J. Mater. Sci. Technol. ›› 2026, Vol. 270: 163-173.DOI: 10.1016/j.jmst.2026.01.027

• Research Article • Previous Articles     Next Articles

On the solute segregation to grain boundaries in SA508 steel

Przemysław Klupśa,1,*, Benjamin M. Jenkinsa, Paul Chekhoninb, James O. Douglasa,1, Megan Cartera,2, Yuanbo T. Tanga,3, Jonathan M. Hydec,a, Nick Riddled, Paul A.J. Bagota, Michael P. Moodya,4   

  1. aDepartment of Materials, University of Oxford, Parks Road, Oxford OX1 3PH, UK;
    bHelmholtz-Zentrum Dresden-Rossendorf, Institute of Resource Ecology, Bautzner Landstraße 400, Dresden 01328, Germany;
    cUK National Nuclear Laboratory, D5, Culham Campus, Abingdon OX14 3DB, UK;
    dRolls-Royce Plc., PO BOX 20 0 0, Raynesway, Derby DE21 7XX, UK
  • Received:2025-09-29 Revised:2026-01-21 Accepted:2026-01-21 Published:2026-11-01 Online:2026-01-26
  • Contact: * E-mail address: p.klups@imperial.ac.uk (P. Klupś).
  • About author:1Present address: Department of Materials, Imperial College London, London SW7 2AZ, UK.
    2 Present address: Amentum, Thomson Ave, Harwell Campus, Didcot OX11 0GD, UK.
    3 Present address: School of Metallurgy and Materials, University of Birmingham, Birmingham B15 2TT, UK.
    4 Present address: ANSTO, New Illawarra Rd, Lucas Heights NSW 2234, Australia.

Abstract: Solute segregation to grain boundaries (GBs) within a high-Ni alloy (SA508 Grade 4N) aged at 427 °C was studied to investigate the role of phosphorus in causing non-hardening embrittlement in these steels. Electron backscatter diffraction (EBSD) and transmission Kikuchi diffraction (TKD) were employed to identify and characterise grain boundaries prior to targeted atom probe tomography (APT) analysis. Boundaries were classified as prior-austenite grain boundaries (PAGBs) and packet/block (lath) boundaries, enabling segregation behaviour to be directly correlated with crystallographic misorientation and boundary type. Distinct segregation patterns were observed at PAGBs compared to other boundaries, with strong anti-correlation between P/C and Ni/Mn/Si at PAGB interfaces. In unaged PAGBs, non-equilibrium segregation driven by vacancy drag promoted Ni enrichment, whereas W-shaped Ni concentration profiles in aged PAGBs indicate P-driven reverse vacancy flow. In contrast, solute enrichment at lath boundaries was found to depend strongly on misorientation angle. These results highlight the critical importance of controlling the 5-DoF when assessing segregation-driven embrittlement mechanisms in bainitic/martensitic steels. They also emphasise the potential of grain boundary engineering as a design strategy for improving resistance to embrittlement in nuclear and other demanding applications.

Key words: Temper embrittlement, GB segregation, Atom probe tomography, Bainitic steel, Phosphorus