Fracture mechanisms of CTOD samples of submerged and flux cored arc welding

Three welding procedures commonly used to rebuild worn shafts in sugar cane mills were analyzed: two processes of submerged arc welding and one of flux cored arc welding. Crack tip opening displacement for the welding was determined according to ASTM E 1290 standard. The fracture surface and microstructure of the samples were characterized using scanning electron microscopy and optical microscopy, respectively. The fracture parameter CTOD was correlated with the fracture surface and microstructures. The single deposit of FCAW process and the outer weld deposits of SAW process present acicular and blocky ferrite and non-metallic inclusions with spherical shape distributed randomly in the welding. The inner deposits for SAW process show equiaxed ferrite and pearlite with fine inclusions. Welding material B-MA 1 presented the highest CTODc with 0.2115 mm, followed by A-MA 2 with 0.1672 mm and A-MA 1 with 0.1238 mm. Each presented ductile fracture surfaces characterized by spherical dimples, microvoids nucleated in inclusions. Deposits B-MA2 and C-MA 1 presented lower CTODc, unstable crack growth and brittle fractures, characterized by intergranular failures due to fine inclusions in the grain boundaries.