황 도핑 실리콘 옥시카바이드 합성과 고성능 리튬 이온 배터리 음극소재로의 응용

학위논문 (석사) -- 서울대학교 대학원 : 융합과학기술대학원 융합과학부(나노융합전공), 2021. 2. 박원철.Silicon oxycarbide (SiOC) attracts soaring attention as an anode material for lithium ion battery due to its outstanding cycle life and unique structure of Si-O-C hybrid bonding. However, poor electrical conductivity is the major drawback of SiOC-based electrodes. In this work, I synthesized sulfur-doped silicon oxycarbide (S-SiOC) via facile pyrolysis from a mixture of commercial silicone oil with 1-dodecanethiol. The as-prepared S-doped SiOC was applied as an anode material for lithium ion battery for the first time. The S doping can improve the electrical conductivity of SiOC by providing extra e- pathway and accommodate more Li+ by creating additional reaction sites. The enhanced electrochemical kinetics of Li+ was verified by Randles-Sevcik equation. For the initial cycle, the electrodes demonstrated a high reversible capacity of 700 mAh g-1 at 0.1 A g-1 with initial coulombic efficiency of 66.8%. Additionally, the electrodes exhibit a large specific capacity of 378 mAh g-1 with a high capacity retention of 84.8%, even after 1000 cycles at 1 A g-1. Therefore, this sulfur-doped silicon oxycarbide with excellent electrochemical performances has promising potential as an anode material in lihium ion battery.실리콘 옥시카바이드는 우수한 사이클 수명과 Si, O, C 원자들의 결합들로 이루어진 독특한 구조로 인해 리튬이온전지의 새로운 음극물질로 주목받고 있다. 그러나 실리콘 옥시카바이드 기반의 음극물질은 낮은 전기전도성이라는 단점을 가지고 있다. 본 연구에서는 상용화된 실리콘 오일과 도데칸사이올을 섞어 간단한 열분해 과정을 통해 황이 도핑된 실리콘옥시카바이드를 합성하고 이를 리튬이온전지의 음극 물질로 활용하는 연구를 진행하였다. 황 도핑을 통해 전기전도성을 향상시키고 추가적인 반응 지역을 만들어 더 많은 리튬이온을 저장시킬 수 있었고, Randles-Sevcik 방정식을 통해 향상된 전기화학적 성능을 확인하였다. 결과적으로, 합성된 황 도핑된 실리콘옥시카바이드는 초기 사이클에서 높은 가역용량 (0.1 A g-1에서 700 mAh g-1)과 좋은 사이클 수명 특성 (1 A g-1에서 1000회 충·방전 후, 378 mAh g-1의 가역용량)을 보인다.1. Introduction 10 1.1. Lithium ion battteries 10 1.2. Silicon oxycarbide 11 1.3. Sulfur doping 13 1.4. Objective 14 2. Experimental 15 2.1. Preparation of SiOC 15 2.2. Preparation of S-SiOC 15 2.3. Material characterizations 15 2.4. Electrochemical characterizations 16 3. Result and Discussion 18 3.1. Material analysis 18 3.2. Electrochemical analysis 32 4. Conclusion 44 References 45 국문 초록 (Abstract in Korean) 56Maste

