Analisis Ketahanan Material Baja Karbon Q235 dan Baja Tahan Karat 304 terhadap Korosi pada Tanah Halaman Departemen Teknik Metalurgi dan Material Kampus UI Depok Menggunakan Metode Electrochemical Impedance Spectroscopy dan Polarisasi Linear = Analysis of the Corrosion Resistance of Q235 Carbon Steel and 304 Stainless Steel in Soil at the Metallurgical and Materials Engineering Department, University of Indonesia Depok Campus Using Electrochemical Impedance Spectroscopy and Linear Polarization