fa Railway track and structures Railway track and structures پژوهشي Research The GS20Mn5 steel is a low carbon manganese steel used for cast freight bogies manufacturing. The impact toughness of such steels for freight bogie solebars must be at least 17J/cm² at -60°C according to GOST32400 standard. In the present work, the effect of cooling rate after the austenitizing at two temperatures on the structure and mechanical properties of GS20Mn5 steel is investigated, including toughness at -60°C. The cooling rate varies from 1 to 5.4°C/Sec. The optimum toughness and strength are observed after two hour austenitizing at 930°C and quenching rate of 2.8°C/Sec where the impact energy mean values reached 32J/cm² at -60°C. Heat treatment , Mechanical properties, Cast Bogie, GS20Mn5 steel, Low temperature 73 82 http://ijrare.iust.ac.ir/browse.php?a_code=A-10-210-2&slc_lang=fa&sid=1 Mohammad Hasanpour 180031947532846002078 180031947532846002078 No School of Metallurgy and Materials Engineering, Iran University of Science and Technology, Narmak, Tehran 16846-13114, Iran Amin Owhadi aohadi@iust.ac.ir 180031947532846002079 180031947532846002079 Yes School of Railway Engineering, Iran University of Science and Technology, Tehran, Iran Seyed Mohammad Ali Boutorabi 180031947532846002080 180031947532846002080 No School of Metallurgy and Materials Engineering, Iran University of Science and Technology, Narmak, Tehran 16846-13114, Iran