A Case of Successful Immunotherapy in the Oral Allergy Syndrome

Oral allergy syndrome (OAS), defined as an immediate swelling and itching sensation of mouth and throat after ingestion of fresh fruit, is commonly found in the patients with pollinosis. The high incidence of OAS is due to cross- reactivity between pollen and fruit allergens. Many recent studies show that immunotherapy (IT) with extracts of pollen can relieve symptoms of OAS. A 33 year-old female visited our clinic with the complaint of oral mucosal swelling and itching sensation after ingestion of fresh fruit (apple, pear, kiwi, banana, melon and fresh chest nut) for 13 years, with simultaneous allergic rhinitis worsening in spring and fall. In the skin prick test, she had strongly positive reaction to alder (mean wheal size 23.5 mm), oak (10.5 mm), walnut (12 mm), Japanese cedar (17 mm), bermuda (14 mm), sagebrush (8.5 mm), and Dermatophagoides farinae (17 mm). For pollens, specific IgE to alder (58.6 kU/L), oak (35.2 kU/L), walnut (9.51 kU/L), Japanese cedar (3.99 kU/L), bermuda (6.96 kU/L) and sagebrush (9.88 kU/L) have been proved by CAP-FEIA(Fluorescent Enzyme Immunoassay) (Pharmacia, Uppsala, Sweden). For fruit allergens, specific IgE to apple (13.0 kU/L), peanut (4.1 kU/L), carrot (5.9 kU/L), and pear (1.7 kU/L) have been detected but not to peach and banana. The IT with extracts of alder, oak, walnut, Japanese cedar, bermuda, sagebrush and D. farinae was started. Her allergic symptoms to pollens in spring and autumn were improved after IT. Furthermore the allergic symptoms to fruits began to disappear after initiation of IT. After 9 months of IT, she can enjoy all the fruits that provoking OAS without allergic symptoms.ope

Non-invasive assessment of liver fibrosis by measuring the liver stiffness and biochemical markers in chronic hepatitis B patients

Background: Transient elastography (FibroScan(R)) is a rapid and non-invasive method to measure liver stiffness and this allow the assessment of liver fibrosis. The aim of this study was to assess the diagnostic accuracy of measuring the liver stiffness in addition to measuring the other biochemical markers such as the aspartate transaminase to platelet ratio index [APRI] and the AST/ALT ratio. Methods: We enrolled 228 HBsAg positive patients whose liver stiffness was measured by FibroScan(R) between March 2005 and September 2005. Liver biopsy examinations were performed in 34 patients. The fibrosis (F) was staged on a 0-4 scale according to the Ludwig classification. Results: According to the clinical diagnosis, the median values of liver stiffness were 7.0±2.7 kPa for inactive carriers (n=29), 8.3±5.3 kPa for chronic hepatitis patients (n=106), 15.9±8.3 kPa for compensated cirrhosis patients (n=63), 31.8±20.3 kPa for decompensated cirrhosis patients (n=26), and 45.1±34.5 kPa for HCC patients (n=4). The degree of liver stiffness was significantly different between the different disease groups (p<0.001). Liver stiffness was well correlated with the fibrosis stages (r=0.726; p< 0.001). The AUROC of FibroScan(R), the APRI and the AST/ALT ratio values were of the same order; 0.72, 0.61 and 0.58, respectively, for F≥2; 0.92, 0.73, and 0.56, respectively, for F≥3; and 0.97, 0.79, and 0.55, respectively, for F=4. FibroScan(R) offered the best diagnostic performance both for significant fibrosis (F≥2) and severe fibrosis-cirrhosis (F3-F4). Conclusions: FibroScan(R) is a reliable, rapid non-invasive method to diagnose the severity of chronic liver disease and to predict fibrosis in patients with chronic hepatitis B, in addition to using the APRI and AST/ALT ratio.ope

The risk factors associated with Low Back Pain in mothers of children with Cerebral Palsy

