고강도-고인성 라인파이프강 개발 동향

유장용(Jang-Yong Yoo),강기봉(Ki-Bong Kang) 대한기계학회 2004 대한기계학회 춘추학술대회 Vol.2004 No.4

Linepipe steels with a low carbon acicular ferrite microstructure have been recently developed to accommodate the current transportation condition of the gas and oil industry, and they are finally applied to West- East pipeline project in China. By adopting acicular microstructure, both better formability and better toughness could be obtained due to low yield ratio and fine grained microstructure. Mechanical properties of pipe are not greatly different from those of base plates or hot coils with a microstructure of acicular ferrite. Merits of introducing higher strength steels are well known, i.e., reducing the gauge of pipe and the material cost, increasing the welding speed and decreasing construction cost because of reducing the construction period. Threfore, gas and oil industry has required higher strength steel than API-X70 grade steel. Under this background, API-X80 steel has been developed and shall be applied to the several projects. In this paper, developing stage of API-X80 steel is also presented and discussed.

라인파이프 강재의 개발동향 및 용접성

송우현,서동한,유장용,Song, Woo-Hyun,Seo, Dong-Han,Yoo, Jang-Yong 대한용접접합학회 2009 대한용접·접합학회지 Vol.27 No.1

양이온 성분이 수산화철 형성에 미치는 영향 조사

오세진,이재영,권순주,유장용,주웅용,Oh, Sei-Jin,Lee, Jae-Yong,Kwon, Soon-Ju,Yoo, Jang-Yong,Choo, Wung-Yong 한국재료학회 2002 한국재료학회지 Vol.12 No.10

Effect of nine different cations to the formation of iron oxyhydroxide was studied using Mossbauer spectroscopy, XRD and BET. The Redox Potential and pH were measured for the determination of the internal reaction rate, as well. The phases of iron oxyhydroxide could not be the same with each other, due to the present of different cations in solution. Although the oxyhydroxide compound were composed of the same phases, the fraction of each phase was different from each other. The internal reaction rate was varied by the substitution of cation. It could be a cause of the different phase and particle size of oxyhydroxide compound.

Cu - Ti 계 합금의 스피노달 분해

주웅길(Woong Kil Choo),유장용(Jang Yong Yoo) 대한금속재료학회(구 대한금속학회) 1988 상변태 심포지엄 Vol.1 No.-

수분함량과 발효기간이 발효사료의 품질에 미치는 영향

장장용,유성오 진주산업대학교 농업기술연구소 2001 農業技術硏究所報 Vol.14 No.-

This experiment was conducted to investigate the effect of moisture content and fermentation period on quality of fermented feed. The feed were mixing with cage layer excreta (40%), corn meal (20%), wthat bran (30%), malt sprout (5%) and rice bran (5%), and was adjusted to 40 and 60% moisture contents, and were kept in a fermentator with 60℃ for 2, 4, 8 and 16 days. The quality of fermented feed was evaluation on the basis of chemical composition, nutrient content, micro-organisms and in vitro dry matter and crude protein digestibilities. The results obtained were summarized as follows : 1. Crude protein contents of fermented feed with 60% moisture content was slightly higher in 4, 8 and 16 days of fermentation period than that of 2 day of fermentation period, and crude fiber content of fermented feed with 60% moisture content was slightly lower than that of fermented feed with 40% moisture content. 2. pH of fermented feed with 60% moisture content was slightly lower than that of fermented feed with 40% moisture content, and pH of fermented feed with 60% moisture content were slightly decreased in 4, 8 and 16 days of fermentation period than that of 2 day of fermentation period. 3. Latic acid, total-VFA, acetic acid and propionic acid of fermented feed with 60% moisture content was slightly higher in 4, 8 and 16 days of fermentation period than that of 2 day of fermentation period. 4. Latic acid to total acid of fermented feed with 60% moisture content was slightly higher than that of fermented feed with 40% moisture content, and Latic acid to total acid of fermented feed with 60% moisture content were slightly decreased in 4 and 8 days of fermentation period than that of 2 day of fermentation period(P<0.05). 5. Total bacteria and lactic acid contents of fermented feed with 60% moisture content were slightly higher than that of fermented feed with 40% moisture content, and Total bacteria and lactic acid contents of fermented feed with 60% moisture content were slightly higher in 4 and 8 days of fermentation period than that of 2 day of fermentation period. 6. In vitro dry matter and crude protein digestibilities of fermented feed with 60% moisture content were higher than that of fermented feed with 40% moisture content, and in 4, 8 and 16 days of fermentation period than that of 2 day of fermentation period.

