장시간 열간노출에 따른 247LC 초내열합금 보수용접 열영향부의 액화균열민감도 변화

• Published in: 대한금속·재료학회지, 61(2) Vol. 61; no. 2; pp. 69 - 75
• Main Authors: 정혜은, Hye-eun Jeong, 서성문, Seong-moon Seo, 천은준, Eun-joon Chun
• Format: Journal Article
• Language: Korean
• Published: 대한금속재료학회 05.02.2023; 대한금속·재료학회
• Subjects: 247LC superalloy; carbides; liquation cracking; repair welding; Varestraint test; 재료공학
• ISSN: 1738-8228; 2288-8241

In this study, the liquation cracking temperature range (LCTR) of over-aged 247LC superalloy repair welds was quantitatively evaluated using spot-Varestraint testing, especially for application in the repair weld heat-affected zone (HAZ). The metallurgical mechanism of the evaluated liquation cracking susceptibility and variation of the LCTRs of the over-aged 247LC superalloys was clarified by analyzing the microstructural characteristics at the liquation cracking surface, and using thermodynamic calculations. From the spot-Varestraint tests of the over-aged materials, the LCTR was quantitatively evaluated to be 410 and 620 K for the 500 and 1000 h over-aged specimens, respectively. These results demonstrate that the over-aged 247LC superalloys face significant and serious liquation cracking susceptibility in repair weld HAZ. Based on local element distributions at the liquation cracking surface, analyzed by transmission electron microscopy and the Thermo-Calc calculations, the underlying metallurgical mechanism of high LCTRs of over-aged materials could be attributed to the precipitation of fine MC and M 6 C carbides during the over-aging treatment. The carbides promote local liquation at the interface between the gamma phase at temperatures lower than the equilibrium solidus (1530 K) of the 247LC. The estimated liquation initiation temperatures at the MC/γ and γ/M 6 C interfaces were 1125 and 1420 K, respectively. (Received 3 November, 2022; Accepted 28 November, 2022)