Steel is relatively strong, but there are many ways you can make it stronger by heating the steel and then cooling it, a process known as quenching. The quenching process forms martensite. This can only be done with steel that has very high carbon or that has medium carbon and contains special additives.
Choosing the Right Steel
Mild steel is that which has a carbon content of less than 0.4 percent. Mild steel can only be made harder with case hardening. Medium steel is that which has about 0.7 or 0.8 percent carbon. Large amounts of manganese can make the steel harder and allow for oil quenching. Silicon can make the steel stronger. Vanadium improves hardness. Chromium not only makes the steel harder, but also makes it tougher and more resistant to wear.
Testing the Steel
The steel must be heated gradually until it has reached a point where it reaches a high temperature. One of the concerns is whether the steel is hot enough. To determine if this is the case, try the magnet test. When you have made the steel hot enough, a magnet will not attach to it.
Cooling the Steel
Once the steel has been heated to a sufficient temperature, it is either placed in water or oil. The water needs to be cleaned or it will introduce impurities to the steel. Fresh water is most often used because it does not corrode steel as fast as salt water. However, salt water will quench the steel faster than fresh water. It simply needs to be wiped down faster.
With high carbon steels, another option is to use cryogenic quenching. This will reduce the risk of soft and brittle spots forming on the steel. This approach is most often used with high carbon and medium carbon steels.
Cleaning and Correcting Brittleness
Once the steel has been cooled, it will be hard and brittle. Before the steel can be improved further, it should be wiped down to remove impurities. Make sure that the steel is completely cool before doing this. To correct the brittleness, the steel will need to be tempered. The steel is heated until it is blue and then the steel is allowed to cool on its own rather than cooling it rapidly.
Checking the Hardness
If the steel has been hardened, it will be impossible to file it and form a mark. However, if the steel has not been tempered, filing it will create a mark. With this test, you can determine whether the steel needs to undergo the hardening process or if it has already been hardened. Contact your local steel experts such as Moorhead Machinery & Boiler Co. for more information.