1999 Volume 48 Issue 6 Pages 362-368
Austenitic stainless steel castings, such as SCS 13, SCS 14, which consists of δ/γ duplex phase, are extensively used as structural material in seawater environments. It is known that SCS14 involving 2wt% Mo is more resistant to pitting corrosion than SCS 13. In this paper, effects of Mo on the pitting corrosion are discussed in terms of microstructure of the material. The corrosion behavior of the materials with different δ ferrite contents and cleanlinesses have been evaluated by seawater exposure testing, electrochemical polarization, and TEM-EDX analysis. The results indicate that pits mainly nucleate at nonmetallic inclusions such as MnS and δ/γ boundaries, and materials containing δ ferrite above 7vol% have high pitting corrosion resistance. The nucleation at δ/γ boundaries is assumed to be due to the segregation of P. It is considered that because of segregation of Mo along δ/γ boundaries, SCS 14 is much resistant to pitting corrosion than SCS 13.
