Understanding the microstructural evolution of silicide-strengthened hardfacing steels

Highlights: • Hardfacing steels with various triplex matrix phase fractions (austenite, ferrite and π-ferrosilicide) can be produced. • Alterations to the Si and Ni contents of these alloys are shown to be crucial to controlling the phase balance. • Greater fractions of the π-ferrosilicide matrix phase increase the alloy strength. • Adapting the phase balance allows hardfacing alloys, tailored to a particular application, to be created. -- Abstract: New powder-processed hardfacing Fe-based alloys are being developed to provide high wear and corrosion resistance in demanding pressurised water reactor environments. The triplex stainless steel alloy RR2450, developed from the parent austenitic alloy Tristelle 5183, has been created for this purpose. A detailed study into the stoichiometric sensitivity and phase balance within these alloys has been carried out, in order to better predict the microstructural evolution within this chemically complex class of alloys. After undergoing a hot isostatic pressing cycle, the RR2450 alloy is shown to evolve a triplex matrix of austenite, ferrite and a novel π-ferrosilicide phase, alongside numerous niobium, titanium and chromium precipitates. Investigation into large austenite and π-ferrosilicide phase variations between different batches of the RR2450 and Tristelle 5183 alloys has indicated that small stoichiometric adjustments allow these hardfacing alloys to be tailored to produce different microstructures for specific applications.