Volume 2, Issue 3 (March 2005)
The Role of Grain Boundary Engineering on the High Temperature Creep of Ferritic-Martensitic Alloy T91
Ferritic-Martensitic alloys are expected to play a major role in supercritical water reactor internals. These steels offer better swelling resistance than austenitic alloys but may suffer from grain boundary or matrix creep and loss of strength at higher temperatures and unacceptably low toughness at lower temperatures. The focus of this investigation is to improve the creep resistance of T91 by grain boundary engineering. By increasing the fraction of coincident site lattice (CSL), or special boundaries, the grain boundaries are strengthened against sliding and deformation, thus improving the creep resistance. Thermo-mechanical treatment for coincident site lattice enhancement of T91 has already been developed. High temperature (500°C) creep experiments in argon are conducted to assess the effectiveness of the CSL enhanced microstructure on the creep rate. Experimental analysis shows that the CSL-enhanced condition results in a lower creep rate by a factor of 3-4 as-compared to A/R condition for T91 at a temperature of 500°C and in the stress range of 200–225 MPa by reducing the effective stress.