• Journal of the Korean Society for Nondestructive Testing
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• v.27 no.5
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• pp.417-425
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• 2007

The ferritic 9Cr-1Mo-V-Nb heat-resisting steel was experimentally studied in order to characterize its microstructural evolution during creep-fatigue by coercivity measurement. The creep-fatigue test was conducted at $550\;^{\circ}C$ with the tensile holding time of 60s and 600s, respectively. The coercivity decreased until the failure and the hardness monotonously decreased for the whole fatigue life. As the life fraction of creep-fatigue increased, the $M_{23}C_6$ carbide coarsened following the Ostwald ripening mechanism. However, the MX carbonitrides did not grow during creep-fatigue due to so stable at $550\;^{\circ}C$. The width of martensite lath increased because of the dislocation recovery at the lath boundaries. The magnetic coercivity has an influence on the microstructural properties such as dislocation, precipitates and martensite lath boundaries, which interpreted in relation to microstructural changes. Consequently, this study proposes a magnetic coercivity to quantify the level of damage and microstructural change during the creep-fatigue of ferritic 9Cr-1Mo-V-Nb steel.

• Applied Chemistry for Engineering
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• v.5 no.5
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• pp.786-794
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• 1994

The strength and durability of polymer-cement mortars were investigated. The specimens of polymer-cement mortar were prepared by using styrene-butadiene rubber(SBR) latex, ethylene-vinyl acetate(EVA) emulsion and polyacrylic ester(PAE) emulsion with various polymer-cement ratios(5, 10, 15, 20wt%). For the evaluation of durability of polymer-cement mortars, freezing-thawing, acid resistance and heat resistance tests were conducted. With an increase of polymer-cement ratio, the frost resistance of polymer-cement mortars was greatly improved, but acid and heat resistance were deteriorated. The compressive and flexural strengths of SBR polymer-cement mortars were improved with an increase of polymer-cement ratio, whereas those of EVA and PAE polymer-cement mortars reached maximum value at polymer-cement ratio of 10wt%.

• Journal of Welding and Joining
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• v.20 no.6
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• pp.99-99
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• 2002

In order to evaluate the proper fracture strength of microstructures in a steel weldment, smaller size loading ball than used for a conventional small punch(CSP) testing is required due to regional limitation on constitutive structures. In this study, the minimized loading ball(φ 1.5mm) and bore diameter of lower die(φ 3mm) were designed for an advanced small punch(ASP) test. The results obtained from the ASP test were compared with those from a CSP testing for a X20CrMoV121 steel weldment. It was found that the ASP test clearly showed the microstructural dependance on fracture strength and ductile-brittle transition behavior of the weldment. In the ASP test, especially, the cracks tend to initiate for various directions within hemispherical indentation region of an objective structure in SP test. This indicates that the evaluation of more proper fracture strength for F.L+CGHAZ, FGHAZ and ICHAZ can be performed by means of the ASP test in a steel weldment.

• Proceedings of the KSR Conference
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• 2008.06a
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• pp.2080-2093
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• 2008

Disk brake system take charge of maximum braking energy among the mechanical brake systems for high speed train. For this reason, Metallic friction materials and heat resistant steel disk is adopted at disk brake system for high speed train. It was investigated tribological characteristics(friction coefficient, friction stability, wear rate and braking temperature) between some kinds of metallic friction materials and heat resistant steel disk. Cu-based friction material for high speed train have suitable tribological characteristics.

• Journal of Welding and Joining
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• v.20 no.6
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• pp.823-829
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• 2002

In order to evaluate the proper fracture strength of microstructures in a steel weldment, smaller size loading ball than used for a conventional small punch(CSP) testing is required due to regional limitation on constitutive structures. In this study, the minimized loading ball(${\varphi}1.5mm$) and bore diameter of lower die(${\varphi}3mm$) were designed for an advanced small punch(ASP) test. The results obtained from the ASP test were compared with those from a CSP testing for a X20CrMoV121 steel weldment. It was found that the ASP test clearly showed the microstructural dependance on fracture strength and ductile-brittle transition behavior of the weldment. In the ASP test, especially, the cracks tend to initiate for various directions within hemispherical indentation region of an objective structure in SP test. This indicates that the evaluation of more proper fracture strength for F.L+CGHAZ, FGHAZ and ICHAZ can be performed by means of the ASP test in a steel weldment.

• Journal of Ocean Engineering and Technology
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• v.13 no.1 s.31
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• pp.1-10
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• 1999

The engine exhaustive valve became essential as the important element. The dissimmilar welding method of exhaustive valve head to stem was asked for manufacturing the engine exhaustive valve, for which the electric resistance are welding has been conventionally used, resulting in poor quality of the welded joint. In this paper, not only the development of optimizing of friction welding with more reliability and more applicability but also the development of in-process real-time weld qudlity(such as strength and toughness) evaluation technique by acoustic emission for friction welding of the engine exhaustive valve(SUH3-SUH35 dissimilar steels) were perfomed. The high temperature(500, 500, 600$^{circ}$C) creep properties prediction of the friction welded joint of SUH3-SUH35 was investigated relating to the initial strain meethod(ISM) as a new approach, resulting in obtaining an experimental equation of creep life prediction.

