Impact of Processing on the Creep Properties of High Performance Ferritic (HiperFer) Steels

Abstract

High performance ferritic (HiperFer) stainless steels constitute a new class of low-cost, heat resistant, hardenable materials which combine high creep and fatigue strength with increased steam oxidation and wet corrosion resistance. The fundamental relationships regarding the alloy composition, microstructure, and resulting mechanical properties are largely known and already published, while relevant commercialization issues, such as the effect of processing on the microstructure, have not yet been addressed. The current paper outlines the impact of the forming parameters on the resulting microstructure and the achievable creep properties. Thermomechanical treatment is demonstrated as an effective method for increasing the creep strength for a given chemical composition. This may constitute a key enabler for cost savings in component production, e.g., for the simple machining of “drop-in” turbine blades or bolts from forged bar stock material.