ASTM F1941 - zinc plating high-strength cap screws? 2

[btrueblood]

Ok, it may have been done to death, but I had not heard of the ASTM F1941 and its cohort spec. F1940 before. A quick search failed to deliver a succinct answer.

If zinc plating is applied per F1941, can an ASTM A574 alloy socket head cap screw be reasonably said to be free of hydrogen embrittlement?

Or are does the standard warning (don't zinc plate on steel with tensile strength > 150 ksi) still apply?

My fallback is to specify a good zinc-rich primer paint or similar anti-corrosion coating on standard black oxide finished fasteners.

 

[hydtools]

There should be a baking process following the plating.

http://engineers.ihs.com/document/abstract/PWDGKAAAAAAAAAAA

Ted

 

[hydtools]

Here is an IFI white paper also:

http://www.bestbolt.com/white_papers/white_paper_14.pdf

Ted

 

[SnTMan]

You might also see:

http://www.galvanizeit.org/aga/resources/technical-faq-dr-galv/fasteners/194

Regards,

Mike

 

[btrueblood]

Thanks all. Finally got my copy of the spec. from my purchasing person (I'm not able to purchase them directly). Here are the last two paragraphs of the introduction of ASTM F1941-07, with my edits [] and italics added:

"Although this risk [of hydrogen embrittlement from plating] can be managed by selecting raw materials suitable for the application of elecrodeposited coatings and by using modern methods of surface treatment and post heat-treatment (baking), the risk of hydrogen embrittlement cannot be completely eliminated. Therefore, the application of a metallic coating by electrodepostiion is not recommended for such fasteners [HRC > 40]."

Weirdest spec. I've ever read, but that last sentence pretty much sums things up for us. We will coat the fasteners after installation to mitigate corrosion concerns. The product is designed to meet ASME B31 standards, and will be shipped overseas. My service tech doesn't relish the thought of travelling to BF East Asia to replace some cap screws.

 

[MintJulep]

There is an SAE document that states that black oxide has the potential to induce hydrogen embrittlement in high-strength fasteners too.

I don't have access to it at the moment, so I can't give you the number.

 

[btrueblood]

Oh lovely. Thanks, Mint. Would appreciate the reference when/if you get a chance.

 

[MintJulep]

It will be a few days before I'm back in my office to confirm the content, but I think it's SAE J1648 Protective Coatings for Fasteners.

It's one of the standards that included in the SAE Fastener Standards Manual, HS-4000 if you have that book handy.

 

[TVP]

bt,

There is only a very brief mention of hydrogen embrittlement related to black oxide coatings in SAE J1648. It appears in Table 1 under Description and Requirements. The following is an excerpt:

Porous thin; hydrogen embrittlement susceptible; oiling may be necessary.

SAE AMS 2485 Coating, Black Oxide includes a section that requires inspecting parts for surface and intergranular attack after the coating process. The following is an excerpt:

4.2.2 Periodic Tests: Surface and Intergranular attack (3.3.4) when parts 36 HRC or higher are being processed, and tests of cleaning and coating baths (See 8.2) to ensure that coatings will conform to specified requirements are periodic tests and shall be performed at a frequency selected by the processor unless frequency is specified by the purchaser.

 

[btrueblood]

Hmm. Thanks Mint and TVP. Food for thought. From a risk standpoint, I'm going to stick with the earlier decision, and avoid plating. What research I have done still tends to indicate that plating is one of the bigger drivers in HE of fasteners.