Fragility analysis under low temperature of steel alloy used in helicopter bolt

Steels parts used in helicopters are critical in terms of mechanical performance and safety issues where failure can lead to catastrophic consequences. The objective of this study was to evaluate the influence of low temperatures on toughness, through impact testing, on 45NiCrMo16 steel alloy used in the manufacture of bolts used on a helicopter rotor. The aircraft that the studied bolt is used can operate in the Antarctic environment. The temperatures used in the Charpy tests were -40 ºC, -20 ºC, 0 ºC, and 25 ºC. Besides, microstructural analysis (optical and scanning microscopy) and microhardness were done to identify the steel phases/microconstituents and any surface treatment presence. The results showed the presence of a hardened layer, a decrease in impact toughness with decreasing temperature, and a transition from ductile to brittle fracture. The conclusions indicate behavior that can restrict or limit this steel grade application in extreme temperature conditions, that is the ductile-brittle transition region begins from a decrease in temperature starting from -20 ºC.