Hydrogen Embrittlement (Page 1) - Duro-Chrome Industries

Hydrogen Embrittlement:
How Small Details Can
Have Large Effects
Knowing the facts of hydrogen embrittlement from the beginning will save
both time and money down the road.
John Demakis
Hydrogen embrittlement — an ugly
plague that cast its shadow on the
steel industry and was identified
almost 150 years ago — is the same culprit
that has claimed responsibility for the
majority of nautical and aerospace/aircraft
disasters in the last 40 years. It causes what
is known as catastrophic fracture failure.
This refers to an instance in which a steel
structure has fractured due to a loss in
strength and ductility — or the ability to
bend. The reason for this is quite logical.
The steel fractures as a result of an
overabundance of cracks in the structure.
Every structure is going to have some
cracks somewhere — this is inevitable.
However, because of hydrogen embrittlement,
primarily high-strength steel structures
such as fasteners are failing prematurely
and abruptly, causing many complications
and, in some cases, disaster.
But What Is It?
Most people in the industry have heard
the term hydrogen embrittlement, but not
everybody may be aware of its seriousness.
Hydrogen embrittlement is a brittleness of
metal and chrome layer structures,
resulting from the occlusion of hydrogen
or condition of low ductility, which itself
results from hydrogen absorption and the
internal pressure developed subsequently.
Basically, the hydrogen is interfering with
the metal’s ductility, which in turn makes
the chrome build-up weaker and greatly
increases the chances of breaks or cracks
in the chromed area.
But what does damaged airplanes and
ships have to do with the moldmaking
industry? Just as a disaster could occur to
an airplane, similar disasters also could
occur in molds. When dealing with a part
that will endure at least 140 psi, one should
consider the risks of not acknowledging
hydrogen embrittlement and the detrimental
effects it could have on your
molding process. While it could affect
molds and mold inserts enduring less than
140 psi, hydrogen embrittlement is more
likely to occur with a structure that is
bearing a heavier load. It also is important
Understanding hydrogen embrittlement and its effects on the mold
and die industry is important when looking at money flow and
worker efficiency. The more you can get done right the first time
saves you money in the long run by avoiding that rework order.
www.moldmakingtechnology.com
to keep in mind that the hydrogen embrittlement
becomes more of a threat as the
amount of chrome applied increases. In a
build-up — one in which you are applying
layers of chrome — hydrogen becomes
trapped between every layer of chrome
applied, thus increasing the chances of
hydrogen embrittlement. In a flash chrome
situation — one in which a minimal
amount of chrome is applied — the probability
of this problem occurring becomes
less likely because the hydrogen doesn’t
have as many chances to embed itself
within the structure.
Electroplating is a cost-effective way to
protect your molds from corrosion while
increasing releasability. It is a widely used
process. When someone pays money to
have a mold plated, it is an investment for
the long run. It is an investment in which
they trust the application and service of the
chrome platers to prepare their mold to be
able to endure many applications of plastic.
The mold and die industry is one
founded on teamwork. Parts of the team
include mold builders, heat treaters,
polishers, molders and even the store at
MoldMaking Technology ■ April, 2002
MOLD MAINTENANCE

which the parts are sold. All of these
people rely on one thing — the quality and
efficiency of the parts. All it takes is for
one mold to crack, or fracture, and all of
these people are delayed. In an industry
that is based on efficiency, time is money.
Understanding hydrogen embrittlement
and its effects on the mold and die industry
is important when looking at money flow
and worker efficiency. The more you can
get done right the first time saves you
money in the long run by avoiding that
rework order. This is why people chrome
plate parts in the first place — to avoid the
maintenance of an unprotected one.
We’re Surrounded!
The real problem is that hydrogen is
everywhere, being a simple atomic
element. It readily bonds with the base
metal in the structure and embeds itself in
the actual makeup of the part. When does
this “infection” occur though?
