A cylinder of Carbon Steel S45C with a ferrite and pearlite structure was analysed to improve the hardness and surface layer as well as the toughness. Accordingly, it is important to undertake a heat treatment process for the hardness and surface layer of this steel. The heat teatment process was carried out using induction heating with five different temperatures of 800°C, 900°C, 1000°C, 1100°C and 1200 °C followed by water quenching with certain cooling speed. The chemical compositions and microstructures of these samples were characterized by spectrometer and optical microscopy. The microhardness of the samples was measured and the surface treatment of the samples was examined using an induction heating furnace. The results showed significant case depth and surface hardness as well as microstructure with martensite and retained austenite that is hard and brittle because of internal stress. Further, to reduce the amount of retained austenite and internal stress, it is necessary to carry out tempering of 300°C, 500°C and 700°C in order to produce toughness of the steel with slightly reduce in hardness. Abstract. A cylinder of Carbon Steel S45C with a ferrite and pearlite structure was analysed to improve the hardness and surface layer as well as the toughness. Accordingly, it is important to undertake a heat treatment process for the hardness and surface layer of this steel. The heat teatment process was carried out using induction heating with five different temperatures of 800 0 C, 900 0 C, 1000 0 C, 1100 0 C and 1200 0 C followed by water quenching with certain cooling speed. The chemical compositions and microstructures of these samples were characterized by spectrometer and optical microscopy. The microhardness of the samples was measured and the surface treatment of the samples was examined using an induction heating furnace. The results showed significant case depth and surface hardness as well as microstructure with martensite and retained austenite that is hard and brittle because of internal stress. Further, to reduce the amount of retained austenite and internal stress, it is necessary to carry out tempering of 300 0 C, 500 0 C and 700 0 C in order to produce toughness of the steel with slightly reduce in hardness.

The purpose of this research was to study the microstructure change of ASSAB 760 (equivalent to AISI 1045 and JIS S45C) steel subjected to the gas cementation and the quenching process. Gas cementation is a heat treatment surface process by means of carbon diffusing into steel. This process is carried out in a furnace in a fluidized bed by using media of liquid petroleum gas (LPG) and nitrogen gas at a temperature of 1203 K and various holding times of 7.2, 10.8 and 14.4 ks, respectively. The rapid quenching process is carried out in oil media for 420 sec. The results shows, that remnant austenite is formed on the specimen with a holding time of 7.2 ks and the networks of existing bainite structure are clearly spread on the specimen with holding time of 10.8 and 14.4 ks. Additionally, this gas cementation process when followed by the quenching process is effective in forming the martensite and austenite microstructures.