One of the mistakes made when tempering steel is to not have enough carbon content. The amount of carbon in the steel affects the type of steel that will be produced by the process.
Hardening the Piece
The entire piece of steel does not need to be hardened. Instead, you will simply need to harden the part of the steel that will need to be hardened, such as the chisel point. The entire piece of steel should be heated slowly at first before the section to be hardened is heated.
Be Careful When Using Water
Freshwater can be used to quench steel, but freshwater often causes its own problems. Freshwater often corrodes the steel unless it is dried quickly. Also, bubbles will sometimes form on the metal that slow down the cooling process and cause soft spots. Salt water is less prone to this problem because the salt causes the bubbles to pop more quickly.
Challenges When Using Oil
An alternative is to use oils instead of water to quench the steel. This will result in steel that is not as hard, but it will also be less brittle. If you used something other than water, you can rinse the oil off with water. Then, make sure you use an abrasive cloth to finish cleaning the steel.
When using oil to cool metal, make sure that you a fire extinguisher ready in case the oil catches on fire. Place the steel quickly in the vat and use the fire extinguisher to put it out. If you do not have a fire extinguisher, place a lid on the vat to put the fire out. Make sure not to use water because this will not put out an oil fire.
Finishing the Steel
Make sure that you heat the steel again or else the steel will remain brittle. The reheating is a second tempering process. If the steel alloy has a tendency to become brittle, make sure that you cool the metal slowly. If the metal is not prone to becoming brittle, it doesn't matter whether it is cooled quickly or slowly.
Testing the Hardness
If you are wondering how hard the steel is, grab a metal file and use it to file the edge of the metal. Metals that have not been hardened will be easy to make an indentation into. If you have hardened and filed many different types of metals, you will also learn that hardened steel produces a different sound when filed than steel that has not been hardened. Click here for more information on tempering.