초음파 나노 표면 개질(UNSM) 기술에 따른 베어링강의 VHCF 특성 = VHCF(Very High Cycle Fatigue) Characteristics of Bearing Steel by UNSM(Ultrasonic Nano-Crystal Surface Modification) Technology

다국어 초록 (Multilingual Abstract)

STB2 of bearing steel is used for roller bearing and ball bearing due to their high wear resistance and impact resistance. Among many useful surface strengthening technologies, ultrasonic nanocrystal surface modification (UNSM) technology is promising for increasing fatigue strength and wear resistance, and reducing friction as well. The main idea to apply UNSM technology for improving both bending fatigue strength and rolling contact fatigue strength of slim bearing rings is applying not only raceway but also the opposite side of the raceway - in other words, outer side of the outer ring and inner side of the inner ring. The test specimens for the rotary bending fatigue test were made of STB2 bearing steel and treated by the UNSM technology. In this study, fatigue result that was subjected to different loads of the UNSM treatment was investigated and compared with that of the untreated specimen. The microhardness of the UNSM-treated specimens increased by about 20%, higher than that of the untreated specimens. The X-ray diffraction analysis showed that a compressive residual stress of more than 1,000 MPa was induced after the UNSM treatment. Also, electron backscatter diffraction analysis was used to study the surface structure and nanograin refinement. The results showed that the rotary bending fatigue life and fatigue strength of the UNSM-treated specimens increased by about 80% and 31%, respectively, compared to those of the untreated specimen. These results might be attributed to the increased microhardness, the induced compressive residual stress, and the nanocrystal structure modification after the UNSM treatment. In addition, the fracture surface analysis showed that the fish eye crack initiation phenomenon was observed after the UNSM treatment.

목차 (Table of Contents)

• ABSTRACT
• 1. Introduction
• 2. Experimental method and specimen
• 3. Results and discussion
• 4. Conclusion
• Acknowledgement
• 5. Reference