Effect of Surface Processing Variables on Hydrogen Embrittlement of Steel Fasteners Part 1: Hot Dip Galvanizing

Abstract

Incremental step load testing per ASTM F1940 was used to rank a number of industrial fastener coating processes for their propensity to cause internal hydrogen embrittlement. In the case of hot dip galvanizing, 4340 steel test specimens were severely embrittled, even in the absence of any exposure to hydrogen from the coating process. Evidently, the thermal shock caused during immersion in molten zinc releases otherwise innocuous trapped hydrogen. This hypothesis was confirmed with the help of a thermal desorption spectrometer, whereby residual hydrogen was extracted from test specimens prior to galvanizing, thus preventing their embrittlement.

Incremental step load testing per ASTM F1940 was used to rank a number of industrial fastener coating processes for their propensity to cause internal hydrogen embrittlement. In the case of hot dip galvanizing, 4340 steel test specimens were severely embrittled, even in the absence of any exposure to hydrogen from the coating process. Evidently, the thermal shock caused during immersion in molten zinc releases otherwise innocuous trapped hydrogen. This hypothesis was confirmed with the help of a thermal desorption spectrometer, whereby residual hydrogen was extracted from test specimens prior to galvanizing, thus preventing their embrittlement.

La méthode de chargement par accroissement d'étape a été employée selon ASTM F1940 afin d'examiner des processus de revêtement industriels, utilisés dans le domaine des éléments de fixation. Le but était de quantifier la propension de causer la fragilisation par hydrogène interne. La galvanisation à chaud s'est avérée fortement fragilisant, apparemment due à l'hydrogène emprisonné qui se libère par le choc thermique lors de la trempe dans le bain de zinc en fusion. Cette hypothèse fut vérifiée à l'aide d'un spectromètre à désorption thermique par le moyen duquel l'hydrogène résiduel contenu dans les éprouvettes en acier fut extrait avant la galvanisation, ainsi empêchant leur fragilisation.