인간공학치료학전공/석사[한글]본 연구는 뇌성마비 아동을 양육하는 어머니들을 대상으로 어머니의 요통에 영향을 미치는 관련요인을 도출하고자 실시되었다.연구대상자는 강원도에 소재한 대학병원 1곳, 종합병원 1곳, 복지관 2곳 및 경기도에 소재한 종합병원 1곳에서 치료를 받고 있는 뇌성마비 아동의 어머니들을 대상으로 하였다. 자료수집기간은 2007년 2월 1일부터 3월 12일 사이에 이루어 졌으며, 각 기관에 허락을 받은 후 직접 방문하여 설문지를 배포하였다. 총 155부를 배포하여 124부(80.0%)를 회수하였으며 응답내용이 부정확하거나 대상자로 적절하지 않은 30부를 제외한 94(60.6%)부를 분석하였다. 어머니의 요통수준과 기능장애는 숫자평정척도(Numeric Rating Scale)와 Oswestry Disability Index로 측정하였으며, 일상생활에서 뇌성마비 아동의 수행능력을 알아보기 위하여 WeeFIM(Functional Independence Measure for children)을 측정하였다. 수집된 자료는 SPSS WIN 12.0을 사용하여 통계처리 하였다.본 연구의 결과는 다음과 같다.첫째. 어머니의 요통으로 인한 기능장애는 경증장애 41명, 중증도장애 47명, 중증장애 6명으로서 기능장애가 심할수록 요통수준역시 증가하였고 통계적으로도 유의한 차이를 보였다. 어머니의 인구학적인 특성 중 어머니 요통에 영향을 미치는 요인은 주택유형에서 연립주택(빌라)에서의 생활이었으며, 단독주택이나 아파트 보다 요통수준이 높았고 통계적으로도 유의한 차이를 보였다.둘째. 뇌성마비 아동의 인구학적인 특성 중 어머니의 요통에 영향을 미치는 요인은 뇌성마비 아동의 체중인 것으로 나타났다. 아동의 체중이 24kg이상일 때 어머니 요통수준이 가장 높았으며 통계적으로도 유의한 차이를 보였다.셋째 뇌성마비 아동의 일상생활 수행능력에서 이동(transfer)과 보행(locomotion)영역에서 신체적 도움이 필요한 그룹이 신체적 도움이 필요없는 그룹보다 요통수준이 높았으며 통계적으로도 유의한 차이를 보였다.최종적으로 어머니의 요통을 유발하는 요인은 주택유형에서 연립주택(빌라)에서 생활할 경우, 뇌성마비 아동의 보행(locomotion)영역에서 어머니의 도움이 필요한 경우, 뇌성마비 아동의 체중이 많이 나가는 경우 어머니의 요통을 유발하는 요인임을 알 수 있었다.이러한 본 연구가 갖는 의의는 뇌성마비 아동의 어머니를 대상으로 그들이 겪고 있는 요통에 대한 연구가 이루어 졌다는 점과, 이를 통해 뇌성마비 아동 어머니의 요통을 유발하는 관련 요인을 알 수 있었다는 것이다. 이러한 연구 결과를 토대로 뇌성마비 아동을 돌보는 어머니의 요통을 유발하는 관련요인에 대한 적극적인 예방이 이루어져야 할 것이며, 보건의료 전문가의 관심과 조기중재가 필요할 것으로 생각된다.본 연구의 요통 원인에 대한 초점은 연구대상자의 신체적 특성이나 환경적인 요소, 일상생활에서 뇌성마비 아동의 수행능력에 맞춰져있다. 하지만 요통을 유발하는 관련요인으로 사회심리적(socio-pychological)인 요소 역시 중요한 부분으로 작용하고 있으며, 향후 연구에선 이러한 요소를 감안한 연구가 진행되어져야 할 것이다. [영문]This study was conducted to derive the relevant factors influencing the low back pain experienced by mothers who are taking care of their children suffering from cerebral palsy, using a method of conducting surveying on these mothers.The surveys were conducted on mothers of the children who were being treated for cerebral palsy in a university hospital and two welfare centers located in Kangwon-Do, and one hospital complex located in Kyoungki-Do. The period of the survey was from February 1st to March 12th of 2007, and the surveys were conducted with the approvals of the authorities of the institutes, by visiting the mothers in person and handing out questionnaires. Total 155 copies of the questionnaires were distributed to collect 124 copies (80.0%), among which 94 copies (60.6%) were finally selected after 30 copies were left out due to some inaccuracies or inadequacies. The level of the low back pain and the functional deficiency due to the pain were measured by Numeric Rating Scale and Oswestry Disability Index, and to determine the self-sufficiency of the children in the daily activities WeeFIM was measured. The data thus collected were statistically sorted out using SPSS WIN 12.0.The findings derived from the study are as following:First, for functional level deriving from mother's low back pain, 41 were at minimal disability, 47 at moderate disability, and 6 at severe disability. As functional level was severer, low back pain increased, and it showed statically significant differences. Among mother's demographic features, the factor having an impact on mother's low back pain was living in multi-unit villas in terms of housing type. Low back pain was higher in the multi-unit villas than in the detached house type or apartment type, and also demonstrated statistically significant differences.Second, the factor having an impact on mother's low back pain among the children's demographic features was children's weight. Mother's low back pain was highest when children's weight was 24kg or over, and statistically significant differences were demonstrated.Third, concerning children's performance ability in the daily activities, low back pain of the group requiring physical help was higher than the group not requiring physical help in the domains of transfer and locomotion. Statically significant differences were also exhibited in the low back pain of the two groups.In conclusion, as for the characteristics related to the mothers, the housing type were found to be causing the low back pain, and as for the characteristics related to the children, the lack of self-sufficiency in locomotion and over weight values were found to be causing the mother's low back pain.This study revealed important factors influencing the low back pain experienced by the mothers with children suffering from the cerebral palsy. The findings would be useful in the study of the low back pain of such mothers, and in developing programs to prevent such pains. Yet, this study has dealt only with the physical factors, and a further study is desirable for finding out sociological psychology factors as well.restrictio

