Failure Analysis of 35NCD16 Steel M6-Fastener Failed During Assembly of Aerospace Components

Abstract 35NCD16 is nickel-chromium-molybdenum alloy steel with ultra-high strength and good toughness. This alloy is used extensively in aerospace due to its good hardenability and comparatively low cost. Cd coating is used on M6 fasteners to provide corrosion resistance. A failure was observed dur...
Ausführliche Beschreibung

Abstract 35NCD16 is nickel-chromium-molybdenum alloy steel with ultra-high strength and good toughness. This alloy is used extensively in aerospace due to its good hardenability and comparatively low cost. Cd coating is used on M6 fasteners to provide corrosion resistance. A failure was observed during the fastening of M6 fastener in an aerospace component. Fractographic observations revealed shear dimples at the edges and equiaxed dimples in the middle. No evidence of corrosion, fatigue and embrittlement was observed. Optical microscopy revealed microstructure consisted of tempered martensite. Microhardness values were found to be more in thread crest locations than the root and core locations. Based on detailed investigation, reason for the failure is attributed to torsional overload. Ausführliche Beschreibung