Evolution of the Structure of Ferritic Steels Subjected to Torsion

Abstract

The power plants operate in service under conditions of high temperature and applied stress states. Under these conditions the components are subjected to degradation mechanisms that can lead to damage them. The components used in service are usually manufactured with ferritic steels, resistant to high temperature and with different structures of precipitates which change over time and alter the resistance of the material. It is then possible to observe variations in the chemical composition of the matrix, decomposition of areas of pearlite/bainite, and carbide precipitation and transformations by changes in the morphology.The objective of this work is to study the microstructural changes that occur in 2.25Cr 1Mo and 1.25Cr 1Mo 0.25V steels, subjected to creep at stresses between 131 and 205MPa and temperatures between 843 and 923K. Simultaneously, thermal treatments in the same ranges of temperatures are performed on the abovementioned steel, to differentiate structural changes due to temperature than those caused by stress.The microstructure of the material under stress states and high temperature shows deformed grains with smaller size in comparison with the as received material and increased precipitation of carbides.