CASE HARDENING

One of the oldest known heat-treating processes is carburizing. History tells us that sword blades and
primitive tools were made by the carbonization of low-carbon wrought iron. When you are making a
firearm, case hardening is a good way to finish many of the parts. Color case hardening will give a very
attractive finish.

The following carburizing processes are commonly used in industrial applications: (1) pack carburizing,
(2) gas carburizing, and (3) liquid carburizing.

Most mild steels do not come with enough carbon to enable them to be hardened by heating and
quenching, as are the higher-carbon-content tool steels. However, if carbon is added to the steel, it can
be made to harden upon quenching. There are many methods of adding carbon. In the processes, the
heated steel absorbs the carbon from the outside. The interior of the metal does not absorb the added
carbon and so remains soft after quenching. A hard carbonous surface, or case, is formed on the metal.

Case-hardening is accomplished by impregnating the surface of steel with carbon, by heating it at high
temperatures while packed in an iron or steel box with proper carburizing materials, or by heating the
steel in potassium cyanide in an iron pot,

The only practical method for the home shop is one of the cyanide processes. Melted sodium cyanide is
a very good carbonizing agent, but it is also very dangerous to use.

There are several patented compounds on the market, such as Kasenit, Hard and Tuff, which give the
same results and are safer to use. The steel is heated to a cherry red, then covered with the hardening
compound and allowed to soak in it.