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Korean Journal of Metals and Materials > Volume 59(2); > Article
doi: https://doi.org/10.3365/KJMM.2021.59.2.81
고에너지 직접 적층법으로 제조된 경사조성재료의 미세조직 및 경도 변화에 미치는 후열처리 영향 연구
신기승1, 박용호1, 김대환2, 윤지현2, 김정한3
1부산대학교 재료공학과
2한국원자력연구원 신소재융합기술연구부
3한밭대학교 신소재공학과
Effect of Post-Weld Heat Treatment on Microstructure and Hardness Evolution of Functionally Graded Materials Produced by Direct Energy Deposition
Giseung Shin1, Yongho Park1, Dae Whan Kim2, Ji hyun Yoon2, Jeoung Han Kim3
1School of Materials Science and Engineering, Pusan National University, Busan 46241, Republic of Korea
2Advanced Materials Research Division, Korea Atomic Energy Research Institute, Daejeon 34158, Republic of Korea
3Department of Materials Science and Engineering, Hanbat National University, Daejeon 34158, Republic of Korea
Correspondence  Yongho Park ,Tel: +82-51-510-3967, Email: yhpark@pusan.ac.kr
Ji hyun Yoon ,Tel: +82-42-868-8554, Email: jhyoon4@kaeri.re.kr
Jeoung Han Kim ,Tel: +82-42-821-1240, Fax: jh.kim@hanbat.ac.kr, 
Received: 25 September 2020;  Accepted: 24 November 2020.  Published online: 27 January 2021.
In this work, the effects of post weld heat treatment (PWHT) on the microstructure and mechanical properties of functionally gradient materials (FGM) was investigated. The FGM consisted of five different layers which were mixtures of austenitic stainless steel (type 316L) and ferritic steel (LAS). The ratio of type 316L and LAS powder in each deposition layer was 100:0, 75:25, 50:50, 25:75, and 0:100. FGM samples were successfully fabricated without cracks or delamination by a direct energy deposition process. The sensitization phenomenon of the FGM samples was investigated after PWHT. The PWHTs were conducted at 700oC, 900oC, and 1100oC for 4 hours and the samples were then air-cooled. After PWHT, the annealed specimens were observed by optical and scanning electron microscopy to analyze their microstructure. The occurrence of sensitization was found in the specimen annealed at 700oC. The contents of Cr and C increased substantially along grain boundaries. However, the sensitization did not occur in other samples annealed at 900oC and 1100oC. In the C and D layers of the 1100oC annealed sample, micro-hardness was measured to be very high due to the formation of bainitic ferrite and a lath martensite structure. In addition, a reduction of the austenite fraction was confirmed by Electron Back Scatter Diffraction.
Keywords: direct energy deposition, sensitization, functionally gradient material, stainless steel
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