Annealing Steel

Annealing is a heat treatment process that is used to change the properties of metal or glass. Annealing makes steel stronger and harder. It also induces greater ductility. The process eliminates many of the problems caused by forging or rolling steel. Annealing makes it easier to fashion durable objects out of cold steel.

Difficulty:

Moderate

Instructions

Things You'll Need

• Steel
• Annealing furnace or other heat source

1. Heat to a certain critical temperature to anneal steel. The temperature needed depends on the carbon content of the steel. The higher the carbon content, the lower the temperature. Typically, annealing is accomplished at temperatures ranging from 760 to 910 degrees Celsius.

2. Understand that heating the steel is changes its internal structure. Prior to annealing, steel is often pearlite. Pearlite is steel that consists of alternating layers of alpha-ferrite and cementite. The alpha-ferrite makes up 88 percent of the steel. Annealing causes the excess ferrites to dissolve throughout the steel. Pearlite transforms into minute crystals of austenite.

3. Allow the steel to cool slowly. The cooling causes the austenite to turn back into pearlite. However, the steel is different from before. Larger ferrite molecules are now spread evenly among the pearlite. The faster the rate of cooling the smaller the ferrite crystals. Rapid calling will leave small ferrite crystals around the boarders with very fine pearlite in the center of steel.

4. Overheat or under heat the steel and ductility is reduced. Large austenite crystal may be formed and carbon may actually be released from the steel making it resemble iron. Proper temperatures are a must in achieving the beneficial effects of annealing.

Tips & Warnings

• Annealing should be conducted away from combustible materials. Wear protective clothing and eyewear when working with hot metal.

Resources

• Pinson Valley Heat treating annealing furnace
• Industrial Heating annealing furnace