• 한국기계연구소 소보
• /
• 통권20호
• /
• pp.57-63
• /
• 1990

The morphologies of MC carbides (M stands for metal) and creep-rupture properties in directionally solidified Rene 80 having standard and Hf-modified chemistries were studied. It was found that Hf depressed the melting point, $\gamma$- $\gamma$’ eutectic temperature and $\gamma$’ solvus of nickel-base superalloy Rene 80, but did not depress MC carbide forming temperature. The morphologies of MC carbides depended upon solidification sequence, which led to blocky type in the early stage and script type in the late stage of solidification. Creep failure occurs through the crack initiation at the transverse components of longitudinal grain boundaries or interdendritic carbides in directionally solidified superalloys. It could be concluded MC carbide morphologies played an important role in creep properties of DS superalloys, that is, Hf additions increased the creep ductilities and lives of Rene 80.

• 한국분말야금학회:학술대회논문집
• /
• 한국분말야금학회 2006년도 Extended Abstracts of 2006 POWDER METALLURGY World Congress Part 1
• /
• pp.338-339
• /
• 2006

The solubility of Cr in cubic carbides in the systems WC-Co-TaC and WC-Co-ZrC has been determined using equilibrium samples. Thermodynamic calculations were used to design the alloys through extrapolations of Gibbs energy expressions. The alloys were designed to have a microstructure containing the following phases: WC, liquid, $M_7C_3$, graphite and cubic carbide. The alloys were investigated using scanning electron microscopy and analyzed using energy-dispersive X-ray spectrometry. The present work shows how the Cr solubility depends on which cubic carbide former that is present. The WC-Co-Cr-Zr alloy has no detectable amount of Cr whereas the WC-Co-Cr-Ta alloy has 12% Cr in the cubic carbide.

• 한국분말야금학회:학술대회논문집
• /
• 한국분말야금학회 2006년도 Extended Abstracts of 2006 POWDER METALLURGY World Congress Part 1
• /
• pp.552-553
• /
• 2006

The present study investigates the behavior of the sintering and hardness of stainless steel samples reinforced with NbC and TaC. Matrixes of pure stainless steel were compacted with addition of up to 3% wt NbC or TaC in a cylindrical die of steel $(\phi\;=\;5,0\;mm)$ at 700 MPa and sintered in an electrical resistance furnace under argon atmosphere. The sintered samples were characterized by density and hardness measurement, optical microscopy and scanning electron microscopy (SEM). The preliminary results show that the size and distribution of carbides influence in the sintering and hardness of the sintered samples.

• Nuclear Engineering and Technology
• /
• 제34권2호
• /
• pp.132-141
• /
• 2002

The effects of microstructure on fretting wear were investigated in Inconel 690 tube. The microstructure observation indicated that the solution annealing temperature and time affected the grain size of the Inconel 690 tubes. The carbide morphology, along grain boundaries, was mainly affected by thermal treatment time and temperature. The wear test results showed that specimens with larger grain size and with coarse carbides along grain boundaries had better wear resistance. Cracks were found in specimens with carbides along the grain boundary, while few cracks were found in carbide free specimens. It seemed that the carbides on grain boundary assisted crack formation and propagation in carbide containing specimens. On the other hand, the micro-hardness of specimen did not have a major role in fretting wear. It could be inferred from the SEM images of worn surfaces that the main wear mechanism of carbide containing specimen was delamination, while that of carbide free specimen was abrasion.

• 한국주조공학회지
• /
• 제38권5호
• /
• pp.103-110
• /
• 2018

코발트기 주조용 초내열합금 X45를 이용하여 다양한 형태의 열처리에 따른 미세조직과 기계적 특성의 변화에 대하여 고찰한 결과를 요약하면 다음과 같다. 1) 합금의 응고 시 결정립계와 수지상간 경계를 따라 Cr이 다량 함유된 조대한 $M_{23}C_6$ 탄화물과 W과 Co의 함량이 높은 $M_6C$ 탄화물이 형성되어 있었고, $1274^{\circ}C$에서 용체화 처리하면 대부분의 탄화물이 용해되었다. $1150^{\circ}C$에서의 용체화 처리 동안 일부 결정립계 탄화물이 용해되지만 공정탄화물 근처에서 새로운 탄화물의 석출이 일어났다. $927^{\circ}C$와 $982^{\circ}C$에서 시효처리만 했을 때 용체화 처리 후 시효처리 한 시편 보다 공정 탄화물 근처에서 석출되는 탄화물의 양이 많았고, 크기가 작았다. 2) $1150^{\circ}C$에서 용체화 처리한 후 시효처리 하면 경도의 증가가 뚜렷하지 않으며, $927^{\circ}C$와 $982^{\circ}C$에서 시효처리만 했을 때 다량의 매우 미세한 탄화물의 석출에 의하여 경도의 증가 폭이 더 컸다. 상온 항복강도는 $927^{\circ}C$에서 시효처리 했을 때 가장 컸지만 인장강도와 연신율은 $982^{\circ}C$에서 12시간 시효처리 했을 때 가장 컸다. 고온 크리프 특성은 $982^{\circ}C$에서 12시간 시효처리 했을 때 가장 우수하였다. 3) 장시간 고온 노출 되는 동안 탄화물의 석출과 성장이 일어났고, 8000시간 고온에서 노출시킨 시편에서는 수지상 중심부에도 탄화물이 석출되어 크리프 파단 수명이 증가하였다.

