Gas Nitriding and Hydrogen embrittlement

[eagertknow]

Gas nitriding is performed in an atmosphere of Ammonia and dissociated ammonia (Hydrogen and Nitrogen) at high temperature (500-555 deg C).Is Hydgrogen embrittlement a problem during nitriding.If not why?
Some references will be appreciated.

 

[swall]

No, hydrogen embrittlement from nitriding is not a problem. Many heat treating processes use a hydrogen component in the furnace atmosphere. The hydrogen form is molecular, rather than atomic. It is atomic hydrogen that typically causes embrittlement, from electroplating processes, etc.

 

[mcguire]

If one bright anneals austenitic stainless steel, such as 301, it picks up enough hydrogen to experience delayed failure after forming. This annealing is done in dissociated ammonia. Why not worry about hydrogen pickup and delayed failure when nitriding in dissociated ammonia?

Michael McGuire

http://stainlesssteelforengineers.blogspot.com/

 

[swall]

Mcguire--good question. With gas nitriding, you start out with a ammonia at a low dissociation rate and thus, low concentations of hydrogen. Perhaps as the nitriding reaction proceeds, the ingress of nitrogen and formation of nitrides prevents the ingress of hydrogen. As the process proceeds, the dissociation rate increases and more hydrogen is present. Perhaps at that point, the nitride case acts as a barrier to hydrogen ingress. Gas nitrided low alloy steels, 410ss and 17-4 all have a satisfactory history of usage with no hydrogen embrittlement, unless exposed to a hydrogen source after nitriding.

 

[EdStainless]

Mike, 301??? It will not absorb any hydrogen.

I always presumed that you could get away with BA on low alloy ferritic alloys because the hydrogen diffusion rates were so fast that they would reach zero hydrogen during natural cooling.
High alloy ferritics have enough alloy additions to restrict hydrogen diffusion and it makes these alloys problematic. If we BA a ferritic or duplex we will not cold draw for at least 48 hours.
For any austenitic alloy (17-7 and Custom 465 included) we will cold draw the same afternoon as annealing.

= = = = = = = = = = = = = = = = = = = =
Rust never sleeps
Neither should your protection

http://www.trent-tube.com/contact/Tech_Assist.cfm