Evolusi Struktur, Fasa Dan Sifat Mekanik Pada Pengelasan Duplex Stainless Steel (DSS) 31803 Menggunakan GMAW Dengan Penambahan CO2 Pada Shielding Gas Ar – CO2

Baja tahan karat duplex (DSS) merupakan salah satu jenis baja tahan karat yang banyak digunakan dalam konstruksi kelautan, industri minyak dan gas, dan industri kimia dan petrokimia karena kombinasi yang menarik dari sifat mekanik dan ketahanan terhadap korosi.Pengelasan DSS dengan metode GMAW menggunakan campuran gas pelindung Ar - CO2 dapat mempengaruhi struktur mikro dan sifat mekanik weld metal dan HAZ DSS. Tujuan dari penelitian ini untuk menganalisis pengaruh CO2 pada komposisi shielding gas Ar-CO2 pada pengelasan duplex DSS 31803 menggunakan GMAW terhadap pengendapan karbon, fraksi ferit, struktur mikro, sifat mekanik lasan dan HAZ serta evaluasi pitting corrosion berdasarkan nilai PREN. Penelitian ini menggunakan A (100% Ar), M1 (95% Ar + 5% CO2), M2 (90% Ar + 10% CO2), M3 (85% Ar + 15% CO2), M4 (80% Ar + 20% CO2), M5 (75% Ar + 25% CO2) dan C (100% CO2). Dari hasil penelitian, struktur mikro logam las pada masing–masing spesimen terdapat grain boundary austenite (GBA), Widmanstätten austenite (WA), intragranular austenite (IGA), dan partial transformed austenite (PTA). Scanning electron microscopy (SEM) mengidentifikasi terjadinya presipitasi karbida krom (Cr23C6) daerah HAZ pada spesimen M5 dan spesimen C. Kesetimbangan fasa ferrit dan austenite pada daerah weld metal terpenuhi pada spesimen A (34.8), M1 (38.9), M2 (36.4), M3 (38.4) dan M5 (45.9). Nilai kekerasan rata-rata vikers tertinggi daerah weld metal terdapat pada spesimen M5 yaitu 255 HV. Sedangkan nilai terendah pada spesimen C yaitu 238 HV. Nilai kekerasan rata – rata Vickers tertinggi pada daerah heat affected zone (HAZ) terdapat pada specimen A yaitu 271 HV dan kekerasan terendah terdapat pada spesimen C yaitu 245 HV. Nilai kekuatan tarik yang tinggi terdapat pada spesimen M5 dengan nilai 800 MPA. Sementara nilai kekuatan tarik yang rendah pada spesimen M4 yaitu 652 MPA. Pada spesimen A nilai PRENaustenite = 44.75 dan PRENferrite = 46.48. Spesimen M5, nilai PRENferrite = 47.29 and PRENaustenite = 45.02. Spesimen C, nilai PRENferrite = 45.10 and PRENaustenite = 45.26. =========================================================================================================== Duplex stainless steel (DSS) is one type of stainless steel that is widely used in marine construction, the oil and gas industry, and the chemical and petrochemical industry due to an attractive combination of mechanical properties and corrosion resistance. Duplex stainless steel (DSS) has high forming elements such as Cr, Ni, Mo and N so that it has a balanced two-phase micro structure consisting of erit-ferrite (50%) and γ-austenite (50%). The austenite content in the fusion and weld area must be in the range of 30% - 70% or 35% - 65%. DSS welding using GMAW method using a mixture of Ar - CO2 protective gases can affect the microstructure and mechanical properties of weld metal and HAZ DSS. The purpose of this study was to analyze the effect of CO2 on the composition of Ar-CO2 shielding gases on DSS 31803 duplex welding using GMAW on carbon deposition, ferrite fraction, microstructure, weld and HAZ mechanical properties and evaluation of pitting corrosion based on PREN values. This study A (100% Ar), M1 (95% Ar + 5% CO2), M2 (90% Ar + 10% CO2), M3 (85% Ar + 15% CO2), M4 (80% Ar + 20% CO2), M5 (75% Ar + 25% CO2) dan C (100% CO2). From the results of the study, the microstructure of welded metals in each specimen contained grain boundary austenite (GBA), Widmanstätten austenite (WA), intragranular austenite (IGA), and partial transformed austenite (PTA). Scanning electron microscopy (SEM) identified the occurrence of chrome carbide precipitation (Cr23C6) HAZ region on specimen M5 and specimen C. The balance of ferrite and austenite phases in the weld metal area was fulfilled in specimen A (34.8), M1 (38.9), M2 (36.4), M3 (38.4) and M5 (45.9). The highest average vikers hardness value in weld metal area is found in M5 specimen, which is 255 HV. While the lowest value in specimen C is 238 HV. The highest Vickers average hardness value in the heat affected zone (HAZ) is in specimen A which is 271 HV and the lowest hardness is in specimen C which is 245 HV. High tensile strength values are found in M5 specimens with a value of 800 MPA. While the low tensile strength value in the M4 specimen is 652 MPA. In specimen A the value of PRENaustenite = 44.75 and PRENferrite = 46.48. Specimen M5, PRENferrite value = 47.29 and PRENaustenite = 45.02. Specimen C, PRENferrite value = 45.10 and PRENaustenite = 45.26