On origin of low impact toughness for the 12% Cr steels with a low N content
DOI:
https://doi.org/10.52575/2687-0959-2022-54-4-252-260Keywords:
Heat-Resistant Martensitic Steels, Heat Treatment, Alloying, Impact Toughness, Ductile – Brittle Transition Temperature, StructureAbstract
The 12% Cr steels with a low nitrogen content can be used as promising materials for the production of steam turbine blades in the thermal power plants. It was found that the resistance to impact loads of such steels is very low. Under impact load at room temperature, the value of impact toughness did not exceed 30 J cm−2 that didn’t meet the requirements for blade materials of steam turbine thermal power plants. To determine the origin of the low value of impact resistance, two 12% Cr steels with a low N content were analyzed using optical metallography, transmission and scanning electron microscopy. The possible structural elements can be detected as the sources causing brittle fracture of the samples. First, the high fraction of delta-ferrite, the boundaries at which are covered with the secondary phase particles enriched in chromium and tungsten. Second, the large W2B particles, enriched in tungsten, are randomly distributed over the matrix. Third, М23С6 carbides located along the boundaries of the martensitic laths form the continuous chains, which act as the thin brittle layers. These elements restrict the propagation of plastic deformation under impact loads.
Acknowledgements
The work is supported by the inner-university funding of the Belgorod National Research University "Young Leaders in Science"within the framework of the project "Science of the 21st century"of the Priority-2030 program
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