Effect of carbonate in electrode coating on the microstructure and mechanical properties of weld

In this study, various additions of carbonates, MgCO3, Na2CO3, K2CO3 and BaCO3, respectively, were added in electrode coating to investigate microstructure and mechanical properties of weld metal. The results showed that α-Fe phase with bcc structure existed in each weld metal. The microstructure included of the primary ferrite (i.e. grain boundary ferrite and intragranular polygonal ferrite), the ferrite with second phase and acicular ferrite. When the addition of MgCO3 and Na2CO3 increased, the content of primary ferrite increased and acicular ferrite decreased. On the other hand, the addition of K2CO3 and BaCO3 promoted the content of primary ferrite reducing and acicular ferrite increasing. So far as mechanical properties were concerned, the addition of carbonates affected hardness, tensile strength and toughness of weld metal. MgCO3 and Na2CO3 diminished the mechanical properties due to the microstructure became coarser. Oppositely, K2CO3 and BaCO3 improved mechanical properties due to the microstructure became finer.