• 한국주조공학회지
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• 제20권5호
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• pp.336-343
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• 2000

The effects of casting variables and alloying elements on the fluidity of thin wall cast stainless steels were investigated. Melts were poured into the sand molds to produce thin wall test castings. The length of it was 245 mm and the thickness varied at the interval of 0.5 in the range of 1.6 to 2.6 mm. For the same casting condition, the fluidities of austenitic stainless steel, ferritic, precipitation hardenable and martensite ones were better in the order. The higher the pouring temperature, the shorter the pouring rate and the better the fluidity were. The fluidity was increased with the addition of Cr and decreased with W and Nb.

• 한국윤활학회:학술대회논문집
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• 한국윤활학회 2002년도 제35회 춘계학술대회
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• pp.304-309
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• 2002

Fretting wear test in room temperature water was performed to evaluate the wear coefficient of Inconel 600,690 (Pressurized Water Reactor, PWR) and Alloy 800 (CANadian DeuteriumUranium, CANDU) steam generator (SG) tubes against ferritic and martensitic stainless steels. The main focus is to compare the wear behaviors between Alloy 800 and Inconel alloys. Test conditions are $10{\sim}30N$ of normal load, $200{\sim}450{\mu}m$ of sliding amplitude and 30Hz of frequency. The result indicated that the wear rate of Alloy 800 was higher than those of Inconel 690 at various test condition such as normal loads, sliding amplitudes etc. From the results of SEM observation, there was little evidence of plastic deformation layer that were dominantly formed on the worn surfaces of Inconel 690. Also, wear particles in Alloy 800 were released from contacting asperities deformed by severe plastic flow during fretting wear. Main cause of wear rate between Alloy 800 and Inconel 690 may be due to the difference of hardness between martensitic and ferritic stainless steel. The wear rate and wear mechanism of two tubes in room temperature water are discussed.

• 한국주조공학회지
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• 제18권6호
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• pp.563-569
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• 1998

A Study on microstructure and elevated temperature strength of 18Cr-2Mo ferritic stainless steel castings strengthened by alloying small amounts of titanium and carbon, has been conducted. The morphology of titanium carbides showed spherical in shape and their distribution depended on the amount of alloying elements. Maximum density ($7{\times}10^5/cm^2$) of titanium carbides has been formed in the alloy containing 2.0 wt.% titanium and 0.5 wt.% carbon as alloying elements and the size of carbide particles is in the range of 0.5 to $3.0\;{\mu}m$. High temperature tensile and fatigue strength of this alloy were the highest among the alloys tested in this research. The fracture mode of the alloys containing alloying elements less that 2.0 wt.% titanium and 0.5 wt.% carbon showed intercrystalline fracture at room temperature, while the alloys containing higher amounts of alloying elements showed transcrystalline fracture. All of the alloys showed creep or ductile rupture mode at elevated temperature.

• Journal of Welding and Joining
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• 제29권6호
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• pp.40-44
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• 2011

Brazing of a stainless steel was described in this article. Brazing is a joining technology without melting a substrate and joining temperature is higher than $450^{\circ}C$. Brazing can be broadly applicable across industries. In particular, brazing of stainless steel is widely used in aircraft parts, car engines, heat exchangers, etc. due to its excellent strength, corrosion resistance and other suitable characteristics. Characteristics of the stainless steel depend on their classification like austenitic, ferritic and martensitic stainless steels. In addition, there are many processes in brazing and various parameters such as brazing heat source, filler metals, joint design, etc. Therefore, it is necessary to know basic knowledge about brazing to achieve good brazing joint. Accordingly, properties of stainless steel and design of brazing joint and related process were described in this article.

• 한국재료학회지
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• 제14권2호
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• pp.101-109
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• 2004

The influences of solidification rates and carbon contents on the formation of the $\delta$-ferrite were studied by directional solidification in modified 12%Cr-l %Mo steels. Directional solidification experimental results showed that solidification microstructure depended on solidification rate and carbon content and chromium equivalent. The length of the mushy zone increased and the dendrite arm spacings decreased as the solidification rate increased. The volume fraction of the 8-ferrite decreased with increasing the solidification rate and carbon content. The volume fraction of the ferrite showed much higher at low solidification rates with planar and cellular interfaces than that at high solidification rates with dendritic interface. It is expected that macro-segregation of C causes lower C content at the lower solidification fraction in the directionally solidified sample, where lower C results in higher volume fraction of the ferrite. In order to estimate solidification microstructure in modified 12Cr-l%Mo steels, various solidification conditions, such as solidification rate, cooling rate, segregation, alloy composition, should be considered.

• 한국기계가공학회지
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• 제18권1호
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• pp.31-37
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• 2019

This study investigates the effects of long-term artificial-aging on hardness variation in the dissimilar metal weldments for nuclear power plant facilities. These dissimilar welds are inevitably required to join the components in nozzle parts of pressurized vessels, such as austenitic stainless steels and ferritic steels. A artificial thermal aging was conducted in an electrical furnace to simulate material degradation at high temperatures. The test materials were held at the temperature of $600^{\circ}C$ for 10000 hours and interrupted at various levels of degraded specimens. The degradation of hardness is a well-known phenomenon resulting from long-term aging or high-temperature degradation of structural materials. In this study, the variation of hardness at each position was different, and complicated in relation to microstructures such as twins, grains, precipitates, phase transformations, and residual stresses in dissimilar weldments. We discussed the variation of hardness in terms of microstructural changes during long-term aging.

