Effects of long-term annealing on pitting corrosion behavior of Type 304 borated stainless steels
Heon‐Young Ha, Seong‐Hoon Kim, Kyeong‐Won Kim, Tae‐Ho Lee, Chi-Hyoung Won, Chang‐Hoon Lee
Abstract
• Effects of annealing on pitting resistance of borated stainless steels were examined. • Fe18Cr12Ni1.5Mn(0.2–1.8 wt%)B alloys were fabricated and annealed at 1180°C for 192 h. • Long-term annealed alloys had lower pitting resistance than the unannealed alloys. • Passive films formed on the annealed alloys contained larger amount of point defects. • Reduction in pitting resistance was due to grain growth during long-term annealing. The effects of long-term annealing on the microstructure and pitting corrosion resistance of Fe balance -18Cr-12Ni-1.5Mn-(0.2%, 0.8%, 1.8%, mass fraction)B stainless steels were investigated. For the B-containing stainless steels, annealing at 1180 °C for 192 h spheroidized the (Cr,Fe) 2 B phase, increased the grain size, and homogenized the element distribution in the γ matrix around (Cr,Fe) 2 B. Potentiodynamic polarization tests indicated that the long-term annealed samples had lower resistance to pitting corrosion than the unannealed samples, and Mott-Schottky analysis showed that the passive films formed on the annealed samples contained larger amount of point defects. In addition, the films on the annealed samples had a lower cation fraction of Cr than those on the unannealed samples. The changes in the pitting resistance and passive film properties were found to be primarily due to the grain growth during long-term annealing.