EFFECT OF TEMPERING TEMPERATURE ON THE PHASE TRANSFORMATIONS IN THE FERRITIC-MARTENSITIC 12% CHROMIUM STEEL EK-181
The aim of the work is the study of the regularities for the reduced activation ferritic-martensitic steel EK-181 (Fe-12Cr-2W-V-Ta) heterophase structure formation against a tempering temperature to increase the temperature window of the steel application in fusion reactors. An electron-microscopic investigation of the effect of tempering temperature on the features of phase transformations in the steel has been conducted. By the methods of dilatometry and differential scanning calorimetry the critical points of phase transformations have been detected. The characteristic precipitation temperature intervals for nonmetallic phases M 3C, M 23C 6, V(CN) have been revealed. In the tempering temperature range (500-600) ºC particles of metastable carbide M3C are formed. A formation of stable phases М 23С 6 and V(CN) begins at the temperatures above Т = 650 ºС. An important feature of the steel microstructure after tempering at Т = 720 ºС is high density of nanoparticles (≤ 10 nm) of cubic vanadium carbonitride V(CN).