Furnaces to Handle Any Heat Treat Process

The heat treating process to employ varies depending on what the desired finish product is. Surface Combustion has a wide range of standard and custom thermal processing furnaces that are engineered to handle any heat treat process. We will help you determine the most efficient heat treat process and engineer a furnace to maximize manufacturing time.

Age Hardening

Hardening by aging, typically after rapid cooling or cold working, Aging is a change in properties that generally occurs slowly at room temperature and more rapidly at higher temperatures. Other common names include: aging, artificial aging, interrupted aging, over-aging, precipitation hardening, precipitation heat treatment, progressive aging, quench aging and strain aging.


A change in the properties of certain metal and alloys that occurs at ambient or moderately elevated temperatures after hot working or a heat treatment (quench again in ferrous alloys, natural or artificial aging in ferrous and nonferrous alloys) or after a cold working operation (strain aging). The change in properties is often, but not always, due to a phase change (precipitation), but never involves a change in chemical composition of the metal or alloy. Related names; age hardening, artificial aging, interrupted aging, natural aging, precipitation hardening, precipitation heat treatment, progressive aging, quench aging, step aging.


A generic term denoting a treatment, consisting of heating to a soak temperature and holding at a suitable temperature followed by cooling at a suitable rate, used primarily to soften metallic materials, but also to simultaneously produce desired changes in other properties or in microstructure. The purpose of such changes may be, but is not confined to; improvement of machinability, facilitation of cold work, production of a desired microstructure (for subsequent operations), improvement of mechanical or electrical properties, and/or increase instability of dimensions. When the term is used without qualification, full annealing is implied, for stress relieving, or stress-relief annealing.

Automated Press Quenching

In Automated Press Quenching, specialized tools and a press machine help to control the distortion of complex geometries being quench hardened. The goal is to encourage deformation of a component in a controlled and predictable manner. This is generally used on component parts that are prone to distortion or of critical dimensions like gears.


A heat treatment for ferrous alloys in which a part is quenched from the austenitizing temperature at a rate fast enough to avoid formation of ferrite or pearlite and then held at temperature just above martensite transformation temperature, until transformation to bainite is complete. Although designated as bainite in both autempered steel and austempered ductile iron (ADI), austempered steel consists of two-phase microstructures containing ferrite and carbide, while austempered ductile iron consists of two-phase microstructures containing ferrite and austenite.

Black Oxide

A black finish on a metal produced by A) immersing it in hot oxidizing salts or salt solutions. The black oxide coating is produced by a chemical reaction between the iron on the surface of the ferrous metal and the oxidizing salts present in the black oxide solution. B) Atmospheric…


Subjecting the scale-free surface of a ferrous alloy to the action of air, steam, to other agents at a suitable temperature, thus forming a thin blue film of oxide and improving the appearance and resistance to corrosion is done in a bluing furnace. Note: This term is ordinarily applied to sheet, strip, or finished parts. It is used also to denote the heating of springs after fabrication to improve their properties.


A group of welding processes that join solid materials together by heating them to a suitable temperature and using a filler metal having a liquidus above 450°C (840°F) but below the solidus of the base materials is completed in a brazing furnace. The filler metal is distributed between the closely fitted surfaces of the joint by capillary action.

Bright Annealing

In the annealing process, the properties of metal are altered. Bright annealing uses a controlled-atmosphere furnace to anneal the steel.


In calcination, materials are heated in a controlled environment and under a controlled temperature in the presence of oxygen and air to remove volatile components. The release of volatile components during calcination minimizes internal shrinkage in later processing steps that can lead to the development of internal stresses, cracking or warping. In industrial applications, the goal of calcining is to drive off water, remove other volatile materials such as carbon dioxide or to oxidize a material.

