THE EFFECT OF SHORT-DURATION SENSITIZING ANNEALING ON THE SUSCEPTIBILITY OF 12X18H9 AUSTENITIC STAINLESS STEEL TO PITTING AND INTERGRANULAR CORROSION

The article is devoted to the study of changes in the corrosion properties of 12X18H9 austenitic stainless steel as a result of provoking annealing of short durations (1/2 hour, 1 hour, 2 hours) at temperatures of 450, 650, and 850 ℃. The susceptibility of heat-treated steel to pitting corrosion in a 5% solution of iron (III) chloride crystallohydrate FeCl₃·6H₂O was studied using the gravimetric method, and to intergranular corrosion (IGC) in a boiling aqueous solution of sulfuric acid and copper sulfate CuSO₄·5H₂O, using the AMU method. It was shown that the corrosion behavior of steel samples in aggressive solutions depends on the degree of steel sensitization during provoking annealing. Differences in the kinetics of pitting corrosion and the susceptibility to IGC for steel annealed at 450 ℃ and 650 ℃ are related to the nature of the grain-boundary precipitates formed. At 650 ℃, a quasi-continuous network of Cr23C6 carbides forms, leading to the formation of extended Cr-depleted zones. This facilitates the directed development of corrosion along grain boundaries, contributing to the acceleration of pitting corrosion and the susceptibility to IGC. After annealing at 450 ℃, carbide precipitates and Cr-depleted zones are less pronounced, limiting the development of intergranular dissolution and ensuring the retention of resistance to IGC. Samples annealed at 850 ℃ are characterized by a low rate of pitting corrosion and a tendency to IGС, which may be attributed to residual electrochemical heterogeneity of grain boundaries and the presence of discrete carbide precipitates.

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