The characteristics of the Fe-10.5Mn-1.3Mo-2.5Ni steel alloy results of casting were further investigated after a heat treatment process was carried out through 2 stages, namely heating from room temperature to 700 ° C with a holding time of 3 hours, then raising it again to a temperature of 1000 ° C. with variations in holding time for 1 hour, 2 hours, and 3 hours followed by quenchant in water and 1.5% NaCl  solution. The results showed that heat treatment followed by water quenching has produced higher hardness up to 2 hours holding time and subsequently decreased at longer holding time.. Meanwhile, the hardness value gradually increased with a longer holding time in 1.5% NaCl solution cooling process. The highest hardness value reached 235 BHN at the 2 hours holding time followed by water cooling. The results of the impact value of water and NaCl 1.5% varied. In water, the holding time of 1 hour increased at the holding time of 2 hours and decreased at the holding time of 3 hours. Meanwhile, in 1.5% NaCl, the highest value of holding time is 1 hour, then it decreases at 2 hours holding time and increases in 3 hours holding time. The highest impact value of 101 Joule was resulted in heat treatment with 1 hour holding time followed by 1.5 NaCl solution rapid cooling. The microstructure showed that undissolved carbides which dispersed at the grain boundaries and within the grains affecting on high hardness value.

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ABSTRAKTelah dilakukan percobaan pemurnian Metallurgical Grade Silicon (MG-Si) atau silikon tingkat metalurgi melalui proses pelindian. Proses pelindian menggunakan campuran larutan asam pada konsentrasi 2,45 mol/L HCl + 1,2 mol/L HF yang dilakukan dengan memvariasikan waktu pelindian pada suhu 60°C dengan kecepatan putar 300 rpm. Hasil percobaan menunjukkan bahwa proses pelindian MG-Si dengan menggunakan campuran larutan asam pada konsentrasi 2,45M HCl + 1,2M HF dapat menurunkan unsur pengotor yang terkandung di dalam MG-Si dan meningkatkan kemurnian seiring peningkatan waktu pelindian. Pada proses pelindian 12 jam, efisiensi ekstraksi unsur pengotor Al dan Fe mencapai 99,99%, sedangkan untuk unsur Ti mencapai 99,96%. Persentase efektivitas dari larutan pelindian selama 12 jam mencapai 99,96%. Pencapaian tersebut berpeluang untuk ditingkatkan dengan memvariasikan konsentrasi maupun waktu pelindian sehingga diperoleh nilai optimal.Kata kunci: silikon tingkat metalurgi, pelindian, efisiensi ekstraksi, efektivitas larutan. ABSTRACT The purification process of Metallurgical Grade Silicon (MG-Si

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