View A Video on Heat Treating- A Quick Introduction
Heat treating is any of several methods for altering the atomic structure of a metal or other crystalline structure in order to instill beneficial physical, chemical and mechanical properties, such as strength or ductility. These production and manufacturing techniques utilize systematic heating and chilling to modify the behavioral properties of industrial materials.
Bringing a material to extreme high or low temperatures allows engineers to effectively alter its internal microstructure. This in turn changes the physical, chemical and mechanical products of the raw material or finished part. There are several means of heat treatment, each of which produces a unique effect on a given material. Annealing, for example, involves the slow cooling of metals which alters the molecular pattern to improve flexibility and ductility. Case hardening has the opposite effect as it increases rigidity and strength. Additional heat treatments include spherodizing, normalizing, nitriding, tempering, sintering, quenching and brazing. Specialized furnaces also allow for induction heat treating as well as vacuum heat treating. These tools, and others such as lasers, torches, heating blankets and salt bathes are carefully calibrated to manipulate the composition of heat treated materials and products. It is essential that devices are maintained as improper heating and cooling could have disastrous effects depending on the application. When employing heat treated materials in any industry it is important to understand the capacities of heat treated materials which vary depending upon the specific chemical composition of the raw material. Aluminum heat treating is vastly different from heat treating steel which in turn may differ significantly from heat treating stainless steel. While heat treating metals is the most common application other materials such as glasses, ceramics and polymers can also benefit from heat treating processes.
Heat treating service shops often start at the end of the project. Rather than request a certain procedure, many clients communicate the desired result or requirements of a specific part or piece of material. Metallurgists or other heat treatment professionals then determine the necessary operations to achieve the preferred mechanical, chemical and physical properties. The decision begins with an analysis of the materials themselves. As aforementioned, materials can range broadly, but each has a particular microstructure. Small grains or crystallites form a complex lattice, the structure of which is reflected in the characteristics of the raw material and semi-finished products. The material is then heated to its critical temperature, the point at which the lattice begins to come undone. The exact temperature, rate of heating and duration of heat applications varies depending upon the end goal. The cooling likewise varies. For fast cooling, gas or liquids engulf the material. Other processes simply allow the material to cool at room temperature. These decisions result in one of two end goals. If cooling is rapid, the material will have a coarse grain which provides excellent strength and rigidity. Fast cooling on the other hand produces flexibility and ductility by reducing the grain size.
Beyond the determination of heating and cooling periods and temperatures, there are several different types of heat treating available. Annealing is one of the most frequently used heat treatments available. This involves subjecting materials to consistently high temperatures for a pre-determined length of time and then slowly cooling them so as to seal in the strength and durability of the material by reducing compositional segregation. The result of this is more ductile materials as the fine grains allow for bending without brittleness or cracking. While many procedures, like annealing, rely most heavily on the physical properties, others rely on the chemical properties. Case hardening, for example, requires materials with a high carbon or nitrogen content. The heating and cooling forms a hard exterior shell by drawing the carbon and nitrogen to the surface. Quenching, tempering, nitriding and many other processes are also used to alter the hardness, tensile strength, yield strength and impact strength of materials in order to produce finished or stock forms ready for use in a broad range of applications. As material production or preliminary manufacturing processes such as forging, welding and cold-rolling my enact stress in the part or material, a process known as normalizing often precedes heat treating techniques. Normalizing involves heating the material or product and then allowing it to cool at room temperature. This essentially erases any previous heat treatments.
The ability to manipulate the internal atomic structure of metals, glasses, ceramics and polymers allows engineers to produce application specific alloys and products. While some applications are customized, industrial and commercial materials and stock shapes can be treated for secondary options. Heat treating actually extends the possibilities of a given material as the material is often more easily manipulated and machined. Industries such as automotive, hardware, construction, military, tool and die, stamping, trucking, shipping, aerospace and others commonly utilize one or more heat treatment procedures in the production of varying products such as fine cutlery, dies, railroad components and even musical instruments. Because heat treatment alters the physical strength and molecular stability of a material, it is exceedingly important that calculations and equipment be properly maintained. Inaccurate or failing equipment may produce parts unable to withstand the rigors for which they were designed. Additionally, those involved in any heat treating process should wear protective clothing and have fire extinguishers ready in order to avoid scalding or fires. The possibility of accidental fire and splashing is one of the main drawbacks of heat treating as is the cost of these energy intensive processes. Proper maintenance and careful regulation, however, ensure that heat treating applications may continue to serve a number of industrial, commercial and even domestic sectors with application specific materials with improved strength and ductility.
Types of Heat Treating
- Aluminum heat treating is used to soften or harden aluminum materials to a desired level of hardness.
- Annealing is
the process of softening carbon and alloy steels by slowly cooling the
metals after they have been heated.
is a method of hardening steel by quenching into a constant temperature
medium, such as a salt bath. The resulting product is bainite.
- Case Hardening
a hardening method that involves carbon and nitrogen absorption on the
surface of steel by heating it in contact with cyanide salt and then
is used when only a small part of a metal surface needs to be hardened.
This method involves heating the surface with an acetylene torch and
- Heat treating metal is used to harden or soften metal materials by heating or cooling them until the desired level of hardness is reached.
- Heat treating stainless steel is used to soften or harden stainless steel materials to a desired level of hardness.
- Heat treating steel is used to soften or harden steel materials to a desired level of
- Heat treatment is a broad term encompassing a number of thermally involved methods and processes used to modify the physical, mechanical and even chemical properties of industrial materials with the goal of added hardness or ductility.
- Induction heat treating uses induction heaters to harden or soften metal materials.
is used to harden steel by quenching the hot metal in a heat extracting,
constant temperature substance, such as salt, and waiting until the
temperature is uniform. The metal is then air cooled to form martensite,
and tempered as needed.
- Nitriding is a case hardening operation that diffuses nitrogen into metal parts and components to create a strong and more durable outer layer.
the reheating of ferrous metals to increase hardness and reduce brittleness.
- Vacuum heat treating involves heat treating within a vacuum furnace for metallurgical reactions
and then quenching, usually with gas.
Heat Treating Terms
- A type of steel that does not require quenching to cool and harden,
- Two or more metals combined
for desired properties, such as greater strength, hardness or a different
- Solid iron and carbon
that is created by heating steel above its critical temperature.
- The resulting product
when austenite is quenched in a medium at a constant temperature.
- The process of
adding carbon to the surface of steel by heating the metal below its melting
point around solids, liquids or gases that contain carbon.
- The temperature
at which steel will change its structure to austenite.
- The loss of
carbon at the surface of a metal, due to high temperatures and contact
with air, oxygen or hydrogen.
- The measure
of a metal's ability to harden after quenching.
- A metal's ability
to resist penetration.
- A metal's
ability to resist cracking after an impact.
- A type of steel
that results from quenching austenite.
- A prelude to many
heat treatments that involves heating a metal above its critical temperature
range and then cooling it. This process is done to erase any effects of
previous heat treating.
- A corrosion reaction
on a metal that results from exposure to oxygen in the air.
- A type of steel that
is created from the slow air cooling of austenite.
- The substance that
is used to cool a metal in the heat treating process, such as water, oil,
brine, liquid salts and air.
- The process of rapidly
cooling a red hot metal, with a medium such as water, oil or air, to influence
- A substance's
condition, which in most cases can be adjusted.
- The color of
clean steel at different temperatures, which indicates the level of heat
during the tempering process.
- The force
at which a metal will break after being stretched.
- The point at
which a metal will become permanently deformed after stress.