Nanocomposites and nanomaterials

Effect of thermomechanical treatment on the density and size of nanoscale precipitates in T91 steel
Voyevodin V.N. 1,2, Rostova H.Yu 1, Tikhonovsky M.A. 1, Kalchenko A.S. 1
1 National Science Center ” Kharkiv Institute of Physics and Technology” NAS of Ukraine.
Akademichna St., 1, Kharkiv-61108, Ukraine. 
E-mail: rostova@kipt.kharkov.ua
2 V. N. Karazin Kharkiv National University. 
Svobody Sq.,4, Kharkiv-61022, Ukraine.

Ferritic-martensitic (F/M) steels are considered as promising materials for future new generation nuclear reactors [1, 2]. The determining parameters for its successful use in this field are the high radiation resistance and high mechanical characteristics (yield stress, long-term strength etc.) at temperatures above 500 °C. These characteristics are structurally sensitive and can be significantly improved by grains’ refining and creating a large number of nanosized precipitates of carbide phases in the steel.
In this study, we investigated the possibility of controlling of the density and size of precipitates in F/M steel T91 by severe plastic deformation (SPD) and subsequent heat treatment in various modes. 
The multiple “upsetting-extrusion” method was chosen for carry out the severe plastic deformation, which was developed in NSC KIPT [3].
It has been established that M23C6 precipitates density in SPD samples are practically independent on thermal treatment temperature and their mean size increases a few with the temperature increase. Herewith density of MX precipitates is maximal (1.97×1021 1/m3) and size of precipitates is minimal (11 nm) after thermal treatment at 550°C during 25 hours.

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2.	Baindur S. Materials challenges for the supercritical water-cooled reactor (SCWR)// Bulletin of the Canadian Nuclear Society.-2008.-29, iss. 1.-P. 32-38.
3.	I.I. Papirov, G.F. Tikhinskiy. Structure and mechanical properties of fine-grained deformed beryllium // Physics of metals and metal science. -1970.- 29(5).- P. 1057-1060. (in Russian)