Carbon Baking

A carbon bake furnace is a special type of baking kiln for carbon blocks (or “anodes”) that are required in the aluminium production process. The anodes are made by mixing crushed coke or anthracite with a binding agent (example: coal tar pitch). When volatile components are heated over a period of time, the anode hardens, resulting in improved physical properties, such as electrical conductivity and resistance to oxidation.

Carbon Restoration

Replacing the carbon lost in the surface layer from previous processing by carburizing this layer to substantially the original carbon level. Sometimes called recarburizing.


A case hardening process in which a suitable ferrous material is heated above the lower transformation temperature in a gaseous atmosphere of such composition (including hydrocarbons, carbon monoxide, and ammonia) as to cause simultaneous, absorption of carbon and nitrogen by the surface and, by diffusion, create a concentration gradient. The process is completed by cooling at a rate that produces the desired properties in the workplace.


A pyrolytic reaction that converts organic materials into carbon through destructive distillation. Waste gas thermal oxidizer stachs are utilized with the kilns to ensure proper ventilation.


Absorption and diffusion of carbon into solid ferrous alloys by heating, to a temperature usually above Ac3, in contact with a suitable carbonaceous material which may be solid, liquid, or controlled atmosphere gas. A form of case hardening that produces a carbon gradient extending inward from the surface, enabling the surface layer to be hardened either by quenching directly from the carburizing temperature or by cooling to room temperature, then reaustenitizing and quenching.

Ferritic Nitrocarburizing (FNC)

Process in which both nitrogen and carbon are absorbed into the surface layers of a ferrous material at temperatures below the lower critical temperature (AC3) and, by diffusion, create a compound layer on the surface and diffused case. FNC is a low distortion heat treat process because it is performed at temperatures less than the AC3 critical temperature, so no phase change takes place, and it is slow-cooled rather than oil quenched. Nitrocarburizing is done mainly to provide a wear resistant surface, improve corrosion resistance, and to enhance fatigue properties. FNC can be used on low, high carbon, alloy steels, and cast irons. Ferritic Nitrocarburizing (FNC), like nitriding and plasma (ion) nitriding, is more environmentally friendly compared to chrome plating. Related term: Gas soft nitriding (GSN) More Information


The forging process relies on rugged, reliable forging furnaces and thermal processing equipment for the pre-heating of billets, vacuum hardening and nitriding of forging dies, and heat treating of forgings. More Information

Gas Nitriding

A surface-hardening process where nitrogen is added to the surface of steel parts using dissociated ammonia. The parts being nitrided are heat treated to the proper strength level, and final machined. The nitriding exposes the parts to active nitrogen at a carefully controlled temperature, typically in the range of 925°F to 985°F. This produces a very hard case in a low temperature, without the need for quenching.


Increasing hardness by suitable treatment, usually involving heating and cooling. When applicable, the following more specific terms should be used: age hardening, flame hardening, induction hardening, laser hardening, precipitation hardening, and quench hardening.

Heat Flattening

A process where parts are placed under compression in a controlled thermal environment to improve the overall flatness and shape. During this process, the parts are oriented on an engineered tool or fixture. A predetermined load is applied and the material is heated to temperatures in the ferritic or tempering range of the base material. This ensures that post temper distortions are eliminated completely.


The process of making things more uniform or similar. In heat treatment, homogenizing is a form of annealing, where a metal or alloy is heated to a specific temperature for a length of time and then cooled slowly to produce the desired effect. For aluminum, this produces a more workable part with a uniform internal structure.


A treatment process involving a controlled combustion of waste that achieves both volume reduction and energy recovery. The industrial furnace is a type of hazardous waste treatment device that uses thermal energy to recover energy or materials from wastes.

Ion (Plasma) Nitriding

This process introduces nitrogen ions to the surface of metal. Plasma nitriding is carried out in a vacuum-type vessel where the treated part has the cathodic polarization and the vessel wall is the anode. The ions heat the metal, clean the surface, and absorb nitrogen into the surface. The result is a hardening of the surface, extending the life of the part or tool.

