Compositional modification of nonmetallic inclusions in bloomery iron during post‐smelting treatments and its implication

Abstract

AbstractThe chemical composition of nonmetallic inclusions in finished iron artifacts often holds key information on the smelting and post‐smelting processes applied during their production. This possibility was tested with special iron objects deemed product intermediaries from a royal tomb constructed at Gyongju, the former capital of the Silla state during the Korean Three Kingdoms period (c. 300–668 ce). Metallographic examination identified two distinct groups of inclusions with features unique to slags derived from smelting in (a) bloomery furnaces and (b) blast furnaces. Clear evidence was also noted that type ‘a’ inclusions, when subjected to an environment of high carbon activity as in a carburization process, underwent a significant change in chemical composition and microstructure to emulate the other type. This observation is expected to remove significant ambiguities encountered in connecting slag compositions to pertinent engineering processes.