<p>We propose a method for monitoring the process of heat treatment of the cast components of freight cars including, in particular, large-sized side frames made of low-alloy steels. The necessity of development of a procedure of this kind is explained by the fact that, in numerous cases, it is impossible to establish the fact of realization of heat treatment after removing of the surface defects of side frames at the manufacturing plants with the help of electric-arc welding. This does not allow us to formalize the admission of frames to operation, which may lead to serious financial losses. Thus, in order to determine the presence and quality of heat treatment of side frames, we propose to use a method intended for monitoring of the welds by measuring the hardnesses of the base metal, weld metal, and the heat-affected zone. The influence of heat treatment on the microstructure and hardness of welded joints is investigated. The results of approval of the proposed method under the conditions of repair facility are presented.</p>