Analisa Pengaruh Variasi Waktu Penahanan Panas Dengan Proses Normalizing Pada Baja ST 41 Terhadap Kekerasan dan Struktur Mikro

Abstrak

Abstract-The normalizing heat treatment process was carried out of on ST 41 steel which is a medium carbon type steel at 850°C heating with variations in holding time of 15 minutes, 20 minutes, and 25 minutes with air cooling media. The study aims to determine the result of hardness and microstructure of variations in holding time using air cooling media. The result of this study indicate that the (holding time) factor has an effect on the hardness value, the depth value of indentation trace and the microstructure of the research specimen. The specimen with a holding time of 15 minutes has a hardness value of 68,25 HRB with an indentation depth of 0,063 mm, while a specimen with a holding time 20 minutes has a hardness value of 70 HRB with an indentation depth of 0,058 mm and a specimen with holding time of 25 minutes has a hardness value of 68 HRB with an indentation depth of 0,063 mm. From the result of the hardness test, it was found that the specimens with variations in holding time 25 minutes had a smaller hardness value and a deeper depth than variations in holding time of 15 minutes and 20 minutes. In the microstructure of specimen with holding time 25 minutes, ferrite phase was more dominant than specimens with holding time of 15 minutes and 20 minutes. The phase that appeared at the holding time of 25 minutes was 80,367% ferrite phase and 19,633% pearlite phase. So at a holding time of 25 minutes, the ferrite phase is more dominant, so the hardness value of ST 41 steel decreases.