We investigated an optimizing process to improve hardness after the final heat treatment through modification by the Equal Cannel Angular Extrusion (ECAE) processing in a martensite stainless steel (corresponding to SUS420J2). We expected the more refinement in both the chrome carbide particles with relatively large sizes more than 0.5μm and the grain size of the matrix by the sever plastic deformation from the ECAE processing, by the way the less refinement in sizes of neither the particles or the grain size could be obtained than we expected. However, the lattice faults with a high density could be introduced into the matrix by the ECAE processing under the condition without any cracking along the interfaces between the chrome carbide and the matrix. It could accelerate drastically the ability in solid solution of the large chrome carbide particles into the matrix during the final heat treatment by quenching at higher temperatures more than 1323K that led successfully increasing the carbon mass in solid solution into the matrix. In the present study by optimizing the ECAE processing to accelerate the ability in solid solution of the large chrome carbide particles the hardness of the matrix could be improved to Hv = 700 from Hv = 600 achieved by the conventional process. We conformed an affectivity to enhance the hardness of the present martensite stainless steel by the modification from the ECAE processing.
