Development of Heat-Resistant Steels and Alloys with Computational Thermodynamics

This presentation provides an overview of recent developmental efforts at Oak Ridge National Laboratory (ORNL) on heat-resistant ferrous materials, mainly for structural purpose in energy production sectors, with guidance from computational thermodynamics. Alloys of interest include ferritic (FeCrAl) alloys, bainitic-ferritic steels, high Cr containing ferritic-martensitic steels, and austenitic stainless steels. Although the base alloy systems vary depending on the target service conditions, a proper design of microstructure combining with controlled phase stability for long-term service are always the key for developing and deploying new materials for the use under extreme environments. The environmental compatibility (oxidation, corrosion, irradiation, etc.) dominantly favors or restricts some of the specific elements for alloying, so that the developmental activities mainly focus on investigating the compositional effect on phase transformation or strengthening/deteriorating secondary-phase precipitation kinetics within the limited ranges of alloy compositions. Downselection of the materials are mostly made through experimental validation but also combining with machine learning approach to narrow down the compositional range with interest. Computationally and experimentally obtained continuous-cooling transformation (CCT) and time-temperature precipitation (PPT) diagrams in various types of alloy systems are to be discussed. In addition, the knowledge has been extended developing the materials optimized for additive manufacturing process which involves a relatively rapid solidification together with non-periodic thermal exposures. Detailed results of the characterization and property evaluation will also be presented.