• Journal of Advanced Marine Engineering and Technology
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• 제31권8호
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• pp.1035-1041
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• 2007

An improvement of driving motor burning damages on a couplingless type warship fire pump is studied. The pump consists of an induction motor a pump-motor shaft and a volute type impeller. The burning damage had occured by changing the material of the pump-motor shaft from carbon steel(SM 45C) to stainless steel(STS 316) for improving anti-corrision properity in sea water. It is shown that a material change on the pump-motor shaft can reduce the efficiency of driving motor and may cause motor burning in the process of pump development stage. This kind of motor burning problem can be solved by increasing the efficiency of the motor and changing the geometry of the inner parts.

• 한국산업융합학회 논문집
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• 제22권2호
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• pp.191-199
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• 2019

In this paper, dissimilar friction welding were produced using 15 mm diameter solid bar in chrome molybedenum steel(SCM440) to stainless steel(STS316L) to investigate their mechanical properties. Consequently, optimal welding conditions were n=2000 rpm, HP=70 MPa, UP=140 MPa, HT=10 sec and UT=10 sec when the metal loss(Mo) is 8.6 mm. In addition, an acoustic emission technique was applied to evaluate the optimal friction welding condition. AE parameters including the cumulative count, amplitude and energy showed a various changes according to the friction condition. A continuous type waveforms and low frequency spectrum was presented in friction time. On the other hand, a burst type waveform and high frequency spectrum was exhibited in pressing time.

• Nuclear Engineering and Technology
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• 제50권1호
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• pp.116-125
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• 2018

Modified 9Cr-1Mo ferritic steel is a preferred material for steam generators in nuclear power plants for their creep strength and good corrosion resistance. Austenitic stainless steels, such as type 316LN, are used in the high temperature segments such as reactor pressure vessels and primary piping systems. So, the dissimilar joints between these materials are inevitable. In this investigation, dissimilar joints were fabricated by the Shielded Metal Arc Welding (SMAW) process with Inconel 82/182 filler metals. The notch tensile properties and Charpy V-notch impact toughness properties of various regions of dissimilar metal weld joints (DMWJs) were evaluated as per the standards. The microhardness distribution across the DMWJs was recorded. Microstructural features of different regions were characterized by optical and scanning electron microscopy. Inhomogeneous notch tensile properties were observed across the DMWJs. Impact toughness values of various regions of the DMWJs were slightly higher than the prescribed value. Formation of a carbon-enriched hard zone at the interface between the ferritic steel and the buttering material enhanced the notch tensile properties of the heat-affected-zone (HAZ) of P91. The complex microstructure developed at the interfaces of the DMWJs was the reason for inhomogeneous mechanical properties.

• 한국진공학회지
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• 제15권3호
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• pp.325-330
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• 2006

ITER (International Thermonuclear Experimental Reactor) 조달용 일차벽의 제조 건전성을 검증하기 위해서, 일차벽을 구성하는 Cu/SS mock-up을 제작하여 고열부하 시험을 수행하였다. Cu/SS mock-up은 CuCrZr과 SS316L이 사용되었으며, 두 금속은 $1050^{\circ}C$, 150 MPa의 조건에서 고온등방가압법 (HIP, Hot Isostatic Pressing) 과정을 통해 접합되었다. 시험에 사용된 고열부하 장치는 일본 원자력연구소의 JEBIS (JAEA Electron Beam Irradiation Stand)를 이용하였으며, 시험 조건은 FEM 코드인 ANSYS 해석을 통해 결정하였다. 시험은 $5MW/m^2$의 고열부하를 15초간 인가하고, 30초간 냉각하는 방법으로 수행되었으며, 시험 종료 후 얻어진 시험결과와 해석결과가 잘 일치함을 확인하였다.

• 한국기계가공학회지
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• 제19권8호
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• pp.94-103
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• 2020

This study investigated the effects of ultrasonic nanocrystal surface modification (UNSM) on the deteriorated surface of AISI SUS316L additively manufactured (AM) using the powder bed fusion (PBF) technique. Specifically, the effects of UNSM conditions on surface topology, hardness, and anti-corrosion were examined. Before UNSM treatment, the stainless steel 316L powder was processed via the PBF machine to prepare a substrate. We observed surface changes due to UNSM treatments in PBF SUS316L substrates and examined the correlation between topology changes, roughness, hardness, and anti-corrosion. After UNSM treatment, the coarse as-built surface was refined, and a regular micro-profile was implemented. Compared to the non-treated PBF sample, the waviness and roughness of the surfaces after UNSM treatment decreased by up to 56.0% and 94.5%, respectively, and decreased further as the interval decreased. The hardness improved by up to 63.0% at a maximum depth of 500 ㎛ from top surface by the UNSM treatment. The results of the corrosion test showed that the corrosion resistance of the UNSM specimens was moderately improved compared to that of the untreated surface. This study confirmed that UNSM is an effective post-processing technique for additively manufactured parts.