• 비파괴검사학회지
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• 제28권5호
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• pp.407-415
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• 2008

원전 발전소 터빈계통을 구성하는 열교환기 튜브는 일반적으로 구리합금, 스테인리스강, 탄소강, 티타늄합금 등의 재질로 제작된다. 이들 재질중에서 페라이트계 type-439 스테인리스강은 자성 재질로서 오스테나이트계보다 더 높은 열전달율 가지며, 부식에 의해 유발되는 결함에 대해 더 높은 저항성을 가진다. 페라이트계 스테인리스강은 보통 발전소 열교환기의 저압급수가열기와 습분분리재열기에 사용된다. 저압급수가열기는 일반적으로 두께가 얇은 type-439 스테인리스강을 이용하는 반면에 습분분리재열기는 더 두꺼운 핀튜브를 사용한다. 이와 같이 터빈 습분분리재열기 튜브로 사용되는 type-439 스테인리스강 핀튜브는 터빈계통의 운전으로 인하여 손상이 발생할 수 있다. 손상에 의한 가장 대표적인 결함은 진동에 의해 발생할 수 있는 마모, 피로균열 등이며 마모성 결함은 일반적으로 튜브-튜브지지판에서 발생되는 것으로 보고되고 있다. 본 연구에서는 type-439 스테인리스강 자성체 튜브에 발생할 수 있는 결함을 검출하고 크기를 측정할 수 있는 자기포화 와전류탐상검사 기법의 능력을 평가하였다.

• Corrosion Science and Technology
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• 제2권1호
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• pp.12-17
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• 2003

The effects of Cr content and film formation potential on electronic behaviors of the passive film on Fe-Cr alloys were investigated in borate buffer solution. Influence of pH on passive films of both Fe-Cr and Fe-Cr-Mo alloys was also investigated. Mott-Schottky and cyclic voltammetry techniques were used to elucidate electronic behaviors of passive films and their electrochemical characteristics. AES analysis of passive films was carried out. Results showed that doping density decreased as Cr content and film formation potentials increased. The addition of Mo to Fe-Cr alloy had little influence on donor densities in pH 9.2 solution but some effects on the decrease in donor densities in pH 1.6 acidic solution.

• 대한금속재료학회지
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• 제47권11호
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• pp.707-715
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• 2009

This paper deals with cyclic stress and strain responses during isothermal low cycle fatigue (LCF) and thermo-mechanical fatigue (TMF) loadings on Nb and Mo containing 15Cr stainless steel, which is used for exhaust manifolds in automobiles. The test temperatures ($T_{i}$) of the isothermal LCF were 600 and $800^{\circ}C$. The minimum temperature of the TMF test was $100^{\circ}C$ and the maximum temperaures ($T_{p}$) were varied between 500 and $800^{\circ}C$. In both loading conditions, weak cyclic softening is observed at $T_{i}=T_{p}=800^{\circ}C$, but the transition to strong cyclic hardening is completed with the temperature decrease below $T_i=600{\sim}700^{\circ}C$ for LCF and $T_{p}=500{\sim}600^{\circ}C$ for TMF. The stress-strain hysteresis loops in the TMF loading show a significant stress relaxation during compressive (heating) half cycle at $T_{p}>500^{\circ}C$, which develops tensile mean stress during cycling. Due to the stress relaxation, the TMF test sample reveals much lower dislocation density than the isothermally fatigued sample at the same temperature with $T_{p}$. A detailed correlation between fatigue microstructure and cycling deformation behavior is discussed.

• Journal of Welding and Joining
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• 제13권2호
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• pp.139-149
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• 1995

Many pressure vessels for the power plants are fabricated from low alloy ferritic steels. The inner sides of the pressure vessels are commonly weld_cladded with austenitic stainless steels to minimize problems of corrosive attack. The submerged-arc welding(SAW) process is now used in preference to other processes because of the possibilities open to automation to reduce the overaII welding times. The most reliable way to avoid underclad cracks(UCC) which are often detected at the overlap of the clad beads is to use nonsusceptible steels such as SA508 class 3. At present domestically developed forging steel of SA508 cl.S is now being cladded with single layer by using 90mm wide strip, which transfers higher heat input into the base metal compared to the conventional two layers strip cladding which has been in wide use with 30-60 mm wide strip. But the current indices for the influence of heat input on crack susceptibility are not accurate enough to express the subtle difference in crack susceptibility of the steel. Therefore, the purpose of this present study is: l) To determine UCC susceptibility on domestic forging steel, SA508 cl.S cladded with single layer by using submerged arc 90mm strip and, 2) To optimize heat input range by which the crack susceptibility could be eliminated.