The presented paper is focused on study and investigation of structural changes in relation to the selected materials which are exposed to the thermal loading. The given work is connected with closer investigation of such material as Dominial ZF 2 which is commonly used for production of steel moulds and components in the glass industry. Moreover, the given work is also devoted to the investigation of materials which are commercially called Toolox 33 and Toolox 44 because these materials were proposed by firm to be used as substitutive materials of Dominial ZF 2. Both of the mentioned and investigated materials have not been used in glass industry yet. Experimental procedures were proposed on the basis of the fact that the investigated materials are exposed to thermal as well as mechanical loading and they are in direct interaction with hot molten glass. The simulation of the thermal loading was performed by help of welding device which was modified in order to simulate thermal loading consisting of material heating to high temperatures and subsequent rapid cooling. After thermal loading, the investigated materials were exposed to the static tensile test and by this way, it was possible to obtain samples with fracture surfaces and these fracture surfaces were evaluated in terms of characteristic features relating to rupture. The attention was also paid to the imperfections of microstructure because these imperfections are the first representatives of initiators of rupture. On the basis of the obtained results and knowledge from experimental procedures, Toolox 33 and Toolox 44 are not recommended to be used for production of steel moulds and components for glass products.