What temperature is used for full annealing of steel?

Full annealing of hypoeutectoid carbon and low-alloy steels is typically performed at 30–50°C above the Ac3 upper critical temperature. For plain carbon steels with 0.3–0.6% C, this is approximately 830–870°C. The steel is soaked, then furnace-cooled slowly (≤20°C/hr through the transformation range) to produce a fully softened, coarse pearlite microstructure.

What is the difference between full annealing and process annealing?

Full annealing heats above the Ac3 (or Ac1 for hypereutectoid steels) to fully austenitise the steel, followed by slow cooling to produce maximum softness. Process annealing (sub-critical annealing) heats to 550–700°C — below Ac1 — to relieve cold-work stresses and restore ductility without full recrystallisation. Process annealing is faster and uses less energy, but does not achieve the same degree of softening.

How long should I soak during annealing?

A common rule of thumb for annealing soak time is 1 hour per 25 mm of section thickness, with a minimum of 1 hour. Heavy sections or dense furnace loads may require longer soaks to ensure temperature uniformity throughout the load. AMS 2759 and individual alloy specifications may override this general guidance.

What is spheroidising annealing and when is it used?

Spheroidising annealing converts the carbide structure in high-carbon steels (>0.6% C) into rounded (spheroidal) carbide particles within a ferrite matrix. This gives the maximum softness and machinability for these steels. It is done by holding just below or cycling around the Ac1 temperature (typically 700–750°C) for extended periods (4–24 hours depending on the steel and starting microstructure).

Annealing Process Calculator & Temperature Guide — Steel Annealing

Annealing Temperature Reference — Common Steel Grades

Steel Grade	Process	Temperature (°C)	Soak	Cool Rate
EN8 (080M40)	Full anneal	830–860	1 hr/25 mm	≤20°C/hr to 600°C
EN24 (817M40)	Full anneal	840–875	1 hr/25 mm	≤20°C/hr to 600°C
EN31 (534A99)	Spheroidise	750–780	4–12 hr	≤20°C/hr
H13 tool steel	Full anneal	860–900	2 hr/25 mm	≤15°C/hr to 650°C
D2 tool steel	Spheroidise	845–870	4–8 hr	≤15°C/hr
304 Stainless	Solution anneal	1010–1120	Soak + water	Rapid cool
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Annealing Processes Covered

Full annealing — maximum softness, coarse pearlite
Process (sub-critical) annealing — stress relief below Ac1
Spheroidising — carbide rounding for high-carbon steels
Isothermal annealing — controlled transformation temperature
Recrystallisation annealing — cold-worked materials
Solution annealing — stainless and superalloys

Calculator Outputs

Recommended soak temperature (°C / °F)
Minimum soak time by section thickness
Maximum controlled cooling rate (°C/hr)
Expected hardness after annealing (HB/HRC)
Critical temperature Ac1 / Ac3 for the alloy
Furnace atmosphere recommendation

Annealing in Industrial Heat Treatment

Annealing is one of the most widely used heat treatment processes — performed to soften steel for machining, relieve residual stresses from forming or welding, restore ductility after cold working, or prepare a component for subsequent hardening operations. Getting the temperature, soak time, and cooling rate right is critical: too fast a cool produces harder, less machinable structures; too slow wastes furnace time and energy.

The Bloor Engineering annealing calculator draws on AMS 2759, BS EN ISO 14919, and manufacturer data to provide grade-specific recommendations. It accounts for section thickness, alloy hardenability, and your furnace atmosphere to give practical, actionable soak parameters.

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Select your steel grade, enter section size, and get a complete annealing cycle in seconds. Free with a registered account.

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Annealing Process Calculator & Temperature Guide

Annealing Processes Covered

Calculator Outputs

Annealing in Industrial Heat Treatment

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