Quench hardening

tom2005

Quench hardening is a mechanical process in which steel and cast iron alloys are strengthened and hardened. This metals consist of ferrous metals and alloys. This is done by heating the material to a certain temperature, differing upon material, and then rapidly cooling the material. This produces a harder material by either surface hardening or through-hardening varying on the rate at which the material is cooled. The material is then often tempered to reduce the brittleness that may increase from the quench hardening process. Items that may be quenched include gears, shafts, and wear blocks.

tom2005

Quenching metals is a progression; first step is soaking the metal. “Soaking” can be done by air (air furnace), or a bath. The soaking time in air furnaces should be 1 to 2 minutes for each millimeter of cross-section. For a bath the time can range a little higher. 0 to 6 minutes is the recommended time allotment in salt or lead baths. Uneven heating or overheating should be avoided at all cost. Most materials are heated from anywhere to 815-900 degrees Celsius (1500-1650 degrees Fahrenheit).

The next item on the progression list is the cooling of the part. Water is one of the most efficient quenching media where maximum hardness is acquired, but there is a small chance that it may cause distortion and tiny cracking. When hardness can be sacrificed, whale, cottonseed and mineral oils are used. These often tend to oxidize and form a sludge, which consequently lowers the efficiency. The quenching velocity (time to cool) of oil is much less than water. Intermediate rates between water and oil can be obtained with water containing 10-30% Ucon, a substance with an inverse solubility which therefore deposits on the object to slow the rate of cooling.

The way that an object is placed into the containers to soak is also very important and a step that needs to be discussed. To maximize distortion loss, long cylindrical objects should be quenched vertically, flat sections edgeways and thick sections should enter the bath first. To prevent steam bubbles the “quenching bath” should be agitated.