Nitride hardening for firearm parts 1

[Barryleehands]

I am an engraver and work on Hagn single shot rifle actions.
The gunmakers I work with are having difficulty with hardening of these actions, using color case hardening charcoal pack methods.
I was wondering if there is an alternative, perhaps Nitride hardening, and where to go to get it done.
The steel I believe is 8620.
Thank you

 

[swall]

Hard to say. The first step would be to find out why the charcoal pack color case hardening is no longer satisfactory. You would need to get samples of parts considered acceptable and those consider unacceptable and have a metallurgical lab cross section them to check case depth and uniformity of case, as well as case hardness. Nitriding is typically accomplished on alloy steels with a carbon content of around .40, so the 8620 would not be a candidate. An alloy change would be required and then there would be a lot of trial and error to try come up with a nitride case that would be cosmetically pleasing as well as functional.

 

[MikeHalloran]

Another possibility is that someone has deviated from the specified process. No malice or incompetence should be inferred. Check by observing the process, start to finish, without comment. Better, record it on video. Then compare it with the process documentation.



Mike Halloran
Pembroke Pines, FL, USA

 

[Barryleehands]

Thaks for the replies.
The problem, is not that it is not hardening, but warpage, and afterward they are stripping the color to acheive what is called a "coin finish", so we dont really need the case color specifically in this instance. If 8620 does not contain enough carbon for nitriding, is there another method which would be better?
Thanks

 

[swall]

Gas carburizing is typically used to case harden 8620. Two paths here--1)carburize and harden all in one process,i.e. quench directly from carburizing. 2)Carburize, cool to room temperature, then reheat and harden.

 

[Barryleehands]

Hi Swall, where would be a good place to take it for gas carburizing?

 

[ornerynorsk]

Do you think the warpage might be induced stress from machining operations? Not knowing what form your blanks are (cast, forged, barstock) this is just speculation. You might benefit from an anneal or stress relief after rough machining.

Are you tempering afterwards, or just carburizing? 8620 is really an ideal material for carburizing and case hardening.

It is better to have enough ideas for some of them to be wrong, than to be always right by having no ideas at all.

 

[Barryleehands]

Ornerynorsk, thanks for the reply.
I am just the engraver, these actions are from Canada, and the manufacturuer recommends hardening after the final metalwork in building the custom rifle is finished.
The warpage is the main trouble but also if it is case colored, the colors stripped, and the piece then blued, the blue can be blotchy because of the differing areas on I presume, carbon absorbtion and hardening of the action,

 

[ornerynorsk]

If you've always had good success in the past, but only recently seen the problem, I would immediately question the material or the heat treatment.

Are you hot bluing or rust bluing? I've seen case-hardened actions not take a hot blue very well for the exact reasons you mentioned. This could very well explain the warping if the carbon content is varying a lot throughout the surfaces and not homogenizing well.

I had an old Argentine 45 automatic that would not take a blue, and lacking all other explanation, it boiled down to the case hardening that this particular factory had used.

Good luck on the project!

It is better to have enough ideas for some of them to be wrong, than to be always right by having no ideas at all.

 

[Barryleehands]

Thanks, it has been an ongoing concern and will continue to be until I locate a better way.

 

[unclesyd]

You might want to checkout the various for of nitrocarburizing available. There are numerous variations on this process available, commonly mentioned are S-Carb and Tenifer.
Depending on the base metal you can remove the black finish that results from this process.

http://www.burlingtoneng.com/index.html

http://kcjplating.com/salt-bath-nitrocarburizing

I've had a lot of gun parts Nitrocarburized with excellent results.
The main materials were AISI 9310 and 17/4 PH.
Nitrocarburized 17/4 is one of the best anti wear and anti galling materials you can use.

 

[shawnpeter]

I'm scrambling to search for any notes, but I do know we have nitrided 8620 on tool joints with success.

As far as getting rid of the black finish, wheelabrating the parts afterward (trial & error on which mesh to use) will clean them up nicely.