抄録
The following are main results of investigation about the effect of chromium of substrate on corrosion behavior of aluminized steel sheet in neutral or weakly alkaline solution of NH4+ which contains Cl-, SO2-4, CH3COO- and HCOO- which are found in exhaust gas condensate.
(1) Corrosion resistance of aluminized steel is enhanced if the substrate contains more than 5 wt% of chromium. One reason is cathodic corrosion protection of coating layer at coating defects, and the other is improvement in corrosion resistance of base steel itself.
(2) Improvement in corrosion resistance of base steel is due to the covering effect of Cr2O3 oxide film on steel in the ambient air and the effect of being passivated in each solution which contains (NH4)2SO4, CH3COONH4 or HCOONH4 individually. Substrate chromium steel has more stable cathodic protection than low carbon steel due to these films on the surface.
The effect grows as chromium content increases and is remarkable especially in case of 11 wt% Cr steel.
(3) In the synthetic condensate solution including various ions passivation is generated on the surface of 11 wt% Cr steel even in presence of substantial Cl- ion.
Therefore aluminized steel sheet with substrate containing more than 11 wt% Cr is judged to show practically excellent corrosion performance for the reasons described in (2).
