Kafrawi, Muhammad Bayu (2026) Studi Pengaruh Variasi Heat Input, Jenis Kawat Las, dan Gas Pembilas terhadap Struktur Material Sifat Mekanik dan Ketahanan Korosi Baja Tahan Karat Super Duplex Stainless Steel UNS S32750. Masters thesis, Institut Teknologi Sepuluh Nopember.
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Abstract
Super Duplex Stainless Steel (SDSS) UNS S32750 memiliki kombinasi kekuatan mekanik tinggi dan ketahanan korosi yang sangat baik sehingga banyak digunakan pada industri migas, kimia, dan kelautan. Namun, parameter pengelasan yang tidak tepat dapat mengganggu keseimbangan fasa austenit–ferit, memicu pembentukan fasa intermetalik, dan menurunkan performa material. Penelitian dilakukan menggunakan proses Gas Tungsten Arc Welding (GTAW) sesuai ASME Section IX dengan variasi heat input, filler metal, dan gas pembilas. Evaluasi dilakukan melalui analisis komposisi kimia menggunakan Optical Emission Spectrometer (OES), pengukuran ferrite number menggunakan Ferritescope, uji kekerasan Vickers (HV10), uji makro sesuai ASTM E340, karakterisasi mikrostruktur menggunakan mikroskop optik dan SEM-EDS, serta uji korosipitting sesuai ASTM G48.Hasil penelitian menunjukkan bahwa variasi heat input, logam pengisi, dangas pembilas berpengaruh terhadap mikrostruktur, distribusi fasa, kekerasan, dan ketahanan korosi sambungan las Super Duplex Stainless Steel UNS S32750.Penggunaan gas pembilas campuran Ar+N menghasilkan daerah HAZ yang lebihlebar, sedangkan nitrogen murni menghasilkan HAZ yang lebih sempit akibat laju pendinginan yang lebih tinggi. Seluruh sampel mempertahankan fasa utama deltaferrite (δ-Fe) dan austenite (γ-Fe), dengan variasi keseimbangan fasa pada setiap parameter pengelasan. Nilai kekerasan tertinggi diperoleh pada daerah weld metal yang dipengaruhi oleh perubahan morfologi ferrite, ukuran butir, dan kemungkinan terbentuknya secondary phase. Berdasarkan pengujian Cyclic Voltammetry, Potentiodynamic ASTM G5, dan ASTM G48 Method A, sampel low heat input,kawat las ASME IIC, Ar+N menunjukkan ketahanan korosi terbaik, sedangkan sampel tinggi heat input, kawat las ASME IIC, Ar+N memiliki ketahanan korosi terendah. Secara keseluruhan, sampel tinggi heat input, kawat las Non ASME IIC, N memberikan kombinasi sifat metalurgi paling optimum dengan keseimbangan ferrite–austenite yang mendekati ideal, HAZ relatif sempit, kekerasan moderat, dan mikrostruktur yang lebih stabil.
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Super Duplex Stainless Steel (SDSS) UNS S32750 is widely used in the oil and gas, chemical, and marine industries due to its excellent combination of high mechanical strength and superior corrosion resistance. Therefore, this study aims to evaluate the effects of heat input, filler metal, and purging gas on the microstructure, mechanical properties, and corrosion resistance of SDSS UNSS32750. The experimental work was conducted using the Gas Tungsten ArcWelding (GTAW) process in accordance with ASME Section IX, with variations in heat input, filler metal, and purging gas. The welded joints were evaluated through chemical composition analysis using Optical Emission Spectroscopy (OES), ferrite number measurement using a Ferrite scope, Vickers hardness testing (HV10),macro examination in accordance with ASTM E340, microstructural characterization using optical microscopy and SEM-EDS, and pitting corrosion testing in chloride solution according to ASTM G48.The results showed that variations in heat input, filler metal, and purge gas significantly affected the microstructure, phase distribution, hardness, and corrosion resistance of Super Duplex Stainless Steel UNS S32750 welded joints. The use of an Ar+N mixed purge gas produced a wider heat-affected zone (HAZ), whereas pure nitrogen resulted in a narrower HAZ due to its higher cooling rate. All specimens retained the primary delta ferrite (δ-Fe) and austenite (γ-Fe) phases, although differences in phase balance were observed depending on the welding parameters. The highest hardness was observed in the weld metal, which was associated with changes in ferrite morphology, grain size refinement, and the possible formation of secondary phases. Based on Cyclic Voltammetry, Potentiodynamic ASTM G5, and ASTM G48 Method A tests, the specimen welded using low heat input, ASME Section II Part C registered filler metal, and an Ar+N purge gas exhibited the best corrosion resistance, whereas the specimen welded using high heat input, ASME Section II Part C registered filler metal, and an Ar+N purge gas showed the lowest corrosion resistance. Overall, the specimen welded using high heat input, a non-ASME Section II Part C registered filler metal, and pure nitrogen purge gas demonstrated the most favorable metallurgical characteristics, with a ferrite–austenite phase balance close to the ideal ratio, a relatively narrow HAZ, moderate hardness, and a more stable microstructure.
| Item Type: | Thesis (Masters) |
|---|---|
| Uncontrolled Keywords: | UNS S32750, GTAW, heat input, filler metal, purging gas nitrogen, SDSS UNS S32750, GTAW, heat input, filler metal, purging gas, pittingcorrosion. |
| Subjects: | T Technology > TN Mining engineering. Metallurgy T Technology > TN Mining engineering. Metallurgy > TN752.I5 Steel--Heat treatment T Technology > TN Mining engineering. Metallurgy > TN879.6 Welding |
| Divisions: | Faculty of Industrial Technology and Systems Engineering (INDSYS) > Material & Metallurgical Engineering > 27101-(S2) Master Thesis |
| Depositing User: | Muhammad Bayu Kafrawi |
| Date Deposited: | 22 Jul 2026 03:36 |
| Last Modified: | 22 Jul 2026 07:39 |
| URI: | http://repository.its.ac.id/id/eprint/136193 |
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