The topic of this Bachelor’s thesis is an estimation of the depth of hardenability for a defined machine part ''DJ.19-PP.09'' The thesis is divided into two parts. The first part is theoretical and defines thermal processing in general, while also describing some basic methods of thermal processing of materials. Furthermore, phase transformations of steel and its mechanical properties are described, which are of key importance to steel processing. The process of hardening and different methods of hardening are then explained in great detail. Moreover, the process of hardenability of steel is defined as well as the methods with which it can be estimated. Theoretical part ends by listing several methods of testing the hardness of different materials. The second part of the thesis is practical and uses previously defined elements to experimentally estimate the hardenability of a defined machine part. The machine part itself is a chrome nickel molybdenium steel alloy (36 CrNiMo 4) whose characteristics are briefly defined. Lastly, the experiment of estimation was conducted using Jominy's curve and Crafts-Lamont diagrams.