• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 1998.10a
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• pp.313-322
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• 1998

Tappet has wear problems like scuffing or pitting because of high Hertzian contact stress by line contact type between cam and tappet. To overcome this wear problems, we developed the high wear resistant tappet. Developed tappet consists of WC base alloyed tip and steel body. These two parts were directly bonded each other at high temperature under vacuum condition. To estimate the wear resistance of tungsten carbide tappet, we perform the scuffing test and engine dynamo test. As the result, tungsten carbide tappet has better wear resistance than conventionally chilled iron tappet.

• Proceedings of the KWS Conference
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• 2010.05a
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• pp.1-10
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• 2010

강재의 구조화에 필수적인 용접 공정 후의 저합금강 용접 열영향부 미세조직 및 재질 예측을 위해 가열 중 상변태 거동에 미치는 초기 결정립 크기의 영향, 석출물-free 오스테나이트 결정립 성장 예측 모델, 임계 석출물 크기의 영향을 고려한 용접 열영향부 석출물 조대화 예측 모델, 석출물의 Kinetics을 고려한 결정립 성장 모델, 초기 오스테나이트 결정립크기 및 냉각 속도의 영향을 고려한 용접 열영향부 상변태 모델, 용접 열영향부 경도 예측 모델 등에 대해 연구를 수행하였다. 이를 통해 작성된 최종 모델은 실 용접부와의 비교를 통해 신뢰성을 확인하였으며, 저합금강 용접 열영향부의 미세조직과 경도값을 잘 예측하는 것으로 판단된다. 따라서 본 연구를 통해 작성된 모델을 통하여 용접 열영향부에서의 용접부 품질을 확인하기 위한 시간적, 경제적 비용을 절감할 수 있을 것으로 기대된다.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2009.05a
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• pp.102-106
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• 2009

Thermal energy control is a important factor in a large size casting and forging. Good control of thermal energy makes characteristics and defect of large cast-forged part, such as large sized forged shell. We have studied about not only large size ring forging process and after heat treatment by FEM simulation. Also, changes of temperature and microstructure for forged shell were predicted. Therefore, we can choose the proper heat treatment condition by FEA. The sectional properties confirmed by practical experiment and evaluation have presented possibilities of process design by computational analysis.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09a
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• pp.692-693
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• 2006

Behavior of stoichiometric and near-stoichiometric NiAl at plasma spray deposition, without and with a bond coat, for coating layers realization on a low alloyed steel substrate, has been investigated. In all variants, NiAl particle melting and subsequent welding at the impact with substrate were observed, forming a relatively compact and adherent coating layer with the NiAl stability maintaining - all assuring the coating layer oxidation and corrosion resistance. Good results from these points of view, also validated through corrosion tests, were obtained for 45:55 Ni:Al composition without a bond coat but adopting an Ar protective surrounding of plasma jet.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09a
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• pp.385-386
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• 2006

For attaining optimum fatigue resistance of PM steels, high density levels are necessary. In this work, sintered steels Fe-1.5%Mo-0.6%C and Fe-1.5%Cr-0.2%Mo-0.6%C were produced with density levels of 7.1 to $7.6\;g.cm^{-3}$. Ultrasonic fatigue testing with 20 kHz was performed in push-pull mode up to 10E9 cycles. It was shown that the fatigue endurance strength is strongly improved by higher density levels, but also higher sintering temperatures are beneficial. The Cr-Mo steels proved to be superior to the plain Mo alloyed, due to a more favourable as-sintered matrix microstructure.

• Proceedings of the KWS Conference
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• 2002.10a
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• pp.29-37
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• 2002

High alloyed stainless steels stand out for a high corrosion resistance due to a protective passive layer which is formed when the content of chromium exceeds 13%. When welding these steels, heat tints arise in the area of the weldment. They may occur from flint yellow to intensive blue in the spectrum depending on the applied welding process and the quality of the backing gas used. Due to their structures, they partly drastically reduce the corrosion resistance of stainless steels so that they may lead to damages of the technical application of welded components. In the following the pitting resistance by different backing gases and the chemical composition of the stainless steel itself are described.

