[TheForge] Question re: inert gases for welding.

[Andy Vida]

Bruce Freeman wrote:
> 
> Hydrogen is sometimes mixed into TIG inert gas.  CO2 is sometimes used
> in or as MIG inert gas.  Otherwise, the nobel gases (He, Ar) are used.
> 
> What about nitrogen?  Nitrogen can harden steel.  Could this be
> beneficial.
> 
> This is idle curiosity, BTW.

	As far as I know, and I may be wrong here, the only steels
	that have sufficient affinity for nitrogen are the so-called
	"nitriding" steels.  One method of nitriding puts the work
	into a reactor where ammonia at 1200*F is circulated for
	several hours.  The resulting nitride case is perhaps 0.003"
	thick, typically, and extremely hard.  

	These days, they just coat the steel with the various nitrides,
	carbo-nitrides, and oxy-nitrides of titanium, chromium, zirconium,
	and a couple other metals.  Harder, faster, cheaper, and almost
	certainly better.

	I would think that nitrogen hardening would embrittle the weld,
	which in many cases would be highly undesireable.  This is a
	problem with titanium, which has a very high affinity for nitrogen.
	I guess they don't call it a "reactive metal" for nothing. :)