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topic 9912

How to check & prevent hydrogen embrittlement


we are manufacturing hub nut used in mounting of tires of an automobile manufacturer .This consist of an en8d nut hardened tempered to 20 to 24 Rc and en19 washer hardened & tempered to 30 to 34 Rc.

Washer is fitted in one end of nut which is than flared on power press to make the assembly

After this assembly has to be zinc plated & hydrogen embrittlement relief has to be carried (which drg says bake for 2 hrs at 190 degrees) Zn plating & subsequent passivation is carried by my vendor.Vendor is using zinc cyanide bath, & HCl acid pickling & drum instead of barrel

Can somebody help me please:

1.How to check whether hydrogen embrittlement relief has been carried out & what parameter is there for checking

2. since vendor is using zinc cyanide bath, will shifting to acid bath by him accompanied by low pickling & use of barrel result in total elimination of this baking process.

thanks everyone in anticipation

vikas kaushal
- Chandigarh India

July 4, 2008

Hi, Vikas. If the parts are hard enough to be susceptible to hydrogen embrittlement then half-measures like switching to acid zinc or minimizing the strength of pickling solutions will not work. Reading between the lines, it sounds like you are concerned with reducing the cost by eliminating baking, so the things you need to do to prevent embrittlement, like blasting instead of pickling, may be cost prohibitive.

You can plate notched specimens to see if the process causes embrittlement and, on a more casual basis, you can put the parts on an anvil and smack them with a hammer (wear goggles [linked by editor to product info at Amazon] ).

You might consider changing the technology to mechanical plating.


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

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