• Journal of Power System Engineering
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• v.9 no.1
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• pp.70-75
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• 2005

The damping property of Fe-12Cr-22Mn-X alloys has been investigated to develop high damping and high strength alloy. Particularly, the effect of the phase of austenite, alpha and epsilon martensite, which constitute the structure of the alloys Fe-12Cr-22Mn-X alloys, on the damping capacity at room temperature has been investigated. Various fraction of these phases were formed depending on the alloy element and cold work degree. The damping capacity is strongly affected by ${\varepsilon}$ martensite while the other phase, such as ${\alpha}'$ martensite, actually exhibit little effect on damping capacity. In case of Fe-12Cr-22Mn-3Co alloy, the large volume fraction of ${\varepsilon}$ martensite formed at about 30% cold rolling, and in case of Fe-12Cr-22Mn-1Ti alloy, formed at about 20% cold rolling and showed the highest damping capacity. Damping capacity showed higher value in Fe-12Cr-22Mn-1Ti alloy than one in Fe-12Cr-22Mn-3Co alloy.

• Journal of Power System Engineering
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• v.8 no.4
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• pp.31-37
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• 2004

The damping capacity and strength of Fe-2Al-26Mn alloys have been studied for the development of new materials with high strength and damping capacity. Particularly, the effect of ${\alpha}'\;and\;{\varepsilon}$ martensite phase, which constitutes the microstructure of cold rolled Fe-Al-Mn alloys, has been investigated in terms of the strength and damping capacity of the alloys. The damping capacity rises with increasing the degree of cold rolling and reveals the maximum value at 25% reduction. The damping capacity is strongly affected by the volume fraction of ${\varepsilon}$ martensite, while the other phases, such as ${\alpha}'$ martensite and austenite phase, actually exhibit little effect on damping capacity. Considering that tensile strength increases and elongation decreases with increasing the volume fraction of ${\alpha}'$ martensite, it is proved that tensile strength is mainly affected by the amount of ${\alpha}'$ martensite.

• Analytical Science and Technology
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• v.6 no.1
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• pp.141-147
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• 1993

The behavior of reverted austenite in Fe-Ni-Mn(Ti) maraging steels has been investigated in the temperature range from $400^{\circ}C$ to $550^{\circ}C$ using TEM equipped with EDX. Four kinds of reverted austenite appeared depending on the aging temperatures and time : Widmanstatten, granular, lath-like and recrystallized austenite. The reverted austenites are enriched in Ni and Mn due to the dissolution of precipitates and redistribution of alloying elements. Widmanstatten austenite appears unformly in the lath martensite having the K-S orientation relationship with the martensite lath, while lath-like martensites showed K-S and N relations depending on the chemistry and heat treating condition. The recrystallized austenite forms at $550^{\circ}C$ after long aging times : some becomes unstable and transforms to lath martensite on cooling.

• Journal of the Korean Society for Heat Treatment
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• v.13 no.2
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• pp.85-90
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• 2000

The influence of transformation cycles (${\alpha}^{\prime}{\leftrightarrow}{\gamma}^{\prime}$) on the microstructure and mechanical properties of lath and lenticular martensites has been studied in Fe-Ni alloys. The width of lath in Fe-15%Ni alloy decreased with increasing the number of transformation cycles, while no appreciable change in dislocation density inside the lath was observed. In case of Fe-31%Ni alloy, a number of dislocations were additionally introduced into the martensite plate after the transformation cycling. Tensile strength and Vickers hardness of lath martensite decreased with the increase in number of transformation cycles, whereas those of lenticular martensite increased up to 1 cycle and then remained constant. Elongation of two alloys was deteriorated after 1 transformation cycling, corresponding to the tensile strength. But the decrement of elongation in Fe-31%Ni alloy was smaller than that in Fe-15%Ni alloy.

• Korean Journal of Materials Research
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• v.8 no.5
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• pp.436-443
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• 1998

2.3%C-26%Cr-1%Ni-0.5%Mo 조성의 다합금계 고크롬백주철을 고주파유도용해로를 사용하여 주조한 후 응고조직, 열처리조직 및 기계적성질간의 상관관계를 연구하였다. 주방상태에서는 초정덴드라이트조직인 기지조직과 공정탄화물로 구성되어 있었으며 기지조직의 73%가 오스테나이트, 27%가 마르텐사이트조직이었다. $900^{\circ}C$에서 5시간동안 균질화열처리만 행한 시편의 경우, 기지조직은 거의 페라이트로 구성되어 있었으며 $1100^{\circ}C$에서 불안정화열처리후 강제공냉시킨 시편의 경우, 유지시간에 따라 기지조직내의 잔류오스테나이트함량은 48.9-57.6%의 범위에 놓여 있었다. 주방상태 및 열처리시편 공히 마모량과 마모시간과의 관계가 직선적으로 얻어 졌는바 마모속도는 $2.77x10^{-2}$ /$~4.12x10^{-2mg}$ /sec의 범위에 걸쳐 있었다. 주방상태의 시편이 내마모성이 가장 우수하였으며 균질화열처리만 행한 시편이 가장 열악하였다. 기지조직내 잔류오스테나이트함량의 비율이 높아짐에 따라 경도는 감소하였고 반면에 내마모성은 향상되었다. 이는 마찰마모시험시 접촉부위의 오스테나이트가 가공경화를 일으켜 마르텐사이트로 변태되었기 때문으로 사려된다.

