Investigation of hardening mechanisms and size effects in proton-irradiated HT-9 steels

Ferritic/martensitic steels, such as HT-9, are known for their complex microstructural features and mechanical properties. In this paper, in-situ micro-tensile tests and traditional fractography methods were utilized to study the fracture behavior of proton-irradiated HT-9 steels. First, to evaluate the viability of micro-tensile tests for nuclear material qualification process, meso-tensile tests on as-received HT-9 steels were performed. Fracture mechanisms of unirradiated HT-9 steels at both length scales were compared and underlying mechanisms discussed. The direct comparison of micro- and meso-scale data shows a distinctive size effect demonstrated by the increase in yield stress (YS). Upon completion of initial assessment, specimens were irradiated with 4 MeV+ protons to three fluences, all of which were lower than 0.01 displacements per atom (dpa). As expected, the YS increases with irradiation. However, at 7 x 10(-3) dpa, the reversal of the trend was observed, and the YS exhibited sharp decline. We demonstrate that at lower length scales, grain structure has a more profound impact on the mechanical properties of irradiated materials, which provides information needed to fill in the gap in current understanding of the HT-9 fracture at different length scales. Published by Elsevier B.V.

Automated summary

This paper investigates the fracture behavior of proton-irradiated HT-9 steels using in-situ micro-tensile tests and traditional fractography methods. The study reveals that grain structure has a more profound impact on the mechanical properties of irradiated materials at lower length scales, providing valuable information for understanding the HT-9 fracture at different length scales.