Measurement of intra-granular Strain in Creep of 2.25Cr-1Mo Steel

摘要

Intra-granular distortion of 2.25Cr-1Mo steel tested at 843K and 106 MPa has been investigated by Transmission Electron Microscope (TEM). Crystal misorientation within a grain was detected by Kikuchi pattern shifting at an early stage (<1% strain) before the formation of sub-grain structure. Magnitude of misorientation was proportional to the distance between measurement points in a grain. This was also the case after sub-grain formation. In order to determine average internal distortion e{sub}d of the material, mean value of tilt angle/distance was calculated in several grains. Internal distortion e{sub}d showed good correlation with creep strain e{sub}c under the test condition and a method of creep strain measurement was proposed based on the correlation. The method was applied to the 2.25Cr-1Mo steel used for 150,000 hours in fossil plant and creep strain was estimated to be 1.2%. Considering the relation between creep strain and life, the amount of creep strain corresponds to 70% consumption of creep life when the material is deformed by dislocation creep.