Evaluation of mechanical properties of a medium carbon Cr-Mo alloy steel subjected to tempering heat treatment and its effect on hydrogen embrittlement

Sourav Kr. Saha,Byungrok Moon,Jimin Nam,Chang-Hoon Lee,Jun-Ho Chung,Namhyun Kang 대한용접·접합학회 2022 대한용접학회 특별강연 및 학술발표대회 개요집 Vol.2022 No.5

Hydrogen embrittlement of multi-pass weld metal with respect to the strength level and heat input variation for DH36 and S500 steels

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.

Enhancement of hydrogen embrittlement resistance by raising tempering temperature for medium-carbon high-strength steel

Sourav Kr. Saha,Byungrok Moon,Jimin Nam,Donghyeon Choi,Changhoon Lee,Junho Chung,Namhyun Kang 대한용접·접합학회 2023 대한용접학회 특별강연 및 학술발표대회 개요집 Vol.2023 No.10

Self-organized honeycomb-like nanoporous oxide layer for corrosion protection of type 304 stainless steel in an artificial seawater medium

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>

Relative Apoptosis-inducing Potential of Homeopa-thic Condurango 6C and 30C in H460 Lung Cancer Cells In vitro

Sourav Sikdar,Rahman Khuda-Bukhsh,Santu Kumar Saha 대한약침학회 2014 Journal of pharmacopuncture Vol.17 No.1

Objectives: In homeopathy, it is claimed that more homeopathically-diluted potencies render more protective/curative effects against any disease condition. Potentized forms of Condurango are used successfully to treat digestive problems, as well as esophageal and stomach cancers. However, the comparative efficacies of Condurango 6C and 30C, one diluted below and one above Avogadro’s limit (lacking original drug molecule), respectively, have not been critically analyzed for their cell-killing (apoptosis) efficacy against lung cancer cells in vitro, and signalling cascades have not been studied. Hence, the present study was undertaken. Methods: 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenylte-trazolium bromide (MTT) assays were conducted on H460-non-small-cell lung cancer (NSCLC) cells by using a succussed ethyl alcohol vehicle (placebo) as a control. Studies on cellular morphology, cell cycle regulation, generation of reactive oxygen species (ROS), changes in mitochondrial membrane potential (MMP), and DNA-damage were made, and expressions of related signaling markers were studied. The observations were done in a “blinded” manner. Results: Both Condurango 6C and 30C induced apoptosis via cell cycle arrest at subG0/G1 and altered expressions of certain apoptotic markers significantly in H460 cells. The drugs induced oxidative stress through ROS elevation and MMP depolarization at 18-24 hours. These events presumably activated a caspase-3-mediated signalling cascade, as evidenced by reverse transcriptase- polymerase chain reaction (RT-PCR), western blot and immunofluorescence studies at a late phase (48 hours) in which cells were pushed towards apoptosis. Conclusion: Condurango 30C had greater apoptotic effect than Condurango 6C as claimed in the homeopathic doctrine.

Post-cancer Treatment with Condurango 30C Shows Amelioration of Benzo[a]pyrene-induced Lung Cancer in Rats Through the Molecular Pathway of Caspa- se-3-mediated Apoptosis Induction -Anti-lung cancer potential of Condurango 30C in rats-

Sourav Sikdar,Anisur Rahman Khuda-Bukhsh,Avinaba Mukherjee,Kausik Bishayee,Avijit Paul,Santu Kumar Saha,Samrat Ghosh 대한약침학회 2013 Journal of pharmacopuncture Vol.16 No.3

Objectives: The present investigation aimed at examining if post-cancer treatment with a potentized homeopathic drug, Condurango 30C, which is generally used to treat oesophageal cancer, could also show an ameliorating effect through apoptosis induction on lung cancer induced by benzo[a]pyrene (BaP) in white rats (Rattus norvegicus). Methods: Lung cancer was induced after four months by chronic feeding of BaP to rats through gavage at a dose of 50 mg/kg body weight for one month. After four months, the lung-cancer-bearing rats were treated with Condurango 30C for the next one (5th), two (5th -6th) and three (5th-7th) months, respectively, and were sacrificed at the corresponding time- points. The ameliorating effect, if any, after Condurango 30C treatment for the various periods was evaluated by using protocols such as histology, scanning electron microscopy (SEM), annexinV-FITC/PI assay, flow cytometry of the apoptosis marker, DNA fragmentation, reverse transcriptase-polymerase chain reaction (RT-PCR), immunohistochemistry, and western blot analyses of lung tissue samples. Results: Striking recovery of lung tissue to a near normal status was noticed after post-cancerous drug treatment, as evidenced by SEM and histology, especially after one and two months of drug treatment. Data from the annexinV-FITC/PI and DNA fragmentation assays revealed that Condurango 30C could induce apoptosis in cancer cells after post-cancer treatment. A critical analysis of signalling cascade, evidenced through a RT-PCR study, demonstrated up-regulation and down-regulation of different pro- and anti-apoptotic genes, respectively, related to a caspase-3-mediated apoptotic pathway, which was especially discernible after one-month and two- month drug treatments. Correspondingly, Western blot and immunohistochemistry studies confirmed the ameliorative potential of Condurango 30C by its ability to down-regulate the elevated epidermal growth factor receptor (EGFR) expression,a hallmark of lung cancer. Conclusion: The overall result validated a positive effect of Condurango 30C in ameliorating lung cancer through caspase-3-mediated apoptosis induction and EGFR down-regulation.

