plates having a capability
of arresting brittle cracks. The arrestability was improved by a new thermo mechanical control process
(TMCP), in which the process temperature is strictly controlled to refine crystal grains.
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| 6 |
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 T-weld joints of an actual large structure has not
been well investigated. In this report, the brittle crack length and steel toughness were found to affect brittle
crack arrest behavior. Furthermore, it was suggested that a horizontal plate with sufficiently large Kca can
arrest brittle cracks even for the T-weld joint of an actual large-scale structure.
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| 11 |
Study of Strengthening Method of Strength by Air-cooled Type TMCP |
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Satoshi SHIMOYAMA / Dr. Tokutaka TANI / Yoshinobu OMIYA
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Steel plates produced by thermo-mechanical control process (TMCP) are widely used because of its
excellent weldability which allows high heat input welding with high efficiency. Some consumers, however,
require high strength steel plates processed by controlled rolling without water cooling to avoid residual
stress which deteriorates bending accuracy and to prevent softening during high heat input welding. This
study quantitatively analyzes the increase of strength by solid solution strengthening, dislocation
strengthening and particle dispersion strengthening. The result clearly indicates that a high strength steel
plate of YP550 grade can be produced by a controlled rolling without water cooling.
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| 16 |
Mechanical Properties and Microstructural Control of TS 780MPa Steel Pipe with Low Yield Ratio and Excellent HAZ Toughness for Building Structures |
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Tetsuo YAMAGUCHI / Hiroki IMAMURA / Toyoaki SHIWAKU / Soichi KAWABE |
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Recently, since thicker steel pipes with higher tensile strength are being used for large building construction
and large spans, TS 780MPa steel pipes with high earthquake-resistant performance are in demand. To meet
this demand, we have developed TS 780MPa steel pipes (KSAT®630) with low YR and excellent HAZ
toughness. The application of the DQ-N'-T process and a chemical composition low in carbon, plus the
inclusion of Mn, Ni, and Cr in steel plates for steel pipes enables multi-phase microstructural control
including M-A and refining of the effective grain size in HAZ. As a result, advanced steel pipes formed from
developed steel plates satisfied target properties.
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| 20 |
Design Technology for Column to Beam Connection of Circular Hollow Section and Square Hollow Section Steel Columns |
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Masahiro MATSUSHITA / Takeshi TAKADA / Hiroki IMAMURA /
Toyoaki SHIWAKU / Yasufumi SASAK / Dr. Tsuyoshi TANAKA
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The column-to-beam connections in a steel-structure building require the development of a reasonable
design approach that attempts to decrease the amount of processing and welding. Kobe Steel has paid
attention to the problem of the non-through type of column and developed a method of designing circular
hollow section steel columns without diaphragms and square hollow section steel columns with exterior ring
diaphragms to improve productivity and gain more freedom in architectural planning.
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| 28 |
Corrosion Prediction Method for Ni-added High-performance Weathering Steel |
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Dr. Shinji SAKASHITA / Akihiko TATSUMI / Hiroki IMAMURA /
Yasushi FUCHITA / Masahiro MATSUSHITA
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The use of weathering steel in bridges has been increasing with a view to maintenance reduction. It is
important to accurately predict corrosion in order to select the optimum steel for the environment. Kobe
Steel has researched and developed a method of corrosion prediction for weathering steels, considering the
effect of environmental factors such as air-borne salt and annual mean temperature on corrosion behavior in
atmospheric exposure testing. Based on the developed method, a proposal will be advanced for reducing lifecycle
costs by applying the use of weathering steel to steel structures.
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| 32 |
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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| 36 |
Cold-rolled Steel Sheets of 1,470MPa Grade with Superior Delayed Fracture Resistance Characteristics |
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Kouji KASUYA / Michiharu NAKAYA / Michitaka TSUNEZAWA / Youichi MUKAI
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It has been reported that a TBF steel (TRIP-aided steel with Bainitic Ferrite matrix) has superior delayed
fracture resistance. This study researched the effects of austemper conditions on the delayed fracture resistance
of TBF steel. The results indicate that austempering below Ms point for a period until the end of the bainite
transformation is effective in achieving both high tensile strength and excellent delayed fracture resistance. Based
on this finding, a TS 1,470MPa grade TBF steel sheet for automotive parts was manufactured on production lines.
The TBF steel exhibited excellent performance for elongation and delayed fracture resistance.
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| 41 |
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 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 TRIP
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 practically
required performance including good spot weldability and high coating quality.
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| 45 |
Galvannealed Steel Sheets for Induction Hardening |
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Sae HAMAMOTO / Yukihiro UTSUMI / Tatsuya ASAI |
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In recent years, ultra-high-strength steel sheets have been increasingly applied in automotive body parts to
improve crashworthiness and decrease body weight. Induction-hardening and die-quenching are
technologies which enable the production of ultra-high-strength parts having complex shapes. Kobe Steel
has developed several types of steel sheets for induction hardening. This article describes the features of
1,470MPa grade after-quenched galvannealed steel sheets for induction hardening.
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| 49 |
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 are 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 improved compared with 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 small-sized model die and a large-sized actual part die. The result
clearly indicates that the developed steel sheet has a press formability significantly improved compared with
conventional DP steel sheets.
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| 53 |
Roll-formed Lightweight Door Beam |
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Noriyasu YOSHIOKA
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High tensile strength (Hi-ten) steel is increasingly used for bodies in white (BIW) to reduce the weight of
automobiles. Roll forming is a method for processing super hi-ten steel and has an advantage that it
increases design freedom for cross-sectional shapes. This design freedom is exploited to develop a light door
beam with high performance by adequately stiffing the cross sectional shapes to prevent the cross section
from collapsing. The newly developed door beam is expected to reduce the weight of a conventional door
beam by 10%.
