No abstract

Microstructures of a maraging steel subjected to equal-channel angular pressing (ECAP) up to 16 passes at room temperature were investigated. Electron backscattered diffraction (EBSD) and transmission electron microscopy (TEM) examinations showed that the microstructures of the as-processed samples were characterized by a well-defined lamellar structure. With increasing the number of ECAP passes from 1 to 16, the lamellar spacing was significantly decreased from ~323 nm to ~54 nm, while the volume fraction of high-angle lamellar boundaries (HALBs, having the misorientation larger than 15o) was obviously increased form ~46% to ~80%. The real lamellar-type nanostructured microstructures were completely accomplished in the tested steel after 8 or more ECAP passes. In addition, the grain refinement mechanism of maraging steel during the processing was discussed in detail.