• Journal of Welding and Joining
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• v.32 no.6
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• pp.70-74
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• 2014

On this study, we researched the in-process monitoring during fiber laser welding as well as on the first paper. On the previous/formal study, we analyzed the change of emission signal on thin plate welding. On this study, however, we analyzed RMS and FFT with emission signals in laser welding on lap joint and butt joint of 8mm-thick 316L stainless steel. As the result, the movement of specific frequency peak was observed according to welding speed changes. Furthermore, frequency peak as a result of FFT on the thick plate welding are much clearer than on the thin plate welding. Therefore, it is expected that the welding parameter changes can be predicted in case of applying FFT to in-process monitoring.

• Journal of Advanced Marine Engineering and Technology
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• v.35 no.6
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• pp.802-808
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• 2011

One of the important mechanical properties of cryogenic temperature structure material is fracture toughness. Research on normalization of fracture toughness test method is becoming very important issue with development of cryogenic structural elements. Specially, mechanical properties estimation by each micro-structure of welding department is important because it can cause unstable fracture when use under cryogenic environment in case of welding department. In this study, fracture toughness estimation test was carried out to unloading compliance method and sensitization heat-tread minimized test specimen at liquid nitrogen (77K), liquid helium (4K), 293K temperature to STS-316L base metal and weld metal.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2011.11a
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• pp.481-487
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• 2011

This paper provides a comparison between finite element analysis results and test data of rupture disc. Rupture disc is safety device of high pressure equipment. Rupture disc of solid rocket motor is a device to control rupture pressure. Rupture discs were made of AISI 316L. By the elastic-plastic analysis, the stress limit of rupture discs were compared to the test results. The results can be used to control the rupture pressure by the change of the disc size.

• Proceedings of the Korean Nuclear Society Conference
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• 1996.05c
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• pp.73-78
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• 1996

Type 316L 스테인레스강에 대한 질소첨가의 효과를 분석하기 위해 질소를 소량(0.024%)첨가한 합금과 적정량(0.15%) 첨가한 합금을 용해하여 입계부식특성 평가를 하였다. Oxalic시험 및 DL-EPR 시험 결과 적정량의 질소를 첨가한 합금이 소량 첨가한 금보다 우수한 예민화 특성을 보였다. TEM에 의한 미세구조 분석 결과 저질소 합금의 경우 비교적 짧은 열처리 시간에 M$_{23}$C$_{6}$ type의 석출물이 입계를 따라 형성되고 시효시간이 경과 할수록 그양이 급격히 증가하는 양상을 보인 반면에 적정 질소 첨가 합금의 경우 탄화물 생성이 비교적 긴 시효시간으로 늦추어져 예민화 실험 결과와 일치된 결과를 보였다. 두 합금 모두에서 탄화물 이외에 Mo의 함량이 매우 높은 석출물이 관찰되었는데 적정질소 첨가강의 경우 시효 시간의 경과에 따라 초기의 작은 cluster들의 형태에서 시작하여 얇은 박막의 형태로 입계면을 따라 성장하는 양상을 보였고, 반면에 저질소합금의 경우 입계를 따른 작은 석출물들이 cluster들로는 성장하였으나 장시간 시효가 진행됨에 따라 탄화물의 성장에 의해 박막 형태로는 성장하지 못하였다. Mo-rich 박막형상 석출물에 대한 분석 결과 20-면체 준결정상의 형태에 매우 가까운 결정구조를 보였으며 때로 η상과 매우 밀접한 회절 패턴도 관찰되었다. 이러한 상은 적정 질소첨가 합금에서의 탄화물 생성 지연과도 관련이 있을 것으로 추정되었다.

• Proceedings of the KWS Conference
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• 2002.10a
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• pp.133-138
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• 2002

Microbiologically Influenced Corrosion (MIC) was suspected in a corrosion failure of cooling system of stainless piping welded joint, carrying marine water. Marine water which is used for cooling water in a plant was transferred to the laboratory and used for experiment. In the first experiment, weld metal samples were exposed to the test solution for 56 days (marine water and sterilized marine water (control)). Surface condition of experimental coupons was observed using a Scanning Electron Microscope (SEM). In another experiment, free corrosion potential of these material was monitored for 56 days. Pitting corrosion was found in the coupons exposed to marine water. Free corrosion potential ennoblement was found to be significant compared to control. It was suspected that this corrosion case was MIC. In the second experiment, coupons were exposed to diluted nutrient medium containing single culture of microbes isolated from the MIC causing marine water sample used for the first experiment. After exposure test, surface condition of experimental coupon was observed using SEM. Pitting corrosion was found in coupons exposed to some of the isolates. The results indicate that they contribute to the corrosive effect of the SUS316L welds.

