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Fe-Cu계 소결합금의 마찰마모 특성에 미치는 흑연의 영향

Title
Fe-Cu계 소결합금의 마찰마모 특성에 미치는 흑연의 영향
Other Titles
The Effect of Graphite on the Friction and Wear Properties of Fe-Cu Sintered Alloy
Author
송석원
Alternative Author(s)
Song, Seok Won
Advisor(s)
이재성
Issue Date
2015-08
Publisher
한양대학교 대학원
Degree
Master
Abstract
소결 함유 베어링의 재질별 차이점을 보면 일반적으로 철계는 동계에 비해 경하고 축(shaft)과의 친숙도가 나쁘고 내식성이 떨어진다. 그러나 기계적 성질이 높아 고하중에 견딜 수 있을 뿐만 아니라 열팽창계수가 shaft에 유사하고 원료분말인 철분이 싸다는 등의 이점이 있다. 현재는 대체로 철계가 고하중 저속도용으로, 동계가 저하중 고속도용으로 각각 사용되고 있다. 또 알루미늄계는 경량일 뿐만 아니라 열전도성이 동계나 철계에 비해 약 3배 정도 높고 알루미늄 자체가 비교적 연질이며 shaft와의 친숙도가 좋다. 게다가 운전성능 면에서도 동계나 철계에 비해 뛰어난 점이 많다. 다만 기계적 성질이 동계나 철계에 비해 낮아 내마모성이 충분히 개선되지 않아 실용화 되지 못하고 있다. 본 연구에서는 환경적 또는 기구적으로 충분한 급유를 행할 수 없는 기기에 소결 함유베어링의 적용이 증가되고 있고 그 중 원료분말이 동 보다 저렴하고 열팽창계수가 shaft와 유사하며 기계적 성질이 높아 고하중에 견딜 수 있다는 이점 때문에 현재 생산되고 있는 소결 함유 베어링의 약 60%를 이루고 있는 Fe-Cu계 소결 함유 베어링의 마찰·마모 특성에 관해 고찰하였다. 특히 Fe-Cu-C계 소결 함유 베어링의 경우, 보다 높은 경도와 내하중성을 높이기 위해 탄소를 소량 첨가하고 후처리를 통해 Fe의 기지를 강화하여 사용되고 있다. 일반적으로 탄소는 흑연상태로 첨가되고 그 역할은 기지강화와 고체윤활제 역할을 수행하는데 본 연구를 통해 흑연의 형상과 함량이 Fe-Cu계 소결체에서 기지강화 및 고체윤활제 역할로써 마찰·마모에 미치는 영향을 평가하여 그 활용도를 명확히 하고자 하였다. 총 6가지 조성으로 혼합분말 샘플을 제작하고 흑연의 종류와 함량 변수에 따른 영향을 마찰·마모 실험을 통해 알아보고, 윤활성능을 향상시키기 위해 Fe의 기지 강화로만 첨가되는 탄소를 최적화하여 고체윤활제로써의 역할 가능 여부를 평가하였다. Size가 작은 UF-4 흑연은 1.5wt.% 첨가 시 Fe 기지에 탄소가 확산되어 강화되고 고용되지 못한 고체 상태로 존재하는 흑연이 고체윤활제로써의 역할 수행이 가능하였다. UF-4 흑연 0.5wt.%에 Size가 큰 HC-398 흑연 0.5wt.%를 첨가할 경우와 UF-4 흑연 1.0wt.% 첨가 시에도 고체윤활제로써의 역할 수행이 가능하였다. 하지만 HC-398 흑연만 1.0wt.% 첨가할 경우는 탄소의 확산량이 줄어들어 Fe기지를 강화해주는 역할을 하지 못해 오히려 마모량이 증가하는 경향을 보였다. HC-398 흑연의 첨가량을 1.5wt.%로 증가시킨 경우 전체적인 흑연량이 증가함에 따라 탄소의 확산량도 충분해지고 고체윤활제로써의 역할 역시 가능함을 확인하였다. 위의 실험 결과를 통하여 흑연 Size를 혼합할 경우 흑연의 탄소가 Fe의 기지를 강화시키는 역할 뿐 아니라 고체윤활제로써의 수행이 가능함과 Fe-Cu-C계 소결체의 마찰·마모 특성을 개선시킬 수 있음을 확인하였다.|The sintered oil impregnated bearing is widely used for self-lubricating components of automobile- and industrial machine parts. This is because the sintered oil impregnated component offers self-lubricating function to the machine parts which are mostly located at the complicated site in the machines, as a result leading to difficulty in oil refueling. Such bearing materials should be in form of porous structure to impregnate oil. In general, the most popular processing of porous material is known to be made by powder metallurgy process. Regarding the porous bearing material system, various powder alloys such as Fe-based, Cu-based, and Al-based powder materials are used according to their optimal applications. Among them the Fe-Cu alloy material accounts for 60% of sintered oil impregnated bearing production because of their high mechanical properties, similar thermal expansion property with neighboring shaft material, and cost-effectiveness of raw powders. In order to increase the hardness as well as the load resistance of sintered Fe-Cu alloy for oil impregnated bearing, a small amount of carbon in graphite phase is added to the composite mixture, thereby strengthening the Fe matrix during heat-treatment process. The present study focused on investigating the effects of graphite size and content on the friction- and wear properties of Fe-Cu-C sintered alloy fabricated by powder metallurgy process. By using various graphite powders with two particle size condition of 4 ㎛ and 30 ㎛ and three compositions of 0.5wt%, 1.0wt% and 1.5wt%, six kinds of Fe-Cu-C mixtures having a composition of Fe-20wt%Cu-(1.0-1.5wt%)C were prepared by blending of Fe powder (100 ㎛), Cu powder (75 ㎛) and graphite. The mixtures were compacted into a disc-shape by double action cold press with a green density of 6.3-6.4 g/㎤ which corresponds to 18-20% in porosity. Sintering was performed at 1080oC for 40 min in a N2-5%H2 atmosphere. After sintering, the annealing for carbon diffusion into the matrix was conducted at 850oC for 30 min and then oil quenched. Finally the tempering treatment was performed at 180oC for 