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Letter 40088
Hydrogen Bakeout
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I would like to have a better understanding of the term "Hydrogen
Bakeout". I work in the petrochemical industry and have heard this
term quite often. I understand how its is done but not why. Can any
one shed some light on this for me.
Gary Tibbetts
- Saint John N.B.
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Hydrogen bakeout is something of a misnomer. The hydrogen that
accumulates in the coating may be baked "out" of the part, but the
hydrogen that actually diffuses into the steel is only redistributed,
not removed completely. This process is correctly called
embrittlement relief. Steels that have a hardness > 32 HRC (320
HV) or a tensile strength > 1000 MPa are required to be baked
after electroplating because the hydrogen that diffuses into the
steel can embrittle it, causing delayed fracture. If a high strength
steel that has a high hydrogen concentration is stressed, the
hydrogen diffuses to areas of high tensile stress, and promotes early
fracture. Steels with a microstructure of as-quenched martensite or
tempered martensite are most susceptible, with the failure mechanism
being intergranular fracture along prior austenite grain boundaries.
Toby Padfield
Automotive module supplier - MI, USA
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