Effect of the microstructure on fatigue strength of structural steels used in power engineering

1.	The microstructure of the steel has a strong effect on the resistance to low-cycle fracture. The highest fracture resistance in cyclic loading is shown by the steel with the austenitic structure, that of the steel with the ferritic-pearlitic structure is slightly lower, whereas the lowest resistance was recorded for the steel of the transition grade (ferritic-martensitic). This is explained by special features of deformation of their microstructural components and different properties of the crystal lattice.
2.	In low-cycle loading, the austenitic steel shows susceptibility to hardening, the steel of the ferritic-pearlitic grade is stable, and the steel with the sorbitic and ferritic-martensitic microstructure softens.
3.	The low-cycle deformation resistance of the steels of different structural grades depends on the strength properties in static loading: the resistance is always higher In the material with a higher ultimate strength, i.e., in the steel with a martensitic microstructure.
4.	The microstructure of the steel has the maximum effect in the near-threshold region of the fatigue failure diagram.

Translated from Fiziko-Khimicheskaya Mekhanika Materialov, No. 2, pp. 7–13, March–April, 1992.