Enhancement of mechanical properties of heat-resistant martensitic steel processed by equal channel angular pressing

The microstructures and tensile properties of a commercial heat-resistant martensitic steel processed by equal channel angular pressing (ECAP) for one pass and subsequent ageing treatment were investigated. Both optical and TEM examinations showed that many martensite laths had been broken into dislocation cells and subgrains after ECAP deformation. At the same time, the fragmentation of rod-shaped precipitates was also observed and the distribution of precipitation was more uniform than that in the as-received sample. After ageing in the temperature range of 640–720 °C for 2 h, dislocation recovery took place resulting in the decrease of dislocation density and formation of many ultrafine grains with sizes of several hundred of nanometers, and spherical particles that were uniformly dispersed in the matrix of fine subgrains/grains. By ECAP deformation and subsequent ageing treatment, a simultaneous increase in both strength and toughness was achieved, compared with those of as-received state. The enhancement of tensile properties was attributed to microstructural refinement and uniform distribution of precipitates.