The Strain Rate Effect on High-Temperature Tensile Properties of High-Cr Oxide Dispersion Strengthened Steels

Abstract

The development of heat resistant structural materials is essential to sustain zero-emission energy for reducing greenhouse gas emission such as carbon dioxide gas by elevating operation temperature of nuclear and fossil power plants. Oxide dispersion strengthened (ODS) steels have received considerable attention because they show superior performances at high temperatures. In this research, the effect of strain rate on the deformation behavior was investigated at high-temperatures to apply it to advanced fossil and nuclear power plants. The materials used were three kinds of 15Cr-4Al-2W-ODS steels of which the other chemical compositions were slightly changed by the addition of small amount of alloying element. Steady strain rate tests (SSRT) were performed at a strain rate ranging from 1 × 10⁻³ to 1 × 10⁻⁶s⁻¹ in a vacuum of 2.3 × 10⁻³Pa at a temperature of 773 K. The test temperature was controlled within in an error of ±3 K. The fractured surface was observed by scanning electron microscope (SEM), and the reduction in area of the specimens was measured to investigate the effects of strain rate on the deformation and fracture mode. Tensile yield stress is remarkably dependent on the strain rate, showing a large increase with increasing strain rate, while tensile elongation is not remarkably influenced by strain rate. According to the precise observations of fractured surface, there was no strain rate effect on the fracture mode, and only ductile fracture was observed for all the specimens tested in the study. This trend was independent of material.