Impact of Asian Games Official Sponsorship on Brand Equity: Cross-cultural approach of 17th Asian Games Incheon 2014 Official Sponsor Partner

학위논문 (석사)-- 서울대학교 대학원 : 체육교육과, 2015. 8. 임충훈.Abstract Impact of Asian Games Official Sponsorship on Brand Equity: Cross-cultural approach of 17th Asian Games Incheon 2014 Official Sponsor Partner Keun Ho Lee Department of Physical Education Graduate School Seoul National University Recently, number of companies and brands choose sports sponsorship as a marketing communication tool. In order to strengthen companys existing brand or company image, companies are using sport sponsorship for positive positioning of their image. Sports sponsorship is one of the most important marketing communication strategies that has increased its influence power in the market therefore it is essential for companies and brands to involve in the sport sponsorship to increase its competitively strong marketing communication effects. It is learnt from literature reviews that companies and brands need to aggressively review sports sponsorship activities for image strengthening. Sports sponsorship has specialized characters differentiated from ordinary commercials or advertisements and most of companies and brands are involved with sports sponsorships in order to strengthen its brand equity and increase sales revenue. The purpose of this research is to measure the difference of brand equity for 361° brand between the aware group and non aware group in involvement of the brand as an official sponsor of 17th Asian Games Incheon 2014. The research studies about the difference and measures the sport sponsorship effect in various aspects. According to this research, it is evidenced that sport sponsorship does have effects on strengthening the brand equity, especially high in the developing countries where exposure to global sport brands are relatively low.I. Introduction 1 1. Research Rationale 2 2. Research Objective 8 2-1. Purpose of Study 8 2-2. Research Variable 11 2-3. Research Questions 12 3. Research Limitation 13 II. Literature Review 14 1. Sponsorship 14 1-1. Definition of Sponsorship 14 1-2. Sponsorship Objective 20 1-3. Measuring Sponsorship Effectiveness 23 1-4. Sports Sponsorship 27 2. Brand Equity 32 2-1. Definition of Brand Equity 32 2-2. Components of Brand Equity 38 2-3. Measuring Brand Equity 43 2-4. Value of brand equity 46 2-5. Obstacles to Brand Valuation 47 2-6. Valuation Approaches 48 III. Research Methodology 51 1. Research Sample 52 2. Research Tools 54 3. Research Process 56 4. Data collection and Analysis 57 IV. Research Results 58 1. Analysis on brand equity of Asian Games official sponsor partner based on demographic data. 58 2. The brand equity value difference between the aware group and non aware group of Asian Games official sponsor partner 66 3. Brand equity value analysis by different countries. 70 4. Brand equity value analysis by final record on Asian Games. 75 V. Discussion 81 1. Discussion 81 2. Finding 84 VI. Conclusion 85 1. Conclusion 85 2. Limitation and Future Research 90 VII. List of Reference 92Maste

Analysis of survival according to treatment method in the hepatocellular carcinoma(HCC) with curable status

