The effects of cyclic welding and heat treatments on the microstrucrure and mechanical properties of Inconel 718.
Date Issued
2005
Date
2005
Author(s)
Huang, I-Chen
DOI
zh-TW
Abstract
The Inconel 718, a nickel-based superalloy with its high strength and high corrosion resistance at elevated temperature, becomes a popular superalloy for high temperature application in the past decades. It has good castability, workability, and weldability. Therefore, Inconel 718 has been widely used to produce aero-parts and as structural material. In practical manufacturing, the base metal and welded parts must conduct cyclic heat treatments and repeat welding, respectively. The effects of a series of different and cyclic heat treatments after the welding processes on the microstructure and mechanical properties of 718 alloy have been throughly investigated in this study.
Experimental results show that the base metal conducting the solid solution treatment at 980℃ and double ageing-treatment at 720/620℃ would have the highest tensile strength at room temperature. However, this heat-treatment would significantly change the strength and deteriorate the impact toughness of the weldment. Additionally, the solid solution treatment at 1065℃ and double ageing treatment at 760/650℃ would enhance the strength, elongation, and toughness of the weldment. Because solid solution treatment at 980℃ and 1065℃ can not dissolve all the Laves phase in the weld pool, the weldments have low impact toughness. After post weld heat treatment, the weldments would fracture in the area of weld pool.
Weldments would have the highest tensile strength at room temperature after solid solution treatment at 980℃ and double ageing treatment at 720/620℃. Additionally, after the solid solution treatment at 1065℃ and double ageing treatment at 760/650℃, the weldments would have the highest high-temperature tensile strength. According to the similar results of mechanical test, the repeated welding is not the primary reason causing the fracture. The weldments conducting post weld heat treatments of H8 (solid solution treatment at 1065℃ and double ageing treatment at 720/620℃) and H9 (solid solution treatment at 1065℃ and double ageing treatment at 760/650℃) have better mechanical properties at 704℃. Procedure of both post weld heat treatments are recommended since the weldments conducted heat treatment of H8 and H9 have better strength and elongation, respectively. The opportunity of heat treatments depends on the actual situation.
Subjects
氬銲
鎳基超合金
熱處理
顯微結構
TIG
GTAW
superalloy
Inconel 718
heat treatment
microstructure
Type
thesis
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