조선용 C-Mn 강의 제조방법에 따른 미생물 부식 특성 연구

鄭歡敎,兪張鎔,禹宗秀 대한금속재료학회 2002 대한금속·재료학회지 Vol.40 No.6

The MIC(Microbiologically Influenced Corrosion) of lower deck steel plates in double hull VLCC(Very Large Crude Oil Carrier) cargo tanks has been focused because of severe localized corrosion. Recently, ship companies have reported that TMCP(Thermomechanical Control Process) steel plates have been showed more severe localized corrosion than conventional rolled steels. In order to elucidate the MIC resistance of TMCP steels by comparison with conventional rolled steels and normalized steels in environments of double hull VLCC cargo oil tanks, various measurements and corrosion tests were performed such as measurements of polarization curves, immersion tests in bacteria culture medium. All results revealed that three types of steels have almost the same corrosion resistance in bacteria culture medium. Three kinds of steel exhibit almost the same polarization behavior and the corrosion rate. The movement of the open-circuit potential first towards more negative values and later to more positive values is a phenomenon common to all kinds of specimens. This phenomenon resulted from an initial stimulation of the anodes by sulphide ions produced by the bacteria from the reduction of sulphate ions in the medium, followed by the formation of an insoluble partly protective film of ferrous sulphide on the surface of the electrode. The effect of SRB (Sulphate Reducing Bacteria) is clearly showed in the cathodic polarization curve. When the SRB is in a condition of rapid growth, there is a strong cathodic depolarization. However, as the sulphate is depleted and reaction products accumulate, the activity of the bacteria declines and the cathodic polarization curve returns the same form as in the inoculated culture.

합금원소 첨가가 구조용 강의 해변 내후성에 미치는 영향 연구(Ⅱ) : Ni, W, Mo의 첨가 효과 Ni, W and Mo Effects

정환교,유장용,김규영 대한금속재료학회 2004 대한금속·재료학회지 Vol.42 No.12

The objective of this study is to understand the effect of W and Mo on the corrosion property of the Ca-modified weathering steel and to determine the optimum chemical composition to maximize the corrosion resistance at seaside corrosion environment. The effects of various alloying elements on the weathering steel were evaluated through a series of electrochemical test and analysis of the corrosion product formed on the steel surface. The polarization resistance of Ca-modified weathering steel can be increased by the addition of Ni, W and Mo, thus the corrosion resistance of Ca^(-)modified weathering steel containing Ni, Mo and W is increased at the initial stage of corrosion in a solution with high NaCl concentration. From the measurement on the permeability of Cl^(-) ions, the rust membranes formed from weathering steel of thin plate shape showed the anion-selectivity and the addition of various alloying elements (Ni, W and Mo) contributed to lower the permeability of Cl^(-) ions toward rust membranes. Particularly, Mo and W are more effective than Ni to suppress the permeation of Cl^(-) ions. It has an industrial significance for alloy design of the weathering steel since design of a lower cost weathering steel with higher corrosion resistance can be possible with addition of Mo or W instead of increasing the high cost Ni content to 2% or even higher. (Received May 19, 2004)