• Corrosion Science and Technology
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• v.6 no.6
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• pp.286-290
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• 2007

Biocompatible Hydroxy apatite (HAp) coatings on metallic substrate by plasma spray techniques have been developed. Long-term credibility of plasma spray HAp coatings has been evaluated in physiological saline by electrochemical measurements. It was found that the corrosion resisitance of SUS316L based HAp/Ti conbined coatings was excellent even after more than 10 weeks long-term immersion. It was shown that postal heat treatment improved both the crystallinity and corrosion resistance of HAp. By lowering cooling rate during heat treatment process, less cracks produced in HAp coating layer, which lead to higher credibility of HAp during immersion in physiological saline. The ICP results showed that the dissolution level of substrate metallic ions was low and HAp coatings produced in this research can be acceptable as biocompatible materials. Also, the concentration of dissolved ions from HAp coatings with postal heat treatment was lower compared to those from samples without postal heat treatment. The adherence of HAp coatings with Ti substrate and other mechanical properties were also assessed by three-point bending test. The poor adhesion of HAp coating to titanium substrate can be improved by introducing a plasma spray titanium intermediate layer.

• Journal of Environmental Science International
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• v.17 no.3
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• pp.335-342
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• 2008

This study based on electro-coagulation & oxidation reaction is applied to wastewater treatment. Electro-oxidation reaction is used to remove cyanide(CN) which is contained in plating wastewater. Cyanide is transferred by gases such as $NH_3,\;NO_x,\;CO_2$. Analysis result and removal efficiency of Cyanide which is contained in heavy metal wastewater of plating plant, are shown as following paragraph. In electrode arrangement experiment, removal efficiency of carbon electrode(-)/STS316L electrode(+) arrangement method is superior to carbon electrode(-)/carbon electrode(+) arrangement method. Removal efficiencies of cyanide in different HRT such as 30 min, 45 min, 60 min, 75 min and 90 min are 85.5%, 93.1%, 98.0%, 98.7% and 99.4% respectively in carbon electrode(-)/STS316L electrode(+) arrangement method. Finally we can estimate the critical point at HRT of 60 min which the variation of removal efficiency is decreased and HRT to obtain removal efficiency of less than 1 mg/LCN is minimum 90 min.

• Journal of Advanced Marine Engineering and Technology
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• v.33 no.4
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• pp.533-538
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• 2009

The magnitude of constraint effect $A_2$ values on the non-linear elastic plastic fracture toughness was experimentally estimated by using displacement at various measuring positions near crack tip. Constraint effect $A_2$ value was dependent on specimen configuration and on the measured displacement near crack front. The crack tip opening displacement in the vicinity of the crack tip front should be estimated within plastic region when appropriately constraint effect was calculated. It was found that the magnitude of constrain effect |$A_2$| is below 8.0 at the crack tip. But an appropriate location to measure the effective constraint effects $A_2$ at the critical value of J that crack initiation is characterizable by is r = 2mm and ${\theta}=90^{\circ}$ away from original crack tip, and the constraint effect |$A_2$| estimated is 5.3.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.27 no.11
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• pp.1856-1863
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• 2003

Overlay model had several advantages to describe hysteretic behavior of material and showed good capability for many engineering materials. However, this model is only applicable to material obeying Masing postulate. Some materials such as 316L stainless steel do not follow Masing postulate and show cyclic hardening(or softening) and strain range dependence. Low cycle fatigue tests of 316L stainless steel at 600$^{\circ}C$ were performed to investigate the characteristics of cyclic behavior of non-Masing material. From all tests cyclic softening was observed. There were differences in elastic limit of hysteresis loop according to applied strain range. To consider these features, modified overlay model was developed. Yield stresses of subelements were divided into isotropic and anisotropic part to describe the non-Masing behavior. The plastic strain range memorization was introduced to consider the strain range dependence. The prediction using modified overlay model showed a good accordance to actual hysteresis loops.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.24 no.9 s.180
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• pp.2211-2219
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• 2000

Near net shape forming of 316L stainless steel powder was investigated under hot isostatic pressing. To simulate densification and deformation of a powder compact in a container during hot isostatic pressing, the constitutive model of Abouaf and co-workers was implemented into a finite element analysis. An optimal design technique based on the design sensitivity was applied to the container design during hot isostatic pressing. The optimal shape of the container was predicted from the desired final shape of a powder compact by iterative calculations. Experimental data of 316L stainless steel powder showed that the optimally designed container allowed precise forming of the desired powder compact during hot isostatic pressing.