• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 2002년도 Proceedings of the International Welding/Joining Conference-Korea
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• pp.273-275
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• 2002

The effect of post-weld heat treatment (PWHT) of marine structures steel was investigated at electrochemical viewpoint. In addition, slow strain rate test (SSRT) was carried out to investigate both electrochemical and mechanical properties by PWHT effect during impressed current cathodic protection. The optimum cathodic protection potential by SSRT was -770 mV(SCE). At the applied cathodic protection potential of -770 mV -850 mV(SCE), the fracture morphology was dimple pattern with ductile fracture, while it was transgranular pattern (Q.C: quasi cleavage) under -875 mV(SCE).

• Corrosion Science and Technology
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• 제14권4호
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• pp.195-199
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• 2015

Materials of choice for offshore structures and the marine industry have been increasingly favoring materials that offer high strength-to-weight ratios. One of the most promising families of light-weight materials is titanium alloys, but these do have two potential Achilles' heels: (i) the passive film may not form or may be unstable in low oxygen environments, leading to rapid corrosion; and (ii) titanium is a strong hydride former, making it vulnerable to hydrogen embrittlement (cracking) at high temperatures in low oxygen environments. Unfortunately, such environments exist at deep sea well-heads; temperatures can exceed $120^{\circ}C$, and oxygen levels can drop below 1 ppm. The present study demonstrates the results of investigations into the corrosion behavior of a range of titanium alloys, including newly developed alloys containing rare earth additions for refined microstructure and added strength, in artificial seawater over the temperature range of $25^{\circ}C$ to $200^{\circ}C$. Tests include potentiodynamic polarization, crevice corrosion, and U-bend stress corrosion cracking.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 1996년도 춘계학술대회 논문집
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• pp.697-703
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• 1996

Fatigue strength of high strengthsteels are variable with many different surface treatment. It is well known that residual compressive stress retard fatigue crack growth rate(or arrest crack). High strngth steels are manufactured by following process. Heat treatment, shot peening and chromium plating process. High strength steel(HRC40 or above) which are subjected to fatigue load and dynamic load, chromium plated parts shall be peened in accordance with requirements and baked after plating. The purpose of this paper is to compare and discuss the influence of surface treatment and hydrogen embrittlement on fatigue strength of high strength steel. Therefore, fatigue test was performed to investigate influence of surface treatment. The results shows that shot peening is very effect method in creasing fatigue life and after plating, baking process is essential to prevent hydogen failure. In this paper, the experimental investigation is made to clarify the influence of shot peening conditions and baking process on fatigue strength of high strength steel.

• Structural Engineering and Mechanics
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• 제14권2호
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• pp.209-221
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• 2002

In this paper a fracture criterion is proposed for cracked cylindrical samples of high-strength prestressing steels of different yield strength. The surface crack is assumed to be semi-elliptical, a geometry very adequate to model sharp defects produced by any subcritical mechanism of cracking: mechanical fatigue, stress-corrosion cracking, hydrogen embrittlement or corrosion fatigue. Two fracture criteria with different meanings are considered: a global (energetic) criterion based on the energy release rate G, and a local (stress) criterion based on the stress intensity factor $K_I$. The advantages and disadvantages of both criteria for engineering design are discussed in this paper on the basis of many experimental results of fracture tests on cracked wires of high-strength prestressing steels of different yield strength and with different degrees of strength anisotropy.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2004년도 춘계학술대회
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• pp.54-59
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• 2004

In this paper probabilistic fracture mechanics(PFM) approach is employed to evaluate the integrity of CANDU Zr-2.5Nb pressure tubes. Modified failure assessment diagram(Jr-FAD), plastic collapse, and critical crack length(CCL) approach are used for evaluating failure probability of the tubes. Jr-FAD was extended from the Kr-FAD because fracture of pressure tubes occurs in brittle manner due to hydrogen embrittlement of material by deuterium fluence. For developing the probabilistic integrity evaluation module, AECL procedures and fracture toughness parameters of EPRI were used.

• 한국표면공학회:학술대회논문집
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• 한국표면공학회 2011년도 춘계학술대회 및 Fine pattern PCB 표면 처리 기술 워크샵
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• pp.193-195
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• 2011

강판재 사용에 있어 수소취성현상은 강판재가 고강도화됨에 따라 그 감수성이 커지는 것으로 알려져 있다. 특히 노출강판재의 경우, 표면으로부터 침투해 들어가는 수소에 의한 수소취화 거동에 대한 연구가 필요하다. 본 연구에서는 고강도 DP강을 시험편으로 하여, 음극전기분해법에 의해 수소를 강제주입시킨 후, DP강 표면하 subsurface zone의 수소취화 거동을 평가하고자 하였다. 미소경도분포 측정결과, 수소주입시간이 증가함에 따라 표면하 subsurface zone의 경도 또한 증가하는 것으로 조사되었다. 이는 수소에 의해 표면하 subsurface zone의 경화가 일어나 DP강의 기계적 특성에 영향을 미친것으로 판단된다. 미소경도분포의 측정결과와 미세조직 관찰결과로부터 수소임계침투깊이를 평가하였고, 이를 통해 DP강내 수소확산에 의한 수소임계침투깊이가 존재함을 확인할 수 있었다.

