melonite/heat treating/dimensional shift

[NICKNICK]

If I'm interpreting things correctly, one reason Remington's need truing is that they are machined PRE-heat treatment for easier machinability in high-rate production. Custom actions are machined in an already hardened state, so while they are more difficult to manufacture, they don't have the dimensional changes/warping that can happen with a Remington.

With the high temperature of salt bath nitriding, would the melonite process put a custom action at risk of warping, or is all that taken care of by the original heat treatment that happens before machining?

 

[Pusher591]

I'm having my Defiance Deviant done now. There have been several people melonite their customs with great success. Don't let anyone do it though, I would use MMI if I were you.

 

[turbo54]

Most steel actions are made of 4140.

4140 is hardened by heating it to above the transfer temp (about 1650°) on the equilibrium phase diagram, letting it soak at temp allowing the grains to grow, then quenching rapidly to near room temp.

This results in very hard, strong, but brittle properties.

So it won't snap, it is tempered (softened/toughened) by cooking for a few hours at more moderate temperatures, like ~550°

SBN isn't a thru-hard process, occurs at cooler temps (~1000°), and only for 15-20 minutes.

Dimensional changes are minimal.

 

[proneshooter]

I concur with turbo54 based on my experience dealing with 4140 and gas nitriding. Actually, IME 4140 cuts better if it's somewhat hard. Where I work we turn 4140 and 17-4 PH at mid 40's Rockwell C at upwards of 600 SFM and pretty good feed speeds. Carbide inserts work pretty good.