Carburizing Stainless Steels Made Simple

March, 19, 2012

Why is stainless steel “stainless”? Stainless steel is resistant to oxidation or corrosion due to a nano thick layer located on its surface. This protective barrier, a chrome “passive” oxide film, is created through a chemical bond of oxygen and chrome. The steel must have a minimum of 10.5% chrome in composition to be considered a “stainless steel”. This is such a spontaneously formed, tenacious film that even when mechanically removed, the layer will effortlessly reform when the surface is exposed to the open air or “self-passivate.” It can also inhibit some heat treating processes where this layer must first be removed – such as carburizing.

With traditional carburizing, it is very difficult to reduce the chrome passive oxide layer. The procedures required to do so may be dangerous, expensive, uncontrolled, non-uniform, and environmentally unfriendly.

On the other hand, carburizing a stainless steel alloy in a vacuum furnace easily and seamlessly reduces the chrome passive oxide layer. The reducing atmosphere in the furnace created by the vacuum conditions paired with elevated temperatures provides the energy to dissociate the oxide. It breaks down the “passive” state and prevents it from reforming which means it has been transformed to an “active” state.

Since low pressure vacuum carburizing produces this natural effect of reducing chrome oxide on stainless steels, Solar can perform surface treatments on a much broader range of materials that are challenging or even impossible to attempt to using traditional methods.