When preparing a part for electroplating,
the steel needs to be ground and cleaned —
usually with an acid. The mineral acid
becomes absorbed into the steel, which is
then put into the tank to be chromed. In
electroplating, only about 20 percent of the
electricity used in the process is utilized to
apply the chrome. The other 80 percent of
the electricity helps to create a side
reaction called hydrolysis, which is a
chemical process of decomposition
involving the splitting of a bond and the
addition of the hydrogen cation (a
positively charged ion) and the hydroxide
anion (a negatively charged ion) of water.
Unfortunately, this hydrolysis is unavoidable
during the electroplating process.
When chrome plating, the chrome is
applied in layers to assure the proper
buildup of chrome throughout the piece.
However, this means layers of trapped
hydrogen, which at the molecular level is
creating hydrogen blisters. When the piece
is removed, that hydrogen wants to escape,
and does so by creating micro-cracks in the
surface — greatly impairing the strength of
the piece.
It is important to understand that it is not
because of the plating process that these
parts are being affected by the hydrogen
embrittlement, but it is the way in which
the pieces are handled before and after the
plating process.
Hydrogen embrittlement is putting an
overabundance of stress on the steel, so it
It is important to understand that it is not because of the plating
process that these parts are being affected by the hydrogen
embrittlement, but it is the way in which the pieces are handled
before and after the plating process
makes sense to say that a “stress relief
process” to alleviate this unwanted tension
is very necessary. Timing is crucial at this
point. It is imperative that within one hour
of a piece’s withdrawal from electroplating
that it be put through the relief process.
One hour is the maximum permitted wait
time — but in dealing with this realistically,
sooner is better. What the stress relief
process does is basically temper — heat or
bake — the piece to allow the hydrogen
that is trapped within the chrome to escape
with virtually no stress, cracking or
weakening, ensuring a strong efficient part.
The time a piece remains in the oven
varies. Usually a piece will be in no less
than three hours. However, depending on
the actual make-up of the piece, size and the
amount of chrome applied, it could be in
there for up to 24 hours or longer. The
harder the steel, the longer it should be in
the oven. Steel with tensile strength of 1,000
would be treated for about eight hours. For
every 2,000 MPa increase, one should
increase the oven time two hours. The heat
at which the structure is baked at should be
no less than 375∞F and closer to 400°F.
This process is extremely necessary to
alleviate the potential problems that could
arise due to the hydrogen embrittlement.
You cannot avoid it — although many
people do try to ignore the reality of
hydrogen embrittlement and do not put the
pieces through the stress relief process.
This only leads to frustration, misunderstandings
and pointed fingers and reflects
poorly on chrome plating as a process. For
example, when trying to build up the edge
of a piece with chrome, every time it was
taken out it would crack, thus causing more
time to be spent on it than was necessary.
With all of the layers of chrome that were
being applied, the accumulation of excess
hydrogen was obvious. This accumulation
was what was causing the chrome to crack.
The hydrogen was trapped within the
layers of chrome and needed to escape.
Once this was realized, the part was put
through the stress relief process immediately
following the plating. The cracking
stopped, and the problem was solved.
Knowledge is power
It is important to realize the harmful
effects of hydrogen embrittlement, and to
know how to prevent them from affecting
the customer’s productivity in the long
run. Whether you are flying an airplane,
molding plastic parts or dealing with
high-strength industrial steel, you should
understand that hydrogen embrittlement
plays a part in all of these. The only way
to relieve the stress caused by this
accumulation of hydrogen is through a
heated process specialized for this one
problem. When looking for a supplier,
make sure that they not only know the
facts about hydrogen embrittlement, but
also how to keep it from emptying your
pockets. Through reworking and trial and
error, the service of chrome plating can
get expensive. Find a place that will do it
right the first time. Save yourself the time
and sanity. You and your supplier should
both have the same number one priority
— long-run efficiency and customer
satisfaction.
MMT
For more information contact Duro-
Chrome Industries, Inc. (Wauconda, IL)
at (847) 487-2900.
©2002 Communication Technologies, Inc., All Rights Reserved.
Reprinted from MoldMaking Technology magazine. Contents cannot be reprinted without permission from the publisher.
MoldMaking Technology ■ April, 2002 www.moldmakingtechnology.com