KARAKTERISTIK STRUKTUR MIKRO DAN SIFAT MEKANIK BESI TUANG PUTIH PADUAN KROM TINGGI HASIL THERMAL HARDENING UNTUK APLIKASI GRINDING BALL[Microstructure Characteristic and Mechanical Properties of Thermal Hardened of High Chromium White Cast Iron for Grinding Ball Application]

Abstract

ASTM A532 Type II-A is a high chromium white cast iron with carbon content 2.3% and chromium more than 13.3%. This material is widely used as a grinding ball. In this study, heat treatment process which is thermal hardened, was conducted to increase the hardness of this material. Quenching process used two kind of quench media, such as oil and forced air (which was blown directly from fan), while the tempering process was conducted with various temperatures, 250 °C, 300 °C, and 350 °C. After thermal hardening process, material was characterized by hardness testing, metallography by OM (optical microscopy) and SEM (scanning electron microscopy), and XRD (X-ray diffraction). The optimum hardness value is 723 BHN resulted from thermal hardening process at 300 °C. Higher hardness value was obtained due to form of tempered martensite and numerous of chrom carbide disperse in this material.