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| 57 |
Effect of Heating Rate during Continuous Annealing on Microstructure of Multiphase Cold Rolled Steel Sheet |
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Tatsuya ASAI / Michiharu NAKAYA / Seiko HYODO
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The effect of the heating rate during continuous annealing on the microstructure of multiphase cold rolled
steel sheet was examined. Cold rolled Nb-added steel sheets were heated up to austenite temperature at
various heating rates and were subsequently cooled under the same conditions. The results indicated that
the microstructure and the mechanical properties of annealed steel sheet had changed with the heating rate.
The phenomenon is attributable to the micro-segregation of Mn caused by the redistribution of Mn in
austenite during heating. The redistribution of Mn takes place when the interface between the ferrite and
austenite migrates slow enough to allow the diffusion of Mn from ferrite to austenite. It was found that the
redistribution of Mn affects the transformation behavior of austenite, varying the microstructure of
multiphase steel sheet.
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| 61 |
Influence of Substructures on Mechanical Properties of Low Carbon Tempered Martensite Steels |
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Dr. Toshio MURAKAMI / Dr. Kenji SAITO
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We investigated the influence of substructures on the mechanical properties of tempered martensite, which
was the microstructure making up dual phase steel used as advanced high strength steel. Water-quenched
specimens were tempered at various temperatures, keeping the tempering parameter at a constant value in
order to control the substructures of tempered martensite. In the results, YS, TS and EL were in proportion to
the square root of dislocation density, and the hole expansion ratio showed an inverse association with
cementite size. On the other hand, the dislocation density could be controlled by the tempering parameter, and
cementite size could be changed by the tempering temperature, while keeping the tempering parameter at a
constant value. These results suggest that the mechanical property balance of tempered martensite can be
improved by optimizing the tempering conditions.
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| 65 |
Evaluation of Delayed Fracture of High Strength Steel Sheets for Cyclic Corrosion Test |
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Junichiro KINUGASA / Dr. Fumio YUSE / Michitaka TSUNEZAWA /
Youichi MUKAI
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Delayed fracture in steel is considered to be affected by the amount of hydrogen and stress conditions. This
study aims to verify the applicability of cyclic corrosion test (CCT), an accelerated test for cyclic corrosion, to
an accelerated testing for delayed fracture. Considerations were made on iron dissolution, the mechanism of
hydrogen generation under conditions of atmospheric corrosion, hydrolysis reaction, the surface
morphology of corrosion and on the influence of stress state.
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| 69 |
Cooling Behavior of Steel Sheets with Detoriorated Flatness on Hot-run Table |
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Shusuke YANAGI / Akashi YAMAGUCHI / Toshiaki OKUNO /
Masanori KOBAYASHI
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Deteriorated flatness of steel sheets on a hot-run table (HRT) is considered to change the flow pattern of
water retained on the steel sheets and affect their cooling characteristics. Techniques have been reported for
predicting the flatness after cooling from the cooling history of the sheets on an HRT, however, no sufficient
study has been made for the cases where the sheets has a deteriorated flatness. The present study evaluates
the effect of the flatness on the average heat transfer coefficient based on actually measured temperature
and flatness. An analysis model was constructed for the temperature and flatness, accounting for strains
induced thermally and by transformation to clarify the effect of rolled shapes on cooling.
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| 75 |
Coiling Temperature Control at Hot-run Table in Hot Strip Mill |
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Takehiro TSUKUDA / Takanari SHIRASAKA / Dr. Yoshiharu NISHIDA /
Hiroyuki HASEGAWA / Masanori KOBAYASHI / Kodai DOI
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The coiling temperature is a very important factor in determining the mechanical properties of a strip during
the cooling process at the run-out table in a hot strip mill, and it is necessary to control the coiling
temperature with a high degree of accuracy. This paper states that a 32% decrease of the standard deviation
of the coiling temperature has been achieved by applying strict temperature models (difference model) to
calculate the temperature distribution in the thickness direction, as well as applying a learning system to
ascertain the heat transfer coefficient, which is a boundary condition in water cooling.
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| 80 |
Integrated Application Method for KOBEHONETSUTM Steel Sheet |
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Dr. Yasuo HIRANO / Tetsuya IGARASHI / Haruyuki MATSUDA /
Makoto NISHIMURA
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KOBEHONETSU is the trade name of a steel sheet having heat-releasing ability. A method was developed
for applying this steel sheet to dissipate heat in high-performance 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, making KOBEHONETSU more applicable to
heat sources, such as CPU. For example, this steel sheet can be machined into heat sinks which otherwise
may interfere with other parts while maintaining its area and heat dissipation capability.
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| 83 |
Effect of Surface Condition of Hot Dipped Zinc Coating on Corrosion Resistance of Chromate-free Coated Hot-dip Galvanized Steel Sheet |
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Minoru CHIDA / Hiroshi IRIE
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In recent years, chromate-free hot-dip galvanized steel sheet has been developed for reducing environmental
pollution. Many studies on chromate-free coating have been reported. However, there are not many studies
concerned with the effect of the surface condition of a zinc-coated layer on the performance of chromate-free
hot-dipped galvanized steel sheet. This study revealed that aluminum oxide on the surface of a zinc-coated
layer strongly affects the corrosion resistance of chromate-free coated hot-dipped galvanized steel sheet and
adhesion between the zinc-coated layer and chromate-free coating.
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| 87 |
Papers on Advanced Technologies for Steel Plate and Sheet in R&D Kobe Steel Engineering Reports (Vol.51, No.1～Vol.61, No.1)
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