• Tribology and Lubricants
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• v.34 no.6
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• pp.254-261
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• 2018

In order to reduce resistance torque and energy loss, minimizing friction between race surface and rolling elements of a bearing is necessary. Recently, to reduce friction in bearing element, solid lubricant coating for the bearing raceway surface has been receiving much attention. Considering the operating conditions of real bearings, verifying the effect of solid lubricant coatings under extreme conditions of high load that is more than 1 GPa is necessary. In this study, we evaluated the friction and wear characteristics of SUJ2 bearing steels deposited by carbon-based coatings (Si-DLC, ta-C), $MoS_2$ and graphite. In case of $MoS_2$ and graphite coatings, different surface treatments were applied to the coatings to verify the effect of surface treatment. A pin-on-disc type tribotester was used to evaluate the tribological characteristics of the coatings. It was possible to quantitatively estimate the friction and wear characteristics of solid lubricant under dry and lubrication conditions. The carbon-based coatings improved the friction and wear properties of SUJ2 bearing steels under the high load condition, but $MoS_2$ and graphite coatings were not suitable for high load conditions due to its low hardness. Different friction and wear behaviors were found for different substrate surface treatment method. Also, it was confirmed that solid lubricant coatings had a more positive effect than just applying the lubricant for improving the tribological characteristics.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.8 no.1
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• pp.24-30
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• 2009

In this paper, the effect of heat treatment on forgeability is investigated and an improved heat treatment cycle is proposed for the bearing steel, SUJ2. An application example of a bearing inner race cold forging, which has small cracks in the bottom after backward extrusion and piercing, is found from a cold forging industry. The process is evaluated by finite element analysis and several heat treatment cycles are examined in order to propose an improved heat treatment cycle. The effect of heat treatment on material hardness and tool life, dimensional accuracy and forming load is revealed through experiment.

• Tribology and Lubricants
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• v.38 no.4
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• pp.170-178
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• 2022

Mechanical surface treatment is an excellent approach widely used to modulate and improve the performance and service life of bearings, gears, and frictional joints. The main purpose of this study is to investigate and compare the effect of ultrasonic nanocrystal surface modification (UNSM) and wonder process craft (WPC) on the surface and tribological properties of SUJ2 bearing steel. The surface roughness and hardness of the untreated and treated (UNSM- and WPC-treated) specimens were measured and compared. Their tribological properties were evaluated using a micro-tribometer under grease-lubricated and dry conditions against itself. Surface hardness measurement results revealed that both the UNSM- and WPC-treated specimens had a higher hardness than that of the untreated specimen. The surface roughness of the untreated specimen was reduced after UNSM and WPC treatments. Abrasive wear mode was observed on the surface of the specimens worn under grease-lubricated conditions, while adhesive wear mode was found on the surface of the specimens worn in dry conditions. According to the tribological test results, the friction coefficient and wear rate of the untreated specimens were reduced by the application of both the UNSM and WPC treatments under grease-lubricated and dry conditions.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2012.11a
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• pp.101-102
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• 2012

Thermal Diffusion Process(TD Process)을 통하여 베어링강 소재인 SUJ2 표면에 Vanadium Carbide를 석출시켜 표면 물성에 관한 연구를 진항하였다. $900{\sim}950^{\circ}C$ 온도와 2~6H 공정시간에 따라 TD Process에 의한 코팅층의 변화를 Micro Vikers Hardness Tester와 광학현미경, SEM, EDS를 통하여 관찰하였다. 그 결과 공정시간 및 온도는 코팅층 성장과 비례한다는 것을 확인 할 수 있었고 SUJ2 표면에 성장된 코팅층은 높은 경도값을 갖는 VC, CrC 코팅층임을 확인하였다.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2015.05a
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• pp.96-97
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• 2015

확산을 이용한 표면 개질법인 Thermo-Reactive Diffusion(TRD) 기술 기반 2단 표면처리를 통해 고경도의 Nb(C,N) 코팅층을 고탄소 베어링강인 JIS-SUJ2강에 형성시켰다. 2단 표면처리는 암모니아 가스 질화와 분말 확산 코팅법으로 구성된 2step 열처리이다. 본 연구에서는 가스질화 화합물층의 두께가 코팅층 성장 거동에 어떤 영향을 미치는지 알아보기 위해서 $550^{\circ}C$에서 3, 6시간 암모니아 가스 분위기에서 가스질화를 실시하고, $900^{\circ}C$에서 3시간 분말 확산법을 통해 표면 코팅층을 형성하였다. 생성된 코팅층의 형상과 두께 측정을 광학현미경(OM) 과 주자전자현미경(SEM)을 통해 한 결과, 가스 질화는 약 10uu와 16um, 최종 코팅층은 약 정도 생성이 되었음을 확인하였다. 코팅층의 성분 분석은, EDS, FE-EPMA, XPS 분석을 통해서 실시하였다. EDS와 FE-EPMA 원소 mapping을 통해 모재에 비해 높은 농도의 Nb, C 그리고 N이 코팅층 내부에 존재함을 확인하였다. XPS분석의 결합에너지 peak를 통해 NbC, NbN 그리고 Nb-oxide가 생성이 되었음을 분석하였다. 생성된 코팅층의 경도는 low mode에서 10회 측정한 후 평균값을 내었고, 각각 Hv이었다.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.35 no.9
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• pp.1119-1129
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• 2011

Shot-peening effects on the fatigue behavior of bearing steel were investigated under the high cyclic loading. Hourglass shape specimens were made of bearing steel(JIS-SUJ2) for rotary bending fatigue tests. Two kinds of treatments were performed : a heat treatment and a shot-peened surface treatment after the heat treatment. The fracture surfaces of specimens were classified into two types of fracture mode : the surface fracture mode induced by a surface defect and the internal fracture mode induced by a nonmetallic inclusion. Inclusion depth and shape affected considerably the fatigue life. Shot-peening treatment improved much the fatigue life of the bearing steel under low and high levels of cyclic loads. Probabilistic-stress-life (P-S-N) curves were suggested for the reliable fatigue life estimation of the improved bearing steel.