Flame cutting is a widely used process in industry. It is one of the most important forming technologies in steel processing, as it is used in almost every metalworking plant. Flame cutting requires various combustible gases and combustion gases. The most used combustible gases are acetylene and hydrogen. The aim of this thesis is to explore the possible differences between the two gases when used on an S355 JR grade steel plate. To this end, one plate was cut using acetylene and the other using hydrogen. Samples were taken from the cut plates and then subjected to hardness testing and microscopic examination. Both material tests showed that the use of hydrogen as a combustible gas results in more favorable microstructural changes than acetylene. Although the microscopic examination revealed that the samples cut with hydrogen were more quenched and tempered in the immediate vicinity of the cut, the hardness measurement proved that, away from the cut, the microstructure changes were more favorable in the case of hydrogen gas, and the use of hydrogen combustible gas for flame cutting resulted in a smaller heat-affected zone and a more favorable microstructure.