Effects of single-pass and multi-pass TIG welding on the microstructure of CA6NM steel

This work aims to evaluate the effect of the number of welding passes and the thickness of ASTM A743 CA6NM martensitic stainless-steel plates on joints welded by the TIG process. Plates with 5 mm and 15 mm thickness were welded in a single pass and in eight passes, respectively. The filling material used was the ER410NiMo alloy, in the form of rods with a 2.4 mm diameter. Before the welding passes, the samples were preheated up to 150 °C. The characterization of the welded samples was performed with the aid of optical microscopy, scanning electron microscopy (SEM-FEG), electron backscatter diffraction (EBSD), and Vickers hardness. The experiments revealed that the sample welded in a single pass presented a higher amount of delta ferrite, with a network morphology, preferably located inside the weld bead and in the high-temperature (HT) heat-affected zone (HAZ). In the sample welded in eight passes, the delta ferrite presented different morphologies, preferably observed in the inter-pass regions, inside the weld beads, and in the high-temperature HAZ. Overheating in the inter-pass region resulted in HAZ width variation, which increased towards the bottom of the welded joint.