1Engineering Department, Toray Industries Ltd., Nagoya
Anodic polarization and corrosion cracking behavior of 80 kg/mm2 high strength steel (HT 80) were investigated in liquid ammonia containing ammonium carbonate (saturated-accelerated corrosion cracking environment) or ammonium chloride at 30°C. The results obtained are as follows:
(1) Corrosion potential vs Pt electrode (Ec) for HT 80 was -0.10 V in liquid ammonia and -0.7 V in the accelerated environment, respectively. In the latter environment, HT 80 showed an unstable active-passive behavior, and corrosion cracking occurred in quenched HT 80 when it was in contact with 304 stainless steel. Under this cracking condition Ec for HT 80 was easily shifted to a noble potential in the active-passive transition region.
(2) In the accelerated environment, the passivation current density for HT 80 decreased with an increase of air content in the nitrogen gas used for purging the test vessel before filling it with liquid ammonia. But no corrosion cracking occurred in quenched HT 80 under this condition.
(3) Although cracking occurred when 0.20 mA/cm2 cathodic current was applied to the HT 80 specimen, general corrosion was only accelerated when anodic current was applied to it at a constant strain in the accelerated environment.
(4) HT 80 showed an unstable active-passive behavior in the accelerated environment when the test vessel was purged by argon instead of nitrogen, and corrosion cracking occurred in quenched HT 80 when it was in contact with 304 stainless steel under this condition.
(5) In the liquid ammonia containing chloride, an unstable active-passive behavior was shown in HT 80, but no corrosion cracking occurred in HT 80 even if it was in contact with 304 stainless steel. Ec for HT 80 was slightly shifted to a noble potential under this condition.
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