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균질화, 열간단조, 어닐링 조건이 개량된 STD61 열간 금형강의 미서― 조직과 경도에 미치는 영향
박규진 ( Gyu Jin Park ),강민우 ( Mm Woo Kang ),정재길 ( Jae Gii Jung ),이영국 ( Young Kook Lee ),김병훈 ( Byung Hoon Kim ) 한국열처리공학회 2013 熱處理工學會誌 Vol.26 No.2
The effects of homogenization, hot-forging, and annealing condition on microstwcture and hardness of a modified STD61 hot-work tool steel were investigated. The ingot specimen had a dendritic structure consisting of bainite and martensite. Spherical VC particles of approximately 50 nm and cuboidal (V, TI)C particles of about 100 nm were observed in the ingot specimen. After homogenization, the dendritic structure was blurred, and the difference in hardness between martensite and bainite became narrow, resulting in the more homogeneous microstructure. Needle-shaped non-equilibrium (Fe, Cr)3C particles were additionally observed in the homogenized specimen. The hot-forged specimen had bainite single phase with spherical VC, cuboidal (V, Ti)C, and needle-shaped (Fe, Cr)3C particles. After annealing at 860°C, the microstructures of specimens were ferrite single phase with various carbides such as VC, (Fe, Cr) 7C3, and (Fe, Cr)23C6 because of relatively slow cooling rates. The size of carbides in annealed specimens decreased with increasing cooling rate, resulting in the increase of hardness.