DDK - Die Deutschen Klassiker

Bear in mind we manufacture bolts for the MOD, F1, Aerospace etc. and I'm a qualified Metallurgist. Company is www.tachart.com
8.8 bolts or any high tensile bolt with a tensile below 1000N/mm2 don't need Hydrogen De-embrittlement after stripping and replating.
10.9 and 12.9 without a doubt definately need replating otherwise you'll have problems further down the line.
For for general zinc & yellow plating to BS3382 Pt2 we use a company called Northern Blacking (Sheffield), sensibly priced (small minimum order charge)and ok managing small amounts. Not sure how they'll manage with carriers though as we drop and collect on daily basis.

OK, so looks like I can get my 8.8's plated locally with no need to bake. I'll see how they come out.

Don't know what rating the bolts in the spring plates are so I'll just buy new.

Thanks all!

Al.

dean1057 wrote:Bear in mind we manufacture bolts for the MOD, F1, Aerospace etc. and I'm a qualified Metallurgist. Company is http://www.tachart.com
8.8 bolts or any high tensile bolt with a tensile below 1000N/mm2 don't need Hydrogen De-embrittlement after stripping and replating.
10.9 and 12.9 without a doubt definately need replating otherwise you'll have problems further down the line.
For for general zinc & yellow plating to BS3382 Pt2 we use a company called Northern Blacking (Sheffield), sensibly priced (small minimum order charge)and ok managing small amounts. Not sure how they'll manage with carriers though as we drop and collect on daily basis.

Dean, whats your take on baking well after plating e.g. >> 4 hours ? Its hard to imagine absorbed H atoms doing anything nasty while sitting around in storage at room temperature. HE is not a precise science, and I havent come across any test data to say one way or the other, but I didnt spend much time looking. I think you should be able to bake them years later - what can you tell us? Maybe residual stresses and H don't mix well even at room temp? All the best, Dean (also from Donny, but Materials Scientist, reliability of platings in oxygen at high temperatures)

Hi Dean,
I wouldn't rely on baking them any later than 1 hour after cleaning and plating on grades above 8.8.
In the 32 years I've been here I can't recall having any fasteners fail due to hydrogen embrittlement cracking.
We do have one offshore customer that has there special fasteners Zinc Nickel plated in 8.8 strength material that request all their parts have a 8 hour bake at 200deg C, so they are taking no chances. These are all related to the API20E bolting specs, so a bit more critical.

dean1057 wrote:10.9 and 12.9 without a doubt definately need replating otherwise you'll have problems further down the line.
we use a company called Northern Blacking (Sheffield), sensibly priced (small minimum order charge)and ok managing small amounts. Not sure how they'll manage with carriers though as we drop and collect on daily basis.

Hi, I assume you mean 'definitely need baking'

The reason I set up my own small plating system in the garage is that the majority of platers have a get out clause that they take no responsibility for LOST items. Some of the restoration work that I do I could not afford to lose items, hence even during the sand blasting I wire up every part as I have showed in one of the pictures above.

I am not a metallurgist but did study 'properties of materials and forming at Lancaster University' as part of my degree and just wonder from memory we used to case harden metals by heating and dropping in some carbon particles and as a lot of harder steels can be referred to as carbon steel......are the materials used for higher tensile fasteners of a higher carbon content and is it then the hydrogen somehow affects this carbon content.

I bake all my fastenings immediately after plating even 8.8 stuff. Some older fastenings don't even have the embossed grade stamped on and many times I have taken old classic parts apart particularly the brake areas only to find at some point mechanics have fitted wrong spec bolts at some point just because the thread probably matched.

Steve

dean1057 wrote:Hi Dean,
I wouldn't rely on baking them any later than 1 hour after cleaning and plating on grades above 8.8.
In the 32 years I've been here I can't recall having any fasteners fail due to hydrogen embrittlement cracking.
We do have one offshore customer that has there special fasteners Zinc Nickel plated in 8.8 strength material that request all their parts have a 8 hour bake at 200deg C, so they are taking no chances. These are all related to the API20E bolting specs, so a bit more critical.

Thanks for sharing your insight, its great to hear other opinions and learn from others

- I think there are some curves in a (maybe ASTM) standard document that simply plot yield strength versus bake period for a flat (zero) failure rate due to HE, and the one in the magazine article that another member posted suggested 7 hours for 8.8 yield strength so going for 8 hours sounds like a great bet. Its interesting that other sources say that 8.8's are not HE susceptable, and maybe that's true, and maybe the guy or gal that specified 8 hours just went off the same curve without looking further because the boss needed an answer yesterday. In my experience of the wider materials sciences, and both writing and reviewing papers for publication in scientific journals, there are so many different combinations of variables at play, that there is rarely ever one answer. I think that must apply to bolts as much as anything - real application experience counts for a lot though, and customer is always right and always king anyway!