THE EFFECT OF SILICON CONTENT ON THE PITTING CORROSION OF DUPLEX STAINLESS STEEL WELDMENT

摘要

In this study, the effect of Si content at a welded DSS on the pitting resistance was investigated. FCAW (Flux Cored Arc Welding) was conducted using 22Cr-9Ni-3Mo as the basic composition and adjusting the Si content to 0.6wt%, 0.9wt%, and 1.8wt%. The δ-ferrite fraction increased due to addition of Si, and the amount of γ_2 decreased. In the ferric chloride pitting test, the weight reduction range decreased due to an increase in the Si content. As to the location, pittings occurred intensively at the grain boundary or within the austenite grain due to the difference in PREN caused by the differential solid solubility in each phase. However, the higher the addition of Si, the more the number of pittings generated at the grain boundary decreased as the coherence of the passive film increased by the Si accumulated at the boundary. As a result of the potentiodynamic polarization test, while the E_(pit)(Critical Pitting Potential) of all specimens depending on the temperature were observed to be similar at room temperature up to 45°C, the reduction range of the E_(pit) was found to be small at the temperature higher than 45°C as Si content increased. This was found to be because of formation of SiO_2 in the passive film.