ANALISA PENGARUH MEDIA PENDINGIN AIR GARAM TERHADAP KEKERASAN DAN STRUKTUR MIKRO PERLAKUAN PANAS BAJA AISI 1045

Abstract

Abstrak

Penelitian ini bertujuan menganalisis pengaruh variasi kadar nominal NaCl dalam media pendingin Brine terhadap kekerasan dan struktur mikro baja AISI 1045 setelah perlakuan panas. Spesimen berbentuk silinder berdiameter 30 mm dan tebal 10 mm dipanaskan pada temperatur 900°C dengan waktu penahanan 60 menit, kemudian didinginkan cepat selama 15 menit menggunakan media Brine berkadar nominal 30%, 35%, dan 40%. Kekerasan diuji dengan metode Rockwell skala C pada empat titik setiap spesimen, sedangkan struktur mikro diamati melalui metalografi optik dan dianalisis menggunakan metode hitung titik kisi 10 x 10. Data kekerasan dianalisis secara deskriptif, diuji asumsi normalitas dan homogenitas, kemudian dianalisis dengan ANOVA one way serta uji lanjut Tukey. Kekerasan bahan awal sebesar 46,50 HRC meningkat menjadi 61,58 HRC pada Brine 30%, 58,17 HRC pada Brine 35%, dan 55,42 HRC pada Brine 40%. Analisis varian menunjukkan perbedaan yang signifikan antarkelompok. Estimasi struktur mikro menunjukkan martensit sebesar 74%, 61%, dan 43% secara berurutan pada ketiga variasi. Kadar nominal 30% menjadi kondisi paling optimal dalam rentang penelitian karena menghasilkan kekerasan tertinggi dan struktur martensit paling dominan serta merata.

Kata Kunci: AISI 1045, Brine, kekerasan, quenching, struktur mikro

Abstract

This study analyzed the effect of nominal sodium chloride content in Brine quenching media on the hardness and microstructure of heat-treated AISI 1045 steel. Cylindrical specimens with a diameter of 30 mm and a thickness of 10 mm were heated at 900°C, held for 60 minutes, and rapidly cooled for 15 minutes using Brine media with nominal contents of 30%, 35%, and 40%. Hardness was measured by the Rockwell C method at four locations on each specimen. Microstructures were examined by optical metallography and evaluated using a 10 x 10 grid point-count method. Hardness data were analyzed descriptively, followed by normality and variance-homogeneity tests, one-way analysis of variance, and Tukey post hoc comparisons. The initial material hardness of 46.50 HRC increased to 61.58 HRC with 30% Brine, 58.17 HRC with 35% Brine, and 55.42 HRC with 40% Brine. The analysis of variance confirmed significant differences among all treatment groups. Estimated martensite fractions were 74%, 61%, and 43%, respectively. Within the investigated range, the nominal 30% Brine condition was the most effective because it produced the highest hardness and the most dominant and uniformly distributed martensitic structure.

Keywords: AISI 1045, Brine, hardness, microstructure, quenching