Influence of Preheating on Lamellar Gray Cast Iron for Surface Layer Welding applications with Plasma-Transferred Arc Powder and Metal Inert Gas Welding Processes with Duplex Steel as Filler Material

The good capacity of gray cast iron for the manufacture of complex geometry components is widely recognized, but its low resistance to corrosion and low weldability complicate the use of this material for some industrial applications. The corrosion resistance can be improved by metallic surface layers using welding processes with low percentages of dilution between the filler and base material. However, the welding processes impose very high heat load on the base material, which in the case of cast iron could promote the formation of hard and brittle microstructures, facilitating the formation of cracks. This work deals with weld beads of duplex steel on lamellar gray cast iron made either by plasma-transferred arc powder (PTA-P) or by metal inert gas (MIG) using the cold metal transfer (CMT) technology, with emphasis on achieving low dilution, hardness and imperfections (internal porosities). Preheating was used to reduce the hardness in the heat-affected zone, while different levels of helium were added in the shielding gas to study its effect on the geometry and hardness of the weld beads. The results showed that the PTA-P process resulted in lower values of dilution and hardness because of a low cooling rate compared to that of the MIG-CMT process. In addition, it was observed that preheating the base material reduced the hardness of the heat-affected zone but increased the dilution of the weld bead.