• 한국재료학회지
• /
• 제10권2호
• /
• pp.144-147
• /
• 2000

10%C-5%Mo-5%W-10%Cr 및 10%C-5%Mo-5%W-10%V 백주철의 응고거동을 열분석을 통하여 연구하였다. 15Kg 용량의 고주파 유도옹해로에 선철, 고철, Fe-Mo, Fe-W, Fe-Cr, Fe-V 등을 장입시켜 용해시킨 후 슬래그를 제거시키고 $1550^{\circ}C$에서 Y블럭의 펩 주형에 주입하였다. 응고거동을 조사하기 위하여 50g을 Y블럭에서 채취한 뒤 알루미나 도가니에 넣어 재용해시킨 후 1$0^{\circ}C$/min의 냉각속도로 냉각시키면서 여섯 종류의 다른 온도에서 도중에 급냉시켜 응고조직을 광학현미경으로 관찰하였다. 10%C-5%Mo-5%W-10%Cr 백주철의 경우 초정 오스테나이트, 오스테나이트와 M(sub)7C(sob)3의 공정, 오스테나이트와 M(sub)6C의 공정으로, 10%C-5%Mo-5%W-10%V 백주철의 경우 초정 MC, 오스테나이트와 MC의 공정, 오스테나이트와 M(sub)2C의 공정으로 각각 순차적으로 정출하였다. 정출하였다.

• 한국주조공학회지
• /
• 제6권4호
• /
• pp.315-320
• /
• 1986

• 한국재료학회지
• /
• 제10권6호
• /
• pp.409-414
• /
• 2000

3%C-10%Cr-5%Mo-5%W, 3%C-10%V-5%Mo-5%W 및 3%C-17%Cr-3%V의 3종류 고합금백주철에 있어서 열처리후의 기지조직의 변태거동을 연구하였다. 15kg 용량의 고주파 유도용해로에 선철, 고철, Fe-Cr, Fe-V, Fe-Mo 및 Fe-W 등을 장입시켜 용해시킨 후 슬래그를 제거시키고 $1550^{\circ}C$에서 Y-block의 펩 주형에 주입시켰다. 적당한 크기로 절단한 시편을 진공분위기하에$950^{\circ}C$에서 5시간동안 우선 균질화처리를 실시하였다. 그 후 다시 이 시편을 $1050^{\circ}C$에서 2시간동안 오스테나이징시킨 후 강제공냉을 행하였다. 강제공냉된 시편을 $300^{\circ}C$에서 3시간 유지시킨 후 템퍼링을 실시하였다. 주방상태에서의 기지조직은 3합금 공히 퍼얼라이트이었으며 강제공냉후에는 마르텐사이트 및 오스테나이트로 변태하였다. 또한 기지조직내에 무수히 많은 이차탄화물 입자들의 석출되었다. 템프링 후 일부 오스테나이트 및 마르텐사이트는 템퍼드마르텐사이트로 변태하였다. 변태하였다.

• 한국주조공학회지
• /
• 제27권5호
• /
• pp.203-208
• /
• 2007

The high temperature properties of vanadium and molybdenum added high silicon ductile iron, so called V-Mo-Si ductile iron, were investigated. The (V,Mo) complex carbides and Mo carbides precipitated at the cellular boundaries of the as-cast specimens. The microhardness of the (V,Mo) carbides were in the range of 553-619, while that of the Mo carbides in the range of 341-390. The thermo-mechanical tests were carried out with a Gleeble system at 700 and $800^{\circ}C$ under vacuum condition. The tensile strengths of the specimen tested at $700^{\circ}C$ with the dynamic deformation rate of 50 mm/sec and those with the static deformation rate of 0.15 mm/sec were 235.7 and 115.3 MPa, while the reduction in area were 23.7 and 22.4%, respectively. At the high dynamic deformation rates, the tensile strength was steeply increased due to promoting the brittle fracture of pearlite in the matrix of the specimens. But the changes of the reduction in area with the deformation rates on the same specimens were negligible. The weight gain of the V-Mo-Si specimens oxidized in the air atmosphere for 6 hours at 800 and $900^{\circ}C$ were 1.1 and 4.1.%, respectively. The cross-sectional microstructure of oxidized specimens consisted of the porous external scale layer grown outside from the original surface, the dense internal scale layer grown into the original surface, the decarburized ferrite layer between the internal scale and the matrix of base metal. The (V,Mo) carbides and Mo carbides formed in the matrix of as-cast specimen did not decompose during oxidation at 900 for 24 hours in air atmosphere.

