This study aims to obtain information about the price of tensile, hardening , and changes in microstructure as well as changes in material properties at hot temperature variations 800 O C to 900 O C. The method used in this study is an experimental method, where the material used is ST - 60 steel bolts, with a tensile test sample form referring to the ASTM D 638-03 standard, while for testing hardness and chemical composition based on machine standards, namely Ø16 mm x 20 mm. In this study, 5 samples were made at each temperature of 0 0 C, 800 0 C, 850 0 C, 900 0 C, 950 0 C and 1000 0 C with the type of heat treatment in the normalizing process and the hardening quenching process. This research was conducted in the Laboratorium Pengujian Bahan, Jurusan Teknik Mesin, Politeknik Negeri Pontianak . The test results on the normalizing process for tensile strength decreased by an average of 230.78 N/mm 2 or 50%, Vickers hardness decreased by an average of 33.99 HV or 31% and the carbon content decreased by an average of 0.19 or 48% of the normalizing process is not done. Whereas in the hardening quenching process, the average tensile strength increased by 93.22 N/mm 2 or 20 %, the Vickers hardness on average increased by 19.29 HV or 18 % and the average carbon content increased by 0.06 or up 17 % of the hardening quenching process was not done. So to overcome the decrease in mechanical strength and changes in the microstructure of the ST-60 bolt due to hot temperatures, the hardening quenching process can be applied, namely by polishing with used oil after the bolts work at hot temperatures.