합금원소 첨가가 구조용 강의 해변 내후성에 미치는 영향 연구 (Ⅰ) : Ca, Si의 첨가 효과 Ca and Si Effects

정환교,유장용,김규영 대한금속재료학회 2004 대한금속·재료학회지 Vol.42 No.11

The objective of this study is to understand the effect of Si, on the corrosion property of the Ca-modified weathering steel and to determine the proper range of such alloying elements to maximize the effect of Ca on the corrosion resistance of the steel. The pH of a thin water film covering the steel was measured to evaluate the effect Ca addition on pH value. The electrochemical impedance spectroscopy (EIS) was employed to evaluate the corrosion resistance of the Ca-modified weathering steel. The characteristics of rust formed on the weathering steels having different alloy chemistry were examined. Analysis on the inclusion morphology and composition showed that the Ca-containing inclusions were mainly composed of Ca-Al-Mn-O-S,and Si was not founded in them except the specimen containing 0.6%Si. In distilled water, the Ca-modified specimens with or without Si showed higher pH values as Ca content was increased. The effect of Ca addition was not greatly affected by the addition of Si when the steel contained a proper Ca content of 50-70 ppm. In the impedance test, the specimens containing higher amounts of Ca showed higher polarization resistance, meaning better corrosion resistance. The analysis on the rust layers formed on the Ca-modified steel surface showed that the dense inner layer was mainly composed of a-FeOOH and y-FeOOH, whereas the loose outer layer was composed of ν-FeOOH and β-FeOOH. Fe₃O_(4) was distributed randomly throughout the rust layer. The specimens containing a high amount of Ca showed a dense and compact morphology, and the specimens containing Si also showed a dense and compact one. The result of Mossbauer analysis showed that more α-FeOOH was formed as Ca content was increased. (Received May 24, 2004)

직접퀀칭된 Cu 함유 고강도강의 미세조직과 기계적 성질

이성학,주웅용,유장용,황근철 대한금속재료학회(대한금속학회) 1998 대한금속·재료학회지 Vol.36 No.2

The present study is concerned with the processing of copper-bearing high strength steels by direct quenching and tempering (DQ&T) processes. Two DQ&T steels were rolled at different finish rolling temperatures, and their microstructures and mechanical properties such as strength and impact energy were compared with those of a reheat quenching and tempering(RQ&T) steel. The microstructural analyses indicated that the as-quenched microstructure of the DQ steels consisted of refined lath martensite including a number of dislocations, which acted as preferred precipitation sites for NbC or ε-Cu particles during tempering. These fine precipitates were not coarsened much up to the tempering temperature of about 650℃ and thus played a role in improving the tempering resistance. Especially in the DQ&T steel quenched at 760℃ and tempered at 660℃, yield strength reached 1050㎫ and Charpy impact energy at -18℃ showed 140J, indicating the potent effect of the DQ&T process. These findings suggest that copper-bearing low carbon alloy steels with high strength and toughness can be made by the DQ&T process.

고인성 API X70 라인파이프강의 파괴특성 : Ⅲ. Drop-Weight Tear Test 시 발생되는 역파면에 대한 연구 Ⅲ. Inverse Fracture Occurring during Drop-Weight Tear Test

황병철,김양곤,이성학,김낙준,유장용 대한금속재료학회 2004 대한금속·재료학회지 Vol.42 No.4

This study is concerned with the effects of microstructure on inverse fracture in the hammer-impacted region during drop-weight tear test(DWTT) of three high-toughness API X70 pipeline steels. Pressed notch or Chevron notch DWTT and Charpy V-notch impact test were conducted on the rolled steel specimens, and the results were discussed in comparison with the data obtained from tensile and Charpy impact tests of pre-strained specimens. In the hammer-impacted region of the DWTT specimens, cleavage-type inverse fracture appeared, and its fracture area was correlated well with upper shelf energy (USE) obtained from the Charpy impact test and with microstructure. The steel specimens having higher USE or having coarse polygonal ferrite had the larger inverse fracture area than those having lower USE or having fine acicular ferrite because of the larger compressive pre-strain induced by work hardening of the hammer-impacted region. These results were confirmed by relating to the Charpy impact test data of pre-strained steel specimens. (Received January 19, 2004)