Heat treatment and properties of EhP 557 alloy

Investigated is the effect of heat treatment on the properties of the EhP557 precipitation-hardening alloy of the Ni-Cr-Ta-Ti-Si system applied for heat and corrosion resistant sensitive elements. The peculiarities of alloy strengthening, the kinetics of precipitation and solution of strengthening phases in the process of heat treatment are found out. Found is the connection between the structural transformations and mechanical properties. Considered have been the microstructure, phase composition and properties of the alloy tested on tension, bending, resistance-to-stress relaxation, creep and fatigue. It is shown that the heat treatment of the EhP557 alloy sheet is carried out according to the following regime: water quenching from 1080-1100 deg C, and ageing at 750 deg C for 4-6 hours. Such a treatment provides high fatigue strength and good service behaviour