Full Anneal
Annealing & softening · Softening
Full annealing heats steel through its critical transformation range and then furnace-cools it slowly.
Full anneal at a glance
Four scores, each 0–100 against every heat treatment in this catalog. Hardness is derived from the HRC target (20 HRC = 0, 70 HRC = 100) — treatments without a hardness target (anneals, stress relief, HIP, cryo) are not rated. Toughness, dimensional stability and cost are FabDigit's engineering assessment.
What is Full anneal?
Full annealing heats steel through its critical transformation range and then furnace-cools it slowly. Designers specify it to soften forgings and castings, improve machinability, and produce a near-equilibrium ferrite-pearlite structure.
How it works
Hypoeutectoid steel is heated above Ac3 so ferrite and pearlite transform to austenite; hypereutectoid steel is normally heated only above Ac1 and below Acm to avoid a continuous carbide network. After equalization, controlled furnace cooling through the transformation range forms coarse pearlite with ferrite or carbides. The slow transformation lowers hardness and residual stress compared with normalizing. Temperature, hold time, and maximum cooling rate must follow chemistry and section size because overheating coarsens austenite grains and excessive cooling rate defeats the softening objective.
Why specify it
- Reduces many medium-carbon steels to roughly 150–220 HB
- Improves chip formation before heavy machining
- Restores ductility after forging or nonuniform cooling
Where it falls short
- Requires slow furnace cooling and commonly occupies a furnace for 8–24 h
- Produces lower strength than normalizing
- Can create scale or decarburization without atmosphere control
The Full anneal cycle
Typical furnace parameters from the governing specifications and shop practice; the heat treater sets the exact recipe from the alloy, section size and required result.
| Temperature | 790–925 °C (1,454–1,697 °F) — Grade dependent; heat relative to Ac1, Ac3, and Acm. |
|---|---|
| Soak | 1–4 h — Commonly based on section thickness after equalization. |
| Cooling | Furnace cool |
| Atmosphere | Endothermic gas / vacuum |
| Door to door | 8–24 h — Slow cooling dominates total time. |
Stages
- 1Heat through the specified critical range
- 2Equalize and soak for section size
- 3Furnace cool slowly through transformation
What Full anneal does to the part
| Hardness | 150–220 HB — Representative medium-carbon and low-alloy steel annealed range; grade controls acceptance. |
|---|---|
| Section affected | The whole section transforms. |
| Toughness | Ductility and machinability increase as coarse ferrite-pearlite replaces harder transformed structures. |
| Distortion | Low risk. Slow heating and furnace cooling minimize thermal gradients, but long parts still require support. |
| Surface after treatment | Oxide and decarburization are possible in air; vacuum or protective atmosphere keeps surfaces bright. |
| Machining sequence | Use as a pre-machining condition; remove any decarburized stock before final hardening. |
Specifications for Full anneal
The documents a drawing cites to define this treatment. Each links to a page explaining the standard, its classes and the tests it invokes.
| Standard | Role | Classes used | Status |
|---|---|---|---|
Heat Treatment of Steel Parts, General Requirements | Governing | — | Active |
Heat Treatment of Carbon and Low-Alloy Steel Parts, Minimum Tensile Strength Below 220 ksi (1517 MPa) | Governing | — | Active |
Test and related methods: ASTM E10 (Standard Test Method for Brinell Hardness of Metallic Materials), ASTM A1033 (Standard Practice for Quantitative Measurement and Reporting of Hypoeutectoid Carbon and Low-Alloy Steel Phase Transformations), ISO 683-1 (Heat-treatable steels, alloy steels and free-cutting steels — Part 1: Non-alloy steels for quenching and tempering), ISO 683-2 (Heat-treatable steels, alloy steels and free-cutting steels — Part 2: Alloy steels for quenching and tempering), ISO 683-3 (Heat-treatable steels, alloy steels and free-cutting steels — Part 3: Case-hardening steels), MIL-H-6875 (Heat Treatment of Steel Raw Materials).
Drawing call-out
FULL ANNEAL PER AMS 2759/1; FINAL HARDNESS 150–200 HBW; TEST PER ASTM E10 ON END FACE SHOWNWhich alloys take Full anneal?
