WINTER 2016

26 THE DISTRIBUTOR’S LINK
Carmen Vertullo Lead Trainer, Fastener Training Institute ®
FASTENER TRAINING INSTITUTE ®
5318 East 2nd Street #325, Long Beach, CA 90803
TEL 562-473-5373 FAX 661-449-3232
EMAIL info@fastenertraining.org WEB www.fastenertraining.org
TO BAKE OR NOT TO BAKE?
Sooner or later most suppliers of electroplated
fasteners get around to asking and answering this
question. Unfortunately for many the answer comes too
late because the question comes too late. They have
already experienced a hydrogen embrittlement failure
event as the result of a half-baked baking strategy, or
they have wasted untold thousands of dollars baking
plated fasteners that did not need to be baked.
This article is not about hydrogen embrittlement, so
when you finish reading it you will not know all about
hydrogen embrittlement. This article is about baking, so
what you will know is how to make the best decision
about embrittlement relief baking from a risk
management perspective - and if you do want to know
all about hydrogen embrittlement in fasteners you will
have access to the best and most current technical
resources available to the fastener supplier,
manufacturer, or user. The most current research and
experience is not reflective of many older specifications
which most platers, users and suppliers are following.
However, some standards are up to date and there are
some new resources that we all need to be aware of.
Of course there is a little more to the question than
just “to bake or not to bake”. Some of the more obvious
rejoinders are:
Why do we bake?
At what temperature?
What fasteners require baking?
What fasteners do not require baking?
Which ones, if any, are borderline?
What processes require baking?
What processes do not require baking?
For how long do we need to bake?
• When in the process sequence should the
baking be done?
TECHNICAL ARTICLE
Who decides?
•
How much does it cost?
What specifications address baking?
How do I know if the baking was effective or not?
Before we attack these questions, just to get us all
on the same page let’s get a basic definition of Hydrogen
Embrittlement (HE) as it relates to fasteners:
Hydrogen Embrittlement: Certain metals, such as
carbon steel and alloy steel may absorb atomic hydrogen
which is generated in processes such as acid cleaning,
pickling, and electroplating. When higher-strength
fasteners are placed under a load, (tightened above a
certain percentage of their yield strength), the hydrogen
migrates in the metal to the areas of high stress, usually
at the head-body junction or the first loaded thread. The
hydrogen concentration at these high stress locations
causes micro-cracks to form. The micro-cracks become
larger cracks which eventually (usually in a few hours to
a few days’ time) leads to catastrophic failure of the
fastener. This defines a type of HE that is process
induced and it is called Internal Hydrogen Embrittlement
(IHE) because the source of hydrogen is internal at the
time the fastener is put under a load. Another type of HE
is caused when the source of hydrogen is external to the
fastener under load, usually caused by corrosion of the
fastener, of its coating or of the assembly in the
environment. This type of HE is called Environmental
Hydrogen Embrittlement (EHE). The mechanisms
involved in these two types of HE is the same, only the
source of the hydrogen and the timing is different.
Because this article focuses on the HE relief baking
process, only IHE is of concern here and we will refer to
it as simply HE.
CONTINUED ON PAGE 114