Pengaruh Proses Austempering pada Temperatur 300o C Selama 60 Menit terhadap Struktur Mikro dan Ketangguhan Besi Cor Nodular

This study aims to determine the effect of the austempering process at a temperature of 300 C for 60 minutes on the microstructure and toughness of nodular cast iron. The austempering process begins with austenitization at a temperature of 850 C for 60 minutes, then the quenching process is carried out in a salt bath until a temperature of 300 C is held for 60 minutes and then cooled as the final step. In the raw material’s microstructure test (SEM), there is a ferrite phase with a light color, coarse pearlite is gray, and graphite is black. After the austempering process, the graphite is round in black with a larger size than the raw material, surrounded by fine pearlite in gray color. The results of the Charpy method of impact testing on raw materials obtained an impact value of 0.06375 Joule/mm2. After the austempering process, the impact price increased to 0.12 Joule/mm2. This happens because graphite does not combine with ferrite (Fe) when the material is cooled. Then the longer the holding time, the more carbon from the austenite that diffuses to form graphite. The remaining austenite which turns into pearlite is getting smaller, so the graphite size becomes larger and the pearlite becomes less. Thus the toughness value increases