• 한국생산제조학회지
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• 제26권3호
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• pp.337-343
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• 2017

The laser cladding process on structural steel (SCM440) and gray cast iron (GC250) substrates with Co-based powder (Stellite 12) was studied. A diode laser (2 kW) was used as a heat source, and the powder was supplied by a disc rotary powder feeder. The relationship between the laser cladding process and the cross-sectional analysis of coating was examined based on coating shape and microstructure. Additionally, the microhardness was measured to confirm the mechanical property improvements. As a result, proper laser cladding conditions were selected through this study and verified by cross-sectional analysis. In addition, the evaluation process for laser cladding feasibility was conducted on the selected materials.

• 열처리공학회지
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• 제7권3호
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• pp.184-189
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• 1994

The heat treatment charaterristic of SCM 440 and B 16 steels has been investigated in various condition(A, B and C) to the effect of heat treatment on mechanical properties, and the following results were obtained. 1. We are obtained a good nitriding characteristic in bainitic structure than other heat treatment cycle in our experiment. 2. Fatigue characteristic has shown in order of B)C)A condition as heat treatment cycle. 3. The effective hardening depth and fatigue characteristic has been excellented in B 16 than SCM 440 after the nitriding and Q. T for Band C condition. 4. Nitriding depth has been increased in addition of Cr, V and the nitriding efficiency is increased as easiness of banite formation to wide range of cooling rate by addition of Mo. 5. The depth of compound layer in parallel surface, notched slop plane and notched bottom has been varied to the nitriding depth of 5, 4 and 3 ${\mu}$ in relatively uniform pattern after 10h nitriding treatment for SCM 440 into A condition.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2008년도 추계학술대회B
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• pp.2750-2753
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• 2008

This paper introduce the CFD analysis for predicting the heat transfer at the Ultrasonic horn. Approximately Ultrasonic horn separates two part. One is preheating part and the other is cooling part. Temperature of preheating part rise up by $260^{\circ}C$ that make it possible to attach a chip to a semiconductor. Also there is a piezo material in the cooling part. When piezo work, it generates heat of $100^{\circ}C$. It can stand by $150^{\circ}C$. But the high temperature conducted from the preheating part has a bad affect on the piezo. These situation make it necessary cooling at piezo. Previously except of the piezo, all of them are composed of the SUS440c that has good thermal conductivity. This study shows way that not only cooling the piezo but also cutting off the conduction between preheating part and cooling part by using the Ti and Duralumin that have low thermal conductivity compare with the SUS440c. Conclusion of CFD analysis that the heat coming from the piezo can't be transferred the horn cause of the Ti and Duralumin.

• 열처리공학회지
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• 제26권3호
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• pp.120-125
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• 2013

In this study, the effect of tempering treatment on the mechanical properties in modified 440A steel has been investigated. The amount of remaining carbide decreased with increasing the austenitizing treatment temperature, and all carbides were completely dissolved at $1250^{\circ}C$. The amount of remaining carbide decreased with increasing the time of austenitizing, but the carbide remained insoluble up to 120 minutes at $1050^{\circ}C$. With increasing the tempering temperature, tensile strength decreased, and elongation increased slowly, while hardness rapidly decreased, and impact value unchanged and then rapidly increased over $500^{\circ}C$. The strength and hardness slowly decreased, while the elongation and impact absorbed energy increased with increasing the tempering time. $Cr_{23}C_6$ type carbide was precipitated and sharp decrease of elongation and toughness by tempering did not appear.

• 한국표면공학회지
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• 제48권6호
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• pp.275-282
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• 2015

The cost for maintenance (replacement cost) of Ni-superalloy components in plant industry is very expensive because of high unit price of INCONEL 718. A development of repairing technology using kinetic spray process can be very helpful for reducing the maintenance cost. However, it is very difficult to produce well-deposited INCONEL 718 layer showing high interfacial bond strength via kinetic spraying. Thus, INCONEL 718 was deposited on SCM 440 substrate and the interfacial properties were investigated, in order to elucidate the cause of hindrance to the bonding between INCONEL 718 layer and SCM 440 substrate. As a result, it was revealed that the dominant obstacle to the interfacial bonding was excessive compressive residual stress accumulated in the coating layer, resulting from low plastic-deformation susceptibility of INCONEL 718. Nevertheless, the bonding state was enhanced by the post heat-treatment through relieving the residual stress and generating a diffusion/metallurgical bonding between the INCONEL 718 deposit and SCM 440 substrate.