• Tribology and Lubricants
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• v.36 no.3
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• pp.124-132
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• 2020

The effect of the stoichiometry on the sliding wear properties of NiAl coatings has been investigated. Three different powder mixtures with the compositions of Ni-50at%Al, Ni-54at%Al and Ni-42at%Al were diepressed respectively, and which were subsequently coated on mild steel through combustion synthesis in an induction heating system. Sliding wear behavior of the coatings was examined against an alloyed tool steel using a pin-on-disc type sliding wear test machine. As results, it could be seen that powder mixture(Ni-54at%Al) with displaying Al-rich deviations from the stoichiometry of NiAl(Ni-50at%Al) was promoted the most the synthetic reactivity. The microstructure of the coating layer with the compositions of Ni-54at%Al exhibits the porous NiAl single phase structure. However, the microstructure of the coating layer of the compositions of Ni-42at%Al exhibits the denser multi-phase structure containing several intermediate phases in addition to NiAl. Densification of the coating layer was enhanced by increasing the reacting temperature. On the other hand, the wear properties of the coating layers showed that the wear mode at speeds of around 1 m/s was severe wear, regardless of the stoichiometry and reacting temperature. However, wear properties of coating layer with the compositions of Ni-42at%Al were superior to those of coating layer with the compositions of Ni-54at%Al. This would be attributed by the fact that coating layer with the compositions of Ni-42at%Al develops little void and much intermediate phases with high strength.

• Journal of Welding and Joining
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• v.34 no.1
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• pp.21-25
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• 2016

The automotive vehicle is made through the following processes such as press shop, welding shop, paint shop, and general assembly. Among them, the most important process to determine the quality of the car body is the welding process. Generally, more than 400 pressed panels are welded to make BIW (Body In White) by using the RSW (Resistance Spot Welding) and GMAW (Gas Metal Arc Welding). Recently, as the needs of light-weight material due to the $CO_2$ emission issue and fuel efficiency, new joining technologies for aluminum, CFRP (Carbon Fiber Reinforced Plastic) and etc. are needed. Aluminum parts are assembled by the spot welding, clinching, and SPR (Self Piercing Rivet) and friction stir welding process. Structural adhesive boning is another main joining method for light-weight materials. For example, one piece aluminum shock absorber housing part is made by die casting process and is assembled with conventional steel part by SPR and adhesive bond. Another way to reduce the amount of the car body weight is to use AHSS (Advanced High Strength Steel) panel including hot stamping boron alloyed steel. As the new materials are introduced to car body joining, productivity and quality have become more critical. Productivity improvement technology and adaptive welding control are essential technology for the future manufacturing environment.

• Korean Journal of Materials Research
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• v.21 no.1
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• pp.50-55
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• 2011

Energy resistance welding (ERW) is a pipe-producing process that has high productivity and low manufacturing cost. However, the high heat input of ERW degrades the mechanical property of the pipe. This study investigates the effect of heat input and alloying elements on microstructure and mechanical properties of ERW pipes. As the heat input increased, the ferrite amount increased. The ferrite amount in the weld centerline was larger than t at in the weld boundary. Medium carbon steels (S45C and K55) having 0.3~0.4wt.% carbon yielded a significant difference of ferrite amount in the weld centerline and weld boundary. High alloyed steels (DP780 and K55) having 1.5~1.6wt.% Mn showed a ferrite rich zone in the weld centerline. These phenomena are probably due to decarburization and demanganisation in the weld centerline. As the ferrite fraction increased, the hardness decreased a little for the S45C steels. In addition, DP780 steels and K55 steels showed that the hardness drops when those steels have a ferrite rich zone. But we demonstrated the good tensile property of the DP780 steels and K55 steels in which Mn is included.

• Transactions of Materials Processing
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• v.32 no.2
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• pp.81-86
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• 2023

The hot stamping process is widely used for high strength of vehicle parts, with heating 900 ℃ or higher in a furnace and in-die quenching to achieve strength above 1.5 GPa of the quenchable boron alloyed steel 22MnB5. First of all, the hot stamping process consisted of heating, forming, quenching and trimming. In the trimming process case, the laser method has been conventionally adopted. For laser trimming process, it has the problems pertaining to low productivity and high cost while the hot stamping process, accordingly the trimming process need to investigate the research for alternative method. In order to overcome these issues, many research groups have studied the mechanical trim solution on the hot stamped parts at high temperature. In this study, the mechanical piercing was performed during the hot stamping process at the high temperature for overcome the disadvantages of laser cutting. Also, the process parameters such as piercing time after die closing, clearances of between die and punch were controlled for obtaining the reasonable shear characteristics.