海水飞溅区Ni-Cu-P钢的锈层和耐点蚀性能研究

Abstract

Ni-Cu-P steel is well known as a seawater corrosion resistance steel due to strong corrosion resistance in marine splash zone. However, corrosion resistance mechanisms of alloying elements in Ni-Cu-P steel remain unclear. Because the steel exhibits obvious characteristic of pitting corrosion in marine splash zone, rust layers and pitting corrosion resistance were investigated in this study. The experimental steels were smelted in vacuum induction melting furnace. In order to evaluate the corrosion resistance of Ni-Cu-P steel, hanging plate test was performed in marine splash zone for 660 d. Rust layers formed on the steel surfaces were studied by means of scanning electro microscopy (SEM), energy dispersive analysis of X-ray (EDAX), Fourier transform infrared resonance (FTIR) and inductively coupled plasma atomic emission spectrometry (ICP-AES). The results indicated that average corrosion rate and pit penetration of Ni-Cu-P steel was obviously smaller than that of carbon steel after exposure test. For all the steels, the inner and outer rust layers were composed of α-FeOOH, β-FeOOH, γ-FeOOH, δ-FeOOH, Fe3O4 and a small amount of amorphous oxides. However, the inner rust layer exhibited higher content of Fe3O4 and lower content of γ-FeOOH and β-FeOOH than the outer rust layer. Under the same condition, the rust layers both in macro cathodic region and pits of Ni-Cu-P steel were much more compact than those of carbon steel. According to the composition and distribution of alloying elements, Ni, Cu and P were mainly observed in the inner rust layer and pits, and Cu and P were found to enrich in pits. In macro cathodic region, alloying element Cu made inner rust grains small and dense.