• 한국재료학회지
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• 제29권4호
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• pp.258-263
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• 2019

Since the directly bonded interface between TiAl alloy and SCM440 includes lots of cracks and generated intermetallic compounds(IMCs) such as TiC, FeTi, and $Fe_2Ti$, the interfacial strength can be significantly reduced. Therefore, in this study, Cu is selected as an insert metal to improve the lower tensile strength of the joint between TiAl alloy and SCM440 during friction welding. As a result, newly formed IMCs, such as $Cu_2TiAl$, CuTiAl, and $TiCu_2$, are found at the interface between TiAl alloy and Cu layer and the thickness of IMCs layers is found to vary with friction time. In addition, to determine the relationship between the thickness of the IMCs and the strength of the welded interfaces, a tensile test was performed using sub-size specimens obtained from the center to the peripheral region of the friction-welded interface. The results are discussed in terms of changes in the IMCs and the underlying deformation mechanism. Finally, it is found that the friction welding process needs to be idealized because IMCs generated between TiAl alloy and Cu act to not only increase the bonding strength but also form an easy path of fracture propagation.

• 한국의학물리학회지:의학물리
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• 제5권2호
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• pp.13-20
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• 1994

본 연구에서는 감마선 조사, 전자선 조사방법에 의한 전자만의 주업 및 이온 주업 후 전자선조사 방법으로 전자들이 주입된 $\alpha$-$Al_2O_3$의 열자극 발광(Thermoluminescence : TL)에 관련된 결함 형태를 조사하였다. 감마선 조사된 $\alpha$-$Al_2O_3$의 열자극 발광 곡선은 380K, 415K, 440K, 460K 및 475K에서 TL peak가 나타났다. 광흡수 스펙트럼과 자외선 photobleaching 결과로부터 감마선 조사된 $\alpha$-$Al_2O_3$의 380K와 475K TL peak는 F center에, 415K TL peak는 $F^{+}$ center에 기인함을 알았다. 전자선 조사방법에 의하여 전자 주입된 $\alpha$-$Al_2O_3$의 열자극 발광 곡선은 380K, 415K, 440K 및 460K TL peak를 가졌고, $Li^{+}$ 이온 주입 후 전자선 조사방법으로 전자들이 주입된 $\alpha$-$Al_2O_3$는 440K에서 TL peak가 나타났다. 전자선 조사방법에 의한 전자만의 주입과 $Li^{+}$ 이온 주입 후 전자선 조사방법으로 전자들이 주입된 $\alpha$-$Al_2O_3$의 열자극 발광 특성은 380K TL peak는 F center에, 440K TL peak는 $F^{+}$ center에 기인함을 보였다.

• 한국산학기술학회논문지
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• 제20권8호
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• pp.133-138
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• 2019

본 논문은 자동차 구조용 열간 압연 강재인 SAPH440을 GMAW 겹치기 용접을 하여 용접 변수인 용접 전류, 용접 전압, 이송 속도를 달리하여 인장 특성을 평가하였다. GMAW 공정의 접합 변수에 따라 인장 시험을 수행하기 위하여 겹치기 용접 하여 KS B ISO 9018에 따라 시험편을 제작하여 실험하였다. 각 조건에 따른 비드 외관을 관찰하였고 그에 따른 인장시험을 하여 용접성을 평가하였다. 평가 결과 용접전류가 높을수록 깊은 용입이 형성되는 것을 알 수 있었으나 인장강도 측면에서는 모재부 파단으로 인해 일정 변수 이상부터는 큰 차이는 없는 것으로 확인되었다. 용접 전류 200A, 용접 전압 17V의 조건에서와 같이 전압에 비해 전류가 높으면 다량의 스패터가 발생하며 용접이 불안정하고 이로 인해 용접부 파단이 일어나는 것을 확인 하였다. 전압이 높을수록 대체로 결함이 발생 되지 않을 정도의 비드외관을 관찰할 수 있었으며 너무 높은 전압 또한 용접성에 영향을 끼치는 것을 확인하였다. 너무 낮은 전류와 전압의 조건에서는 용접이 정상적으로 되지 않아 인장강도를 측정할 수 없었다. 그러나 용접이 가능한 용접 조건에서는 전류가 증가함에 따라 전압과 이송속도가 증가하더라도 인장강도에는 큰 영향을 미치지 않았다.

• 열처리공학회지
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• 제4권3호
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• pp.54-62
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• 1991

The effect of tempering temperature on the ultrasonic propagation velocity at SCM 440 steel quenched from $870^{\circ}C$ and $1000^{\circ}C$ has been studied by metallurgical and crystallographical observation. The measurements of ultrasonic velocity were made on the specimen by appling an immersion ultrasonic pulse-echo technique with a constant frequency of 10 MHz. The quenched microstructure of this steel was a lath martensite. As the tempering temperature was increased, the martensite was transformed into the tempered martensite composed of cementite and carbide. The ultrasonic velocity increased with increasing the tempering temperature. It was thought that these were resulted from the microstructural transformation. The change of ultrasonic propagation velocity with quenching and tempering heat treatment was resulted from microstrain due to the change of internal stress. Considering these results concerning to the change of ultrasonic propagation velocity. the phenomena of microstructural transformation were estimated. Consequently, it was thought that the degree of quenching and tempered heat treatment of steel could be nondestructively evaluated with the change of ultrasonic propagation velocity.

• 대한수학회논문집
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• 제9권4호
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• pp.873-879
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• 1994