• Title, Summary, Keyword: STS Content

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Effect of nitrogen content on pitting formation at low nickel duplex stainless steel (듀플렉스상 스테인리스강에서 질소의 함량이 공식의 형성에 미치는 영향)

  • Choe, Jong-Beom;Lee, Gyeong-Hwang;Gang, Hyeong-Gu;Lee, Myeong-Hun;Yang, Jeong-Hyeon;Gang, Jun;Yun, Yong-Seop
    • Proceedings of the Korean Institute of Surface Engineering Conference
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    • pp.61-61
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    • 2018
  • 듀플렉스 스테인리스강은 페라이트와 오스테나이트 상이 공존하는 특징을 갖는다. 그러한 구조에 의해서 페라이트와 오스테나이트상의 장점을 동시에 갖는 특성이 있다. 높은 강도와, 우수한 내식성, 응력 부식 균열 그리고 낮은 니켈의 함량 때문에 안정적인 가격을 갖는 장점을 갖기 때문에 운송, 기름과 가스, 해양플랜트, 건축 그리고 높은 강도와 우수한 내식성이 필요한 분야에서 수요가 증가할 것으로 사료된다. 이러한 듀플렉스 스테인리스강의 형성에서 페라이트와 오스테나이트상의 균형과 내식성을 개선하기 위해 질소가 첨가된다[1,2]. 본 연구는 저니켈 듀플렉스 스테인리스강(STS 329 FLD)의 공식 형성 과정에서 질소의 함량이 공식 형성과 내식특성에 미치는 영향을 동전위분극, XPS(X-ray Photoelectron Spectroscopy) 그리고 GDOES(Glow Discharge Optical Emission Spectrometry)를 이용하여 규명하였다. GDOES를 이용하여 깊이별 원소 분포를 정량적으로 비교한 결과, 부동태막에서 질소는 기저에 비하여 증가하였고, 질소의 함량이 증가함에 따라 wt.% 또한 증가하였다. 이러한 부동태막의 깊이별 원소 분포특성이 내식특성과 공식의 크기에 미치는 영향을 동전위분극을 이용하였다. 질소의 함량이 증가하였을 경우, 부식전위는 증가하였으며, 부식전류는 감소하였다. 또한 부동태전류가 감소한 것을 확인할 수 있었다. 이러한 차이의 원인을 확인하기 위하여 XPS를 이용하여 질소의 화학적 상태를 확인하였다. 질소는 암모니아의 형태로 존재하는 것으로 확인되었다. 암모니아 상태로 부동태막에 존재함에 따라 공식이 형성될 때, 암모늄 화함물을 형성하여 공식 내부의 산성도를 낮춤으로써 공식의 형성이 억제된 것으로 사료된다. 또한 공식 이후의 표면을 관찰 할 경우 질소의 함량이 증가함에 따라 표면에서 공식이 거의 관찰되지 않았다.

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Development of High Erosion Resistant Fe-based Alloy for Continuous Hot Dipping Line (연속용융 도금라인 용 고내침식 Fe계 합금 개발)

  • Baek, Min-Sook;Kim, Yong-Cheol;Baek, Kyeong-Cheol;Kwak, Joon-Seop;Yoon, Dong-Joo
    • Journal of the Korean institute of surface engineering
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    • v.53 no.3
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    • pp.95-103
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    • 2020
  • In this study, the material used in the hot dip galvanizing equipment was poorly corrosion-resistant, so it was performed to solve the cost and time problems caused by equipment replacement. The theoretical calculation was performed using the DV-Xα method(Discrete Variational Local-density approximation method). The alloy (STS4XX series) of the equipment currently used has a martensite phase. Therefore, the theoretical calculation was performed by applying P4 / mmm, which is a tetragonal structure. The new alloy was chosen by designing theoretical values close to existing materials. Considering elements that contribute to corrosion, most have high prices. Therefore, the design was completed by adjusting the content using only the components of the reference material in the theoretical design. The final design alloys were chosen as D6 and D9. Designed D6 and D9 were dissolved and prepared using an induction furnace. After the heat treatment process was completed, the corrosion rate of the alloys was confirmed by using the potentiodynamic polarization test. The surface of the prepared alloys were processed horizontally and then polished to # 1200 using sand paper to perform potentiodynamic polarization test. Domestic products: 4.735 mpy (mils / year), D6: 0.9166 mpy, D9: 0.3372 mpy, alloys designed than domestic products had a lower corrosion rate. Therefore, the designed alloy was expected to have better erosion resistance.

