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Hastelloy X in this study was applied in jet engine F-15 air fighter as shroud to isolate the engine from outer skin. After 15 years operation at elevated temperature the mechanical properties decreased gradually due to the precipitation of continues second phases in the grain boundaries and precipitated inside the grain. The crack happened at the edge of the shroud due to the thermal and mechanical stress from jet engine. Selective TEM analysis found that the grain boundaries consist of M 23 C 6 carbide, M 6 Ccarbide and small percentage of sigma(σ) phase. Furthermore, it was confirmed the nano size of σ and miu (μ) phase inside the grain.In this study, it was investigated the microstructure of the degraded shroud component and HAZ of repair welded shroud. In the HAZ, it was observed the dissolution of the M 23 C 6 carbides and smaller precipitates, the migration of the undissolved larger M 23 C 6 carbide and M 6 Ccarbide. It is also observed the liquation due to the simply melt of the segregated precipitates in the grain boundaries. Interestingly, the segregated second phases which simply melt in the grain boundaries more easily happened at higher heat input welding condition. High temperature tensile test was done at 300ﾟC,700ﾟC and 900ﾟC. It was obtained that the toughness of welded sample is lower compare to the non-welded sample.The solution heat treatment at 1170ﾟC for 5 minutes was suggested to obtain a better mechanical properties of the shroud. The high cycle fatigue number of the repair welded shroud shows a much lower compare to the shroud. In addition, the high cycle fatigue number at room temperature after solution heat treatment was almost double compare to the before solution heat treatment under 420-500MPa stress amplitude. However, the high cycle fatigue number of repaired welded sample was shown a much lower compare to the non-welded shroud and solution treated shroud. One of the main reasons to decrease the tensile strength and the high cycle fatigue properties of the repair welded shroud is the formation of the liquid phase in HAZ.

Penerapan active flux pada proses las TIG atau A-TIG bertujuan untuk menaikkan penetrasi las sehingga produktifitasnya meningkat. Pengelasan pada bahan tebal penetrasinya meningkat, lapisan lasan berkurang sehingga mengurangi efek cost to cast pada pengelasan multi layer. Dalam penelitian ini dilakukan pengelasan pada bahan AISI 316L dengan 3 jenis serbuk oksida active fluxyaitu: Fe2O3, TiO2, dan Cr2O3, dan sebagai pembanding dilakukan proses las SMAW dengan elektroda AWS A5.4 (E308-16) dan proses las TIG konvensional. Hasil penelitian menunjukkan bahwa penetrasi meningkat dibandingkan terhadap proses pengelasan  konvensional hingga mencapai 22 s.d 50 % dan terhadap proses pengelasan SMAW (49 s.d 83)%. Distorsi proses las A-TIG cenderung menurun dibandingkan  terhadap proses las TIG konvensional dan SMAW. Nilai kekerasan di HAZ dan WM pada semua proses A-TIG terutama proses las A-TIG flux Cr2O3 meningkat secara signifikan. Komposisi δ-ferit di WM semua jenis proses las meningkat, terutama pada proses las SMAW, fraksi volume δ-ferit meningkat secara signifikan.Kata Kunci : TIG, A-TIG, active flux, δ-ferit, SMAW