Question

Studs used in a turbo pump were made from 0.35C-1.5Ni-1.0Cr-0.2Mo steel, quenched and tempered to 400 HV hardness, cadmium-plated and baked at 200°C for 2 h. The studs used in a turbo pump failed after 3 months of assembly. A fractograph of a failed stud revealed a predominantly intergranular mode mixed with ductile failure features. Increasing the baking time to 12 h considering the low diffusivity of hydrogen across the relatively impervious cadmium coating solved the problem. Explain the cause and mode of this failure.

Answer 1

The role played by hydrogen in premature failures of components protected

by electroplated coatings can be illustrated by the following example. This is because of hydrogen premature failures of components protected by electroplated coatings.

The studs used in a turbo pump failed after 3 months of assembly. The studs

were made from 0.35C-1.5Ni-1.0Cr-0.2Mo steel, quenched and tempered to

400 HV hardness, cadmium-plated and baked at 200°C for 2 h. The delayed

failure was predominantly in intergranular mode

mixed with ductile failure features characteristic of delayed failure due to

hydrogen embrittlement. Increasing the baking time to 12 h considering the

low diffusivity of hydrogen across the relatively impervious cadmium coating

solved the problem.

The examples cited indicate that innumerable defects originate during

various stages of manufacture and all of them affect the component performance

and reliability.