Surface heat treatment is an effective method for improving the properties and performance of many metals and alloys. The purpose of surface heat treatment is to improve the surface properties in terms of hardness, wear resistance, corrosion resistance and dimensional stability. There are several types of surface heat treatments. These include annealing, normalizing, quenching, nitriding and shot peening.
Annealing is a process of heating a metal or alloy in order to soften it, making it more workable and less brittle. Annealing also reduces the stress caused by strain, machining and welding. Annealing can make a metal more homogeneous, which can increase its strength, toughness, and ductility. In addition, it helps to improve machinability and can help to improve fatigue life. Annealing of metal and alloys is also used to reduce hardness and improve electrical, thermal and dimensional stability.
Normalizing is a heat treatment process that is used to refine the material properties of a metal or alloy. Normalizing is typically applied to low alloy steels to reduce temper brittleness and increase toughness. The process involves heating the material to 30-50 degrees above its critical temperature and then quickly cooling it in air. This creates a finer option and distribution of carbides in the grain structure of the material, which enhances its mechanical and physical properties. Normalizing can also be used to relieve residual stresses created by welding or other fabrication uses.
Quenching is a process of cooling a metal from its austenitizing temperature in order to obtain a desired microstructure. Quenching is usually followed by tempering in order to reduce internal stress and improve ductility. Quenching is often used to improve the strength and wear resistance of materials. It involves rapidly cooling the metal or alloy in order to form martensite, which is the hardest form of steel, making the metal tougher and harder.
Nitriding is a process where nitrogen is added to the surface of a metal or alloy to improve surface hardness, corrosion and wear resistance and increase fatigue strength. The process is typically done at temperatures between 500oF and 1050oF. Nitriding creates a hard, wear resistant and corrosion resistant surface on the material. It also provides superior wear resistance, fatigue strength and increases overall strength. The nitrided layer is typically very thin, ranging from 0.0005” to 0.005” thick.
Shot peening is a surface finish process used to improve a material’s fatigue life and resistance to stress corrosion cracking. In shot peening, spherical particles are propelled onto the surface of a material using a high pressure air stream. The particles embed themselves in the surface of the material, creating an “indentation” and thereby improving the stress corrosion cracking and fatigue life of the material.
Surface heat treatments are used to improve the properties of metals and alloys. The different treatments can affect the material in different ways and can be used in combination for even better results. The different types of treatments include annealing, normalizing, quenching, nitriding and shot peening which are used to improve the properties of the material such as hardness, wear resistance, corrosion resistance and fatigue strength.
