Grinchenko O. Materials bases of increase of durability of blades of steam turbines

The object of research - the process of strengthening the inlet edge of the blades of steam turbines made of steel 15H11MF-W in a combined way: hardening with high frequency currents and electrospark alloying of the same name 15X11MF-W. The aim of the dissertation is to increase the durability of steam turbine blades made of steel 15H11MF-W by introducing a comprehensive strengthening of the inlet edges of the blades to protect against erosion and corrosion damage based on the control of structure parameters and functional properties. The subject of research is the regularities of formation of the structure and properties of surface reinforced layers of steam turbine blades. Research methods: to achieve this goal and solve these problems, a system of general scientific methods and techniques was used. Evaluation of the properties of materials was performed using standard methods of mechanical research (microhardness tester PMT-3, Nano Indenter G200), metallographic (optical microscopes MMO-1600, MIM-8), X-ray diffractometer (PHILIPS PW3710 diffractometer), micro X-ray spectroscopic analysis X 30 ESEM), methods of electron microscopy (electron microscope JSM 7001F), determination of corrosion resistance (Voltalab 40), determination of erosion resistance by ultrasonic dispersion (Hielscher UIP-1000). Laboratory tests were performed using methods that meet the state standards of Ukraine and ISO standards. Industrial tests of work blades with reinforced inlet edges according to the proposed method were carried out jointly with JSC "Turboatom" at the NPP "Paks" in the Republic of Hungary. Scientific novelty of the obtained results: for the first time it was established that the combination of surface hardening methods - hardening by high frequency currents and electrospark alloying of steel 15Х11МФ-Ш, allowed to increase the hardness of the blade edge of steel 15Х11МФ-Ш 2.2-3.0 times to 5500-7000 MPa and increase the resistance to erosion-corrosion destruction due to the formation in the surface layer of the structure of doped martensite, residual austenite and complex carbides Cr3C2 and Cr7C3; for the first time it was found that the use of corrosion-resistant steel 15H11MF-W, which is identical to the main material of the blade, to strengthen the method of electrospark doping of the inlet edge of the working blade of the steam turbine allowed to increase erosion resistance by 72% by increasing chromium concentration to 44%; the method of comparative evaluation of efficiency of strengthening technologies of increase of durability of working blades of steam turbines is improved and tested; the method of estimation of corrosion resistance of protective strengthened layers was further developed, dependences of corrosion parameters on a structural-phase condition of the strengthened layers of blades from steel 15Х11МФ-Ш were received for the first time. The practical significance of the obtained results: the technology of increasing the durability of steam turbine blades due to the use of a combined method of hardening by combining in one technological process of hardening with high frequency currents and electrospark alloying; a technique for strengthening the inlet edge of the blade of the last stage of low pressure of the steam turbine rotor has been developed. Theoretical and practical developments proposed in the dissertation are used in the educational process of Kharkiv National Automobile and Road University in the teaching of disciplines, in the performance of master's theses.