[논문]700 MPa급 고강도 내진 철근의 미세조직과 기계적 특성에 미치는 템프코어 공정의 영향

신승혁; 김승규; 임휘강; 황병철

doi:10.5228/kstp.2021.30.2.91

700 MPa급 고강도 내진 철근의 미세조직과 기계적 특성에 미치는 템프코어 공정의 영향
Effect of TempCore Processing on Microstructure and Mechanical Properties of 700 MPa-Grade High-Strength Seismic Resistant Reinforced Steel Bars 원문보기

소성가공 = Transactions of materials processing : Journal of the Korean society for technology of plastics, v.30 no.2, 2021년, pp.91 - 98

신승혁 (서울과학기술대학교 신소재공학과, 대학원) , 김승규 (서울과학기술대학교 신소재공학과) , 임휘강 (서울과학기술대학교 신소재공학과) , 황병철 (서울과학기술대학교 신소재공학과)

Abstract ▼ AI-Helper

The present study deals with the microstructure and mechanical properties of 700 MPa-grade high-strength seismic resistant reinforced steel bars fabricated by various TempCore process conditions. For the steel bars, in the surface region tempered martensite was formed by water cooling and subsequent self-tempering during TempCore process, while in the center region there was ferrite-pearlite or bainite microstructure. The steel bar fabricated by the highest water flow and the lowest equalizing temperature had the highest hardness in all regions due to the relatively fine microstructure of tempered martensite and bainite. In addition, the steel bar having finer microstructures as well as the high fraction of tempered martensite in the surface region showed the highest yield and tensile strengths. The presence of vanadium precipitates and the high fraction of ferrite contributed to the improvement of seismic resistance such as high tensile-to-yield strength ratio and high uniform elongation.

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표/그림 (7)

표 Table 1 TempCore process conditions and microstructures of the reinforced steel bars investigated in this study
그림 Fig. 1 Schematic diagram of TempCore process used for the fabrication of high-strength reinforced steel bars
그림 Fig. 2 Optical micrographs of the reinforced steel bars fabricated by TempCore Process. Microstructure was observed on the surface and center regions of the steel bars
그림 Fig. 3 SEM micrographs of the reinforced steel bars fabricated by TempCore Process. Microstructure was observed on the surface and center regions of the steel bars
$Fig. 4 Photographs of the cross-section of the reinforced steel bars. The volume fraction of tempered martensite (V<sub>TM</sub>) was determined from hardenability depth (d<sub>h</sub>) corresponding to the average thickness of relatively dark regions in each steel bar. In the photographs, relatively dark regions are hardened regions indicating the formation of tempered martensite$ 그림 Fig. 4 Photographs of the cross-section of the reinforced steel bars. The volume fraction of tempered martensite (V_TM) was determined from hardenability depth (d_h) corresponding to the average thickness of relatively dark regions in each steel bar. In the photographs, relatively dark regions are hardened regions indicating the formation of tempered martensite
그림 Fig. 5 Hardness as a function of location of the reinforced steel bars
표 Table 2 Mechanical properties of the reinforced steel bars investigated in this study

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