The master thesis entitled "The influence of microstructure on the corrosion behavior of low-alloy steel" conducts research into the corrosion behavior of samples of low-alloy steel in an electrolyte, during which the microstructure of the samples was affected by heat treatment procedures. In the theoretical part of the paper, corrosion processes and internal and external factors affecting corrosion processes are described, classifications of corrosion processes according to the mechanism of action and the form of corrosion destruction are given. For both classifications, divisions of the corresponding corrosion processes are given and they are described and explained. Also, the methods of protecting metals from corrosion are listed and explained. In the experimental part of the work, the characteristics of 51CrV4 steel are listed and its chemical composition obtained using a spectrometer is presented. An electrochemical test of the corrosion rate of steel samples in a 3.5% NaCl solution was carried out before and after heat treatments of tempering at a temperature of 850 °C and tempering at temperatures of 400 °C and 600 °C. All samples show a drop in the potential of the open circuit, which indicates the development of corrosion processes. Hardened steel has the most positive corrosion potential, while normalized steel has the most negative potential. The non-heat treated sample shows the lowest corrosion rate, which is not expected. The corrosion rate of hardened steel is three times lower than the corrosion rate of improved steel because the hardened microstructure is martensitic, while during heat treatment, carbides are released by softening, which can be the cause of the appearance of microgalvanic articles.