Laterite Steel A-588 has the potential to be a high strength low alloy for Corten steel application. Laterite steel A-588 is developed through a thermomechanical process followed by a tempering process to obtain high strength and corrosion resistance. This study aims to determine the correlation between the addition of nickel content, the variation of the cooling rate during heat treatment to the mechanical properties, and the corrosion resistance of A-588 laterite steel. The Cu, Cr, Ni, P, and Si elements significantly impact microstructure transformation. Laterite Steel A-588 with nickel and thermo-mechanical process variation has been focused on in this research. Laterite steel with 0,42%, 1%, 2%, and 3% nickel varied was homogenized, hot rolled, and heat treated with three cooling variations by water, oil, and air. They are processed with 150 C tempering. Low tempering temperature caused fine carbide precipitation and phase transition of martensite to bainite. This resulted in bainite as the final microstructure, lath tempered martensite, carbide, and ferrite. 3% Ni with a fast cooling rate increased the tempered martensite and bainite phase formation. It allowed the strength and hardness to increase relatively, followed by decreased elongation and corrosion resistance caused by the galvanic reaction. Most optimal of mechanical properties determined at a sample with 2% nickel in a water medium (strength 1203 MPa, elongation 10%, hardness 404 BHN, corrosion rate 1,306 mpy).
Sorption of a series of alkali metals (Ca, Mg, Li, and K) from Bledug Kuwu’s Brine into Lewatit MonoPlus S-108 resins has been studied. Bledug Kuwu’s Brine comprised 15.11 ppm Li, 179.91 ppm K, 72.01 ppm Ca, and 29.76 ppm Mg. The adsorption was carried out by varying pH of brine (4, 6, 8, and 10) and contact time (1, 2, and 4 hours) with continuous flow in column test at room temperature. The result showed the quantity adsorbate in outer resin: K>Li>Ca>Mg in all conditions, which is 0.038–0.043 mmol/g lithium, 0.087–0.09 mmol/g potassium, 0.031–0.035 mmol/g calcium, and 0.023–0.024 mmol/g magnesium into outer resin surface. The selectivity factor to lithium followed Mg/Li > K/Li> Ca/Li in all conditions. Contact time variable provided high lithium separation after the adsorption process for 2–3 hours, while pH had little effect. FTIR results affirm that resin was changed at new peaks M-O-M at low wavenumber with polystyrene crosslinked-divinylbenzene matrix and contains the sulfonic type. The results obtained from ICP were fitted to isotherm models in ion exchange, as follows: Langmuir, Freundlich, Temkin, and Dubinin-Radushkevic models. The best model of lithium adsorption into Lewatit S-108 is represented by Freundlich and Temkin Model (R2 ≥ 0.82) with 1.0056 mg/g of adsorption capacity (Kf) and 64.885 J/mol of heat process of sorption.
High strength low alloy (HSLA) yang diaplikasikan menjadi baja tahan cuaca merupakan terobosan terbaru untuk menghasilkan sifat mekanik dan ketahanan korosi yang tinggi. Modifikasi Baja Laterit dengan penambahan kadar nikel yang diterapkan proses termomekanikal (TMCP) berupa kombinasi proses penempaan panas dan perlakuan panas menjadi fokusan penelitian ini. Sampel yang digunakan merupakan Baja Laterit A-588 hasil investment casting yang telah ditambahkan kadar nikel sebesar 1, 2, dan 3% kemudian diproses penempaan panas dengan pembebanan 100 ton pada temperatur 1050 ℃. Nikel berfungsi sebagai penstabil austenit. Variabel perlakuan panas yang digunakan yakni (1) langsung pendinginan udara, (2) dilanjutkan proses pemanasan pada temperatur 750 ℃ yang diikuti pendinginan cepat. Karakterisasi material menggunakan uji metalografi, uji keras, uji tarik, dan uji polarisasi. Pada sampel tempa panas+pendinginan udara, pertambahan kadar nikel hingga 3% mempengaruhi nilai fraksi fasa ferrit-perlit yang terbentuk, pertambahan ukuran butir hingga ±0,1 mm, penurunan kekerasan hingga 185,22 BHN, penurunan kekuatan hingga 554 MPa, dan pertambahkan elongasi sebesar 29.1%. Sedangkan pada sampel tempa panas+perlakuan panas dengan pendinginan air, pertambahan nikel hingga 3% menyebabkan terbentuknya fasa dislokasi lath martensit+ferrit+retained austenite, penurunan kekerasan hingga 236,18 BHN, penurunan kekuatan hingga 852 MPa, penurunan elongasi hingga 24,7%. Fasa retained austenite memiliki efek merusak pada sifat mekanis.
The mechanical improvement and "self-protection" properties are mainly needed to develop weather-resistant steel materials. In this study, A588 steel was given thermomechanical treatment (hot-rolling) followed by a quench-tempering process. The A588 is modified by adding 1, 2, and 3 wt% nickel to the primary alloy. Steel is made using a hot rolling process at 750 ℃ for 1 hour with 70% thickness reduction. The sample is heat-treated at 850 ℃ for 1 hour and quenched in water, oil, and open air. The tempering process is conducted at 400 ℃ for 30 minutes. Metallography test is confirmed final microstructural and compared with CCT simulation result. The fast cooling (water and oil quenchant) produces tempered martensite, ferrite, and pearlite, while the air-cooled forms a ferrite-pearlite. The cooling rate significantly affects strength and hardness and the nickel addition on hardness, and both factors have no significant on ductility. The sample owns the highest tensile strength value (~1226 MPa) with 1 %Ni, and the highest ductility value (around 17.1–27.43%) is obtained by air cooling. With 3% Ni, the corrosion rate decreases to 0072 mpy with -432.5 mV for corrosion potential and 0.12µA/cm-2 for current density.
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