Ammonia mitigation and induction effects on hydrogen environment embrittlement of SCM440 low-alloy steel

Abstract

The effect of ammonia (NH 3 ) contained in hydrogen (H 2 ) gas on hydrogen environment embrittlement (HEE) of SCM440 low-alloy steel was studied in association with the NH 3 concentration, loading rate, and gas pressure. NH 3 worked as both mitigator of the HEE and inducer of hydrogen embrittlement (HE) depending on the testing conditions. The mitigation of the HEE was achieved by the deactivation of the iron (Fe) surface for H 2 dissociation caused by the preferential adsorption of NH 3 on the Fe surface, which is enhanced by the increase in the NH 3 concentration and decrease in the H 2 gas pressure. NH 3 induced HE was caused due to creating hydrogen by the NH 3 decomposition. Since the NH 3 decomposition rate is low, the induction effect was observed when the loading rate was low. The effect of NH 3 was determined by the competition of the mitigation and induction effects. • NH 3 worked as both mitigator and inducer of hydrogen embrittlement. • The effects of NH 3 depended on NH 3 concentration, loading rate, and gas pressure. • NH 3 mitigated hydrogen environment embrittlement by hindering hydrogen uptake into the material. • NH 3 induced hydrogen embrittlement by creating hydrogen by its decomposition.