Thermal Processing Simulations of Multi-Constituent Austenite-Containing Steels for Explosive Confinement Vessel Construction

Abstract Explosive confinement vessels (ECVs) require materials that exhibit high strength and toughness that are also amenable to manufacturing and vessel fabrication. There have been considerable challenges identifying materials that exhibit suitable mechanical performance while also being manufacturable in thick sections and weldable without post-weld heat treatment. Multi-Constituent Austenite-Containing (MCA) steels are candidate alloys for ECV construction that are anticipated to exhibit greater performance and increased manufacturability relative to currently available materials. The fine-scale microstructures associated with MCA steels predominantly consist of ferrite, bainite, and/or martensite, with retained austenite. Austenite retention is accomplished through chemical stabilization by partitioning of carbon (C), manganese (Mn), and/or nickel (Ni) during thermal processing. The resulting composite micro structure can enable ductility at low temperatures while maintaining high strength. Due to the amount of Mn and/or Ni in MCA alloys, there is sufficient hardenability to achieve uniform microstructures in thick-section ECV components. The relatively low C content is anticipated to enable good weldability. The present work discusses progress toward developing MCA steels for ECVs. Understanding the effects of austenite characteristics, such as volume fraction, solute enrichment, and morphology, on mechanical performance, are of particular interest. Toward this goal, twelve experimental alloys have been developed with a range of Mn and Ni concentrations as the predominant austenite stabilizing alloy. Thermo-Calc® was used to calculate austenite characteristics for multiple austenite re-forming heat treatments that are intended to develop MCA microstructures. Heat treatments considered here include intercritical annealing (IA), quench-lamellarize-temper (QLT), and double-soaking (DS).