Maraging steels are used where we wish or we need a material with good mechanical properties such as hardness, strength, good weldability, toughness, etc. Desires and demands for cost reductions and time constraints on product manufacturing are increasingly at the forefront, so additive technologies, which are used primarily to make more complex products, are on the rise. At the beginning of the graduation, theoretical basics of welding based on the MIG / MAG process are presented, welding equipment, additive technologies are presented, as well as other applied procedures for the very implementation and analysis of heat treatment. The task involves welding maraging steel into a flat vertical wall using the MIG / MAG process with CMT + pulse welding machine with Capilla 2709 MAG welding wire. The carved wall welding specimens were heat treated, then metallographically analysed and Vickers hardness tested. We determined the dependence of temperature and time of the heat treatment on the mechanical and chemical properties of the material. We find that the microstructure of the material in the welded state is coarse-grained and inhomogeneous. Precipitates are eliminated by heat treatment, the microstructure becomes homogeneous and the hardness increases. The increase in hardness depends on the choice of heat treatment, as incorrect heat treatment can contradict our goals.