The Role of Cu Addition in Microstructural Characteristics and Mechanical Properties in Submerged Arc Welded Joint of Low Carbon Low Alloy Steel

A good strength-toughness combination is difficult to be obtained in welded joint of low carbon low alloy steel. In this work, a new idea was proposed to improve the strength and toughness of welded joint by strengthening effect of Cu precipitation and toughening effect of retained austenite. The results show that a multiphase microstructure consisting of ferrite, martensite-austenite island, retained austenite as well as precipitates was obtained in welded metal of Cu-free and Cu-containing steel, while the retained austenite and precipitates were found in fine grained heat affected zone (FGHAZ) and coarse grained HAZ (CGHAZ). It is noted that Cu addition changed the ferrite from polygonal-like to acicular-like, increased amount of retained austenite and promoted the Cu-rich precipitates. Accordingly, a better combination of strength, ductility and toughness was achieved in welded joint of Cu-containing steel. Cu-rich precipitates and strain-induced martensitic transformation of retained austenite maintained high strength in welded joint. Meanwhile, high toughness was ascribed to strain-induced martensitic transformation of retained austenite, acicular ferrite and high angle grain boundary. [doi:10.2320/matertrans.MT-M2022095]