Kepekaan Retak Korosi Tegangan Baja Nirkarat Austenitik Aisi 304 dalam Lingkungan Air Laut Buatan

Abstract

The component of AISI 304 stainless steel construction is used as a prop of linking up the ropes on the boat on the sea, such as socket swaged, chain plate, turnbuckle, and so on. This component usually has a failure problem of Stress Corrosion Cracking (SCC) although the stress which operates mechanically is far from its yield strength. The aim of this research is to analyze the SCC susceptibility of AISI 304 austenite stainless steel in artificial sea water which is represented by its polarization behavior. The experiment was conducted by preparing twenty specimens of ASTM G38 standard C-ring which had been annealing from solid cylindrical bar. The load was obtained from FEM simulation, using Ansys 9.0 program packet, produced varied maximum application stress (σapp) of 0.0σy, 0.21σy, 0.30σy, 0.40σy, and 0.49σy. 3.5% of NaCl which represent the artificial sea-water solution of room temperature was used for testing environment. The influence of application stress on anodic cathodic polarization behavior with the stress level variation as given above was conducted without considering the treatment of immersion time. In order to study the influence of immersion time on the cathodic polarization behavior with, the stress level variation the spesimens were immersed in the solution for 0, 240, 480, and 720 hours. In addition, the study of the influence stress level on the SCC susceptibility, was conducted by observing the corrosion initiation on the surface specimen periodically. The result of the research shows that the stress level and immersion time influenced the polarization behavior on the surface of specimen. It indicated that the higher the stress level, the higher the potential (Ecor) and the current density of corrosion (icor). When σapp < 0.40σy, SCC initiation was not happen for immersion time < 720 hour. In other words, the SCC will be initiated if the σapp > 0.40σy, and the immersion time more then 720 hours. The polarization behavior for the applied stress were, Ecor <-520 mVsce and icor > 4.66 μA/cm2 (53,68 mpy). Keywords : Stainless Steel AISI 304, C-ring Specimen, Sea Water Artificial, Immersion Time, Stress Level, Potential, Current Density

Komponen kontruksi baja nirkarat AISI 304 sebagai penahan beban penyambung tali temali pada perahu di lingkungan air laut, seperti socket swaged, chain plate, turnbuckle dan lain-lain, sering mengalami kegagalan retak korosi tegangan (SCC) meskipun tegangan yang bekerja secara mekanik masih jauh di bawah kekuatan luluhnya. Penelitian ini bertujuan mempelajari kepekaan SCC baja nirkarat austenitik AISI 304 dalam lingkungan air laut buatan, yang direpresentasikan oleh perilaku polarisasinya. Eksperimen dilakukan dengan menyiapkan dua puluh spesimen C-ring standar ASTM G38 yang telah di anil dari batang silindris pejal. Pembebanan di dapat dari simulasi FEM menggunakan paket program Ansys 9.0, dihasilkan variasi tegangan aplikasi (σapp) maksimum 0,0σy, 0,21σy, 0,30σy, 0,40σy, dan 0,49σy. Larutan 3,5% NaCl menyerupai air laut temperatur kamar menjadi lingkungan pengujian. Studi tentang pengaruh level tegangan terhadap perilaku polarisasi anodik katodik dengan variasi level tegangan tersebut di atas dilakukan tanpa perlakuan waktu rendam. Untuk mempelajari pengaruh waktu perendaman terhadap perilaku polarisasi yang katodik dengan variasi level tegangan tersebut di atas di rendam dengan waktu 0, 240, 480, dan 720 jam. Selanjutnya untuk mempelajari pengaruh level tegangan terhadap kepekaan SCC, pengamatan inisiasi korosi pada permukaan spesimen dilakukan secara berkala sesuai dengan waktu perendaman. Hasil penelitian menunjukan bahwa level tegangan dan waktu perendaman berpengaruh terhadap perilaku polarisasi di permukaan spesimen, dimana semakin tinggi level tegangan maka semakin tinggi potensial (Ecor), dan densitas arus korosi (icor). Untuk batas σapp < 0,40σy inisiasi SCC belum terjadi pada waktu perendaman < 720 jam atau dengan kata lain SCC kemungkinan akan ter inisiasi apabila spesimen mendapat σapp ≥ 0,4σy setelah di rendam selama 720 jam. Pada kondisi ini perilaku polarisasi pada tegangan aplikasi tersebut adalah, Ecor ≤ -520,1 mVsce dan, icor ≥ 4,66 A/cm2 (53,68 mpy). Kata kunci: Baja Nirkarat AISI 304, C-ring Spesimen, Air Laut Buatan, Waktu Rendam, Level Tegangan, Potensial dan Densitas Arus Korosi.