MICROSTRUCTURE EVOLUTION AND HARDNESS IMPROVEMENT OF GRAY CAST IRON BY ADDITION OF FeSiMg FOLLOWED BY FLAME HARDENING PROCESS

The addition of magnesium alloy elements followed by a flame-hardening process will change the phase configuration in gray cast iron. This study aims to investigate changes in microstructure and hardness due to these two processes. The addition of magnesium is conducted by adding FeSiMg as a carrier for magnesium. Metallographic examination to observe changes in microstructure was carried out using a Scanning Electron Microscope (SEM) and Energy-Dispersive X-ray Spectroscopy (EDS). The formed phase is examined by X-Ray Diffraction testing. The hardness test was carried out using the Vickers technique on the surface of the gray cast iron, the nodular cast iron, and the flame-hardened nodular cast iron. Whilst for flame-hardened nodular cast iron, the Vickers technique was also conducted on a cross-section. The addition of the FeSiMg compound changed flake graphite into spherical graphite with increased hardness from 130 VHN to 313.22 VHN. The flame-hardening process in nodular cast iron results in the formation of a martensite phase and the disappearance of graphite on the surface of the material. The hardness on the surface of the material due to the flame-hardening process increased by 82.4% compared to the substrate.