Effects of Alloying Elements on Sticking Occurring During Hot Rolling of Ferritic Stainless Steels (페라이트계 스테인리스강의 열간압연 시 발생하는 Sticking에 미치는 합금원소의 효과)

  • Ha, Dae Jin;Kim, Yong Jin;Lee, Jong Seog;Lee, Yong Deuk;Lee, Sunghak
    • Korean Journal of Metals and Materials
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    • v.46 no.9
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    • pp.593-603
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    • 2008
  • In this study, effects of alloying elements on the sticking occurring during hot rolling of five kinds of ferritic STS430J1L stainless steels were investigated by analyzing high-temperature hardness and oxidation behavior of the rolled steels. Hot-rolling simulation tests were conducted by a high-temperature wear tester which could simulate actual hot rolling. The simulation test results revealed that the sticking process proceeded with three stages, i.e., nucleation, growth, and saturation. Since the hardness continuously decreased as the test temperature increased, whereas the formation of Fe-Cr oxides in the rolled steel surface region increased, the sticking of five stainless steels was evaluated by considering both the high-temperature hardness and oxidation effects. The addition of Zr, Cu, or Si had a beneficial effect on the sticking resistance, while the Ni addition did not show any difference in the sticking. Particularly in the case of the Si addition, Si oxides formed first in the initial stage of high-temperature oxidation, worked as initiation sites for Fe-Cr oxides, accelerated the formation of Fe-Cr oxides, and thus raised the sticking resistance by about 10 times in comparison with the steel without Si content.

Perceptions of Korean Science and Social Science Teachers Regarding Teachers/Learning Methods for Environmental Education (환경 교수학습법에 대한 과학과와 사회과 교사들의 인식)

  • 최경희
    • Hwankyungkyoyuk
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    • v.14 no.2
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    • pp.40-50
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    • 2001
  • To meet the objectives of environmental education, teachers especially have to perceive the importance of environmental education, comprehend various characteristics of teaching/learning methods, and be able to conduct classes by choosing proper teaching/leaming methods in accordance with a specific purpose and educational focus about environmental education. Therefore, it Bs necessary to investigate the current status of Korean environmental education and provide teachers with appropriate environmental teaching/leaming methods. To this end this study aims to examine Korean science teachers'perceptions'on environmental education and the kind of teaching/learning methods which can be utilized in environmental education. Teachers who completed the survey were 135 science teachers from middle and high schools in Seoul, and 126 social science teachers from Kyoungki province. The majors of the science teachers were in physics, chemistry, biology, geology, and earth science. Also, there was one teacher who majored in special education. For social science teachers two majors were common, geography and general sociology. After analysis of the data from the surveys the results are as follows. First, science and social science teachers in middle and high school recognized the necessity of environmental education in school education. Second, most teachers had applied environment related topics to their subject of study occasionally, but they mostly concurred that environment related contents should be included in their textbooks. Third, science teachers agreed that field trip, discussion, and the STS approach were the most proper methods for environmental education, and social science teachers agreed that field trips, inquiry, and discussion were the most appropriate methods for a teaching environment. They realized that they should decide good teaching-learning methods appropriate to the objectives and content needed for effective environmental education as they selected different teaching-learning methods according to detailed environmental objectives and contents in their textbooks.

