한국주조공학회

The pitting corrosion behavior of 329LD cast lean duplex stainless steel and CF3M cast austenitic stainless steel was investigated in chloride environments. The pitting corrosion resistance of the 329LD alloy was superior to that of the CF3M alloy because the pitting potential, passive region, and critical pitting temperature of the low Ni-low Mo 329LD alloy were higher than those of the high Ni-medium Mo commercial CF3M alloy. There are two main reasons for the enhancement of the pitting corrosion resistance of high Cr-low Mo- medium N 329LD alloy compared to the low Cr-medium Mo CF3M alloy: First, the pitting resistance equivalent number (PRENδ+γ) value of the 329LD alloy is higher than that of the CF3M alloy. Second, the passive region of the 329LD alloy is larger than that of the CF3M alloy. It indicates that the synergistic effect of the three elements by adding high Cr and low Mo-medium N to the 329LD alloy enhances the passivity of the passive film, thereby increasing the pitting corrosion resistance. It was verified that based on the PRENγ of austenite (γ) and PRENδ of ferrite (δ) values calculated using an N-factor of 16, the pitting corrosion of the 329LD alloy was selectively initiated at the γ-phases because PRENγ value of austenite (γ) was smaller than that of ferrite (δ), and finally propagated from the γ-phase to the δ-phase.

Pitting corrosion, Lean duplex stainless steel, PREN, γ-phase and δ-phase.