Verdict per material family, with the grades that behave differently. Each family links to its datasheets in the material library. Typical grades: 1045, 4140, 4340, 52100, O1.
| Material family | Verdict | Notes |
|---|---|---|
| Yes | The cycle is established for carbon, alloy, and tool steels within grade-specific temperature limits.
| |
| With care | Sintered steel can be treated after density and residual porosity are qualified.
| |
| With care | Printed steel may use the cycle after density, chemistry, and build-orientation effects are qualified.
| |
| Limited | Only stainless grades covered by a compatible ferrous cycle are suitable.
| |
| No | Aluminum does not use this ferrous transformation cycle. | |
| No | Brass requires lower-temperature stress relief or recrystallization annealing. | |
| No | Bronze requires composition-specific annealing or precipitation treatment. | |
| No | Cobalt-chrome requires alloy-specific solution or aging practice. | |
| No | Copper alloys require alloy-specific annealing or precipitation-hardening cycles. | |
| No | Magnesium requires tightly controlled alloy-specific cycles. | |
| No | Nickel alloys require alloy-specific solution, anneal, or age cycles. | |
| No | Precious metals require alloy-specific annealing or age-hardening practice. | |
| No | Refractory metals require material-specific vacuum annealing practice. | |
| No | Titanium requires alloy-specific annealing or solution-and-age cycles. | |
| No | Tungsten heavy alloys require supplier-specific sintering and stress-relief practice. | |
| No | Zinc alloys melt or lose properties at temperatures used by this process. |
Design rules for Full anneal
What to decide on the drawing before the part goes to the heat treater.
- Identify the alloy designation and incoming condition on the purchase order.A temperature that is correct for one grade can overtemper, sensitize, or fail to transform another grade.
- Place hardness test locations at least 3 mm from an edge where geometry permits.Edge decarburization, local cooling, and indentation spacing can bias the reported result.
- Leave 0.2–0.5 mm finish stock on critical ground surfaces when a quench or scale-producing atmosphere is used.Final grinding removes oxide, decarburization, and dimensional movement after the thermal cycle.
- Allow 3–7 working days beyond machining.Furnace scheduling, controlled cooling, hardness testing, and certification extend beyond the soak time.
- Support shafts longer than 10 times their diameter during the cycle.Creep and stress relaxation at annealing temperature can convert residual stress into permanent bow.
Full anneal versus the alternatives
Treatments engineers weigh against Full anneal, and when each wins.
| Treatment | Hardness | Toughness | Stability | Cost | Choose it when |
|---|---|---|---|---|---|
Full anneal this page | — | 95 | 80 | $$ | — |
| — | 75 | 65 | $ | when finer grain and higher strength are preferred over maximum softness | |
| — | 85 | 85 | $$ | when high-carbon steel needs maximum machinability or cold-formability |
Cost, lead time and applications
Relative cost
Full Anneal is a standard-cost treatment ($$) relative to the other heat treatments in this catalog.
Heat treatment is priced per lot with a furnace minimum. The exact figure appears on the instant quote once the part is uploaded.
Lead time
| Added lead time | 3–7 working days |
|---|---|
| Furnace time | 8–24 h |
What Full anneal is used for
- Forged gear blanks
- Steel castings before machining
- Heavy-section shaft stock
- Tool-steel blanks before rough machining
Full anneal — frequently asked
What temperature is used for Full anneal?
The representative process window is 790–925 °C, but the exact setpoint follows the alloy and governing specification. The listed soak is 1–4 h after the load reaches temperature.
What hardness does Full anneal produce?
The catalog result is 150–220 HB. Hardness must be verified on the part or a qualified witness coupon using the test method called out on the drawing.
How long does Full anneal take?
The thermal cycle is typically 8–24 h door to door. Commercial lead time is normally 3–7 additional working days because loading, certification, and inspection are separate from furnace time.
Will Full anneal distort the part?
The catalog rates distortion risk as low. Reserve machining stock and verify critical datums after treatment when tolerances are tighter than 0.05 mm.
How should Full anneal be specified on a drawing?
State the governing process specification, alloy condition, required result, and inspection location. Report hardness to ASTM E18 or ASTM E10 as applicable, and do not substitute a furnace recipe for an acceptance requirement.