Fracture features of heat-resistant 12% Cr ferritic-martensitic steel EK-181 in the temperature range of its ductile-brittle transition

Abstract

The features and fracture mechanisms of a promising low-activation heat-resistant 12% chromium ferritic-martensitic steel EK-181 after static tensile tests and dynamic impact tests in the range from 20 to –196°C, including the temperature region of its ductile-brittle transition, are studied. It is shown that the fracture of steel samples after impact tests at temperatures of –15, –40 and –70°C (below the cold brittleness limit) occurs by the mechanism of brittle transcrystalline quasi-spalling. A fractographic study of fractures of plane rectangular steel samples in tension showed that with the temperature decreasing below 20°C, the fraction of the brittle component in them increases, and upon reaching T ≈ –80°C the fracture mechanism changes from the mixed fracture (by the mechanisms of ductile dimple rupture and quasi-spalling) to brittle quasi-spalling. A comparison of steel EK-181 fractures after dynamic and static tests indicates that the type of loading and the sample geometry have a significant influence on the type of its fracture at a given temperature. Since the impact tests are more rigorous, they are characterized by an increase in the ductile-brittle transition temperature of steel, as compared to tensile tests, and, accordingly, a change in the type of fractures. Moreover, we note as a general feature that at temperatures below the ductile-brittle transition temperature steel is fractured by the transcrystalline quasi-spalling mechanism regardless of the test method.