• 한국분말재료학회지
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• 제4권4호
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• pp.243-251
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• 1997

Engine valve-shaped TiAl-Mn intermetallics containing 43.5 to 47.5at%Al (Mn/Al=0.036) are successively fabricated by reactive sintering the elemental powder mixtures near-net shaped by extrusion and die forging. A duplex structure consisted of lamellar grains and equiaxed $\gamma$ grains is developed for all compositions, and the areal fraction of the lamellar grains(or equiaxed $\gamma$ grains) decreases (or increases) with increasing Al content. As Al content increased, the elongation increases with accompanying decrease in yield strength and ultimate tensile strength at both room temperature and 80$0^{\circ}C$. This indicates that the suitable composition is Ti-45at%Al-1.6at%Mn in considering the balance of ambient and elevated tensile properties. The reactive-sintered Ti-45Al-1.6Mn alloy shows superior oxidation resistance not only to the plasma arc melted one but also to the heat resistance steel STR35(representative exhaust valve head material for automotive engine). The reactive-sintered Ti-45Al-1.6Mn alloy coated with an oxidizing scale exhibits a better wear resistance than induction hardened martensitic steel STR11(representative exhaust valve tip material for automotive engine).

• Journal of Welding and Joining
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• 제25권3호
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• pp.78-84
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• 2007

Laser Material Processing has been replaced the conventional machining systems - cutting, drilling, welding and surface modification and so on. Especially, LTH(Laser Transformation Hardening) process is one branch of the laser surface modification process. Conventionally, some techniques like a gas carburizing and nitriding as well as induction and torch heating have been used to harden the carbon steels. But these methods not only request post-machining resulted from a deformation but also have complex processing procedures. Besides, LTH process has some merits as : 1. It is easy to control the case depth because of output(laser power) adjustability. 2. It is able to harden the localized and complicated a.ea and minimize a deformation due to a unique property of a localized heat source. 3. An additional cooling medium is not required due to self quenching. 4. A prominent hardening results can be obtained. This study is related to the surface hardening of the rod-shaped carbon steel applied to the lathe based complex processing mechanism, a basic behavior of surface hardening, hardness distribution and structural characteristics in the hardened zone.

• 대한기계학회논문집
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• 제13권3호
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• pp.451-460
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• 1989

본 논문에서는 기계용 부품소재로 많이 사용되는 SM45C에 대하여 이온질화 처리시 N$_{2}$:H$_{2}$ 가스조성비 변화에 따른 효과가 반복인장-압축하중을 받는 부식피로파괴의 거동에 미치는 영향을 중점적으로 연구하였다.

• 한국재료학회지
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• 제12권7호
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• pp.568-572
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• 2002

Plasma sulfnitriding technology was employed to harden the surface of SKD61 steel. The plasma sulfnitriding was performed with 3 torr gas pressure at $580^{\circ}C$ for 20 hours. Plasma sulfnitriding resulted in the formation of very thin $2-3\mu\textrm{m}$ FeS sulfide layer on top of $15-20\mu\textrm{m}$ compound layer, which consisted of predominantly $\varepsilon$- $Fe{2-3}$ N and a second phase of $\Upsilon'-Fe_4$N. In comparision with plasma nitriding treatment, plasma sulfnitriding treatment showed better surface roughness and corrosion resistance due to the presence of the thin FeS layer. which coated microvoids and microcracks on top of the nitrided layer. It was also found that plasma sulfnitrided sample showed better wear resistance due to the presence of the thin FeS layer which acted as a solid lubricant.

• 열처리공학회지
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• 제3권2호
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• pp.10-19
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• 1990

The tempering behavoirs of 0.45% carbon steel treated by automatic progressive high frequency induction hardening equipment have been investigated. In order to examine the correlation of hardness with both tempering temperature and time, simple regression analysis has been made using the statistical quality control package. The maximum surface hardness value of induction hardened zone and its effective hardening depth have been determined to be Hv 810 and 0.76mm, respectively. The hardness obtained after tempering has been shown to vary lineary with tempering time at six different temperatures. The activation energies during tempering have been calculated to be 25.34kcal/mole, 32.73kcal/mole and 49.24kcal/mole for HRcs 60, 50 and 40, respectively, showing that tempering process occurs by a complex mechanism, The tempering hardness equation of $H=90.113{\sim}4.531{\times}10^{-3}$ [T(11.996+log t)] has proved to be in a reasonably good agreement with experimently determined data and it is also expected to be useful for the determination of tempering treatment conditions to obtain a required hardness value.

