# Open-die forging

Open-die forging operations, starting-stock control, reduction ratios, heat treatment and acceptance of worked metal sections.

Reviewed: 2026-11-01

Tags: processes, shaping, forging

Scot Forge gives **3:1** as usual guidance for its general consolidation objective, with lower reduction possible under strict control and higher reduction needed for some alloys or orders. State the reference stages and area basis. Qualify core condition and directional properties separately, and specify the ultrasonic quality level when ordering examination under ASTM A388/A388M. [Scot Forge reduction guidance](https://www.scotforge.com/customized-solutions/metallurgy-testing/metallurgical-faqs)

Repeated strokes, repositioning and rotation develop the section in open dies. Specify alloy, working and thermal history and acceptance for the delivered section. [Scot Forge, forging definitions](https://www.scotforge.com/why-forging)

## How the shape develops

In hot open-die work, heating improves plastic flow and reduces forming force. Flat dies are common, but V-shaped, concave and convex tools also guide deformation. Operators or manipulators control workpiece position through successive bites rather than relying on a fully enclosing cavity. The Forging Industry Association distinguishes these operations:

| Operation | Intended change | Planning implication |
|---|---|---|
| Upsetting | Shorter axial length and larger cross-section | Friction can produce barreling; the shape is not an ideal cylinder throughout the stroke. |
| Drawing | Smaller cross-section and greater length | Provide enough starting section and subsequent machining allowance. |
| Cogging | Progressive reduction and elongation using relatively narrow dies | Advance the stock between bites and rotate it where required by the deformation plan. |

Several operations can be combined in one route. Rotation is a way to distribute working around the section, not evidence that every point experiences the same strain. [FIA, *Product Design Guide for Forging*, §5.2.1](https://www.forging.org/Common/Uploaded%20files/Design%20Engineering%20Center/Product%20Design%20Guide%20for%20Forging.pdf)

The drawing should identify the final component and the required delivery shape separately. A rough-forged shaft, a heat-treated blank with test prolongations, and a finish-machined shaft are different purchases. Include datum stock, sacrificial ends and examination access in the agreed manufacturing plan rather than assuming the nominal finished envelope describes the starting billet.

## Starting stock and effective reduction

An ingot introduces solidification history as well as chemistry. Scot Forge identifies segregation, centerline variation, shrinkage and piping as upstream concerns; selecting ingot dimensions and controlling feeding and solidification affect the material available for subsequent working. Forging cannot be assumed to remove fundamental metallurgical defects. Cropping, conditioning and traceability therefore belong in the agreed route, with their extent determined by the stock and specification. [Scot Forge, *Forging at Scale*, “Ingot Procurement and Metallurgical Control”](https://www.scotforge.com/_files/ugd/256da1_8460fe8888764ba29dabec34057b8c42.pdf)

A reduction ratio needs a stated definition and reference stages. In a simple drawing operation, an initial-to-final cross-sectional area ratio describes bulk reduction. It does not identify local strain, core penetration, prior upsetting or the distribution of working. Scot Forge's metallurgical FAQ says 3:1 is usually sufficient for its general open-die consolidation objective, while allowing lower ratios under strict control and noting that alloy or customer requirements can demand higher reductions. This is supplier guidance, not a universal acceptance minimum or a guarantee of pore-free material. [Scot Forge, metallurgical FAQs, “optimum reduction”](https://www.scotforge.com/customized-solutions/metallurgy-testing/metallurgical-faqs)

**Original geometry example.** Assume a solid round is drawn uniformly from 300 mm diameter to 150 mm, with constant volume and no scale, crops or machining loss:

- Area ratio = (300 / 150)² = **4:1**.
- Area reduction = 1 − 1/4 = **75%**.
- A 400 mm initial length becomes **1,600 mm** ideally.

The diameter ratio is only 2:1. If the forged 150 mm section is later machined to 140 mm, that removed metal does not increase the forging reduction. These calculations reconcile ideal geometry; they neither predict local deformation nor demonstrate consolidation. Real stock sizing must add the agreed process losses and allowances.

## Directional properties and thermal route

Working creates directional structure. Specify which properties must be met longitudinally, transversely or in other relevant orientations, and where test material represents the component. FIA specifically recommends communicating properties in all required directions and locating test prolongations. A favorable longitudinal result should not silently become a transverse or core guarantee. [FIA, *Product Design Guide for Forging*, §3.5.4.3](https://www.forging.org/Common/Uploaded%20files/Design%20Engineering%20Center/Product%20Design%20Guide%20for%20Forging.pdf)

Large-section heat treatment requires attention to temperature uniformity, surface-to-core response, cooling capability and distortion. Scot Forge describes these as section-dependent limitations: a furnace that accommodates a part geometrically does not by itself establish the required thermal response. [Scot Forge, *Forging at Scale*, “Heat Treatment at Scale”](https://www.scotforge.com/_files/ugd/256da1_8460fe8888764ba29dabec34057b8c42.pdf)

For a quotation, state the alloy and delivery condition together, then identify which operations remain after delivery. Normalizing, annealing, quenching and tempering are not interchangeable labels. Agree whether rough machining precedes final heat treatment, when test pieces are removed, and which dimensions are inspected after the final thermal operation. A subsequent customer heat treatment can change the condition represented by the supplier's test report.

## Machining, examination and acceptance

Order the applicable product specification and edition, not simply “forged steel.” ASTM A788/A788M-26b is a general-requirements standard used with specified steel-forging product standards; the individual product specification prevails where its requirements conflict. It does not supply a universal alloy, strength level or finished-part acceptance class. [ASTM A788/A788M-26b](https://store.astm.org/a0788_a0788m-26b.html)

Ultrasonic examination also needs an acceptance basis. ASTM A388/A388M-26 covers contact pulse-echo ultrasonic examination of steel forgings, using straight- and angle-beam techniques as applicable. Its public scope requires the purchaser to state the ultrasonic quality level clearly in the order. “UT tested” alone leaves the consequential acceptance decision unspecified. [ASTM A388/A388M-26](https://store.astm.org/a0388_a0388m-26.html)

Agree examination stage, accessible surfaces, coverage, reporting and disposition of indications with the supplier. Keep internal examination separate from surface examination and destructive property tests. As a concrete procurement distinction, Scot Forge states that Nadcap-accredited NDT is not automatically applied to every order requesting NDT; that requirement must be specified on the purchase order. Supplier accreditation is therefore not a substitute for the contracted examination scope. [Scot Forge, metallurgy and testing](https://www.scotforge.com/customized-solutions/metallurgy-testing)

A useful handoff contains the finished and delivery drawings, alloy/product standard, stock traceability, agreed working basis, thermal condition, property locations and orientations, examination requirements, machining responsibility and certification deliverables. Resolve these before treating a quoted envelope as a qualified component capability.

## Source versions

Reviewed 2026-11-01. ASTM publisher records identify A788/A788M-26b and A388/A388M-26. The cited FIA guide and Scot Forge technical whitepaper do not show a verified issue date in the retrieved documents; their hosting paths are not treated as publication dates. Supplier web guidance describes that supplier's practice and does not override the ordered product specification.