60 min. Microstructural study by image analysis revealed that the amount of residual carbon was decreased after annealing process. This might be due to carbon reduction by reducing gas reaction. It was also found that with increasing carbon content fractional phase of ferrite decreased while that of pearlite increased, followed by improvement of hardness and friction coefficient of the sintered materials. The wear test showed that the sample having higher residual carbon content underwent a better wear resistance performance. This is because the residual carbon acts as a solid lubricant against the wear. The experimental findings in this study enable us design the optimal microstructure of Fe-Cu sintered material for oil-impregnated bearing.; The sintered oil impregnated bearing is widely used for self-lubricating components of automobile- and industrial machine parts. This is because the sintered oil impregnated component offers self-lubricating function to the machine parts which are mostly located at the complicated site in the machines, as a result leading to difficulty in oil refueling. Such bearing materials should be in form of porous structure to impregnate oil. In general, the most popular processing of porous material is known to be made by powder metallurgy process. Regarding the porous bearing material system, various powder alloys such as Fe-based, Cu-based, and Al-based powder materials are used according to their optimal applications. Among them the Fe-Cu alloy material accounts for 60% of sintered oil impregnated bearing production because of their high mechanical properties, similar thermal expansion property with neighboring shaft material, and cost-effectiveness of raw powders. In order to increase the hardness as well as the load resistance of sintered Fe-Cu alloy for oil impregnated bearing, a small amount of carbon in graphite phase is added to the composite mixture, thereby strengthening the Fe matrix during heat-treatment process. The present study focused on investigating the effects of graphite size and content on the friction- and wear properties of Fe-Cu-C sintered alloy fabricated by powder metallurgy process. By using various graphite powders with two particle size condition of 4 ㎛ and 30 ㎛ and three compositions of 0.5wt%, 1.0wt% and 1.5wt%, six kinds of Fe-Cu-C mixtures having a composition of Fe-20wt%Cu-(1.0-1.5wt%)C were prepared by blending of Fe powder (100 ㎛), Cu powder (75 ㎛) and graphite. The mixtures were compacted into a disc-shape by double action cold press with a green density of 6.3-6.4 g/㎤ which corresponds to 18-20% in porosity. Sintering was performed at 1080oC for 40 min in a N2-5%H2 atmosphere. After sintering, the annealing for carbon diffusion into the matrix was conducted at 850oC for 30 min and then oil quenched. Finally the tempering treatment was performed at 180oC for 60 min. Microstructural study by image analysis revealed that the amount of residual carbon was decreased after annealing process. This might be due to carbon reduction by reducing gas reaction. It was also found that with increasing carbon content fractional phase of ferrite decreased while that of pearlite increased, followed by improvement of hardness and friction coefficient of the sintered materials. The wear test showed that the sample having higher residual carbon content underwent a better wear resistance performance. This is because the residual carbon acts as a solid lubricant against the wear. The experimental findings in this study enable us design the optimal microstructure of Fe-Cu sintered material for oil-impregnated bearing.
URI
https://repository.hanyang.ac.kr/handle/20.500.11754/127632http://hanyang.dcollection.net/common/orgView/200000427004
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GRADUATE SCHOOL[S](대학원) > MATERIALS ENGINEERING(재료공학과) > Theses (Master)
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