Linear Voltammetry Assessment to Quantitative Determination of the Sigma Phase in Duplex Stainless Steel UNS S31803

Abstract

Precipitation of intermetallic phases in duplex stainless steels constitute a problem regarding the use of such materials in certain temperature ranges, in this way, are necessary methods to quantify, non-destructively, the presence of microstructural changes due to thermal contribution. In this work, electrochemical tests of linear voltammetry, tensile and Vickers hardness were performed in duplex stainless steel UNS S31803 for evaluation of the intermetallic sigma phase presence in the microstructure of the material. Samples of this steel were isothermally aged at 870 °C for times up to 3600 seconds to induce the precipitation of different grades of this phase. Linear voltametry tests were conducted in 5% KOH electrolyte solution in an electrochemical cell 3.3.10^-6 m², with a reference electrode of the type Saturated Calomel and auxiliary electrode of platinum wire. The results of this technique showed sensitivity to detect sigma phase content greater than 1% in the material enabling its application as a Non-Destructive Testing (NDT).

Keywords:
Duplex steel; Deleterious phases; Sigma phase; Linear voltammetry