Influence of cooling rate on intergranular corrosion susceptibility of super ferritic stainless steel S44660 analyzed through optimized double-loop electrochemical potentiokinetic reactivation method

The influence of cooling rate on the intergranular corrosion (IGC) susceptibility of Nb-Ti dual-stabilized super ferritic stainless steel S44660 following cold rolling and annealing was investigated using an optimized double-loop electrochemical potentiokinetic reactivation (DL-EPR) test, complemented by microstructural characterization. The results revealed that the optimal DL-EPR test conditions consisted of a 2 mol/L H₂SO₄ and 3 mol/L HCl solution, with a scanning rate of 0.1 V min^-1 at 30 °C. Notably, the resistance to IGC in S44660 steel increased progressively with higher cooling rates after annealing. Transmission electron microscopy and electron probe microanalysis showed that the sensitization of S44660 steel was attributed to the formation of Cr-depleted zones along grain boundaries due to M₂₃C₆ precipitates. IGC was no longer observed in S44660 steel when the cooling rate after annealing reached or exceeded 90 °C s^-1. It was confirmed that the nucleation and growth of carbides require a certain amount of time. Increasing the cooling rate after annealing effectively inhibits carbide precipitation and growth, thereby reducing the degree of intergranular Cr depletion and enhancing IGC resistance of S44660 steel.