THE MICRO-STRESS IN PRESSURE BEARING STEEL SA508-III IN POWER PLANT DURING CREEP PROCESS¹⁾

At the long-term service temperature (above 300℃), the pressure vessels and the pipelines are prone to thermal aging and high-temperature creep. The microstructure is characterized by the coarse second phase particles, the grain boundary coarsening and the creep cavities, so the microstructure heterogeneity of the material makes the micro-stress analysis very complicated. Firstly, the Eshelby's equivalent inclusion theory is elaborated in detail. In view of the microstructure change of the pressure bearing Steel SA508-III in service in the power plant, when an inclusion is contained in the matrix, the sparse material system (with a small number of inclusions) combines the first and in the early of the second stage of creep, and the non-sparse material system combines in the middle period of the second stage of creep. The microscopic stress and strain analysis of the inclusions is performed, and the stress and the transition strain are calculated when the temperature changes or an external load is applied. On this basis, combining the microstructure characteristics of the pressure bearing materials in the final period of the second stage and the third stage of creep, the transformation strain and elastic modulus of the two different inclusions in the matrix are obtained.