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Fe-Cr-Al계 합금 빌렛의 상온 표면균열 원인에 관한 연구
김상원,박종혁,김인배,Kim S. W,Park J. H,Kim I. B. 한국재료학회 2004 한국재료학회지 Vol.14 No.1
Metallurgical and mechanical experiments were performed to explain unexpected surface cracks encountered in fabricating ground rolled-billet of Fe-Cr-Al alloys at room temperature. The toughness of these alloys containing between 220 and 236 ppm (C+N) has been assessed using notched-bar impact tests. According to our results, with a larger grain size, a higher interstitial content of (C+N) or a smaller size of precipitates, ductile to brittle temperature(DBTT) increased and absorbed energy decreased at room temperature. These results suggest that the surface cracks at room temperature stem from a poor resistance to brittle fracture, due to dislocation movement by the finely dispersed carbides within grains under the condition of higher (C+N) content.
INCONEL 718 초내열 합금의 열처리에 따른 미세조직 변화
최중환,이기룡,조창용,김인배 ( J . H . Choi,K . R . Lee,C . Y . Jo,I . B . Kim ) 한국열처리공학회 1992 熱處理工學會誌 Vol.5 No.2
Microstructural evolution of wrought Inconel 718 superalloy with different heat treatment conditions was studied. Heat treatment was performed via conventional(CHT), modified(MHT), Merrick(MeHT) and modified Merrick(MMeHT) methods. The size of γ` and γ precipitates which are principal strengthening phases in Inconel 718 superalloy increase in order of CHT, MHT, MeHT. For the case of MMeHT, a coexistence of fine γ` precipitate and very coarse particles due to exess growth of γ which is called bimodal distribution, was observed. CHT gave the finest grain size. (Ti, Nb)C carbide and needle-like δ phase were formed together at grain boundaries for CHT, and were formed both inside and at boundaries of grains for MHT, MeHT and MMeHT. Morphology of partially serrated grain boundaries was developed in all heat treatment conditions except CHT.