熱浸鍍鋁處理對低碳鋼於應力狀態下之熱腐蝕環境的壽命影響

The Effect of Hot-dip Aluminum on Life Duration of Low Carbon Steel under Constant Load in Hot Corrosion Environment

本研究以低碳鋼為底材，進行700℃熱浸鍍鋁120秒表面噴覆2mg/cm2之50/50的NaCl/Na2SO4，置於750℃管狀爐內，外加靜態應力負載，評估鋁化處理對低碳鋼的壽命影響。結果顯示，鋁化試片具較佳延伸率及較長壽命，因鋁化層之抗氧化及抗腐蝕能力，底材成長為抗潛變能力佳的大晶粒。當Fe2Al5相生成裂口導致應力集中，FeAl與FeAl2相仍維持附著性，底材透過再結晶及形變做應力鬆弛。綜觀本研究之結果，熱浸鍍鋁處理有效地改善低碳鋼於應力狀態下之熱腐蝕環境的壽命。

This study investigated the effect of hot-dip aluminum on the life duration of low carbon steel, and the mechanism of failure mode of aluminized layer under constant load in hot corrosion environment with a portion of 50/50 mixture of NaCl and Na2SO4. The specimens were made from SPHC with the thickness about 2 mm, and hot-dip aluminized for 120 seconds. The constant tensile test was performed by hanging specimens covered with 2 mg/cm2 salt mixture under constant load in a tube furnace at 750 ℃℃. The results show that the aluminized specimens have higher elongation and longer lifetime than bare steels’. The fracture analyses and microstructure analyses of the aluminized specimens show that the aluminized layer can provide steel to having grain growth without corrosion which also can increase the creep resistant. The FeAl and FeAl2 phases have good adherent to the substrate while aluminized layer cracked, which can offer steel sufficient time to do stress relaxation by recrystallization and deformation. According to the result of this study, it has been confirmed that the lifetime of steels in hot corrosion under constant load can be remarkably improved by hot-dip aluminizing process.