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Saha, Sourav Kr.,Park, Yang Jeong,Kim, Jung Woo,Cho, Sung Oh Elsevier 2019 Journal of molecular liquids Vol.296 No.-
<P><B>Abstract</B></P> <P>A new passivation technology for growing a self-organized nanoporous oxide layer with a honeycomb morphology on Type 304 stainless steel is proposed. FESEM, cross-sectional EDX and XRD are employed to evaluate the morphology, composition and crystal structure of the developed anodic film. Cross-sectional EDX analysis reveals that the nanoporous oxide layer contains a significant amount of fluoride species, which becomes negligible after successive annealing in air at 773 K for 2 h. XRD indicates that the amorphous nanoporous oxide layer is converted to a crystalline magnetite phase (Fe<SUB>3</SUB>O<SUB>4</SUB>) after annealing. Electrochemical analysis such as potentiodynamic polarization and electrochemical impedance spectroscopy reveals stainless steel with a thermally treated nanoporous oxide layer has improved corrosion resistance in an artificial seawater medium. FESEM analyses are employed to evaluate the stability and microscopic changes in the morphologies of the nanoporous oxide layer after prolonged immersion in the artificial seawater medium. The key factors and corrosion inhibition mechanism by the nanoporous oxide layer are also discussed.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Self-organized nanoporous oxide layer has been developed by one step anodization. </LI> <LI> XRD reveals crystalline magnetite phase (Fe<SUB>3</SUB>O<SUB>4</SUB>) dominant after successive annealing. </LI> <LI> Stable and compact thermal oxide has formed beneath the nanoporous oxide layer. </LI> <LI> Thermally treated nanoporous oxide layer reduces corrosion rate of stainless steel. </LI> <LI> Oxide layer hindered the penetration of corrosive ions towards metal surface atoms. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
Sourav Kr. Saha,Hyoungjin An(안형진),Byungrok Moon(문병록),Jaeseok Yoo(유재석),Jong Min Park(박종민),Kwang Hee Yun(윤광희),Namhyun Kang(강남현) 대한용접·접합학회 2021 대한용접학회 특별강연 및 학술발표대회 개요집 Vol.2021 No.5
The study is devoted towards the investigation of a hydrogen-induced cold cracks (HICC) in welded joints of structural steels. HICC is a well-known phenomenon in structural metals that limit their uses in various valuable applications such as hydrogen transport, marine application, ship building etc. Normally, hydrogen in the weld metal produces hydrogen embrittlement (HE), therefore suppressing the cold crack and HE should be considered. In the present study, multi-pass butt welds were fabricated with low and high heat input conditions (10 kJ/cm and 35 kJ/cm) using various welding fillers having various strength levels as of American Welding Society standard and two base metals (DH36 and S500). HE effects on various specimens were evaluated using the in-situ slow strain rate test (SSRT) and hydrogen permeation test. The HE sensitivity index (HE index) calculated using the SSRT suggests that HE index increased with the strength of welding fillers in low heat input condition. However, reverse phenomenon occurred in high heat input condition. Hydrogen diffusion coefficient (Deff) and reversible hydrogen trap concentration (Crev) calculated using permeation test reflects that Crev increased with the strength level of welding filler. On the other hand, welding specimen fabricated in high heat input condition showed a lower Crev and higher Deff in comparison to the low heat input specimen and thereby decreasing the HE. Microstructure analysis suggests that in low heat input condition, low transformation bainite phase was dominated and vulnerable for HE with increasing strength level of welding filler. On the other hand, high heat input condition produced larger amount of acicular ferrite with increasing strength level and inhibited HE.
다층 FCA 용접금속의 강도 및 입열량에 따른 저온균열 민감도와 수소 트랩 특성
유재석,안형진,이정훈,박종민,윤광희,Sourav Kr. Saha,강남현 대한용접·접합학회 2021 대한용접학회 특별강연 및 학술발표대회 개요집 Vol.2021 No.11
저온균열은 탄소강 구조물 제작 시 가장 주의해야 될 용접 균열로 조선/해양 구조물 제작 시에는 맞대기 이음부 다층 용접부의 횡균열과 초고강도강 필렛 이음부의 종균열 및 횡균열 형태로 주로 발생되고 있다. 저온균열 민감도 평가 방법 중 대표적인 방법은 ISO 17642-2와 JIS Z 3158의 y-groove test이며 이 시험법을 활용한 많은 연구가 수행되었지만, 다층 용접부 횡균열을 평가하기에는 적합하지 않다는 보고들이 다수 존재하며, 저입열 조건에서 균열 민감도가 더 높은 일반적인 y-groove test의 평가 경향과는 달리 다층 용접부 횡균열은 고입열 조건에서 더 민감도가 높다는 보고도 있다. 이에 본 연구에서는 다층 FCA 용접금속의 강도 및 입열량별 저온균열 민감성을 평가하였다. 적용 가능한 가장 낮은 입열량과 높은 입열량으로 용접금속을 제작 해 시편에 수소가 포화될 수 있도록 전기화학적으로 수소를 주입 후 in-situ SSRT(Slow Strain Rate Test)를 수행하여 수소취성 저항성을 평가하고, 그 평가 결과가 실 용접부의 저온균열 발생 경향과 일치하는지 확인하기 위해 window type restrained weld cracking test을 진행하여 그 결과를 비교 하였다. 또한 permeation test를 수행하여 수소 트랩 특성을 확인하였다. 평가 결과 용접금속을 형성하는 미세조직에 따라 횡균열 민감도가 상이하였는데, in-situ SSRT와 window type restrained weld cracking test 모두 AWS spec E71T-1C FCW를 적용한 용접금속은 고입열 조건에서 균열 민감도가 높았고, E91T1-Ni2C FCW를 적용한 용접금속은 저입열 조건에서 균열 민감도가 높았다. E81T1-K2C FCW를 적용한 용접금속은 저입열, 고입열 조건에서 모두 횡균열 민감도가 낮았다. 평가 결과와 AWS D1.1 및 EN1011-2의 추천 예열온도를 비교하여 고찰하였다.