Hydrogen Embrittlement Failure. Details for Chromium Plating Baking

A. Dear Mr. Talathi,
I hope someone else will answer your questions. I can only give you some informations about our use of chrome (we use chrome in abrasive environmental too: chrome vs melt glass). The thickness value for hard chrome is usually 6-8 micron but we can work without problems with 15 micron too. I know that an hardening of components before hard chrome planting can give a bad adherence of chrome.

A. Mr. Tosini,

Lab research has demonstrated that not only Hydrogen but also Oxygen dissolved in the chrome layer have the highest influence on hardness. Vacuum treated Chrome to eliminate these "impurities" has a hardness of only 400-500HV instead of 1000-1100HV.

A. Generally, chrome with hardness above 1,000Kg/mm2 is BCC, whereas hexagonal structure is found in softer plates. Your proposed heat treatment of chrome above 400 °C will eliminate Hydrogen but very little Oxygen. With this treatment hardness may drop up to 30% due to recrystallization, stress relieve and grain growth. Now, it is important to say that hardness is not a linear function to wear resistance.

A. Why are you baking the part at such a high temp? "Normal" bake temp is 375 to 450 °F, not °C. Why do you think that you have a hydrogen embrittlement problem? You can prevent most of any hydrogen embrittlement by simply not etching or pickling it as long. Also, you can avoid sharp corners by employing generous radius on all corners. You can also shot peen before plate. You can also pre-bake. You can extend the length of the bake. You can get it into the bake oven quicker after it comes out of the final rinse.Far too many people have heard of hydrogen embrittlement, so blame every failure on it. It is not Cyanide or Cancer, but far too many people are finding goblins under their bed at night when there are none. In short, make sure that you have a problem before you waste time, money and energy trying to fix it. PS , notch bar testing is the common way to check for a problem. Destructive loading of a part is wonderful if it physically lends itself to the testing.

A. Mr Talathi,
I suggest the following sequence:

1) Clean in an alkaline soak cleaner at 70 °C for 4-6 minutes.
2) Anodic clean at 75 c for 2 Minutes
3) Rinse well twice
4) Check if Rust is present . Anodic de rust in a de-rusting solution. This is alkaline and runs 75 centigrade anodically and is available domestically.
5) rinse twice plain city water
6) neutralise in 5 % dilute sulfuric for 30 secs.
7) Plate Sulfur Free Semi Bright Nickel.. 6 to 10 Microns Dragout + two rinses. ( NOT BRIGHT NICKEL please NOTE)
8) Dilute Chromic dip or dip in Chrome dragout.
9) plate Chrome as usual to regular thickness.
10) drag-out and two rinses
11) Hot Deionised water rinse at 90 °C for 1 Min immersion.

Air dry and replace the DI water daily. The Hydrogen Embrittlement will be present for academic purposes in the part. The Nickel will eliminate corrosion failure.
Best for performance.. Good Luck

A. The only de-embrittlement I've heard of consists of baking the part for up to 23 hours at roughly 375 °F within a few hours of the operation that caused the embrittlement. This is necessary for hardened steels that have been subjected to any processing which generates atomic hydrogen; that processing would include not only the cadmium plating itself, but cathodic pre-cleaning processes and acid activation processes as well. It may be best to blast the components rather than chemically cleaning them.

A. The first question to ask is does an unplated part fail the load test. If so, plating has nothing to do with it! Since this is defense related, the specifications should mandate the post plate bake. Now for the practical side of the problem, most hydrogen embrittlement is caused by an excessive etch cycle prior to the plate. For post plate bake, the secret is to get it into the bake oven as soon as possible after the final rinse in the plate cycle. I insisted on under 15 minutes if it was a critical or complex geometry or very hard part. Some parts only require 4 hours at 375 ° F. Some parts require a preplate heat treat. Some parts require a shot peen step to a given and verified intensity prior to plate.

A. As Mr. Watts stated, this information should already be in your plating specifications. If not, download AMSQQP416 [affil link] F PLATING, CADMIUM (ELECTRODEPOSITED).

A. Dear Sir,

With worldwide rejection of Cadmium, and a move toward alloy plating, it would be worthwhile if you could get the spec changed to zinc-iron plating.

Best regards,

A. Hydrogen de- embrittlement is the release of trapped hydrogen under hard chrome plating. The hydrogen is a by-product of the chrome plating process. To remove, place into a continuous furnace @ 300 °C for 2.5 hours and water quench to room temp. If hydrogen is not removed, potential for parent material substrate to fail under extreme circumstances.

A. Jennifer,

what also will be helpful is to measure the conductivity of the chrome solution, it should be above > 350 mS/cm, is just a quality test.

Regards,

A. After chrome plating, in 2 hrs, you can go to oven for 190&plmn;10 °C for 2 hrs if the hardness is 42 Rc
regards

A. I agree with Dr. Polat, although I have seen (and written) specifications that require baking after plating for parts that are Rockwell C 35 and above.

Among the specifications that address baking after electroplating are AMS2759/9 [affil link] and ASTM B850-98 [affil link]. Those documents also agree with Dr. Polat, calling out 190 °C or 375 °F for an hour.

A. Dr. Polat is right in his recommendations.

A. BAKING AFTER PLATING:- PLATED PARTS WHICH HAVE HARDNESS OF 40HRC OR ABOVE SHOULD BE BAKED AT 190 ± 14 DEGREE C FOR 4H . PROCESS SHOULD BE STARTED IMMEDIATELY AFTER PLATING.

A. Embrittlement relief is normally specified by the spec or the company you are doing it for.

Normally, it is dependent on the hardness.

Boiling is nowhere a high enough temperature to effect a de-embrittlement.

The proof is verified by doing notch bar testing.

A. I believe that the information you seek is in ASTM B850-98 [affil link]-98(2009) "Standard Guide for Post-Coating Treatments for Steel for Reducing the Risk of Hydrogen Embrittlement." They advisedly use the term 'reducing' rather than 'eliminating' for reasons discussed in the standard. There are also non-embrittling processes such as phosphate and oil and phosphate and paint, and, for those who require sacrificial protection, mechanical plating and zinc-rich paints.

A. Hi Jem,

De-embrittlement requirements are usually dependent on either the hardness or the ultimate tensile strength (UTS) of the material.

Pretty much everyone has their own take on what the times and temperatures are for various hardnesses and UTS. If it isn't being specified by your customer you could use AMS2759/9 [affil link] as a guide.