The process of tempering is using a heating and cooling process in order to harden the alloys that are contained in certain steels. You would use this tempering process if you were interested in making one of your tools harder, making it easier to do the job its use is intended for. Tools that are made from steel that is too soft might not have the force that you would need when you use it. Hardening would be the answer to make your tool more efficient. Here are some instructions that you can use if you are interested in trying to temper one of your tools at home.
Can It Be Hardened?
Steels have different carbon contents. In order for thermal processing to be effective in hardening a steel, it will need to have a high content of carbon. The process will crystallize the carbon, making the entire metal harder. Low carbon steels can only be hardened with a chemical spray. This would not harden the entire tool, only the outer layers. This may not be enough for the work you have at hand. If you have a tool that is of high content carbon, however, you will be able to harden it to maximum levels using the thermal process.
The Tempering Process
You will first need to heat the area of the steel tool that you would like hardened. Heat it over a flame until it turns a bright red. Right away, dip the tool into a cooling material to quench the metal. This process, the heating and quenching, will harden the steel considerably. The process, however, is just beginning.
When quenching, you can use several different mediums. Water is the most readily accessible, but it has the tendency to corrode metal if left on too long. Bubbles will start to form on the metal right after being dipped in the water, and this can make soft spots in your metal if it is kept in too long. Salt water is a better medium, but still has a tendency for corrosion if it is not rinsed off immediately.
Many people prefer to use an oil, such as cottonseed oil. This will temper slower, but has a better outcome against bubbling and corroding. The downside is that the metal will not be as hard as it would be if you used water to temper.
Repeating The Process
After you have decided what material you are using to quench, and you have cooled the metal, you will need to clean off the tempering material using an emery cloth. You will need to repeat the process by heating the metal once again. This time the heating is done in order to take away any chance of brittleness. The heating can be done in a furnace or a vat of hot oil. The hotter the temperature, the harder the steel will become. Allow the steel to cool, once again. This time it can be cooled slowly by lying on a surface away from the heat.