• 비파괴검사학회지
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• 제30권4호
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• pp.345-351
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• 2010

본 연구에서는 고주기 피로를 받은 SUS316L 강에서의 초음파 비선형 특성평가를 위한 종파 경사입사기법을 연구하였다. Dog-bone형의 판상시편을 준비하여 시편 중심부에서 응력집중이 되며 각 위치마다 피로 손상이 다르도록 제작하였다. 수직투과법 외에 본 연구에서 새로이 제안한 경사입사법을 이용하여 초음파 비선형 파라미터를 측정하였다. 두 기법 모두에서 피로 손상 전보다 고주기 피로 손상 후 초음파 비선형 파라미터가 높게 나타났다. 특히, 응력 집중을 받은 시편 중심부에서 크게 증가하였다. 상대적인 초음파 비선형 파라미터는 피로 손상과 밀접한 상관성을 보였으며 결과적으로 종파를 이용한 경사입사기법은 피로 손상을 평가하는데 효과적인 기법이라 할 수 있다.

• 한국안전학회지
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• 제7권1호
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• pp.20-29
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• 1992

Effects of strain hardening exponents on the retardation behavior of fatigue crack propagation are experimentally investigated. The retardation of fatigue crack propagation seems to be induced by the crack closure at crack tip. The phenomenon of crack closure becomes remarkable with the increment of strain hardening exponent and magnitude of percent peak load. The ratio of crack growth increment(a$\_$d//w$\_$d/) is influenced by a single overloading (a$\_$d/) and estimated plastic zone size (W$\_$d/=2r$\_$y/) is increased according with the increasing of strain ha.dening exponents. The number of retarded crack growth cycles were (N$\_$d/) decreased as the baseline stress intensity factor .ange( K$\_$b/) was increased. Within the limitation of these experimental results obtained under the single overload, an empirical relation between crack retardation ratio (Nd/N＊), strain hardening exponent (n) and percent peak load (％PL) has been proposed as; Nd/N＊＝ exp [PL $.$ PL$.$A(n)＋B(n) ] where, A(n)＝${\alpha}$n＋${\beta}$, B(n)＝${\gamma}$n＋$\delta$, PL＝％PL/100 and ${\alpha}$＝0.78, ${\beta}$＝0.54, ${\gamma}$＝0.58 and $\delta$＝-0.01, It is interesting to note that all these constants are identical for materials such as aluminum(A3203), steel(S4SC), steel(SS41) and stainless steel(SUS316) used in this experimental study.

• 대한기계학회논문집A
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• 제35권5호
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• pp.543-547
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• 2011

원자력발전소의 이종용접부에서 일차응력부식균열이 발생하고 있으며 용접부의 잔류응력이 균열발생 및 성장에 기여할 수 있다. 용접부의 잔류응력은 기본적으로 용접에 의해 형성되지만 기계가공에 의해 표면잔류 응력상태가 변화할 수 있다. 본 논문에서는 기계가공이 원전재료인 SA508과 오스테나이트 스테인리스강에 표면잔류응력에 미치는 영향을 평가하였다. 이를 위해 SA508, TP304, F316L 재료를 연마, 연삭, 방전가공으로 가공한 후 표면에 형성되는 잔류응력을 측정하였다. 측정방법은 구멍뚫기법과 엑스선회절법을 사용하였다. 기계가공방법에 따라 각 재료에 미치는 잔류응력의 크기 및 방향, 잔류응력이 형성되는 깊이 등의 특성을 확인하였다.

• 대한금속재료학회지
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• 제47권11호
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• pp.716-721
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• 2009

The major drive for the application of low-temperature plasma treatment in nitrocarburizing of austenitic stainless steels lies in improved surface hardness without degraded corrosion resistance. The low-temperature plasma nitrocarburizing was performed in a gas mixture of $N_{2}$, $H_{2}$, and carbon-containing gas such as $CH_{4}$ at $450^{\circ}C$. The influence of the processing time (5~30 h) and $N_{2}$ gas composition (15~35%) on the surface properties of the nitrocarburized layer was investigated. The resultant nitrocarburized layer was a dual-layer structure, which was comprised of a N-enriched layer (${\gamma}_N$) with a high nitrogen content on top of a C-enriched layer (${\gamma}_C$) with a high carbon content, leading to a significant increase in surface hardness. The surface hardness reached up to about $1050HV_{0.01}$, which is about 4 times higher than that of the untreated sample ($250HV_{0.01}$). The thickness of the hardened layer increased with increasing treatment time and $N_{2}$ gas level in the atmosphere and reached up to about $25{\mu}m$. In addition, the corrosion resistance of the treated samples without containing $Cr_{2}N$ precipitates was enhanced than that of the untreated samples due to a high concentration of N on the surface. However, longer treatment time (25% $N_{2}$, 30 h) and higher $N_{2}$ gas composition (35% $N_{2}$, 20 h) resulted in the formation of $Cr_{2}N$ precipitates in the N-enriched layer, which caused the degradation of corrosion resistance.

• 한국분말재료학회지
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• 제22권3호
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• pp.197-202
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• 2015

In this study, porous stainless steel (STS316L) sintered body was fabricated by powder metallurgy method and its properties such as porosity, compressive yield strength, hardness, and permeability were evaluated. 67.5Fe-17Cr- 13Ni-2.5Mo (wt%) powder was produced by a water atomization. The atomized powder was classified into size with under $45{\mu}m$ and over $180{\mu}m$, and then they were compacted with various pressures and sintered at $1210^{\circ}C$ for 1 h in a vacuum atmosphere. The porosities of sintered bodies could be obtained in range of 20~53% by controlling the compaction pressure. Compressive yield strength and hardness were achieved up to 268 MPa and 94 Shore D, respectively. Air permeability was obtained up to $79l/min{\cdot}cm^2$. As a result, mechanical properties and air permeability of the optimized porous body having a porosity of 25~40% were very superior to that of Al alloy.