Włodzimierz Dudziński

Corrosion Fatigue Crack Propagation Rates for Steam Turbine Blade 13% Cr Steels

Studies of stress corrosion in X12Cr13 and X20Cr13 steels used for rotor blades of steam turbines have been conducted for determining the average rate of corrosion cracking development da / dt. Specimens were exposed to the salt mist environment of 1,2 ppm NaCl concentration in temperature of 60° C. The research environment represents the initial condensate of humidity from 3÷4%. Average rate of corrosion cracking development for specimens of the X12Cr13 is by 0,005 µm/h higher from specimens of the X20Cr13 steel. Course of the corrosion cracking initiation depends to a high degree on metal structure, and probably the close value of cracking propagation rate depends on the similar structure of those steels – high-tempered martensite with carbides at grain boundaries.

Microstructural Changes vs. Accumulation of Energy in Fatigue Tested Medium-Carbon Steel

The paper is aimed at showing a relationship between the plastic strain energy (hysteresis energy) ΔW and microstructural changes in fatigue loaded material. The investigations were made on medium-carbon steel (0.45% C) specimens within a broad range of life-times encompassing LCF, HCF and fatigue limit regions. A detailed analysis is presented of dislocation structures and slip bands in relation to stress level and accumulated energy values. It was found that the motion of dislocations was hindered by the Fe16N2 solutes forming Cottrell atmosphere. A new precise method was used for determining the hysteresis energy ΔW.