극저온용 고망간 합금에서 합금원소, 온도 및 변형속도가 미세구조와 저온변형거동에 미치는 영향

학위논문(박사) - 한국과학기술원 : 재료공학과, 1991.2, [ vi, 148 p. ]Low temperature deformation behaviors of five cryogenic high-Mn alloys CAM-1 (Fe-30Mn-5Al-0.3C), CAM-2(Fe-25Mn-5Al-5Ni-0.3C), Cl(Fe-30Mn-1.2Al-0.1C), C3(Fe-30Mn-1.2Al-0.3C), and Fe-27Mn binary alloy [wt.\%] have been investigated. Austenitic high-Mn alloys(CAM-1, CAM-2, Cl, and C3) show high strength and excellent ductility at low temperatures. Especially, CAM-1, CAM-2, and C1 alloys exhibit inverse elongation behaviors with decreasing temperature from room temperature to 77 K, which was attributed to gradual formation of strain-induced deformation twinning during tensile testing. The amount of deformation twins formed during plastic deformation was not the major factor for maximum elongation, but the optimum work hardening rate by the gradual formation of deformation twins played an important role. Alloy C3 shows a peak in elongation at the temperature between 233 K and 77K due to the optimum formation rate of deformation twinning (TRIP In the wide sense). Fe-27Mn binary alloy possessing the lower yield strength, compared to other austenitic high-Mn alloys, shows a high rate of work hardening in the plastic deformation region resulting in the high ultimate tensile strength. This Fe-27Mn alloy also exhibits a peak in elongation between RT and 77K. The peak elongation for the Fe-27Mn alloy was due to the rapid work hardening by the formation of $hcp \epsilon$ martensite. The volume fraction of $hcp \epsilon$ martensite formed in the Fe-27Mn alloy after tensile testing at 77 K was 86\%. Total strain-controlled low cycle fatigue testing of CAM-2 alloy showed that the fatigue resistance at 77 K was superior to that at room temperature in the entire fatigue life range tested. The reason exhibiting the longer fatigue life at 77 K than that at 298 K for the CAM-2 alloy was the significant increase in the fatigue ductility coefficient with decreasing temperature; $\epsilon_f^\prime$ increased from 23\% at RT to 54\% at 77 K. The increase in the fatigue ductility coeffi...한국과학기술원 : 재료공학과

Fe-25Mn-5Al-5Ni-0.3C 극저온 강의 저온 변형거동에 관한 연구

학위논문(석사) - 한국과학기술원 : 재료공학과, 1988.2, [ iv, 76 p. ]The low temperature deformation behaviors of cryogenic Fe-25Mn-5Al-5Ni-0.3C steel (named as "CAM-2") have been investigated. A particularly interesting observation in this CAM-2 alloy was the increase in elongation with decreasing test temperature. The total elongation at RT was a 25%, compared to a 50% at 77K. The inverse ductility behavior was ideal for cryogenic material requirements. In order to explain the deformation characteristics of this alloy, the new plastic stress-strain equation for low temperature tensile deformation was proposed: $σ = K ε^Nexp[ (L/2) ε^2 + Mε]$ The extent of true uniform elongation at lower temperatures can be calculated from this model. When no strain-induced phase is formed, the flow equation reduced to the Hollomon``s flow equation. The calculated values of the true uniform elongations were in good agreement with the measured values of this steel at room and subzero temperatures. It is proposed from these results that the application of models to metallic materials which have either a constant or varying strain hardening exponents with strains are possible. It was also found that the yield and tensile strengths of this steel increased with decreasing temperature: the YS increased by 47% from RT to 77K. The Charpy impact energy decreased from 215.3J at RT to 130J at 77K. However, the Charpy impact energy was considerably higher than that of 9%Ni steel. The controlled rolled alloy showed cyclic hardening at RT and LNT. Toal strain-controlled fatigue tests showed that the fatigue resistance at 77K was superior to that at room temperatuer. The reason exhibiting the longer fatigue life at LNT than that at RT for this alloy was caused by the significant increase in the fatigue ductility coefficient at LNT. The fatigue ductility coefficient at RT was 22.5%, compared to 54.1% at LNT.한국과학기술원 : 재료공학과

Al 합금재 소경 주조봉 제조 및 가공 기술 개발 (C2342)

funder : 산업자원부직경이 25~120mm의 알루미늄 합금 소경봉을 Hot Top 방식의 수직 주조에 의해 제조하며, Hot Top 방식을 채용한 주조기의 설계 및 제작 기술을 습득하고 운용기술을 확립하고자 하였다. 표면의 결함을 극소화시킨 양질의 소경봉을 제조하는 주조 조건을 찾아내고, 제조한 소경봉을 사용하여 각종 제조 공정(열간 단조, 냉간 단조)으로 시제품(자동차용 부품등)을 제작하고, 그 물성을 평가하였다. 또한 수평 주조기를 설계하였고 현재 제작중이다.본 연구의 주요 내용 및 범위는 아래와 같다. 1) 수직 주조기 설계 및 제작 기술 습득 - 주조의 핵심부위인 Mold의 설계 및 가공 2) 소경봉 주조 조건 확립 - 반연속주조법으로 직경 25~120mm의 Al합금(A6061, A390 등) 소경봉 주조 - 최적의 용해 및 주조 조건 설정 3) 가공 기술 확립 - 열간 단조에 의해 자동차 부품인 Swash Plate 제작 4) 소재의 물성평가 - 결정 제어를 위한 기초 실험 수행 - 소재의 특성 평가 - 소경봉 특성 평가 - 시제품 특성 평가 5) 수평 주조기 설계 및 제