• Nuclear Engineering and Technology
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• 제48권1호
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• pp.16-25
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• 2016

In severe loss of coolant accidents (LOCA), similar to those experienced at Fukushima Daiichi and Three Mile Island Unit 1, the zirconiumalloy fuel claddingmaterials are rapidlyheateddue to nuclear decay heating and rapid exothermic oxidation of zirconium with steam. This heating causes the cladding to rapidly react with steam, lose strength, burst or collapse, and generate large quantities of hydrogen gas. Although maintaining core cooling remains the highest priority in accident management, an accident tolerant fuel (ATF) design may extend coping and recovery time for operators to restore emergency power, and cooling, and achieve safe shutdown. An ATF is required to possess high resistance to steam oxidation to reduce hydrogen generation and sufficient mechanical strength to maintain fuel rod integrity and core coolability. The initiative undertaken by Electric Power Research Institute (EPRI) is to demonstrate the feasibility of developing an ATF cladding with capability to maintain its integrity in $1,200-1,500^{\circ}C$ steam for at least 24 hours. This ATF cladding utilizes thin-walled Mo-alloys coated with oxidation-resistant surface layers. The basic design consists of a thin-walled Mo alloy structural tube with a metallurgically bonded, oxidation-resistant outer layer. Two options are being investigated: a commercially available iron, chromium, and aluminum alloy with excellent high temperature oxidation resistance, and a Zr alloy with demonstratedcorrosionresistance.Asthese composite claddings will incorporate either no Zr, or thin Zr outer layers, hydrogen generation under severe LOCA conditions will be greatly reduced. Key technical challenges and uncertainties specific to Moalloy fuel cladding include: economic core design, industrial scale fabricability, radiation embrittlement, and corrosion and oxidation resistance during normal operation, transients, and severe accidents. Progress in each aspect has been made and key results are discussed in this document. In addition to assisting plants in meeting Light Water Reactor (LWR) challenges, accident-tolerant Mo-based cladding technologies are expected to be applicable for use in high-temperature helium and molten salt reactor designs, as well as nonnuclear high temperature applications.

• Korean Chemical Engineering Research
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• 제44권2호
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• pp.160-165
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• 2006

니켈 분말을 이용하여 제조된 다공성 니켈 지지체 위에 팔라듐-구리-니켈 합금 수소 분리막을 제조하였다. 다공성 니켈 지지체는 열적안정성과 수소취성에 강한 모습을 나타내었으며, 다공성 니켈 지지체에 기존의 습식 방식인 염산에 의한 표면 전처리 방식을 건식 방식인 플라즈마 표면개질로 대체하였다. 다공성 니켈 지지체의 기공을 매립하기 위해 전해도금방식으로 $2{\mu}m$의 두께로 코팅하였으며, 그 후 니켈 도금된 지지체 위에 스퍼터 방식으로 팔라듐을 $4{\mu}m$, 구리를 $0.5{\mu}m$의 두께로 코팅하였다. 이와 같이 제조된 시편을 $700^{\circ}C$에서 1시간 구리 리플로우를 통해 미세기공이 없는 매우 치밀한 팔라듐-구리-니켈 합금 분리막을 제조하였다. 그 결과 팔라듐-구리-니켈 합금 수소분리막은 다공성 니켈지지체와 좋은 접착성을 가지고 있으며 수소-질소 혼합가스에서 무한대의 분리도 값을 나타내었다.

• 해양환경안전학회:학술대회논문집
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• 해양환경안전학회 2005년도 춘계학술발표회
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• pp.161-165
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• 2005

Recently, it is on the increase interest for Al alloy with new material for ship application to substitute for FRP ship. The reason is thatAl alloy ship has beneficial characteristics such as high sea speed, increase of loadage and easy to recycle compared with FRP ship. In this paper, mechanical and electrochemical properties are investigated by slow strain rate test experiment in various applied potential condition. These results will provide as reference data to design ship by deciding optimum protection potential regard to hydrogen embrittlement and stress corrosion cracking. In general, Al and Al alloys are not corroded with forming film which has the corrosion resistance property in neutral solution. However, it was observed that formation and destruction of passive film by $Cl^-$ ion in sea water environment. At comparison of current density after 1200 sec in potentiostatic experiment, the current density in the potential range of -0.68 $\~$-1.5 V is shown low value. The low current density means protection potential range. Elongation in applied potential of 0 V was high. However, the corrosion protection application in this condition is impossible potential because the toughness is low value by decreasing strength by active dissolution reaction at parallel part of specimen. The film composed with $CaCO_3$ and $Mg(OH)_2$ has a corrosion resistance property. However, the uniform electrodeposition coating at below -1.6 V potential is not formed since the time to form the uniform electrodeposition coating is short. Therefore, it is concluded that mechanical property is poor because effect by hydrogen gas generation is larger than that of electrodeposition coating. It is concluded that the optimum protection potential range from comparison of_maxim urn tensile strength, elongation and time to fracture is -1.3$\~$0.7 V (SSCE).

• 한국초전도ㆍ저온공학회논문지
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• 제25권4호
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• pp.70-74
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• 2023

The Small Punch Test (SPT) was developed to evaluate the softening and embrittlement of materials such as power plants and nuclear fusion reactors by taking samples in the field. Specimens used in the SPT are very thin and small disk-shaped compared to specimens for general tensile test, and thus have economic advantages in terms of miniaturization and repeatability of the test. The cryogenic SPT can also be miniaturized and has a significantly lower heat capacity than conventional universal test machines. This leads to reduced cooling and warm-up times. In this study, the cryogenic SPT was developed by modifying the existing room temperature SPT to be cooled by liquid nitrogen using a super bellows and a thermal insulation structure. Since the cryogenic SPT was first developed, basic experiments were conducted to verify the effectiveness of it. For the validation, aluminum alloy 6061- T6 specimens were tested for mechanical properties at room and cryogenic temperature. The results of the corrected tensile properties from the SPT experiment results were compared with known room temperature and cryogenic properties. Based on the correction results, the effectiveness of the cryogenic SPT test was confirmed, and the surface fracture characteristics of the material were analyzed using a 3d image scanner. In the future, we plan to conduct property evaluation according to the development of various alloy materials.