The effect of low tempering, medium tempering, and high tempering heating temperature variations in the type of medium carbon steel ST 60 on microstructure, hardness, and toughness

Abstract

To determine the changes in the microstructure, impact strength, and hardness of the carbon steel medium type ST 60 with variations in temperature: quenching, tempering 200°C, tempering 400°C and tempering 600°C, then a heat treatment was given at 850°C for 30 minutes then quenched with brine solution with a salt content of 10% and continued with tempering for 30 minutes with variations in tempering temperature: 200°C, 400°C and 600°C. The chemical composition of the ST 60 steel specimen obtained that the main constituent elements are iron (Fe) = 98.1%, manganese (Mn) = 0.572%, silisium (Si) = 0.246%, and carbon (C) = 0.362%. Meanwhile, the hardness, impact, and microstructure test results show that the quenching specimen has the hardest and softest material properties. This is indicated by the highest hardness value of 772.67 VHN and the smallest impact value of 1.24 J / mm2. The martensite phase structure formed causes the material properties to be the hardest. In the 200°C tempering specimen the hardness began to decrease and the ductility increased as indicated by the hardness value of 625 VHN and the impact value of 2.02 J / mm2. In this specimen, a tempered martensite phase was formed, which is softer than martensite. In the 400°C tempering specimen, the hardness value was getting smaller, but the ductility increased as indicated by the hardness value of 448.67 VHN and the impact value of 2.56 J / mm2. The bainite phase structure with ductile / malleable properties was formed in this specimen. In the 600°C tempering specimen the properties of the resulting material were the most ductile and softest indicated by the lowest hardness value of 295 VHN and the highest impact value of 3.11 J / mm2. The structure of the ferrite and fine pearlite phases with very soft properties was formed in this specimen.