Can I Carburize Low Carbon Steel In My Cress Furnace?

Yes, by PACK CARBURIZING. First, let me clarify. There are several ways to carburize low carbon steels, but in an open atmosphere, box type furnaces like Cress furnaces, there are only two ways. One way is to use a carburizing compound. But buyer beware. Many carburizing compounds contain oxidation chemicals that literally eat other chemical elements in stainless steel. And, using these compounds, even just one time, saturates the porous fire brick to a point that if you ever desire to use stainless foil for decarb protection, the chemicals will literally eat holes in the stainless foil.

Now on to pack hardening: Pack hardening is a two step process that works well for low carbon steel carburization. First, you must have a completely sealable steel box. This is often a bolted together box that fits in your Cress Furnace that has sealing insulation rope between sides and ends of the box. A heavy wall pipe with sealable, removable end caps works well.

The box needs to be filled with any good carbon rich material, such as, cast iron turnings or chips, or something like powdered bone meal. When filling the box, parts can be introduced in layers, with no parts touching one another, then more layers upon layers until the box is completely full. The end of the box must be sealed using insulation sealing rope.

Next, the box can be placed in the furnace and heated as required for the grade of steel being treated, usually in the 1700 to 1900oF range. The whole box must come up to temperature, then soaked for 16 to 48 hours, which is dictated by the depth of case needed; the longer it is soaked, the deeper the case will be. The carbon essentially gets absorbed on all exposed surfaces of the parts during the soak process. Once the soak time is complete, the box can be removed from the furnace and cooled. Once cooled to room temperature, the box is opened and the parts can be removed from the box and are then ready to be put through the second step which is the heat treating process as required for the grade of steel being used.

The packing material can be reused several times before it needs to be refreshed for more available carbon.

COPYRIGHT © May 2007, by Advisor In Metals

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