Influence of multi-directional isothermal forging on the microstructure and mechanical properties of low activation ferritic-martensitic steel for nuclear reactors

The microstructure of low activation 12 % chromium ferritic-martensitic steel EK-181 (Fe‐12Cr‐2W‐V‐Ta‐B) formed by multi-directional isothermal forging is studied. It is shown that the refinement of microstructural elements is followed by the formation of new ferrite grains and fragments of martensitic laths. The resulting finely dispersed particles of M23C6 carbides are homogeneously distributed. The mechanical properties under tensile test conditions and microhardness of steel EK-181 are studied. It is shown that multi-directional isothermal forging increases the strength properties by 30 % at 20°C. At 650°C the strength properties of steel after multi-directional forging are comparable to those after traditional heat treatment. The microhardness of steel after thermomechanical treatment reaches 3.42 GPa, which is almost 20 % higher than after traditional heat treatment. The microhardness values over the cross section of the workpiece do not change significantly. A high-temperature tempering at 720°С for 1 hour after multi-directional isothermal forging leads to the formation of a submicrocrystalline ferrite structure, the growth of M23C6 carbides, reduction of dislocation density and decreases the strength properties.

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1. Government Research Assignment for the Institute of Strength Physics and Materials Science of the Siberian Branch of the Russian Academy of Sciences (ISPMS SB RAS) - FWRW-2021-0008