해양용 TMCP강에서 C와 Mo의 첨가가 수소 취화특성에 미치는 영향

남지민,Sourav Saha,문병록,이창훈,정준호,강남현 대한용접·접합학회 2021 대한용접학회 특별강연 및 학술발표대회 개요집 Vol.2021 No.11

최근 기존에 사용하던 육상과 인근 해양 지역의 에너지 자원이 고갈됨에 따라 극지와 심해저에서의 에너지 채굴 산업이 주목받고 있으며, 해양플랜트 설비 관련 강재 역시 수요가 급증하고 있다. 해양구조물용 강재는 해수에 노출되는 환경에서 사용되기에 수소 취성에 대한 고려가 요구되어 진다. 수소 취성은 수소에 의해 강의 인장강도, 연신율, 단면 감소율 등의 기계적 성질이 저하되는 현상으로, 외부환경, 기계적 또는 미세조직적 특성, 응력이 수소 취성에 영향을 미치는 주요한 인자들이다. 최근 C나 Mo의 첨가를 통해 강의 고강도화를 달성하고자 하는 시도가 많아지는 가운데, 이러한 고강도화를 위한 합금 성분의 변화는 수소 취성 민감도를 높이는 미세조직들이 나타나게 된다. 따라서 해양구조물용 강재의 강도 향상을 위해 C와 Mo를 첨가함에 따라 수소 취성 민감도 차이를 평가하고 수소 확산 및 trap에 영향을 미치는 미세조직학적 인자를 파악하는 것이 필요하다. 본 연구에 사용된 강재는 C와 Mo의 첨가량을 달리하여 강도를 향상시킨 TMCP강으로, In-situ H charging SSRT시험을 통해 수소 취화 특성을 평가하였다. C와 Mo의 첨가에 따른 수소 취화 특성 차이를 미세조직 관찰과 Permeation test를 실시함으로써 수소 확산 및 trap에 영향을 미치는 미세조직학적 인자를 통해 고찰하였다.

420 MPa급 해양 플랜트용 H-형강의 위치별 수소취성 특성 연구

문병록,Sourav Saha,남지민,정준호,강남현 대한용접·접합학회 2021 대한용접학회 특별강연 및 학술발표대회 개요집 Vol.2021 No.5

해양 플랜트용 H 형강은 일반적으로 건설 프로젝트당 약 1만톤 이상의 강재가 사용된다. 그리고 향후 해양 플랜트 대부분은 연안을 벗어나 심해저 또는 극지와 같은 곳으로 건설이 이루어질 것이기 때문에, 우수한 저온 충격 특성을 갖는 H 형강의 개발은 전도유망하다. 이를 위한 저온 충격특성 향상은 합금설계, 미세조직 제어 및 압연/냉각 등 다양한 기술개발에 의해 이루어질 수 있다. 이 H 형강은 TMCP 공정을 통해서 생산되는데, 압연 조건과 냉각속도에 따라 위치별 미세조직적 특징에 차이가 발생하게 된다. 해양 플랜트에 사용된 H 형강은 크고 다양한 하중에 많은 영향을 받고, 해수라는 부식환경에 노출될 수밖에 없다. 따라서, 이러한 환경에서는 수소 취성에 의한 응력 부식이 가속화되는 등 소재 사용 중 급작스러운 파괴가 나타나는 지연파괴가 발생할 수 있다. 따라서, 본 연구에서는 이러한 지연파괴를 억제하고자 수소취화 특성을 H 형강 위치별로 평가하고 미세조직적으로 분석하여 보다 고강도, 고내수소취성 강재 개발에 영향을 끼치는 인자를 도출하고자 한다. 이를 위해, 0.1M NaOH 용액에서 시편을 낮은 속도로 인장하는 in-situ SSRT 시험을 실시하여 위치별 수소취성을 평가하였다. 또한, 전기화학적 실험방법인 permeation을 통해 위치별 수소확산 특성과 비확산성 수소량을 비교하고자 하였다. 더 나아가 Ag decoration 기법을 통해 시편 내 수소의 주된 확산 경로와 수소가 머무르는 위치를 미세조직적으로 직접 관찰하고자 하였다. 이러한 일련의 실험을 통해 미세조직이 수소의 확산과 어떠한 관계에 있는지, 최종적으론 H 형강의 수소취성에 미세조직이 어떠한 영향을 끼치는지 규명하고자 한다.

