Everyone is aware of the toughness and strength of metal but why does it need heat treatment? When metals like steel, cast iron, tool steel, stainless steel and alloys are processed through Heat treating equipment, their properties and performance are changed. For example, heat treatment of steel can harden the material but in some cases, heat treatment is applied to soften metal to allow metal working operations that include deep drawing, cold forging and machining.
Heat treating equipment for annealing
Annealing is a process that makes use of Heat treating equipment to make metals more pliable and less likely to fracture when worked on. Metals like copper and brass can harden to become very brittle and heat treatment will remove all the stresses so that it will become softer and easy to work with. The process of annealing copper is the same as brass. After the metals turn dark red they have to be quenched to achieve the pliability required. Steel can also be annealed particularly heat hardened steel. During the annealing process, steel has to be heated until its color turns to cherry red after which it is cooled down naturally. Heat treatment on steel allow its molecules to align properly while slow cooling will keep them aligned so that it can be shaped without too much effort. When annealing stainless steel, a lot more heat is required so that when the metal turns orange, it can be kept for another 5 minutes or longer. However, when subjecting large pieces of stainless to heat, there is a tendency to warp which needs rapid quenching to stop chromium from bonding with carbon.
Various types of annealing
Full annealing – requires the Heat treating equipment to reach a temperature of 30 to 50 degrees Centigrade above the critical temperature of steel. The temperature is maintained for a certain period of time after which steel is cooled down inside the equipment itself without using any forced method of cooling. Full annealing is applied to hot worked sheets, forgings and castings that are made from medium and high carbon steels.
- Process annealing – is mainly used for low carbon steel to improve its characteristics. The Heat treating equipment should reach a temperature that is just below the lower critical temperature of steel.
- Stress relief annealing – removes the internal stresses on large castings and welded structures that have been unevenly cooled during their manufacture. If the internal stresses are not removed it can result into breakage or failure of the material. Temperature on the Heat treating equipment must reach about 650 degrees Centigrade and maintained for a few hours until cooled gradually.
- Spheroidizing – improves the machinability of high carbon and alloy steel. The process involved heating the material to just below its lower critical temperature or 700 degrees Centigrade and maintained for 8 hours before it cooled down slowly.
- Isothermal annealing – is applied to low carbon steel and alloy steel to produce a homogenous structure. When steel is heated above its upper critical temperature, its structure is converted rapidly into austenite structure. The homogenous structure is produced after forced cooling.