주조합금 IN 718 전자빔 용접부의 극저온 기계적 특성에 미치는 미세구조와 후열처리 영향

• Published in: 대한금속재료학회지 Vol. 54; no. 1; pp. 29 - 39
• Main Authors: 권순일, Soon Il Kwon, 도정현, Jeong Hyeon Do, 조창용, Chang Yong Jo, 홍현욱, Hyun Uk Hong
• Format: Journal Article
• Language: Korean
• Published: 대한금속재료학회 05.01.2016
• Subjects: alloys; cryogenic mechanical properties; microstructure; TEM; transmission electron microscopy; welding
• ISSN: 1738-8228

Effects of post-weld heat treatment (PWHT) on the microstructure evolution and the mechanical properties at -196 ℃ have been investigated with electron beam (EB) welds of cast Inconel 718. Coarse Laves particles in EB fusion zones after conventional PWHTs provided a preferential site for crack initiation, leading to a significant decrease in cryogenic Charpy impact toughness. A modified PWHT, which was highlighted as higher-temperature solution treatment followed by slow cooling to 980 ℃, was designed to ensure a sufficient micro-plastic region ahead of crack tip by a significant reduction of the Laves size and fraction. The EB weld after the modified PWHT exhibited no blocky Laves particles. Instead NbC with a size of 200~300 nm were observed. This modified PWHT led to 1.7 times higher CVN impact toughness than base metal. The cryogenic mechanical properties of EB welds are discussed in terms of dendrite arm spacing, the Laves size and fraction.