• 한국재료학회지
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• 제22권11호
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• pp.591-597
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• 2012

For heat exchanger applications, 2-ply clad materials were fabricated by rolling of aluminum (Al) and mild steel sheets. Effects of annealing temperature on interface properties, especially on inter-layer formation and softening of strain hardened mild-steel, for Al/mild steel clad materials, were investigated. To obtain optimum annealing conditions for the Al/mild steel clad materials, annealing temperature was varied from room temperature to $600^{\circ}C$. At the annealing temperature about $450^{\circ}C$, an inter-layer was formed in an island-shape at the interface of the Al/mild steel clad materials; this island expanded along the interface at higher temperature. By analyzing the X-ray diffraction (XRD) peaks and the energy dispersive X-ray spectroscopy (EDX) results, it was determined that the exact chemical stoichiometry for the inter-layer was that of $Fe_2Al_5$. In some samples, an X-layer was formed between the Al and the inter-layer of $Fe_2Al_5$ at high annealing temperature of around $550^{\circ}C$. The existence of an X-layer enhanced the growth of the inter-layer, which resulted in the delamination of the Al/mild-steel clad materials. Hardness tests were also performed to examine the influence of the annealing temperature on the cold deformability, which is a very important property for the deep drawing process of clad materials. The hardness value of mild steel gradually decreased with increasing annealing temperature. Especially, the value of hardness sharply decreased in the temperature range between $525^{\circ}C$ and $550^{\circ}C$. From these results, we can conclude that the optimum annealing temperature is around $550^{\circ}C$ under condition of there being no X-layer creation.

• 한국생산제조학회지
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• 제9권2호
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• pp.87-95
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• 2000

By using AIP(Arc Ion Plating) of a physical vapor deposition for the first time in Korea a ceramic tool whose surface is coated single layeredly with TiN is developed. In addition cutting resistance appearing in the process of finishing cut of hardened carbon tool steel STC3 is studied. The principal and radial components of cutting resistance in those cutting conditions appear to be the same or similar and the feed component is relatively small. The feed component is found to be in proportion to cutting width and the radial component in proportion to cutting thickness. Owing to coating the cutting resistance of a TiN coated ceramic tool increas-es compared with that of a general ceramic tool.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2002년도 춘계학술대회 논문집
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• pp.69-72
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• 2002

The geometry parameter of tool such as rake angle and clearance angle is defined clearly to solve the difference in communication between design and measurement stage. Using the developed simulation program, wheel is properly determined and end mill can be manufactured accurately. The performance test with well defined end mill provides sufficient information to decide optimal geometry. For machining hardened steel, end mills are designed and manufactured. Optimal rake angle and clearance angle is obtained from performance test. A specific software for automatic end mill production is developed far simulation and fur generation of NC code as Cad/CAM system.

• 한국정밀공학회지
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• 제14권12호
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• pp.121-126
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• 1997

The use of CBN tool material has been greatly increased because of the superior metal cutting performance for the machining of hardened steel. This paper presents some experimental results on the ball endmiling of harened steels. Three different hardnesses of STD11 workpieces were machined using CBN ball endimills, and the machining characteristics including cutting forces tool wear, and surface roughness of machined surface were compared. It has been found that the CBN ball endmill works better in the machining of harder workpieces. The microscopic examination explains that this unusual phenomenon is caused by the difference of microstructure of each workpieces.

• Tribology and Lubricants
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• 제9권2호
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• pp.56-62
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• 1993

Al-Pb-Cu and Al-Si-Pb-Cu bearing alloys were produced by forced-stirring method and water-cooled copper mold casting to investigate the effect of the precipitation hardening on the wear properties. Sliding of produced alloy pin against a steel disc were performed under various applied loads. Lowering the wear rate and material transfer phenomena were explained by the strengthening of $\theta'$ precipitates on AI matrix. The transmission electron microscope observation reveals the role of the precipitates in the alloys with Cu. The movement of dislocations was hindered by precipitates which resulted in the reduction of plastic deformation at the worn surfaces.