JASCO Heat Treating Services

Additional Industry terms

Alloy: A substance of metallic properties composed of two or more elements, at least one of which is a metal.

Austempering: A heat treating process for ferrous metals which increase hardness, fatigue strength, and impact resistance while reducing distortion of the parts. Typically the part is heated high enough to change the microstructure to the austenitic phase and cooled rapidly to avoid the pearlite phase. When it cools to a temperature slightly above the martensitic start temperature an isothermal hold is set up for a specified time in order to achieve the desired microstructure (bainite for steel).

Degassing: A heat treatment process that removes gas from the metal; vacuum processing is used to degas titanium, copper, and tantalum.

Magnetic Annealing: An annealing process utilized on certain ferrous materials to achieve uniform magnetic properties. This is usually done in vacuum or in a hydrogen atmosphere in order to avoid decarburization. This process requires tight temperature uniformity, extended soak times and accurate control of the cooling rates to control the microstructure of the material without loss of magnetic properties.

Marquenching/Martempering: A heat treatment involving transformation of austenite to martensite followed by step quenching, at a rate fast enough to avoid the formation of ferrite, pearlite or bainite. This is typically performed at temperatures slightly above the Ms point. Soaking must be short enough to avoid the formation of bainite before the temperature is lowered below Ms. The advantage of martempering is the reduction of thermal stresses compared to normal quenching. This prevents cracking and minimizes distortion.

Metal Oxide: A compound of oxygen with a metal. Most metals react with oxygen under appropriate temperature and pressure conditions, and oxidation can occur slowly at room temperature to form a thin oxide coat that can serve to protect the metal.

Nitriding Potential: The nitriding potential is directly proportional to the nitrogen activity in the gas mixture containing ammonia as the nitriding species. It is defined as K = pNH3/pH23/2, where “p” is the partial pressure of the ammonia and hydrogen.

Normalizing: Heating a ferrous alloy to a temperature above the transformation range in order to create a phase change in the metal’s microstructure and refinement of the grain structure. After heating for the required time the material is cooled in air, or in vacuum at a rate equivalent to air cooling.

Overaging: Aging at a higher temperature, and/or for a longer time than required for formation of a coherent precipitate, thus causing loss of coherency in the precipitating phase (coarsening) and loss of strength and hardness.

Partial Pressure: The partial pressure of a gas introduced into a vacuum furnace is the force exerted by the gas (or gases) constrained in the vacuum vessel. If only a single gas is present, the partial pressure of the system is the same as the total pressure. In vacuum systems, partial pressure usually refers to the operation of a vacuum furnace at or above 1 torr (1000 microns). The chamber is usually evacuated to a higher vacuum level; commonly between 10-3 torr and 10-5 torr (0.1 to 0.01 microns) then an inert gas is introduced at a controlled rate to a set partial pressure range which is maintained during the heating cycle.

Solution Treating: A process of heating an alloy and holding it at a suitable temperature until one or more of the constituents enters a solid solution, at which point the solution is cooled rapidly to hold the alloy in a supersaturated condition.

Spheroidize Annealing: A heat treating process used to soften metals for ease of stamping and forming. Heating to a set temperature followed by cooling very slowly changes the metallurgical structure such that the end product looks like spheres or balls

Spring Temper: A steel temper process which results in an increased upper limit of elasticity; obtained by hardening and tempering in the usual way followed by reheating until the steel turns blue.

Stopping Off: Applying a physical barrier (copper plate, specialized paints) to selected areas of a part to prevent unwanted hardening during carburization, or to prevent adverse reactions between the parts and the furnace supports.

Subcritical Anneal: A heat treatment process typically in the temperature range of 1300 F-1400 F used to produce a softened condition with less microstructural refinement than a full anneal process. Also referred to as a “process anneal” it is used to improve ductility to the material for subsequent cold-working/forming operations.

Stress Relieving: A uniform heating process followed by slow, uniform cooling; the process reduces stresses in fabricated or machined parts, and results in dimensional stability.

Temper: Tempering is a post-heat treat process used after a hardening process. The secondary heating cycle reduces hardness slightly and increases ductility.

Vapor Pressure: The gas pressure exerted when a substance is in equilibrium with its own vapor. The vapor pressure is a function of the substance and the temperature.