Discrete ManufacturingFree referencePDF, Excel, Word exportHeat Treating

Steel Heat Treatment Processes: Types, Temperatures and Purpose

Heat treat terms get mixed up on drawings and routings all the time. This reference lists the common processes, the temperatures they usually run at, how the part is cooled and the reason each one is used, so engineers, buyers and planners can speak the same language.

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Process	Applies to	Typical temp (deg C)	Cooling	Purpose
Full annealing	Steel	Austenitize about 30-50 above Ac3 (hypoeutectoid)	Slow furnace cool	Soften, refine grain, improve machinability
Process annealing	Low carbon steel, cold worked	550-700	Air or furnace	Restore ductility after cold work
Spheroidize annealing	High carbon and tool steel	Just below A1, about 680-760	Slow	Form spheroidal carbides for machining and forming
Stress relieving	Steel, cast iron, weldments	Steel 550-650, gray iron 510-565	Slow cool	Reduce residual stress without changing structure much
Normalizing	Steel	Austenitize about 850-920	Still air	Uniform fine grain, refine forgings and castings
Hardening (quench)	Medium and high carbon steel	Austenitize about 800-870	Water, oil, polymer or air by grade	Form martensite for strength and hardness
Tempering	Quenched steel	150-650	Air	Trade hardness for toughness, relieve quench stress
Austempering	Steel, ductile iron	Hold in salt bath 260-400	Isothermal then air	Bainite structure, toughness with strength, less distortion
Martempering	Alloy steel	Quench to hold just above Ms	Hot oil or salt, then air	Reduce distortion and cracking before temper
Carburizing	Low carbon and alloy steel	880-955	Quench then temper	Hard high-carbon case on a tough core
Carbonitriding	Low carbon steel	780-900	Oil quench then temper	Thin hard case, lower temperature than carburizing
Gas nitriding	Alloy and nitriding steels	495-565	Furnace or slow	Hard nitride case with little distortion, no quench
Induction hardening	Medium carbon steel	Rapid surface austenitize	Spray quench	Local surface hardness on shafts, gears
Flame hardening	Medium carbon steel	Torch heat of surface	Water or air spray	Local hardening of large parts
Subzero treatment	Tool steel, carburized steel	Below minus 70	Warm to ambient	Transform retained austenite, dimensional stability
Solution treatment (aluminum)	6061 and other heat treatable alloys	About 530 for 6061	Water quench	Dissolve strengthening elements before aging
Artificial aging T6 (6061)	Aluminum 6061	160-175	Air	Precipitation hardening to T6 properties
Ferritizing anneal	Ductile iron	About 700-900 depending on route	Slow or controlled	Convert pearlite to ferrite, raise ductility
Solution anneal (austenitic stainless)	300 series	1010-1120	Rapid cool or water quench	Dissolve carbides, restore corrosion resistance
Precipitation hardening (17-4PH H900)	17-4PH stainless	480 for 1 hour	Air	Age to high strength after solution treatment

Temperature ranges are typical practice for plain guidance. Actual cycles depend on grade, section size, equipment and the governing specification. Use the customer or industry spec (for example AMS or MIL) for any controlled work.

Standard heat treat operation list for your ERP

Optional: we can map your routing operations to a standard list and link vendor certificates to lots.

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How to use the table

Search for a process name or a material to filter the list. Each row shows what the process applies to, the typical temperature range in degrees Celsius, the cooling method and the purpose. Export to Excel to build a controlled list of heat treat operation names for your ERP routing, so every operation points to a single standard description. This is especially useful when a drawing note such as stress relieve or normalize needs to be translated into a work center and operation code.

Use the purpose column to pick the right process
Compare cooling methods to understand distortion risk
Export operation names for ERP routing master data

Softening versus hardening

Annealing, normalizing and stress relieving mostly soften or stabilize the part. Hardening followed by tempering makes it strong and tough. Case treatments such as carburizing and nitriding keep the core tough while giving a hard wear surface. For aluminum, the sequence is solution treat, quench and age. The drawing callout, such as T6 for aluminum or a Rockwell range for steel, tells you which sequence applies. Always check which side of the process is intended before quoting or scheduling.

Normalizing is air cooled, annealing is furnace cooled
Tempering always follows hardening, never replaces it
Nitriding has no quench and so low distortion

Common mistakes

People confuse normalizing with annealing, and the difference matters: normalizing cools in air and gives higher strength and a finer structure, annealing cools slowly and gives maximum softness. Another error is skipping a temper after quenching a high hardenability steel, which leaves a brittle part at risk of cracking. A third is using quench media that is wrong for the grade, such as water on an alloy that wants oil, which causes quench cracks. Record furnace class, load and cycle in the traveler so the result can be proven.

Temper soon after quenching to avoid delayed cracks
Match quench medium to hardenability
Log cycle and furnace for traceability

Frequently Asked Questions

What is the difference between annealing and normalizing?

Both heat steel into the austenite range, but annealing cools slowly in the furnace for maximum softness, while normalizing cools in still air for a finer, somewhat harder and stronger structure. Normalizing is common after forging or casting to refine grain.

What temperature is tempering done at?

Tempering typically runs from about 150 to 650 deg C. Low temperatures keep high hardness for tools and bearings, while higher temperatures give more toughness for shafts and structural parts. The drawing hardness or the spec sets the final temperature.

Why is nitriding used instead of carburizing?

Nitriding runs at a much lower temperature, about 495 to 565 deg C, and needs no quench, so distortion is small. It suits finished or near finished parts. Carburizing gives a deeper case and suits gears and shafts that carry heavy loads.

What is T6 temper for aluminum?

T6 means the alloy was solution heat treated, quenched and then artificially aged. For 6061 that typically means solution treating near 530 deg C, quenching, then aging around 160 to 175 deg C, with times set by the specification.

If heat treat operations are scattered across routings and vendor purchase orders, we can help standardize them in your ERP and connect certificates to lots. This reference needs no sign-up.

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