Hydrogen embrittlement: Failure of a rocket suspension lug

Hydrogen embrittlement: Failure of a rocket suspension lug - Fractography

Figure 1: Rocket suspension lug.

Figure 2: Intergranular fracture of the lug.

Defect name: Hydrogen embrittlement
Record No.: 2947
Type of defect (Internal/Surface): Internal, surface
Defect classification: Fractography
Steel name: Steel
Steel composition in weight %: No data.
Note: Hydrogen embrittlement is a phenomenon commonly found in high-strength steels after they are exposed to environments in which hydrogen is produced. Cadmium plating is a common surface protection treatment for high-strength steels to guard against corrosion. If proper precautions are not taken, the hydrogen produced during plating can diffuse into the metal and lead to intergranular brittle cracking without warning. A lug for suspending a rocket from an aircraft, made of a high-strength steel, had been cadmium plated. The cadmium plated lug (Fig. 1) was kept in the stores in a tightened condition for a length of time. Subsequently, when an attempt was made to loosen the lug for fitting the rocket, it was found cracked inside, with a distinct intergranular fracture, typical of hydrogen embrittlement (Fig. 2). Hence, immediately after cadmium plating, it is mandatory to bake such cadmium-plated steel components to expel the hydrogen absorbed by the material during the plating operation. ASTM standard procedures for baking are available.
Reference: Not shown in this demonstration version.