H2 Embrittlement Relief Bake and Nitrided Parts

[djsugg]

Most of the electroplating specifications call for baking at 275°F when dealing with carburized parts. Does anyone know if the same restriction would apply to parts case hardened by nitriding? by carbon nitriding?

Does nitriding increase or decrease the risk of hydrogen embrittlement?

What bake cycles are recommended for hydrogren embrittlement relief of nitrided parts?

Any help greatly appreciated.

 

[TVP]

Hydrogen embrittlement is associated more with strength/hardness levels than with microstructure, which is obviously not the best approach, but it is how the industry currently works. As such, electroplating any hardened steel component with a core hardness greater than 320 HV or a surface hardness greater than 350 HV must be subjected to a hydrogen embrittlement relief treatment. SAE/USCAR-5 provides details based on these hardness limits, and the necessary time and temperature requirements are dependent on the hydrogen-generating process (acid cleaning, phosphating, electroplating, etc.). ASTM B 850 bases the requirements on tensile strength, and uses the lower limit at 1000 MPa, which is approximately 300 HV.

So, what you need to provide is the hardness level to which your component has been hardened. Based on that, you can use one of the two documents I listed above to prescribe the necessary treatment. By the way, why are you electroplating a surface that has been carburized or nitrided? These layers are usually much more wear resistant that electrodeposited coatings, unless you are using industrial (hard) chromium.

 

[djsugg]

We sometimes are plating other surfaces on the part that have not been case hardened, although we do a lot of cadmium plating, for corrosion resistance, on case hardened parts.

I will try to trac down the SAE document you mentioned, as I have not read that one. My major concern is when the parts have been nitrided as to the heat treatment implications, such as maximum temperature.

 

[metman]

djsugg
You said, "My major concern is when the parts have been nitrided as to the heat treatment implications, such as maximum temperature."

Do you mean max temp for baking?
Are you concerned that the 275F baking (or a higher temp if used) might affect the nitrded microstructure? This is not a problem since the tempering of martensite will occur at temperatures well below temperatures which would affect the ntrided structure.

TVP broached an interesting point and maybe this is part of your question. What effect does the nitrided microstructure have upon restricting evolution of hydrogen during bake-off after plating?

Jesus is THE life,
Leonard

 

[djsugg]

Yes, I did mean the maximum baking temperature. Most of the specifications restrict the hydrogen embrittlement relief bake for carburized parts to 275F, some even limit the time to 3 to 5 hours. None of the specifications give any explicit directions on nitrided parts. I did not want to damage the nitriding during the bake.

I am very interested in the effect of nitriding has on diffusion of hydrogen into the base steel, as well as the diffusion bake out during the bake. I can't recall ever seeing anything on this.

 

[metman]

I also am very interested in this diffusion question and expect that someone will shortly shed light on it. But now you've got me thinking more deeply about the nitrides. The limit on bake-off temperature for carburizing problably is because carburizing is usually only done where max surface hardness is wanted and therefore you don't want to draw down the hardness of the carburized matensitic case structure by baking (tempering) at too high of a temperature.

I have never read anything about nitrides being susceptible to tempering. I doubt that thermal processing would affect the hardness of the nitrides but I could be wrong. Let's see what others have to say.

Jesus is THE life,
Leonard

 

[lgearhart]

Use the standard 375F for electroplated, nitrided parts. Remember that nitriding takes place at roughly 1000F, and is not quenched. The tempering temperature for nitrided steels is usually above 1000F, so you're fine using the default 375.