Comparison of PM-HIP to Forged SA508 Pressure Vessel Steel Under High-Dose Neutron Irradiation

TL;DR

This study compares the irradiation tolerance of PM-HIP and forged SA508 steel for nuclear reactor pressure vessels, finding that PM-HIP exhibits comparable toughness and ductility despite greater hardening, with composition influencing irradiation effects.

Contribution

First direct comparison of PM-HIP and forged SA508 steel under neutron irradiation, highlighting composition effects on irradiation hardening mechanisms.

Findings

PM-HIP SA508 shows greater irradiation hardening and embrittlement.

Uniform elongation and toughness are similar across materials.

Irradiation hardening linked to composition, not fabrication method.

Abstract

Powder metallurgy with hot isostatic pressing (PM-HIP) is an advanced manufacturing process that is envisioned to replace forging for heavy nuclear components, including the reactor pressure vessel (RPV). But PM-HIP products must at least demonstrate comparable irradiation tolerance than forgings in order to be qualified for nuclear applications. The objective of this study is to directly compare PM-HIP to forged SA508 Grade 3 Class 1 low-alloy RPV steel at two neutron irradiation conditions: ~0.5-1.0 displacements per atom (dpa) at ~270C and ~370C. PM-HIP SA508 experiences greater irradiation hardening and embrittlement (total elongation) than forged SA508. However, uniform elongation and approximate toughness are comparable across all irradiated materials, suggesting irradiated PM-HIP SA508 exhibits superior ductility at maximum load-bearing capacity. The irradiation hardening mechanism is linked to composition rather than fabrication method. Since PM-HIP SA508 has higher Mn and Ni concentration, it is more susceptible to irradiation-induced nucleation of Mn-Ni-Si-P (MNSP) nanoprecipitates and dislocation loops, which both contribute to hardening. Conversely, the forged material nucleates fewer MNSPs, causing dislocation loops to control irradiation hardening. These results show promise for the irradiation performance of PM-HIP SA508 and can motivate future nuclear code qualification of PM-HIP fabrication for RPVs.