• 한국주조공학회지
• /
• 제17권5호
• /
• pp.488-493
• /
• 1997

주방상태 및 열처리를 행한 다합금계백주철(Fe-5%Cr-5%V-5%Mo-5%W-X%C(X=0.5, 1.0, 1.5, 2.0, 2.5, 3.0)에 있어서 탄소함량이 탄화물의 형태 및 잔류오스테나이트의 함량에 미치는 영향에 관하여 연구하였다. 주방상태의 경우, 2.0% 이하의 탄소함량에서는 편상MC 및 층상 $M_2C$탄화물만 관찰되었으나 2.5%C 이상의 경우, 편상 및 괴상MC, 층상$M_2C$ 그리고 셀형 $M_7C_3$탄화물이 관찰되었다. 또한, 기지조직내 오스테나이트의 함량도 탄소첨가와 더불어 점차 증가하여 2.5%C에서 84.8%의 최대함량을 나타낸 후, 3.0%C에서는 다시 감소하였다. 또한 열처리한 시편의 경우, 1차탄화물의 형상은 주방상태의 그것과 비슷하였으나 열처리중 기지조직내 용해되었던 C, Cr, V, Mo, W등이 아주 미세한 2차탄화물의 형태로 석출되어 기지조직내 오스테나이트의 함량은 주방상태의 그것에 비해 감소하였다.

• 한국주조공학회지
• /
• 제12권6호
• /
• pp.450-457
• /
• 1992

The study aims to investigate the influence of alloying elements(V,Ti) and heat treatment on the mechanical properties in hypo-eutectic chromium cast iron. Before heat treatment, all of the specimen were fully annealed(950$^{\circ}C{\times}5Hr$) to homogenize their structures. The influence of heat treatment and alloying elements(V,Ti) on hardness, retained austenite volume, and charpy impact energy as well as tensile strength of the specimen was tested systematically. Retained austenite decreased with the increase of V and Ti, but incresed with the increase of number of cycles. The impact energy decreased, and hardness and tensile strength increased with the increase of alloying elements (V,Ti) and the decrease of the number of cycles. The hardness and tensile strength increased, but impact energy decreased with the increase of V and Ti elements and the temperature of destabillization heat treatment. After the destabillization heat treatment at the same temperature, the impact energy is increased, while hardness and tensile strength decreased as the increase of tempering temperature. Retained austenite increased with increase of destabilizatoin heat treatment temperature, while decrease with the increase of tempering temperature.

• Tribology and Lubricants
• /
• 제17권4호
• /
• pp.267-275
• /
• 2001

Friction and wear properties of brake friction materials containing different metal fibers (Al, Cu or Steel fibers) were investigated. Based on a simple experimental formulation, friction materials with the same amount of metal fibers were tested using a pad-on-disk type friction tester. Two different materials (gray cast iron and aluminum metal matrix composite (MMC)) were used for disks rubbing against the friction materials. Results front ambient temperature tests revealed that the friction material containing Cu fibers sliding against gray cast iron disk showed a distinct negative $\mu$-v (friction coefficient vs. sliding velocity) relation implying possible stick-slip generation at low speeds. The negative $\mu$- v relation was not observed when the Cu-containing friction materials were rubbed against the Al-MMC counter surface. Elevated temperature tests showed that the friction level and the intensity of friction force oscillation were strongly affected by the thermal conductivity and melting temperature of metallic ingredients of the friction couple. Friction materials slid against cast iron disks exhibited higher friction coefficients than Al-MMC (metal matrix composite) disks during high temperature tests. On the other hand, high temperature test results suggested that copper fibers in the friction material improved fade resistance and that steel fibers were not compatible with Al-MMC disks showing severe material transfer and erratic friction behavior during sliding at elevated temperatures.

