Microstructure and mechanical properties of ferritic-martensitic steel EP-823 after high-temperature thermomechanical treatment

Abstract

The effect of high-temperature thermomechanical treatment (HTMT) with deformation in the austenitic region on the microstructure and mechanical properties of 12% chromium ferritic-martensitic steel EP-823 is investigated. It is shown that the strength properties of steel after HTMT exceed the corresponding values after traditional heat treatment (THT) at the temperatures of 20 and 650 °C. The features of steel microstructure are studied by optical metallography and transmission electron microscopy. It is shown that under the HTMT conditions the original austenite grains are elongated in the rolling direction, while their dimensions perpendicular to the rolling direction decrease and are found to be ≈ 10 µm on average. HTMT provides the formation of a heterophase microstructure with high dispersion of such nanosized precipitates as MX and high dislocation density. These microstructure features of steel EP-823 after HTMT ensure higher strength properties than those after the THT. At an elevated deformation temperature (650 °C) the hardening effects are reduced.