Low Pressure Carburizing

A case hardening process that uses low pressure and elevated temperatures in a vacuum furnace. This process uses hydrocarbon gasses to obtain a hardened surface layer of tempered martensite and a tough core. This treatment increases the wear resistance and fatigue life of components. It produces a very clean surface, thus eliminating further post cleaning of the part after heat treatment.


Annealing white cast iron in such a way that some or all of the combined carbon is transformed to graphite or, in some instances, part of the carbon is removed completely. Malleablizing white cast iron can also result in oxidation and decarburization, changing its metallographic structures or chemical components into malleable cast iron.


A hardening procedure in which an austenitized ferrous workpiece is quenched into an appropriate medium whose temperature is maintained substantially at the martensite transformation temperature, of the workpiece, held in the medium until its temperature is uniform throughout (but not long enough to permit bainite to form) and then cooled in air. The treatment is frequently followed by tempering.


A form of heat treatment applied as an interrupted quench of steels typically in a molten salt bath at a temperature right above the martensite start temperature. This is used to delay the cooling to equalize the temperature throughout the piece, minimizing distortion, cracking, and residual stress and is a good choice for parts that are sensitive to deformation during the cooling process.


Introducing nitrogen into the surface layer of a solid ferrous alloy by holding at a suitable temperature (below Ac1 for ferritic steels) in contact with a nitrogenous atmosphere, usually ammonia. Quenching is not required to produce a hard case. Variations: ion (plasma), aerated bath nitriding, bright nitriding, and liquid nitriding. More Information


Heating a ferrous alloy to a suitable temperature above the transformation range (and typically above the subsequent hardening temperature) and then cooling in air to a temperature substantially below the transformation range.


In oxy-nitriding, the material has been nitrided and then is purposely oxidized to form an additional performance enhancing layer, improving corrosion resistance. This process also increases fatigue strength by the development of surface compressive stresses.

Precipitation Hardening

Hardening caused by the precipitation of an elemental phase from a supersaturated solid solution.


Bringing a material up to a certain temperature before further processing. Utilized for energy efficiency so a pre-heated load enters a high temperature hot zone.


Enhances receptivity to nitriding of steel surfaces by creating corrosion. Pieces are heated in a controlled, oxidizing environment to just below nitriding temperatures.


Following nitriding or nitrocarburizing, this treatment stage creates an oxide layer on the material surface with the aid of an oxygen donor. This layer increases the corrosion resistance compared to the nitriding treatment. Post-oxidation provides additional corrosion resistance and can improve wear and tear by reducing the coefficient of friction.

Press Quenching

In press quenching, components are held under a controlled force. Press quenching reduces or eliminates distortions in size, roundness, taper, and flatness. In this process, the component is removed from the furnace and placed onto the lower die of a press quench. The upper die descends and pressure is applied to both to ensure the component retains its engineered dimensions.


Removes gaseous combustibles and replaces them with non-combustible gas.

Pyrolysis Resource Recovery

Pyrolysis is the heating of an organic material, such as biomass, in the absence of oxygen. Resource recovery uses wastes to create new outputs, which ultimately reduces waste and the need for processing raw materials in manufacturing.


The thermal treatment of minerals and metallurgical ores and concentrates to bring about physical and chemical transformations in the materials to enable recovery of valuable metals. This process requires some form of combustion or electrical heat.


A metal heat treatment process that involves the rapid cooling of a metal to adjust the mechanical properties of its original state. It is one of the key processes of hardening steel.


A reheating furnace is used to heat the steel stock to a temperature of around 1200°C which is suitable for plastic deformation or re-heat and quench of steel. It is a continuous process where the steel stock is charged at the furnace entrance, heated in the furnace, and discharged at the furnace exit.

Reheating for Press Quench

During press quenching, any prior thermal history and residual stress distribution contained within the part can contribute significantly to distortion.