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Effects of Nb Addition on Corrosion Resistance and Cytotoxicity Behavior of Ti Alloys (Nb이 첨가된 Ti합금의 내식성 및 생체안정성)

  • Lee, Doh-Jae;Lee, Kwang-Min;Lee, Kyung-Ku;Ryu, Chang-Nam;Oh, Tae-Wook;Kim, Soo-Hag;Yoon, Tack-Lim
    • Korean Journal of Materials Research
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    • v.13 no.11
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    • pp.761-768
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    • 2003
  • The corrosion resistance and cytotoxicity behavior of Ti alloys were studied as a function of Nb contents(3wt.%Nb, 20wt.%Nb, 40wt.%Nb). Ti-Nb alloys were melted by vacuum arc furnace and then rolled to 50% reduction ratio after homogenized at 105$0^{\circ}C$ for 24hrs. The corrosion resistance of Ti-Nb alloys were investigated by potentiodynamic polarization test in the 0.9% NaCl and 5% HCI solution. Biocompatibility of Ti-Nb alloys was evaluated by cytotoxicity test. The results can be summarized as follows 1) The microstructure change from equiaxial to acicular and the increased $\beta$ phase in Ti-Nb alloys were obtained as the Nb content increased. 2) For the corrosion test in the solution of 0.9% NaCl and 5% HCI, the corrosion behavior of Ti-Nb alloys was similar to ASTM grade 2 CP Ti. 3) For the cytotoxicity test, Ti-Nb alloys showed excellent biocompatibility compared to ASTM grade 2 CP Ti, 316L STS and Co-Cr alloys.

Awareness and Eductional Needs Concerning SSI of Korean Pre-service Elementary Teachers Related to Nuclear Power Plant Accident (원전 사고 관련 SSI에 대한 초등 예비교사들의 이해도와 교육 필요성에 대한 인식)

  • Wee, Soo-Meen;Lim, Sung-Man
    • Journal of Science Education
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    • v.37 no.2
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    • pp.294-309
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    • 2013
  • This study addressed the awareness of social issues related to science of future elementary school teachers. Fukushima Nuclear Power Plant Accident was used by concrete issue connected with SSI for this study. Twelve second-year students attending a university of education participated in the study, who were taking a class of science teacher preparation at that time that consists of the content of the elementary science education courses. The study revealed that all the pre-service elementary teachers recognized Fukushima Nuclear Power Plant Accident and received such information through various medias. In particular, they were receiving more information about the Nuclear Power Plant Accident through the internet than any other media by using the internet a lot, and also gained additional information through the internet. However, despite the fact that they recognized Nuclear Power Plant Accident, they neither had much information about it nor had been interested in SSI such as the Nuclear Power Plant Accident. Moreover, they had been basically uneducated about SSI. Despite of having no interest in SSI such as Nuclear Power Plant Accident, the study revealed that the pre-service elementary teachers recognized that scientific problems such as Nuclear Power Plant Accident may affect a society closely. In addition, they together sympathized with the point that SSI education should be applied on the current education courses by identifying the problem in application. As the study revealed above, the application of SSI education to the formal education courses as well as more lively research on that subject is very important and urgent for boosting interest in science subjects and enlightening the nature of science that is one of the objectives of science education.

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Research Trends of Web-Based Inquiry Learning Effectiveness in Science Education: A Review of Publications in Selected Journals from 2000 to 2014 (과학교과 웹 기반 탐구학습의 효과성 연구 동향)

  • Lee, Jeongmin;Park, Hyunkyung;Jung, Yeonhwa;Noh, Jiyae
    • Journal of The Korean Association For Science Education
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    • v.35 no.4
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    • pp.565-572
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    • 2015
  • The purpose of this paper is to offer an analysis on the research trends of web-based inquiry learning effectiveness in science education, and to present suggestions for future studies. This study compiled data on 43 articles in Korea and international journals. The content analysis of articles published were from academic journals related to science education and educational technology from 2000 to 2014. The results are as follows: Among domestic articles, the participants ranged from school children to high school students. On the contrary, among foreign articles, the participants are centralized on secondary school students; most used experimental studies; most of the studies resulted with web-based inquiry learning in science education showing effectiveness on science learning performance or science inquiry ability; all web-based inquiry learning were designed using different models of teaching and learning, with the result in the case of domestic research, the utilized models refer to the STS learning model, Internet utilization problem-center inquiry learning model, Procedural model, while in the case of overseas research, the utilized models are SCY, IBLE, and TESI model. Implications of the findings are then discussed, which implies considerations for further research related to web-based inquiry learning.

