Abstract:
The low-temperature fracture of a high-temperature low-activated ferritic-martensitic EK-181 chromium (12%) steel (RUSFER-EK-181: Fe-12Cr-2W-V-Ta-B) is studied using impact and static concentrated bending tests as a function of the specimen dimensions (standard, small), the type of stress concentrator ($V$-shaped notch, fatigue crack), and the temperature (from -196 to +100$^\circ$C). The ductile-brittle transition temperature falls in the range from -85 to +35$^\circ$C. The temperature dependences of stress-intensity factor $K_{Ic}$ and fracture toughness $J_{Ic}$ are determined. The severest type of impact toughness tests is represented by tests of $V$-notched specimens with an additional fatigue crack and two lateral $V$-shaped notches (three-sided $V$-shaped notch with a central fatigue crack). The fracture energy of the steel depends on the type of stress concentrator and the specimen dimensions and is determined by the elastic energy and the plastic deformation conditions in the near-surface layers of a specimen, which are controlled by the lateral notches. At the same test temperature, the impact toughness and the fracture toughness are interrelated. Irrespective of the type of specimen (including notches and a fatigue crack), the ferritic-martensitic steel exhibits the same fracture mechanism.
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