No abstract

In order to investigate the effect of phase separation (PS) on the super duplex stainless steel SAF 2507, the evolution of the nanostructure, mechanical properties, and corrosion resistance of the alloy was studied after aging at 500 °C for 1, 10, 100, and 1000 h. The nanostructure of PS was quantitatively characterized by small-angle neutron scattering. The hardness, impact toughness, and pitting corrosion resistance were measured for different conditions. The results show that the early stage of PS had a more significant impact on the nanostructure and properties of SAF 2507. The fracture behavior of the alloy was likely determined by the mechanical properties of ferrite for aged conditions. The pitting corrosion resistance of SAF 2507 aged at 500 °C was closely related to the Cr depletion caused by PS, and the resistance became weaker with the progression of PS. The evolution of the passivation region with aging time correlated well with that of mechanical properties and characteristic parameters of PS, indicating that it is possible to develop a new nondestructive electrochemical method to quantify the evolution of PS in SAF 2507.

The Laves phase precipitates in ASTM A335 P92 (P92) steel were found to dissolve in solutions with NaOH concentration higher than 7 mol l−1. Such behaviour was utilized to detect and quantify the precipitates in P92 specimens aged at 650 °C for times from 0 to 5000 h. The amount of precipitates was acquired by potentiodynamically polarizing the sample and integrating the dissolution current over time. The result was compared to that of a traditional SEM observation method, and a good linear correlation was found between the results. The dissolution mechanism was discussed based on the electrochemical behaviour of an artificially synthesized Fe2Mo laves phase specimen, pure Fe, and pure Mo in the strong alkaline solution.