의학과/석사[한글]간세포암종의 다양한 치료법들 중 수술적 절제 혹은 간이식만이 완치 목적의 치료로서 장기 생존이 가능하다고 인정되었으나, 병기가 낮거나 크기가 작고 간기능이 좋은 경우 간동맥 화학색전술 혹은 고주파 열치료, 알코올 주입술, 경피적 홀뮴 주입술과 같은 경피적 국소 치료에서도 장기 생존을 보이는 경우가 흔히 관찰되고 있다. 그러나 이들의 치료 성적을 직접적으로 수술적 절제와 비교한 연구는 거의 없는 실정이다. 본 연구는 간세포암종 환자들에서 수술적 절제와 간동맥 화학색전술 및 경피적 홀뮴 주입술의 장기 생존율을 직접 비교하여 예후를 분석하고자 하였다. 1997년부터 2003년 사이에 TNM 병기가 I 혹은 II인 간세포암종을 진단받은 177명의 환자들을 수술군, 간동맥 화학색전술군, 경피적 홀뮴 주입술군으로 나누어, 동일한 JIS score에서 세 가지 치료법의 무병 생존 기간, 전체 생존율을 구하여 치료 성적을 비교하였다. 완전 관해를 이룬 환자들 중 JIS score 0점인 경우 수술군, 간동맥 화학색전술군, 경피적 홀뮴 주입술군의 무병 생존 평균 추적 관찰 기간은 각각 30.2개월, 23.1개월, 27.5개월이었고 Kaplan Meier curve 상 통계학적 유의성을 보이는 차이는 없었으며(P = 0.4), JIS score 1점인 경우 각각 41.1개월, 22.8개월, 21.5개월이었고 Kaplan Meier curve 상 수술군의 무병 생존율이 다른 두 군에 비해 유의하게 높았다(P < 0.0001). 전체 환자들 중에서 JIS score 0점인 경우 수술군의 1년, 3년, 5년 생존율이 100%, 88.9%, 88.9%이었고, 간동맥 화학색전술군에서는 100%, 77.8%, 55.6%이었으며, 경피적 홀뮴 주입술군에서는 100%, 66.7%, 58.3%이었다. 그러나, Kaplan Meier curve 상 세 군 간에 전체 생존율의 차이는 없었다(P = 0.34). JIS score 1점인 경우 수술군의 1년, 3년, 5년 생존율이 96.4%, 92.9%, 91.1%이었고, 간동맥 화학색전술군에서는 83.7%, 61.2%, 46.9%이었으며, 경피적 홀뮴 주입술군에서는 85.7%, 46.4%, 32.1%로 나와 수술군의 5년 생존율이 다른 두 군에 비해 현저히 높았다. Kaplan Meier curve 상에서도 수술군의 전체 생존율이 다른 두 군에 비해 통계적으로 유의하게 높았다(P < 0.0001). 이상의 결과를 바탕으로 JIS score 0점인 경우, 다시 말해 단일 간세포암종의 크기가 2cm 이하이면서 혈관 침윤이 없으며, 간기능이 Child-Pugh A인 경우 간동맥 화학색전술이나 경피적 홀뮴 주입술이 수술적 절제와 차이 없는 결과를 낼 수 있음을 확인할 수 있었다. 그러나 JIS score 1점인 경우 수술군의 무병 생존율과 전체 생존율이 모두 통계학적으로 의미 있게 가장 높은 것으로 나와, 수술적 치료를 우선적으로 고려해야 함을 확인할 수 있었다.핵심되는 말: 간세포암종, 병기, 생존율, 재발율, 수술, 색전술 [영문]In recent years, many HCC patients with low TNM stage or small tumor size and excellent liver function exhibit long term survival after transcatheter arterial chemoembolization(TACE) or percutaneous injection treatment. However, there are few reports comparing the survival of TACE or percutaneous injection treatment with that of surgical resection. This study tried to measure the long term survival duration of the HCC patients receiving surgical resection, TACE or percutaneous holmium injection therapy(PHIT) and to compare them. Between 1997 and 2003, the newly diagnosed HCC patients with TNM stage I or II were classified into three groups, surgery group, TACE group and PHIT group. The results were analyzed among the patients with the same JIS score. In case of JIS score 0, the mean follow-up time of disease-free survival of the patients achieving complete remission in surgery group, TACE group and PHIT group were 30.2, 23.1 and 27.5 months, respectively. There was no statistical difference between three groups on the Kaplan Meier curve(P = 0.4). In case of JIS score 1, the mean follow-up time of disease-free survival were 41.1, 22.8 and 21.5 months with the same order. The disease-free survival rate of the surgery group was higher than that of TACE group or PHIT group with statistical importance on the Kaplan Meier curve(P < 0.0001). In case of JIS score 0, the mean follow-up time of overall survival of all the patients in surgery group, TACE group and PHIT group were 48.2, 51.3 and 58.7 months, respectively. There was no statistical difference between three groups on the Kaplan Meier curve(P = 0.34). In case of JIS score 1, the mean follow-up time of overall survival were 48.4, 50.8 and 38.7 months with the same order. The overall survival rate of the surgery group was higher than that of TACE group or PHIT group with statistical importance on the Kaplan Meier curve(P < 0.0001). According to these results, in case of JIS score 0, in other words, in the patients with single HCC less than 2 cm without vascular invasion and liver function of Child-Pugh A, TACE or PHIT have long term survival comparable to surgical resection. In case of JIS score 1, the surgery group had the best results, thus surgical resection should be considered at first.Key words: carcinoma, hepatocellular; survival analysisope

