Effect of Relative Humidity on Crack Growth Mechanism of Hot Dip Galvanized Steel in Atmospheric Environment

Abstract

In this study, the corrosion fatigue mechanism of the galvanized AISI 1045 steel caused by humidity was discussed. In low-cycle fatigue and middle-cycle one (number of cycles to failure, Nf <105 cycles), the fatigue strength under the condition of RH=80% was mostly equal to that under the condition of atmospheric humidity. In high-cycle fatigue (Nf ≥105 cycles), the fatigue strength and fatigue limit under the condition of RH=80% were larger than the fatigue strength under the condition of atmospheric humidity. Under the condition of atmospheric humidity, the galvanized layer did not oxidize, and its hardness did not change. Under the condition of RH=80%, on the other hand, the galvanized layer oxidized, and its hardness increased. From these results, it seems that the increase of fatigue strength under the condition of high humidity was caused by delaying the occurrence of cracks by formation of the oxide layer.