• 한국재료학회지
• /
• 제7권4호
• /
• pp.310-316
• /
• 1997

The effects of carbide and matrix structures on the abrasion wear resistance of multi-component white cast irons with 3.0 mass%C have been studied in this paper. Four different heats were poured in order to obtain the specimens with different combinations of the carbide structures: a basic iron(3.0 mass%C-5.0 mass%Cr-5.0 mass%V-5.0 mass% Mo-12.5mass%W)for M$_{6}$C and M$_{7}$C$_{3}$ carbides, and a Cr free iron(3.0 mass%C-5.0 mass%V-2.5mass%Mo-12.5 mass%W) for MC and M6C carbides. A conventional high Cr free free iron(3.0 mass%C-5.0 mass%V-2.5 mass%Mo-12.5 mass%W) for MC and M6C carbides. A conventional high Cr white cast iron was also poured to compare its wear resistance with those of the multi-component white cast irons. In the as-cast condition, the range of abrasive wear rate(Rw=mg/min) was from 4.15 to 5.98 . The lowest Rw, which means the highest wear resistance, was obtained in the basic iron with nodular MC, lamellar M$_{2}$C and cellular M$_{7}$C$_{3}$ carbides. On the other hand, the Rw of the high Cr white cast iron ranked between the basic iron and the Mo and W free iron. In each alloy, the Rw of air hardened or tempered specimen was lower than that of the as-cast one because of the change of matrix structures by the heat treatments. The Rw of the hear treated speci-mens increased in the order Mo and W free iron, basic iron, Cr free iron, high Cr iron, and V free iron.n.n.n.

• 한국분말재료학회지
• /
• 제5권4호
• /
• pp.265-272
• /
• 1998

For the purpose of investigating the effect of sintering atmosphere and carbon addition on sintered density and microstructural characteristics, the M3/2 grade high speed steel powders with the addition of carbon are sintered in vacuum and $20%H_2/79%N_2/l%CH_4$ gas atmosphere. With the addition of 0 wt%C, 0.45wt%C and 1.15 wt%C the optimum sintering temperatures decrease down to $1260^{\circ}C$, $1210^{\circ}C$ and $1150^{\circ}C$ respectively for the vacuum sintered specimen, and also decrease down to $1130^{\circ}C$, $1120^{\circ}C$ and $1115^{\circ}C$ for the gas sintered specimen. The threshold temperatures for full densification decrease steeply with increasing carbon content of the sintered specimen, while this temperatures are slowly decreased at high carbon content. The vacuum sintered specimen shows the primary carbides of MC and $M_6C$ type at the optimum sintering temperature, and eutectic carbides of $M_2C$ and Fe-Cr type are produced in the oversintered specimen. The gas sintered specimen exhibits M6C and Fe-Cr type primary carbides at the optimum sintering temperature. The eutectic carbides of $M_6C$ and Fe-Cr type and MX type carbonitride are shown for the oversintered specimen in the gas atmosphere. The hardness of gas sintered specimen shows high value of 830-860 Hv due to the increment of carbide precipitation.