고망간 경량철강 소재의 미세조직과 기계적 거동에 대한 연구

학위논문 (박사)-- 서울대학교 대학원 : 재료공학부, 2017. 2. 한흥남.In recent years, decreasing greenhouse gas emissions and improving fuel efficiency have been growing issues in the automotive and defense sectors. To achieve this goal, the development of advanced high-strength steels (AHSSs), such as dual-phase (DP) and transformation-induced plasticity (TRIP) steels has been long pursued for automotive applications. However, as the strength of steel increases, it gets more difficult to reduce the thickness due to the deterioration of structural stiffness, causing poor crashworthiness. In that sense, alternative concept of designing AHSS has been proposed mainly by lowering the density of steel while maintaining its high specific strength. Based on this concept, low-density steels have been developed containing light substitutional elements such as aluminum and/or silicon, which provide a density reduction effect by means of substitution and lattice expansion. Low-density steels can be categorized into ferrite-based and austenite-based (including multiphase-based) alloys, depending on their constituent phases. Among them, the austenite-based low-density steels show superior mechanical properties and weight reduction rates. After these steels are aged at adequate temperature and time periods, many kinds of micro/nano-scale precipitates or intermetallic compounds are formed, such as κ-carbide, ordered bcc phases, and β-Mn. These precipitates have a profound effect on the mechanical properties of the low-density steels. However, there is still a paucity of characterization research on the β-Mn phase in terms of the formation behavior, microstructural evolution, and its effects on mechanical and fracture properties of austenite-based high-Mn low-density steels. Therefore, this research investigates the microstructure and mechanical behavior of high-Mn low-density steels after processing treatments, by using complementary microstructural and mechanical characterization. Firstly, the microstructure and the intrinsic mechanical behavior of an austenite-based low-density steel containing 11.4 wt.% Al under aging heat treatment were investigated with respect to β-Mn precipitation. Lattice expansion of austenite and κ-carbide after β-Mn precipitation was observed by X-ray diffractometry (XRD) peak shift and electron probe micro-analyzer (EPMA). The Vickers hardness increased dramatically after an aging time of 1,000 minutes. The singular aging behavior also proceeded from precipitation of the β-Mn phase. The intrinsic mechanical property of austenite phase, which was obtained by nanoindentation, was correlated with the increase and inhomogeneous distribution of carbon in the austenite matrix. Secondly, the β-Mn formation behavior of high-Mn low-density steels was investigated in terms of the morphological characteristics and alloying element distribution after aging treatments. A dramatic difference in the formation kinetics and morphology of β-Mn was observed depending on the addition of Al, which may increase the driving force for β-Mn formation. In addition, the effects of the aging process on the fracture behavior were examined in uniaxial tensile tests combined with microstructural observations. A severe loss of ductility resulted from the β-Mn formation and ordering of ferrite into the D03 phase, which was transformed before the β-Mn formation process. Thirdly, the aging behavior and orientation relationships among constitutional phases and precipitates in Fe–31.4Mn–11.4Al–0.89C low-density steel were studied. The misorientation-angle distribution, Rodrigues–Frank vector space, and orientation relationship stereogram (OR stereogram) are used to elucidate the orientation