A Study on Durability Characteristics for Plungers of Conventional Ceramic and Surface Modification by Powder Coating Using High Velocity Oxygen Fuel Thermal Spray (기존 세라믹 및 초고속 용사 분말피막 표면개질 플런저의 내구성 특성에 관한 연구)

  • Bae, Myung-whan;Park, Byoung-ho;Jung, Hwa
    • Transactions of the Korean Society of Automotive Engineers
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    • v.24 no.3
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    • pp.285-293
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    • 2016
  • The high velocity oxygen fuel(HVOF) thermal spray is a kind of surface modification techniques to produce the sprayed coating layer. This process is to form the coating layer after spraying the powder to molten or semi-molten state by the ultra-high speed at the high-temperature heat source and conflicting with a substrate. The efficiency of thermal spraying is dropped, however, because the semi-molten powder in a spray process become a factor that degrades the mechanical property by the formed pore within the coating layer. Therefore, it is necessary to melt completely the thermal spray powder in order to produce the coating layer with an optimal adhesive force. In this study, to improve the wear resistance, corrosion resistance and heat resistance, the plungers of high-speed and ultra-high pressure reciprocating hydraulic pumps used in ironworks are manufactured with STS $420J_2$ and are coated by the powders of WC-Co-Cr and WC-Cr-Ni including the WC of high hardness using a HVOF thermal sprayer developed in this laboratory. These are called by the surface-modified plungers. The surface roughness, hardness, and surface and cross-sectional microstructure of these two surface-modified and conventional ceramic plungers are measured and compared before operation with after operation for 100 days. It is found that the values of centerline average surface roughness and maximum height for conventional ceramic plunger are 9.5 to 10.8 and 5.2 to 5.7 times higher than those of surface-modified ones coated by WC-Co-Cr and WC-Cr-Ni because the fine tops and bottoms on surface roughness curve of conventional ceramic plunger are approximately 100 times higher than those of surface-modified ones. In addition, the pores and scratches in the surface microstructure are considerably formed in the order of conventional ceramic, WC-Cr-Ni and WC-Co-Cr surface-modified plungers. The greater the WC content of high hardness powder is less the change in the plunger surface.

Comparative Analysis of Middle School Science Curriculum between Korea and Israel (우리나라와 이스라엘의 중학교 과학과 교육과정 비교연구)

  • Jang, Jin-Ju;Seo, Hae-Ae;Song, Bang-Ho
    • Journal of The Korean Association For Science Education
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    • v.23 no.5
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    • pp.443-457
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    • 2003
  • The research aimed to compare science curriculum between Korea and Israel and find out characteristics of science curriculum in Israel at middle school level. The middle school 'science' of the 7th revised national curriculum in Korea and middle school 'science and technology' in Israel were compared. Among characteristics of the Israel curriculum of 'science and technology,' distinct ones are as follows: First, 'science and technology' was most highly emphasized with the largest number of time allotment among all subjects at middle school level in Israel. Second, the contents of 'science and technology' were classified into seven areas of 'energy and interaction', 'materials', 'organism', 'earth and the universe', 'technological systems and products' . 'information and communication',and 'ecosystems' rather than four areas of energy, materials, life and earth in Korea. Third, 'organism' was allocated with the highest number of hours among seven areas. Fourth, objectives of each content of 'science and technology' were divided into three categories: scientific aspect, technological aspect, and social value and objectives of each category were related to one another. This characteristic seems to stress STS, multidisciplinary, and interdisciplinary approaches in 'science and technology' in Israel. Such characteristics of the 'science and technology' education in Israel are likely to make significant contributions to establish human resources of highly developing science and technology including IT, BT, NT, ST in the future society. Reflecting upon the characteristics of 'science and technology' education in Israel, Korea might seek for ways to improve its national power based on science and technology through strengthening science and emphasizing science and technology contents among school curriculum.