This final work shows the influence of feritic carbonitriding on the tensile strenght and the effect of improvement of steel and nitration after the improvement. Also, a test was carried out after hardening and test tubes were supported by various temperatures of high temperature release. In this way we wanted to to see how much the nitration effect was after the material was improved. The theoretical part of this final work describes thermochemical procedures of nitration and short-term complex nitration, and the process of thermal improvement and the phase containing it is also presented. They are generally described as steels for improvement. The beginning of the experimental section shows the plan of the entire experiment. The steels Č.4732 and Č.4734 were used for testing. These are the designs and standards of how the test tubes are made. The mechanical properties of the test tubes tested, including microhardness of Brinell method were tested. The obtained values and diagrams gave an analysis and conclusion on the effect of nitration on tensile strenght.