• 대한용접접합학회:학술대회논문집
• /
• 대한용접접합학회 2002년도 Proceedings of the International Welding/Joining Conference-Korea
• /
• pp.551-554
• /
• 2002

As a general rule, the brazing process between cemented carbides and steel used by Silver (Ag) type brazing filler. The composition of Ag type filler were used Ag-Cu-Zn-Cd type filler mainly. But, the demand of Cadmium (Cd)-free in Ag type filler was raised recently. The reason why Cd-free in Ag brazing filler were occupied to vaporize as a CdO$_2$ when brazing process, because of Cd element was almost low boiling point of all Ag type filler elements. And, CdO$_2$ was a very harmful element for the human body. This experiment was developed Cd-freeing on Ag type filler that was used Indium (In) instead of Cd element. In this experiment, there were changed from 0 to 5% In addition in Ag brazing filler and investigated to most effective percentage of Indium. As a result, the change of In addition instead of Cd, there was a very useful element and obtained same property only 3% In added specimens compared to Cd 19% added specimens. These specimens were obtained same or more deflective strength. In this case, there were obtained 70 MPa over strength and wide brazing temperature range 650-800 C. A factor of deflective strength were influenced by composition and the shape of $\beta$ phase and between $\beta$ phase and cemented carbides interface. Indium element presented as $\alpha$ phase and non-effective factor directly, but it's occupied to solid solution hardening as a phase. $\beta$ phase were composed 84-94% Cu-Ni-Zn elements mainly. Especially, the presence of Ni element in interface was a very important factor. Influence of condensed Ni element in interface layer was increased the ductility and strength of brazing layer. Therefore, these 3% In added Ag type filler were caused to obtain a high brazing strength.

• Journal of Welding and Joining
• /
• 제2권1호
• /
• pp.4-17
• /
• 1984

Overlaid weld metals of austenitic stainless steel in a pressure vessel of power reactor are usually post-weld heated for a long period of time after welding. The PWHT is considered as a kind of sensitizing and it is important to check the soundness of the weld metal after PWHT, especially about the precipitation of carbides. The purpose of this report is to obtain information on the relation between the change of microstructure and Post-Weld Heat Treatment in the overlaid weld metals. Metallurgical aspects of the problem on austenitic stainless steel heated at $625^{\circ}C$, $670^{\circ}C$, $720^{\circ}C$ and $760^{\circ}C$ for 3, 10, 30, 100 and 300 hours have been investigated by means of optical-micrography, micro-hardness measurement, scanning electron microscope and electron-probe micro analysis. From the results obtained, the following conclusions are drawn; 1) The PWHT above $625^{\circ}C$ for a long time causes a diffusion of carbon atoms from low alloy steel into stainless steel, and consequently carbon is highly concentrated at the boundary layer of stainless steel. 2) C in ferritic steel migrated to austenitic steel and carbides precipitated in austenitic steel along fusion line. At higher temperatures, the ferrite grains coarsened in the decarburized zone. 3) In the change of microstructure of stainless steel overlaid weld metal, the width of carbides precipitated zone and decarburized zone increased with increase of PWHT temperature and time. 4) At about $625^{\circ}C$ to $760^{\circ}C$, chromium carbides, mainly $M_{23} C_6$, precipitate very closely in the carburized layer with remarkable hardening. 5) Precipitation of delta ferrite from molten weld metal depends on solidification phenomenon. There was a small of ferrite near the bond in which the local solidification time was short, comparing with after parts of weld metal. Shape and amount of ferrite were not changed by Post-Weld Heat Treatment after solidification.

• 한국재료학회지
• /
• 제13권9호
• /
• pp.581-586
• /
• 2003

3%C-18%Cr-1%Mo-2%Ni-1%Mn high chromium cast iron was casted and destabilized at temperatures of 900, 1000 and $1100^{\circ}C$ for 1, 2, 4 and 8hr under $N_2$atmosphere to observe the effect of destabilization temperature and time on the carbide and matrix structures. In as-cast condition, the microstructure consisted of $M_{ 7}$$C_3$ carbides and matrix structures which were composed of 91.50% austenite and 8.50% martensite. Numerous fine secondary carbides were observed in the specimens destabilized at $900^{\circ}C$ for 1, 2, 4 and 8hr. But, the number of secondary carbides were much reduced with the increased destabilization temperature. More austenite was formed in the matrix with the higher destabilization temperature. The amounts of austenite in the matrix were 4.23% at $900^{\circ}C$, 29.68% at $1000^{\circ}C$ and 66.51% at$ 1100^{\circ}C$, respectively. However, the effect of destabilization time on the secondary carbide and matrix was very weak compared with that of destabilization temperature. The ranges of the amount of austenite in the matrix from 1hr to 8hr destabilization heat treatment were: 3.95%-4.35% at $900^{\circ}C$, 28.89%-30.15% at $1000^{\circ}C$ and 65.13%-67.12% at $1100^{\circ}C$, respectively. The variation ranges were very narrow. The equilibrium concentration of C and Cr in austenite was already reached within 1hr during destabilization heat treatment. After an attainment of the equilibrium concentration of C and Cr in austenite, no more secondary carbide was precipitated from the matrix.