The microstructure and mechanical properties of T91 steel processed by ECAP at room temperature

In this paper, the 9Cr–1Mo martensitic steel (T91) was processed by ECAP method at room temperature and annealed at 500 °C for 2 h subsequently. The optical and TEM micrographs exhibit that the average grain size was refined from 20 μm for the initial sample to 200 nm for the sample ECAP extruded six passes and the martensitic laths were severely destroyed during ECAP processing. With the increasing number of the extrusion passes, the microhardness and the tensile strength increase from 2.7 GPa and 730 MPa for the initial sample to 3.8 GPa and 1160 MPa for the sample extruded six passes, while the uniform elongation decreases from 23% to 10%, respectively. After the annealing, the grains grow slightly to 300 nm, and the tensile strength of the samples extruded one and six passes decreases to 880 MPa and 1140 MPa while the elongation increases to 21% and 12%, respectively.