Simple question; I am wondering in which atmosphere steel, at critical temperature more easily absorbs carbon. Carbon monoxide, or carbon dioxide? Thanks.
Are you interested in carburizing, or neutral hardening (i.e. avoiding decarb)? What specific type of atmosphere do you have in mind? Most heat treating atmospheres for steel are a mix of gases, such as CO,N,CO2 and H2. Carbon potential of the atmosphere , carbon content of the steel and temperture are some of the factors that determine how quickly steel absorbs carbon (or loses it).
As swall has mentioned, a standard gas carburizing atmosphere relies on partial pressures between CO/CO2, H2/H20, a carrier gas and methane that can provide a source for carbon potential.
In your case to keep it simple and safe, I would use an Argon gas purge to provide for a neutral or inert atmosphere for heating and cooling.
A straight CO2 atmosphere will not prevent decarb. For a simple atmosphere, I would suggest nitrogen, with some natural gas metered in. The major gas suppliers sell equipment to produce this type of atmosphere.
Thanks for the replies.
The spec for normalizing 4340 mod, requires a long cool down time in the oven. I need as little decarb as possible, without producing a *potentially* dangerous atmosphere. Also I might want to carburize a wee bit during hardening. Thanks again.
