Structural Features and Operational Characteristics of Steel T91

Abstract

The microstructure and radiation resistance of T91 martensitic steel were studied after thermomechanical treatment. The physical and technological foundations of the process of creating of a nanostructured state in T91 reactor steel have been developed. This structure was received by severe plastic deformation of T91 steel by the multiple “upsetting-extrusion” method (developed at the NSC KIPT) in two temperature ranges of deformation: in the region of austenite existing and with a successive decrease in the deformation temperature and an increase in cycles of “upsetting-extrusion” in the field of ferrite existence. For the further heat treatment the particular temperature range and deformation modes were chosen to obtain optimal structure. Also, the optimum temperature of tempering to receive the uniform structure was established. It was found that the average grain size of T91 steel decreases from 20 μm in the initial state to ~ 140 nm after 5 cycles of “upsetting-extrusion” in the ferrite interval and to ~ 100 nm after 3 cycles of deformation in the austenitic region. It was determined that with an increase in the number of cycles and a decrease in the deformation temperature, a rise in the degree of uniformity of grain size distribution occurs. In this case, the microhardness increases from 2090 MPa to 2850 MPa after 5 cycles of “upsetting-extrusion” in the ferritic interval. In the austenitic region, the microhardness values increase from 3400 to 3876 MPa. The swelling of T91 steel in two structural states, martensitic and ferritic, was determined. Thus, steel swelling at a high dose of irradiation with argon ions with an energy of 1.4 MeV (120 displacements per atom, irradiation temperature 460 ° C) is ΔV / V = 0.26% in the initial state (martensitic structure) and 0.65% for samples with a ferritic structure.