relationships across γ-matrix/β-Mn and β-Mn/α-precipitate interphase boundaries. The orientation relationships obtained from the OR stereograms were clarified by checking the deviation angle distributions of interface segments from the ideal orientation relationships, as well as the TEM diffraction patterns at the interface boundaries. In addition, from both orientation relationships for γ-matrix/β-Mn and β-Mn/α-precipitate interfaces, the interface character between γ-matrix and α-precipitate is examined and compared to conventional fcc/bcc orientation relationships. Lastly, the deformation behavior of duplex low-density steel was analyzed by correlation between macro-scale uniaxial tension and nano-scale indentation. A dramatic difference in the tensile behavior was observed between two specimens obtained under specific heat-treatment conditions, despite the same chemical composition and similar microstructures. In order to understand this difference, the intrinsic mechanical properties of each phase were analyzed based on nano-indentation results considering Hall-Petch relationship. In addition, the mechanical stability of retained austenite was investigated by in-situ electron backscattered diffraction. From this study, the β-Mn phase in austenite-based high-Mn low-density steels was described well, in terms of the formation behavior, microstructural evolution, orientation relationships, and its effects on mechanical and fracture properties. In addition, the dramatic differences of the macroscopic tensile behavior regarding the yield strength, yield point phenomenon, and strain hardening in the two duplex low-density steels was successfully explained.Chapter 1 Introduction 1 1.1 Low-density steels 1 1.2 Classification of the low-density steels 4 1.3 Motivations of the thesis 6 1.4 References 9 Chapter 2 Effect of aging treatment on microstructure and intrinsic mechanical behavior of Fe-31.4Mn-11.4Al-0.89C low-density steel 11 2.1 Introduction 11 2.2 Experimental procedure 14 2.3 Microstructural analysis 17 2.4 Intrinsic mechanical properties: Nanoindentation analysis 29 2.5 Conclusion: Effect of aging treatment on microstructure and intrinsic mechanical behavior 35 2.6 References 36 Chapter 3 β-Mn formation and aging effect on the fracture behavior of high-Mn low-density steels 39 3.1 Introduction 39 3.2 Experimental procedure 41 3.3 Influence of alloying elements on the formation behavior of the κ-carbide and β-Mn 44 3.4 Tensile and fracture behavior 50 3.5 Conclusion: β-Mn formation and aging effect on the fracture behavior 57 3.6 References 59 Chapter 4 Investigation of the aging behavior and orientation relationships in Fe-31.4Mn-11.4Al-0.89C low-density steel 61 4.1 Introduction 61 4.2 Materials and methods 65 4.2.1 Microstructure observation and interface characterization 65 4.2.2 Calculation of the deviation angle from the ideal orientation relationship 68 4.3 Microstructural evolution and aging behavior 71 4.4 Orientation relationship between γ-matrix and β-Mn 81 4.5 Orientation relationship between β-Mn and α-precipitate 90 4.6 Interface character distribution of γ-matrix/α-precipitate phase boundaries 98 4.7 Conclusion: Investigation of the aging behavior and orientation relationships 105 4.8 References 107 Chapter 5 Dual-scale correlation of mechanical behavior in duplex low-density steel 110 5.1 Introduction 110 5.2 Experimental procedure 112 5.3 Macroscopic tensile behavior and initial microstructure 114 5.4 Correlation between macro-scale uniaxial tension and nano-scale indentation 119 5.5 Deformation-induced martensitic transformation 126 5.6 Conclusion: Dual-scale correlation of mechanical behavior 129 5.7 References 130 Chapter 6 Total conclusions 133Docto