Carbon atmospheres 2

[Greenleader]

Simple question; I am wondering in which atmosphere steel, at critical temperature more easily absorbs carbon. Carbon monoxide, or carbon dioxide? Thanks.

 

[swall]

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).

 

[Greenleader]

I am designing a simple oven, and want to be able to have a neutral, and, or a slightly carburizing atmospheres without a complicated system.

 

[Greenleader]

Can a 100% CO2 atmosphere be used as a neutral hardening gas for medium carbon steels?

 

[metengr]

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.

 

[swall]

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.

 

[Greenleader]

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.