The Intergranular Corrosion Susceptibility of Metastable Austenitic Cr–Mn–Ni–N–Cu High-Strength Stainless Steel under Various Heat Treatments

oleh: Guangming Liu, Yuanyuan Liu, Yawen Cheng, Jin Li, Yiming Jiang

Format: Article
Diterbitkan: MDPI AG 2019-04-01

Deskripsi

The intergranular corrosion (IGC) behavior of a new metastable austenitic Cr&#8722;Mn&#8722;Ni&#8722;N&#8722;Cu high-strength stainless steel under various heat treatments was studied. The samples were solution treated at 1050 &#176;C for 30 min and then aged at 600 to 900 &#176;C for 10 to 300 min, respectively. The IGC susceptibility of aged samples was investigated using a double-loop electrochemical potentiokinetic reactivation (DL-EPR) test in a solution of 0.1 M H<sub>2</sub>SO<sub>4</sub> and 0.002 M KSCN and the 10% oxalic acid etch. The surface morphologies of samples were characterized using optical microscopy and the scanning electron microscopy after electrochemical tests. Two time-temperature-sensitization diagrams were plotted based on the DL-EPR test and oxalic acid etching. No IGC and precipitate were observed for samples aged at 600 &#176;C and 900 &#176;C. For samples aged at 650 &#176;C to 750 &#176;C, the IGC susceptibility and the amount of precipitate both increased with the extended aging time. For samples aged at 800 &#176;C and 850 &#176;C, the amount of precipitate increased as the aging time was prolonged. However, only the sample aged at 800 &#176;C for 60 min showed slight intergranular corrosion in the DL-EPR test. The IGC of the Cr&#8722;Mn&#8722;Ni&#8722;N&#8722;Cu austenitic stainless steel originated from the precipitation of Cr<sub>23</sub>C<sub>6</sub> and Cr<sub>2</sub>N at the grain boundaries. The chromium-depleted zones near grain boundaries stood as the corrosion nucleation sites, but the dissolution of the weak area followed a consistent crystallographic orientation along each grain boundary.