Dynamic strain aging behavior of an advanced alumina-forming austenite stainless steel based on Fe–30Ni–15Cr–3.5Al

Abstract

Alumina-forming austenite (AFA) steels have emerged as promising candidate materials for ultra-supercritical units because of their excellent high-temperature performance. Dynamic strain aging (DSA) can increase the strength, but at the expense of plasticity, which will inevitably reduce the service life of materials. The aim of this study was to determine the serration behavior of a new AFA steel from room temperature (RT) to 700 °C at different strain rates from 1.33 × 10−5 s−1 to 1.33 × 10−2 s−1. Serrations were found at 300–650 °C under the tested conditions. Regardless of the strain rate, three types of serration arose: type A, A + B, and C. Plateaus of yield strength, ductility minima, and sensitivity to negative strain rates were observed. Ludwik's relationship was more accurate than Holloman's relationship for expressing the relationship between the true stress and the true strain during plastic deformation. Below 600 °C, the critical plastic strain showed a positive DSA, but it showed an inverse DSA above 600 °C. The value of (m+β) at the normal DSA was 2.27, and the activation energy was 81.624 kJ/mol. Depending on the value of the activation energy, the DSA was attributed to pinning dislocations by substitutional aluminum atoms. SEM examination of the fracture surfaces revealed mixed mode with dimples and facets at tested temperature, but facts fracture became more intense with increasing temperature and ductility minima arose at 650 °C. The results of transmission electron microscopy showed increase interaction of dislocations with solute atoms with increase in the temperature up to 700 °C.

Keywords

• Dynamic strain aging
• Alumina-forming austenite stainless steel
• Serration type