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topic 1747

Chrome plating and Hydrogen Embrittlement Relief

A discussion started in 1998 but continuing through 2017 . . .


Q. After chrome plating, how important is it to get a part into an oven for embrittlement relief bake? If the time until baking extends too long, will the hydrogen tie up and be unable to diffuse out of the steel. Also, what time is sufficient to bake a high strength steel that has just been chrome plated? What benefit does shot peening provide during chrome plating? Does chrome plating induce a stress on the substrate during plating and how large? What causes hydrogen embrittlement?

Drake Clarke


A. Hydrogen Embrittlement is caused by the Hydrogen evolved during electrolysis being, to some extent, absorbed into the crystal structure of the steel at its' surface. Normally baking at 200 deg. C will remove the atomic Hydrogen before it has had chance to migrate and become molecular. Documented tests carried out by the Spring Research Institute in the UK have suggested that if baking is carried out within 24 hrs. of plating the Hydrogen can be removed. However it appears that many specifications request that the treatment be carried out within a much tighter timescale. I have heard evidence that suggests that this may, in some cases, be due to the desirability to ensure that the operation is carried out and not forgotten!

If the baking operation is not carried out on High Strength Steels then almost certainly it will be to late after the 24 hr. period and the Hydrogen will become molecular, being tied up with an inability to remove and provide a high degree of risk to failure.

The degree of baking of High Strength Steel would be sufficient at 24 hrs at not less than 200 deg. C. Consultation with UK Defence Standard DEF STAN 03-4/2 would provide more specific info (sorry don't have one to hand to quote at present).

Sorry no details on the third and second last points.


Martyn Grimes
plating company - Farnham, Surrey, England


A. The present aircraft standards and AMS2406 [link by ed. to spec at TechStreet] , average 3 hours post plating bake at 190 °C. Dependent on the weight of the part . Hard Chrome does have a tendency to increase crack propagation sites in steel , due to the micro cracked structure of the coating . There is also a drop in the fatigue strength of the material which can be as much as fifty percent . Shotpeening will increase the fatigue life of some steels as much as 200 percent . Normal treatment of high strength steel parts would be : pre heat treat 190 c for 2 hrs after grind , shotpeen 12A2 , Chromium plate , heat treat 190 °C for 3 hrs , final grind , heat treat 1 hr at 190 °C to relieve grinding stress , magnetic particle inspect . As for the embrittlement problem it is to be taken very seriously when dealing with Chrome due to the high amount of hydrogen evolved at the cathode surface , in the process .

Dave Brackenridge
aerospace plating - Germiston, South Africa

November 6, 2013

Q. On the scale of salt spray test hours, what difference would a baked and non baked hard chrome plated surface would show on a metal like 4140 steel for a thickness of 25 microns ?

Jignesh Panchal
- Vapi, Gujarat, India.

November 8, 2013

A. All chrome is cracked to some degree, not much to very bad. The base metal will rust thru these cracks. It will be worse with large cracks because it can set up a larger "battery" for the corrosion. Micro cracked chrome can be quite resistant to rust.

Thickness of the chrome also has a lot to do with it failing.

In answer to your question, baked or not baked has no, or at least a very tiny effect, on the salt spray test.

The bake is there to reduce the effect of hydrogen embrittlement failure.

James Watts
- Navarre, Florida

November 18, 2013

Q. Thanks for the reply. I appreciate it. In addition to it, I would request you to let me know whether the baking process increases the bonding of hard chrome on 4140 steel with thickness of around 25 microns, as one of our customers insist on this. Also if a component is plated in 3 to 4 set ups, is it required to bake it after each set up?

Jignesh Panchal
engineering - Vapi, India

November 18, 2013

A. Baking at 200 °C will not help adhesion enough to talk about, if at all.

I am a very strong believer in baking as soon as possible after chrome plating operation. On really hard 4140 steel we tried for 15 minutes and no more than 3 hours.

If I read your question correctly, Yes, It requires a bake after every plating operation.

James Watts
- Navarre, Florida

November 20, 2013

thumbs up signHello Mt. Watts,
You understood my question very correctly and I am fully satisfied with your reply. It is of a great help to me. I really appreciate it.

Thank you.

Jignesh Panchal
- Vapi, India

June 17, 2014

Q. Why do we need hydrogen embrittlement after chrome plating?
After hydrogen embrittlement why black colour came?
Kindly send the full detail.

- chennai, tamil nadu, india

Current Solutions to Hydrogen Problems in Steels

(includes 7 papers / 34 pages on electroplating)

June 2014

A. Hi SEETHARAMAN. Hydrogen embrittlement is required because when the electricity is pulling chrome ions out of solution and reducing them to metal on the cathode (workpiece), it is also electrolizing the water of solution into H+ and OH-, and drawing those hydrogen ions into the metal, where they cause brittleness.

If the parts are not defectively plated, yet they turn black during baking, you need to use a vacuum furnace or a nitrogen or argon filled furnace to exclude oxygen from the air. Good luck.


Ted Mooney,
Teds signature
Ted Mooney, P.E.
Pine Beach, New Jersey

Chrome plating turns yellow after hydrogen de-embrittlement

April 19, 2017

Hello, does anyone knows why stainless steels after hard chrome plating and hydrogen de-embrittlement have yellow color?

Alexandru Marian
- Bacau Romania

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