Effect of Tempering Temperature on the Strength and Ductility of a Low‐Activation Martensitic Steel

In this article, a China low‐activation martensitic (CLAM) steel is prepared with layered grains through hot rolling and different tempering process. Testing the room‐temperature tensile properties of steel shows that the room‐temperature yield strength of the 730 °C tempered CLAM steel is 685 MPa, with a maximum elongation of 19% and these values are respectively 600 MPa and 19.5% for the 760 °C tempered CLAM steel. It indicates that, compared to the 760 °C tempered steel, the 730 °C tempered steel exhibits a better strength and ductility matching. Observation of the microstructure of steel shows that the grain structure of 730 °C tempered steel is layered, and its subgrain boundaries and M 23 C 6 carbide sizes are relatively small. In the 760 °C tempered steel, the layered grain structure disappears, and the size of subgrains and carbides significantly coarsens. Analysis shows that the higher yield strength of 730 °C tempered steel compared to 760 °C tempered steel is due to the refinement of grain and subgrain. The excellent tensile ductility of 730 °C tempered steel is due to the layered grains promoting the propagation of tensile layered cracks and increasing the necking area of the steel.