The Effects of Composition of Shielding Gas Mixture on the Microstructure and Toughness of Microalloyed Steel Weld Metal

It has been established that in weld metal of microalloyed steel the ferritic structure dominates, occurring in different morfologic forms. Acicular ferrite is the most desirable morphology of ferrite, so this paper analyses influence of the composition of gas mixture on the ferrite modification in the weld metal, specially on the morphology of acicular ferrite. At the same time, this morphological form of ferrite is very significant, because it has great influence on the mechanical properties, toughness specially. Five different gas mixtures (Ar,CO2,O2) were used to determine the optimal gas shielded metal arc process. For investigated microalloyed steel, the optimum gas mixture has been established (5% CO2, 0.91% O2, balance Ar), providing maximum impact energy due to microstructure, consisting dominantly of acicular ferrite.