Scale Free Heating

In this process, the goal is to reduce scale formation in the steel reheating process using controlled atmosphere like DX exothermic.


A shaped body composed of metal powder and produced by sintering with or without prior compaction. The bonding of adjacent surfaces in a mass of particles by molecular or atomic attraction on heating at high temperatures below the melting temperature of any constituent in the material. Sintering strengthens a powder mass and normally produces densification and, in powdered metals, recrystallization.


Heating an alloy to a suitable temperature, holding at that temperature long enough to cause one or more constituents to enter into solid solution, and then cooling rapidly enough to hold these constituents in solution is a completed in a solutionizing furnace.


Soldering is a joining process used to join different types of metals together by melting solder. Solder is a metal alloy usually made of tin and lead which is melted using a hot iron. The iron is heated to temperatures above 600 degrees fahrenheit which then cools to create a strong electrical bond.

Solution Heat Treatment

Heating an alloy to a suitable temperature, holding at that temperature long enough to cause one or more elements to enter into solid solution, and then cooling rapidly enough to hold these constituents in solution. The application is left in a supersaturated, unstable state and may subsequently exhibit quench aging.


Spheroidizing is an annealing process done in a spheroidizing furnace that produces a round or globular form of carbide in a matrix of ferrite. The cementite (iron carbide) layers of the material are caused by time and temperature to collapse into spheroids, or globules of cementite which is normally required for cold forming processes.

Stress Relieving

Heating to a suitable temperature, holding long enough to reduce residual stresses, and then cooling slowly enough to minimize the development of new stresses or a distortion dimensional.

T6 Heat Treatment

A two-step process which is applied to Aluminium, Copper, or Silicon alloys to increase the strength of the alloy by as much as 30%. The first step is quenching – the alloy is heated to 500⁰C for 9-10 hours which a single phase alloy. The alloy is cooled rapidly with water which supersaturates the aluminium. In the second step, the alloy is heated to 180⁰C for 9-10 hours then cooled by air allowing precipitation hardening.


In heat treatment, reheating hardened steel or hardened cast iron to some temperature below the eutectoid temperature and cooling at any rate desired, for the purpose of decreasing hardness and increasing toughness. A reduction in strength and increase in ductility properties of the material generally results. The process also is sometimes applied to normalized steel.

Thermal Destruction

The action or process of destroying controlled chemicals by fire or heat or incineration.


A mild form of pyrolysis at temperatures typically between 200 and 320 °C. Torrefaction changes biomass properties to provide a better fuel quality for combustion and gasification applications. It produces dry product, which reduces or eliminates its potential for organic decomposition.


A proprietary case-hardening process of gaseous ferritic nitrocarburizing that diffuses nitrogen and carbon into ferrous metals at subcritical temperatures by using gaseous mixtures to diffuse the nitrogen and carbon into the workpiece.

Vacuum Carburizing

Vacuum carburizing furnaces complete gas carburizing process at a high temperature using furnace pressures between 13 and 67 kPa (0.1 to 0.5 torr) during the carburizing portion of the cycle. Steels undergoing this treatment are austenitized in a rough vacuum, carburized in a partial pressure of hydrocarbon gas, diffused in a rough vacuum, and then quenched in either oil or gas. Both batch and continuous furnaces are used.

Vacuum Heat Treating

Air and oxygen is removed from the furnace to create a vacuum. The part may be heated in the vacuum with or without an inert gas to achieve the desired properties while protecting the part’s surface preventing oxidation. This method improves material strength, has high thermal efficiency, and results in no oxidation, decarburization, or carburization.

Water Quench

The rapid cooling of a workpiece in water to obtain certain material properties, increasing its hardness. This is typically used for low alloy steel grades for the steel to achieve maximum hardness. This process can lead to cracking or some distortions, in which case, air or oil quenching would be used instead.

Other Process Types

Other process types:

Air Quench



Gas Carburizing

High Temperature Tempering

Ion Carburizing

Solution Treatments