Image Credit: SMS Elotherm

Heat treating services perform thermal treatments to modify the properties of metals, metal alloys, and other materials. The process requires precise control over temperature, time, and cooling rate of the material. It can be used to change a material's hardness, homogeneity, and strength, among other properties.

When selecting heat treating services, the potential client should consider the types of heat treating techniques and the equipment capabilities of the service.

Types of Heat Treating

Heat treating can include a number of different techniques for different materials and different results. The most common of these processes are annealing, carburizing, case hardening, and conventional hardening.

• Annealing includes a large range of processes designed to produce a refined microstructure within a material (usually for softening) through heating and cooling at a controlled rate.
• Carburizing is a case hardening processin which the cases are formed by adding carbon through a diffusion process. Case hardening causesa surface layer within a material to form and harden. Heat treated parts with a carburized or carbonitride case have a hard, strong surfaceand a tough, ductile core.
• Case hardening consists of the formation and hardening of acompositionally modifiedsurface layer within the material. Cases are formed by adding carbon, nitrogen, chrome, boron or other elements to the steel or metal surface region through diffusion, implantation or other reactions. Case forming or hardening processes are referred to as carburizing, nitriding, ferritic nitriding, carbonitriding, nitrocarburizing, boronizing and carbon restoration.
• Conventional hardening (quenching and tempering) is a process used to harden or strengthen steel or ferrous alloys. Tempered martensite or tempered steel is the product of a conventional hardening process. The martensite transformation is a diffusionless reaction that proceeds rapidly (at the speed of sound) as a shear wave through the material. Careful control is required to avoid or reduce any distortionand cracking that may occur due to the rapid martensite transformation. In some cases, a martempering process is advisable to avoid cracking.

Equipment Capabilities

The GlobalSpec SpecSearch Database provides users the ability to search heat treating services by their equipment capabilities. These capabilities include:

• Furnace - Suppliers have conventional furnaces that use an air, protective, or vacuum atmosphere.
• Induction - Suppliers have induction heating equipment for localized heat treatment processes.
• Presses - Suppliers have presses for hot or cold operations. Hot presses may include isostatic units for HIP processing, or cold bending presses for straightening distorted parts.
• On-site or field - Suppliers provide portable equipment that can be used on-site or in the field. For example, resistive heating blankets can be used for stress relieving large structures.
• Protective atmosphere - Suppliers have furnaces or equipment that use an inert gas, reducing gas (hydrogen-nitrogen) or other protective atmosphere to prevent oxidation or contamination during thermal processing.
• Vacuum heat treating - Suppliers have furnaces or equipment with a vacuum atmosphere to prevent oxidation or contamination during thermal processing.

References

Engineer's Edge - Heat Treating Terms and Definitions