The Effect of Different Heat Treatment Procedures on Duplex Stainless Steel Microstructures and Electrochemical Properties

In this paper, the effects of solutioning and various aging heat treatment processes on the microstructure, the hardness and electrochemical properties of a duplex stainless steel (DSS) were studied. The evaluation of the microstructure and phase compositions were carried out by the optical microscopy (OM) and the X-ray diffraction (XRD), respectively. Electrochemical behaviors of specimens were evaluated by both potentiodynamic polarization and electrochemical impedance spectra (EIS) tests at temperatures of ۲۵ and ۶۰ ºC. The obtained results showed that the solutioning heat treatment increased corrosion rates with respect to the blank specimen. The aging process at ۴۹۰ ºC for ۲۰ hrs increased the volume percent of the carbide phase to the highest value (۲۵.۱%) which resulted in an increase of the hardness value to ۱۷۰ VHN. The specimen which was aged at ۵۴۰ ºC for ۱۰ hrs with the Cr۷C۳ size of ۲۲.۸ µm, exhibited the higher corrosion resistance at both temperatures of ۲۵ and ۶۰ ºC with respect to other aged specimens. In addition, the temperature of ۶۰ ºC promoted the anodic reactions in ۳.۵ wt% NaCl solution which decreased impedance modulus values significantly. Consequently, the carbide size was more effective parameter than the carbide content in predicting electrochemical behaviors of such alloys.

کلیدواژه ها:

Duplex Stainless Steel ، Heat Treatment ، Aging ، Microstructure ، Electrochemical Behaviors ، Hardness