Effect of aluminum on microstructure, mechanical properties and pitting corrosion resistance of ultra-pure 429 ferritic stainless steels

• Al stabilizes ferrite phase and significantly reduces recrystallization temperature.
• Al2O3 refines grain size, increases equiaxed grain ratio, promotes recrystallization.
• Optimum Al content significantly increases intensity of γ-fiber texture {1 1 1}〈1 1 2〉.
• σb and σs increase linearly, n varies slightly, ε and r first increase then decrease.
• Appearance of Al2O3 inclusions with small size benefits pitting corrosion resistance.

Effect of aluminum on microstructure, mechanical properties and pitting corrosion resistance of ultra-pure 429 ferritic stainless steels has been investigated. Aluminum can significantly increase the ratio of equiaxed crystal grains, but the promotion effect has great relation with aluminum content. Aluminum can stabilize ferrite phase and significantly reduce recrystallization temperature. Increased aluminum content can also lead to the precipitate of AlN and Al2O3 at higher temperature. The increased amount of AlN may partly contribute to the reduced nitrogen element to form austenite at high temperature, hence the high temperature phase transformation of α + γ → α occurs. The fine and large number of Al2O3 particles can refine grain size and then promote recrystallization. The highest intensity of γ-fiber texture {1 1 1}〈1 1 2〉 is observed in the steel with 0.19 wt.% aluminum, which can improve the formability of steels. With the increase of aluminum content, the tensile strength increases linearly but the elongation and plastic strain ratio first increase then decrease, the working hardening index varies slightly among the steels. Appearance of Al2O3 inclusions with small size and decreased content of MnS benefit pitting corrosion resistance. However, the large dimension Al2O3 inclusions have significantly negative influence on pitting corrosion resistance.