Investigation of aging kinetics of heat resisting alloy-EhI698

The particularities of the aging kinetics have been studied for the EhI698 alloy conforming to the technological pattern used in the practice of stamped discs fabrication. The main part of the experiments was conducted with the melt of the following chemical composition (%): C 0.08; Cr 13.9; Ti 2.74; Al 1.68; Mo 2.95; Nb 2.11. A study was made of the hardness, the X-ray line widths, the solid solution lattice parameter, the amount of hardening phase and microstructure peculiarities under various aging conditions of the heat-resistant EhI698 alloy. The alloy structure study was made by means of transmission- and electron microscopy. The average size of the intermetallic γ'-phase (the main hardening phase in the alloy studied) corresponding to the structural formula (Ni, Cr)3(Al,Ti,Mo,Nb) was determined from the microphotographies. The estimation of the total amount of hardening phases (intermetallide and carbides) was made by electrolytic precipitation. It is found that the course of the kinetic curves during single and repeated aging is analogous. The main changes in the values studies occur during the first 10 hrs. of aging. The structure of the EhI698 alloy after the optimal heat treatment (quenching 1120 deg C for 8 hrs at 1000 deg C for 4 hrs, aging at 775 deg C for 16 hrs, at 700 deg C for 16 hrs) is characterized by the presence of dispersion hardening γ'-phase particles of 0.05 to 0.06 μm size and a considerable amount of coagulated precipitations of about 0.2 μm size