The findings in a research project financed mostly by an industrial company have shown that is is possible to predict with acceptable reliability if an eventual overheating has decreased significantly the creep resistance by on site checking of the microstructure and hardness. The on site testing results are then evaluated considering the dependence microstructure-hardness-creep rate which is to be determined in advance for every type of steel. Also non destructuive small punch tests can be performed to obtain additional informations on residual creep resistance of the steel. On the base of results of non destructive on site tests the eventual change of a part of high pressure steam boiler can be performed at the optimal opportunity. The results of the investigation of the structural brittleness of the NiCrMo stainless cast steel will be used for the evalution of the state of some vital parts of the equipment in the Nuclear power plant Krško. On the base of the initial findings in the investigation of the higher Charpy transistion in slower cooled welds of the steel Niomol 490 K the steel chemical composition was slightly changed and the brittleness diminished. The developped analytical dependence between Charpy toughness in britlle fracture range and the fracture toughness has simplified the determination of the fracture toughness. Investigations on the corrosion process of stainless steels with increased content of nitrogen have provided informations usefull for the reliability of use of this steel in different corrosion media. The development of the method of damage development in conditions of stress corrosion cracking enables reliable lifetime prediction for stressed steel used in weak corrosive media where the steel is resistsnt to surface corrosion attack. The findings are or will be used in some industrial companies, f. i. : the steel producers in frame of Slovenian Steelworks, in some electrical power producing companies, f.i. Nuclear power plant Krško and Thermal power plant Šoštanj, in civil enegineering and also in different new research and development projects performed for industrial companies.