해양 플랜트용 H-형강과 고강도강재의 수소취성 연구

문병록,Sourav Saha,남지민,이창훈,정준호,강남현 대한용접·접합학회 2021 대한용접학회 특별강연 및 학술발표대회 개요집 Vol.2021 No.11

해양 플랜트를 구성하는 구조재료 중 H-형강은 가장 많이 사용되며, 크고 다양한 하중에 노출될 뿐만 아니라, 해수 분위기에 노출되기 때문에 부식 가능성이 항상 존재한다. 더불어 H-형강을 서로 연결하기 위해 보다 고강도의 기계적 물성을 가진 볼트도 함께 사용된다. 마찬가지로, 볼트도 고하중과 부식 분위기에 노출된다. 이와 같이 강재가 고하중과 부식분위기에 노출된다면 수소 취성이 발생할 수 있고, 이런 현상에 기인하여 응력 부식이 발생 또는 가속화된다고 알려져 있다. 따라서 수소취성에 대한 연구와 내수소취성 향상은 꼭 필요하다. 본 연구에서는 우선, Mo 합금원소가 H-형강의 수소취성에 미치는 영향에 대해 연구하였다. 항복강도 420 MPa급 TMCP강의 Mo 조성에 따른 미세조직을 분석하였다. 이후, 수소취성 평가를 위해 인장시험 및 전기화학적으로 수소를 주입하면서 기계적 물성을 평가하는 in-situ SSRT 시험의 결과를 서로 비교분석 하였다. 더불어, 전기화학적으로 수소의 확산 및 재료내 고용 정도를 평가하는 permeation 실험을 도입하여 Mo에 따른 차이를 분석하였고 이를 통해 수소취성 특성을 설명하고자 하였다. 또한, 어떠한 미세조직이 수소 취성에 좀더 민감한지 살펴보기 위해 미세조직내 수소의 위치를 직간접적으로 관찰하는 silver printing 기법을 통해 수소 취성 변화를 해석하였다. 마지막으로, 고강도 볼트용 중탄소강의 tempering 온도 및 Ni 합금조성에 따른 수소취성 변화를 관찰하였다. 560 ℃에서부터 680 ℃ 온도까지의 변화와 Ni 합금조성에 따른 인장 및 in-situ SSRT 시험결과를 각각 평가하였고, 마찬가지로 수소확산 및 고용도 평가를 위해 permeation을 실시하였다. 추가로, tempering 온도와 Ni 합금조성이 미세조직과 수소취성에 어떠한 영향을 끼치는지 분석하기 위해 silver printing을 실시하였다.

Relative Apoptosis-inducing Potential of Homeopathic Condurango 6C and 30C in H460 Lung Cancer Cells In vitro -Apoptosis-induction by homeopathic Condurango in H460 cells-

Sikdar, Sourav,Saha, Santu Kumar,Khuda-Bukhsh, Anisur Rahman KOREAN PHARMACOPUNCTURE INSTITUTE 2014 Journal of pharmacopuncture Vol.17 No.1

Objectives: In homeopathy, it is claimed that more homeopathically-diluted potencies render more protective/curative effects against any disease condition. Potentized forms of Condurango are used successfully to treat digestive problems, as well as esophageal and stomach cancers. However, the comparative efficacies of Condurango 6C and 30C, one diluted below and one above Avogadro's limit (lacking original drug molecule), respectively, have not been critically analyzed for their cell-killing (apoptosis) efficacy against lung cancer cells in vitro, and signalling cascades have not been studied. Hence, the present study was undertaken. Methods: 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assays were conducted on H460-non-small-cell lung cancer (NSCLC) cells by using a succussed ethyl alcohol vehicle (placebo) as a control. Studies on cellular morphology, cell cycle regulation, generation of reactive oxygen species (ROS), changes in mitochondrial membrane potential (MMP), and DNA-damage were made, and expressions of related signaling markers were studied. The observations were done in a "blinded" manner. Results: Both Condurango 6C and 30C induced apoptosis via cell cycle arrest at subG0/G1 and altered expressions of certain apoptotic markers significantly in H460 cells. The drugs induced oxidative stress through ROS elevation and MMP depolarization at 18-24 hours. These events presumably activated a caspase-3-mediated signalling cascade, as evidenced by reverse transcriptase-polymerase chain reaction (RT-PCR), western blot and immunofluorescence studies at a late phase (48 hours) in which cells were pushed towards apoptosis. Conclusion: Condurango 30C had greater apoptotic effect than Condurango 6C as claimed in the homeopathic doctrine.