Investment Casting and Mechanical Properties of Open‐Cell Steel Foams

Abstract

This study presents a novel manufacturing process for open‐cell stainless steel foams using a modified investment casting process and a novel approach to identify transitions between elastic‐plastic, plateau, and densification region in the stress–strain history of compressed foams, based on its strain and structural hardening behavior. The influence of microstructure on the mechanical properties under quasi‐static compression loading (plateau stress, energy absorption, and strain hardening) of austenitic (AISI 304, 316L) and super duplex (AISI F55) stainless steels is investigated. Microstructure is characterized prior and subsequent to mechanical testing using light microscopy and SEM. The manufacturing process yields open‐cell foams with relative densities in the range of 14–20%, solid struts being circular in shape and defect‐free surfaces. This morphology leads to improved yield strengths compared to open‐cell steel foams produced by the powder metallurgical route. Among the manufactured open‐cell steel foams, F55 foams with fine‐grained duplex microstructures show highest yield strength, strain hardening, and energy absorption with a sufficient ductility. Although a martensitic transformation is present in highly deformed struts of soft austenitic stainless steel foams, strain hardening in the plateau region is lower compared to duplex foams.