• Proceedings of the Materials Research Society of Korea Conference
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• 2009.05a
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• pp.48.1-48.1
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• 2009

Ti합금은 생체적합성이 우수하여 생체재료로 널리 사용되어 왔으며, 특히 Nitinol로 알려진 Ti-Ni합금은 형상기억특성 및 초탄성특성을 지녀 치열교정용 와이어나 혈관확장용 스텐트 등으로 사용되어 왔다. 최근 Ni과 같은 세포독성 합금원소의 용출가능성이 문제가 되어 Ni을 함유하지 않는 Ti합금이 주목받고 있다. 본 연구에서는 Ti-Nb-Ge 합금의 집합조직과 초탄성 및 기계적 특성의 관계를 고찰함으로써, 사용목적이나 요구특성에 부합되는 가공열처리방법을 도출하고자 하였다. 비소모전극식 진공아크용해장치를 이용하여 Ti-Nb-Ge 합금 버튼을 만들고, 이를 $1000^{\circ}C$에서 30분간 유지 후 얼음물에 급랭처리하였다. 이후 집합조직 제어를 위해 등속압연 및 이속압연의 두가지 방법으로 냉간압연한 후, $850^{\circ}C$에서 30분~2시간까지 열처리하였다. 광학현미경과 투과전자현미경을 이용하여 미세조직을 관찰하고, X-선 회절분석법을 이용하여 집합조직을 분석하였다. 또한 순환식 인장시험을 통해 시편의 초탄성 특성 및 기계적 성질을 평가하였다. 등속압연재는 {001}<110>에서 {111}<110>에 이르는 $\alpha$-fiber가 발달하는 한편, 이속압연재는 {001} 및 {111}가 발달하는 것으로 나타났다. 또한 압연방향으로 <110>이 평행한 집합조직이 발달할수록 초탄성 특성이 높게 나타났다. 이는 응력유기 마르텐사이트 변태 시 $\beta$의 <110>방향이 $\alpha$" <010>방향으로 변할 때 길이가 증가하므로, 시편에 인장방향으로 <110>이 평행한 집합조직이 발달할수록 응력유기 마르텐사이트 변태가 용이해지기 때문인 것으로 사료된다.

• Korean Journal of Materials Research
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• v.10 no.6
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• pp.409-414
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• 2000

Three different white cast irons alloyed with Cr, V, Mo and W were prepared in order to study their transformation behavior of matrix structures in heat-treated conditions. The specimens were produced using a 15kg-capacity high frequency induction furnace. Melts were super-heated to $1600^{\circ}C$, and poured at $1550^{\circ}C$ into Y-block pepset molds. Three combinations of the alloying elements were selected so as to obtain the different types of carbides and matrix structures : 3%C-10%Cr-5%Mo-5%W(alloy No. 1), 3%C-10%V-5%Mo-5%W(alloy No. 2) and 3%C-17%Cr-3%V(alloy No. 3). The heat-treatments were conducted as follows: frist of all, as-cast specimens were homogenized at $950^{\circ}C$ for 5h under the vacuum atmosphere. Then, they were austenitized at $1050^{\circ}C$ for 2h and followed by air-hardening in air. The air-hardened specimens were tempered at $300^{\circ}C$ for 3h. The observation of morphology of the matrix structures was carried out in the states of as-cast(AS), air-hardened(AHF) and tempered(AHFT). The matrix structures of each alloy were almost fully pearlitic in the as-cast state but it was transformed to martensite, tempered martensite and retained austenite by the heat-treatments such as air-hardening and tempering.

• The Journal of Natural Sciences
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• v.7
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• pp.83-90
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• 1995

The microstructural and textural development during rolling is compared in two Hadifield's steels (high Mn steel), one having low carbon content (0.65 wt.%) and the other high carbon (1.35 wt.%).In low carbon Hadfield's steel (LCHS) mixed microstructures are formed which contain intrinsic stacking faults, deformation twins, and brass type shear bands. The deformation twins are thought to be formed by the stacking of intrinsic stacking faults. The similar development to 70-30 brass texture is observed in early deformation. However the abnormal texture is developed after 40 % deformation, which is thought to be due to the martensite phase transformation. In high carbon Hadfield's steel (HCHS) mixed substructures of dislocation tangles, deformation twins, and shear bands (both copper and brass type) are found to develop. The texture development is similar to that of 70-30 brass. This is consistant with no carbon segregation and no martensitic phase transformation in HCHS. In spite of the difference of substructure and texture development during rolling in two steels, the difference in stacking fault energy is measured to be small ($2 mJm^-2$). The carbon segregation is only occurred in LCHS. Thus it is thought that the carbon segregation influence the microstructure and texture development during rolling. This is related with martensite phase transformation in LCHS.

• Transactions of the Korean Society of Mechanical Engineers
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• v.9 no.3
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• pp.287-294
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• 1985

본 연구에서는 충격하중하에서 충격파괴거동에 미치는 모상입경과 제2상 형태 의 영향을 분석, 검토하기위해서, 화학성분, 마르텐사이트체적율, 연결도, 강도비등을 되도록 일정하게 하고, 우선 모상입경과 제2상의 형태(연결재와 고립재)를 변화시켜, 충격속도를 달리하였을때 얻어지는 충격하중-시간유선을 토대로하여 충격강도, 하중작 용시간, 흡수에너지 및 연성파괴거동을 고찰하였다.

• Proceedings of the KWS Conference
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• 2004.05a
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• pp.197-199
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• 2004

용접성은 모재의 조직과 기계적 성질 및 Bond 부와 열영향부의 조직과 기계적 성질의 관계로 평가된다. 탈소 함량이 높은 레일강의 경우 용접을 하고 나면 열영향부에 마르텐사이트와 같은 취약조직을 형성하여 경도 값이 높아지고 인성이 저하되어 균열발생 가능성이 높아진다. (중략)