• 한국주조공학회지
• /
• 제16권2호
• /
• pp.109-115
• /
• 1996

Effect of various austempered structures on fracture characteristics of C/V graphite cast iron has studied. The tensile strength and hardness reached the maximum value of 971.4MPa and HB302 at the austempering temperature of $250^{\circ}C$, respectively. As the austempering temperature increased, the amount of retained austenite increased from 18% to 22, 29%, while $K_{IC}$ values ranged from the value of $65MPa{\cdot}m^{12} to 70MPa{\cdot}m^{1/2}, 66MPa{\cdot}m^{1/2}. This fact that $K_{IC}$ value was not sensitive to the increase of the amount of the retained austenite was that $K_{IC}$ was dependent on the matrix structure in lower bainitic matrix, while dependent on the notch effect from C/V graphite shape in upper bainitic matrix. Fractured surfaces showed a ductile fracture pattern at $300^{\circ}C$. Very large coalescence by C/V graphite and relatively small voids by spheroidal graphite were observed.

• 한국재료학회지
• /
• 제8권7호
• /
• pp.607-612
• /
• 1998

다합금계백주철의 성분원소인 Cr, V, Mo 및 W 의 첨가량을 변화시켜 응고조직을 관찰하였다. MC탄화물은 초정 austenite dendrite 내에 괴상 및 구상으로 M7C3탄화물은 intercellular boundary에 꽃형태 또는 bar 형태로, 그리고 M2C 탄화물은 M7C3탄화물과 마찬가지로 intercellular boundary에 침상으로 정출하였다. 기지조직은 주방상태에서 pealite 또는 (pearlite + austenite)의 혼합조직으로 구성되어 있었으며, 또한 EPMA 분석결과 MC탄화물은 V, M7C3 탄화물은 Cr 그리고 M2C탄화물은 Mo 및 W가 주성분으로 되어 있음을 알 수 있었다. 냉각곡선을 측정한 결과 액상에서 MC, M7C3, M2C 순으로 공정반응이 일어나고 있었으며 또한 X-선 회절시험을 통해 각 탄화물의 회절 peak를 관찰하였는바 응고조직의 사진과 잘 일치하고 있음을 알 수 있었다.

• 한국주조공학회지
• /
• 제20권2호
• /
• pp.104-109
• /
• 2000

Three different white cast irons alloyed with Cr, V, Mo and W were prepared in order to study their abrasion wear behavior in as-cast and heat-treated conditions. The specimens were produced using a 15㎏-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 : 3%C-10%Cr-5%Mo-5%W(alloy No. 1: $M_7C_3$ and $M_6C$), 3%C -10%V-5%Mo-5%W(alloy No. 2: MC and $M_2C$) and 3%C-17%Cr-3%V(alloy No. 3: $M_7C_3$ only). A scratching type abrasion test was carried out in the states of as-cast(AS), homogenizing(AH), air-hardening(AHF) and tempering(AHFT). First of all, the 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. 1 ㎏ load was applied in order to contact the specimen with abrading wheel which was wound by 120 mesh SiC paper. The wear loss of the test piece(dimension: $50{\times}50{\times}5$ mm) was measured after one cycle of wear test and this procedure was repeated up to 8 cycles. In all the specimens, the abrasion wear loss was found to decrease in the order of AH, AS, AHFT and AHF states. Abrasion wear loss was lowest in the alloy No.2 and highest in the alloy No.1 except for the as-cast and homogenized condition in which the alloy No.3 showed the highest abrasion wear loss. The lowest abrasion wear loss of the alloy No.2 could be attributed to the fact that it contained primary and eutectic MC carbides, and eutectic $M_2C$ carbide with extremely high hardness. The matrix of each specimen was fully pearlitic in the as-cast state but it was transformed to martensite, tempered martensite and austenite depending upon the type of heat-treatment. From these results, it becomes clear that MC carbide is a significant phase to improve the abrasion wear resistance.