Dynamic polygonizationin 9%Cr heat resistant steel

Abstract

Structural changes in 9%Cr martensitic steel during creep were examined. The grip section of the crept specimen was characterised by a lath martensite structure, which hardly changed during the test. In contrast, quite different microstructure developed in the necking porti on of the specimen. The structural changes were characterized by the evolution of relatively large equiaxed subgrains with remarkably l owered density of interior dilocations at places of initial martensite laths. The development of the well-defined subgrains in the necking portion was accompanied with a coarsening of second phase precipitations. The structural mechanism responsible for the microstructure evolution during creep is considered as a dynamic polygonization