The results of researches of mechanical properties of cast and forged steel with regulation of austenitic transformation at operation, after thermal hardening are resulted. Taking into account the optimal modes of heat treatment (hardening 1100 ±5 oС and tempering) of the investigated steel, the parameters of physical and mechanical properties were determined: hardness, strength threshold, yield strength, toughness, electrical conductivity and microhardness in the metal structure. The proposed improved composition of steel (4Kh4N5М4F2) with an increase in quenching temperature by 60 oС, allowed to increase heat resistance by 35 oС in comparison with steel with regulation of austenitic transformation during operation of 4Kh3N5М3F brand (without deformation-forging). The tempering brittleness of the investigated steel (4Kh4N5М4F2) at the tempering temperature of 475 ±15 °С (first kind) and above 650 °С (second kind) was established. Increasing the brittleness of the studied steel in the temperature range of 460…490 °C causes to reduce the toughness, change the structurally sensitive value (increase in electrical conductivity), increase the hardness of the released martensite, increase the strength threshold and yield strength. The paper shows the possibility of using the investigated steel for the operating temperature range of hot deformation of copper (550…650 oС), copper-nickel (900…950 oС) and aluminum alloy (450…500 oС) with increased service life in comparison with ferritic steels 4Kh5МF1S and 3Kh3М3F of rolled grade. Experimental and industrial tests of die steel with regulation of austenitic transformation during operation (4Kh3N5М3F and 4Kh4N5М4F2) were carried out in Ukrainian and Chinese enterprises: Spetslityo plant (Dnipro, Ukraine); Artemivsk plant for non-ferrous metals processing (Donetsk Region, Bakhmut, Ukraine); Futec Co., Ltd (Ninghai, China); New material technology Co., Ltd (Kunshan, China). Ingots from the investigated steels were obtained by the technology of electroslag remelting: Rivne Research Institute of Mechanical Engineering Technology (Rivne, Ukraine); Tiangong International Co., Ltd (Danyang, China).