• Fire Science and Engineering
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• v.24 no.5
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• pp.94-101
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• 2010

The pipes using in water-based fire protection systems are used steel pipes for ordinary piping, carbon steel pipes for pressure service, copper and copper alloy seamless pipes and tubes, etc. By last buildings of high-rising, complexity, in fire protection systems, the corrosion resistance, easy construction, lightweight and cost-effective use of the pipes is being considered. Among the pipes, the possibility of used for fire protection system being used in the existing copper pipe of material properties, strength, corrosion resistance, heat resistance through and compare the performance was evaluated. As a result of that assessment light gauge stainless steel pipes for ordinary piping (KS D 3595) at a water pressure of less than 1.2 MPa can be used in sufficient physical properties, strength, corrosion resistance, heat resistance and have been observed.

• Resources Recycling
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• v.25 no.2
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• pp.10-16
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• 2016

In this study, the Ni base superalloy was recycled by Argon oxygen decarburization(AOD) process using an inconel 713C scrap. During AOD process, argon gas was continuously injected 1,000 sccm and oxygen gas was injected into 10, 20 and 30 minutes of 100, 250 and 500 sccm.. In early stage of oxygen injection, the oxygen dose increased with increasing Al, Cr, and Mo content and decreasing C content. And Al content was decreased by carburization with added elements in late stage Because of oxidation was occurred with Al, Cr etc. after the reaction of carbon has been finished. From the results, the ratio of ${\gamma}^{\prime}$ phase reduced due to decreasing of Al content for that reason Al is the main element to form the ${\gamma}^{\prime}$ phase. Also carbide reduced owing to decreasing of C content so the mechanical properties of the specimens excessively injected by excess $O_2$ gas were decreased.

• The Journal of the Korean dental association
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• v.47 no.12
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• pp.798-803
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• 2009

지르코니아는 물리적 성질이 금속과 가장 가까운 세라믹이며, 색상이 치아와 비슷하여 치과분야에서 사용빈도가 증가하고 있는 재료이다. 지르코니아는 zirconium dioxide 결정체로서, 1975년 Garvie가 'ceramic steer' 이라고 명명하였듯이 기존의 세라믹과 비교하여 뛰어난 물성을 지니고 있다. 즉, 높은 내열성과 낮은 열전도도, 산성에서 알카리성까지 이르는 내화학 안정성, 낮은 열팽창성, 높은 강도 및 경도, 내마모성을 가지고 있기 때문에 이전부터 공업용 재료로 넓게 시용되어 왔다. 지르코니아의 상변 이를 이용한 toughening방법이 Garvie에 의해 제시됨으로서 세라믹의 최대 단점인 취성은 어느 정도 극복할 수 있게 되었고 이를 계기로 금관 및 계속가공 의치, 임플란트 지대주, 인레이, 온레이 등 치과의 여러 분야에 지르코니아를 적용할 수 있게 되었다. 최근에는 임플란트 매식체에 있어서도 그 적용을 시도함으로서 심미치과치료에 있어서 중요한 부분으로 자리 잡고 있다. 현재 지르코니아는 치과용 세라믹 중에서 가장 높은 기계적 물성을 보이기 때문에 구치부 에서의 사용 가능성이 시도되고 있으며, 코어의 두께를 감소시킴으로써 보철 술식에서 필요한 강도 및 심미성 두 마리 토끼를 잡을 수 있도록 많은 연구가 이루어지고 있다. 이에 지르코니아의 역사 및 이론적 배경에 대하여 알아보고자 한다.

• Journal of the KSME
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• v.28 no.6
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• pp.547-555
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• 1988

강재의 기계 가공성(피삭성 : machinability)에 영향을 미치는 요인은 많다. 그러나 가장 큰 요 인은 치금학적 인자로서 그 중에서도 화학성분, 열처리 조직 및 냉간 가공 등이다. 화학성분은 재료의 기계적 성질(강도, 인성), 열처리 조직, 개재물 종류 및 공구재와의 친화성 등에 영향을 크게 미친다. 이러한 치금학적 인자도 재료의 가공방법 및 가공성 평가 기준에 따라 정 또는 부의 효과를 나타낸다. 바꿔 말하면 아무리 어려운 가공 작업이라도 모든 요인을 고려한다면 최적의 조건을 얻을 수 있다고 할 수 있다. 앞으로의 기계 가공성 개선 연구 방향으로는 재료의 특성을 해치지 않고 기계 가공성을 개선시키는 것과 특수원소 첨가(Te, Se, Bi 등)에 의한 기계 가공성 향상 및 난삭 재료인 고경도 강재, 고 Mn 강, 스테인리스계 및 초내열 합금 등의 기계 가공성 개선이 될 것이라고 판단된다.