Alloy A-286 is a superalloy based on iron, nickel and chromium with the addition of titanium and molybdenum and belongs to the family of precipitation hardened austenitic stainless steels. Since this steel is sold in the form of bars (different diameters) in the precipitation hardened condition, we want to investigate how different degrees of deformation, cooling rate after forging, and different heat treatment parameters affect the microstructure of the steel and, consequently, its resistance to intergranular corrosion. In the company SIJ Metal Ravne d. o. o. the tests against intergranular corrosion are carried out according to the standards EN ISO 3651-2 or ASTM A262 15. For this reason, we tested the samples according to both standards and first checked whether it is possible that poor temperature control of sensitization annealing could be responsible for the negative results of the corrosion tests of the previous batches, or whether there could be any inconsistencies in the performance of the corrosion tests. In the study of the effect of deformation on the corrosion resistance of this steel, three different degrees of deformation were used, and in the study of the effect of the cooling rate of the steel after forging, the test samples were cooled in four cooling media (water, air, oil, furnace). The heat-treated specimens were also tested for intergranular corrosion susceptibility. Heat treatment was performed at a solution annealing temperature of 980 °C/different times and aging at 720 °C/16 hours. Because one of the heat treaded specimens didn’t pass the corrosion test, we performed microstructure analysis with optical and electron microscopy (SEM-EDS). We confirmed the presence of large TiC, TiN and Ti(C, N) inclusions within the crystal grains and of mixed carbides (titanium, molybdenum, chromium, niobium, vanadium, ...) and phosphides along the crystal boundaries. We could not find any corrosion products (oxides, chlorides) in the microstructure and also no chromium carbides at the grain boundaries, which are the cause of intergranular corrosion. We also performed an analysis of the fracture surfaces and measured elevated phosphorus concentrations in some locations. From this we concluded that the reason for the fracture of the material was not the reduced corrosion resistance, but the reduced ductility of the steel due to the segregation of phosphorus at the crystal boundaries.
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