A forging is usually chosen because the part has to carry load: a flange, a yoke, a gear blank, a lifting eye, a shaft with a collar. That is exactly why a forging that looks right can still be wrong. Its value sits in properties you cannot see — the steel actually used, the heat treatment it actually received, and the absence of cracks and laps under the scale.
This article is for engineers and buyers sending a forging drawing to a Vietnamese forge for the first time. It follows the order in which the decisions fall: which forging route, which steel and heat-treatment condition, what the die costs and who owns it, which tolerances apply, and how soundness is proved at first article and in production. Castings are a different product with different defects; they are covered in iron castings from Vietnam.
💬 Not sure whether your part should be forged, cast or machined from bar? Send us the drawing and the annual volume and we will tell you what a Vietnamese forge will ask first.
Which forging route are you actually buying?
Closed-die, open-die and cold forging are different purchases with different tooling, tolerances and volumes, so the enquiry has to name the route or each forge will quote the one it runs.
| Point | Closed-die (impression) hot forging | Open-die hot forging | Cold forging and cold heading |
|---|---|---|---|
| Tooling | A die set per part, sunk to the shape | Flat or simple dies; shape made by manipulation | Dies and punches per part, often multi-station |
| Typical parts | Flanges, yokes, levers, gear and hub blanks | Large shafts, rings, blocks, simple heavy shapes | Small fasteners, pins, shafts with heads, sleeves |
| Dimensional result | Near shape, with flash and draft; machining stock on functional faces | Rough shape; generous machining stock | Close to final; may need little machining |
| Volume fit | Repeated runs that recover die cost | One-off to small lots of large parts | Long runs of small parts |
| What to ask in the quotation | Die cost, die life and re-sinking, flash trimming, heat treatment | Forging reduction, machining stock, ultrasonic testing | Wire or bar grade, annealing, number of stations |
If the part could also be machined from solid bar, compare both routes on identical terms: machining avoids die cost, forging keeps the grain running along the shape. The machining side is covered in CNC machining in Vietnam.
Steel grade and heat-treatment condition go together
A forging is specified by two things at once — the steel grade with its standard number and the delivered heat-treatment condition with a hardness range — and either one alone leaves the result open.
Name the standard, not only the grade. Vietnamese bar stockists and forge shops that work for Japanese customers commonly describe carbon and alloy steel by JIS names such as S45C or SCM440. If your drawing calls for an EN or ASTM grade, the forge may offer “the JIS equivalent” from stock. That can be acceptable, but grades named as equivalents do not share identical composition ranges, so make the substitution your written decision.
Name the delivered condition. Forgings are commonly delivered normalised, annealed, or quenched and tempered. Write which, and give a hardness range — not a single value — with the scale and the place where it is measured. Hardness taken on a scaled or decarburised surface reads differently from hardness taken after the surface is ground back. “Brinell, on a ground spot on face A” is an instruction; “HB 220” is not.
Ask where heat treatment is done. Some forges have their own furnaces; others send parts to a heat-treatment shop. Neither is wrong, but you need to know who controls the furnace, who records the cycle and who answers when hardness is out. Ask for the furnace record or chart for each heat-treatment batch, and for the batch number to appear on the part lot’s paperwork.
Mechanical tests need a test piece. If you require tensile or impact values, agree where the test piece comes from: a prolongation left on the forging, an extra sacrificial forging from the same heat and heat-treatment batch, or the forging itself at first article. A separately forged bar does not see the same reduction or the same quench as a heavy section.
Which certificate type proves the material of the delivered lot — and why only an EN 10204 type 3.1 or 3.2 reports results for your own material — is explained in quality documents to request from a Vietnamese parts supplier. For forgings, add one line to the order: the steel’s heat number must be traceable to each forging lot, and to each heat-treatment batch.
Dies: cost, life and who owns them
A closed-die forging is priced with its die, so ask for the die cost, the expected life before re-sinking and the ownership terms as separate lines.
Forging dies wear: the impression erodes, edges round off, and dimensions drift towards the limits before a die is re-sunk or replaced. A quotation that hides the die inside the unit price cannot tell you what happens when the die is worn out. Ask each forge to state:
- the die cost, and whether trimming tools for removing flash are included;
- how many forgings it expects before re-sinking, on what basis, and who pays for re-sinking and replacement;
- whether the die is yours, and the terms for marking it, storing it and recovering it.
Ownership, marking and recovery belong in the contract; see mould and tooling ownership in Vietnam.
Tolerances, draft and the flash line
A forging drawing needs a named forging tolerance standard and grade, the position of the parting line, draft angles and machining stock; without them the forge applies its own practice.
For steel closed-die forgings, EN 10243-1 gives tolerances for drop and vertical press forgings made under hammers and presses. It offers two grades — normal tolerances and a closer range — and applies to forgings up to 250 kg or 2,500 mm in the largest dimension; tolerances for anything larger are agreed at enquiry. Upset forgings made on horizontal machines are covered by EN 10243-2. If your drawing follows JIS or ASTM practice instead, name that document. What matters is that the forge works to a named table rather than to habit.
Then draw or write:
- Parting line and flash. Where the dies meet, and the permitted residual flash after trimming. Flash on a sealing or locating face is a defect only if the drawing says so.
- Mismatch. The permitted shift between the upper and lower halves of the forging.
- Draft. Draft angles on external and internal walls, and faces where draft is not allowed.
- Machining stock. How much material is left on each machined face, so that scale pits and decarburisation are removed by machining.
- Datums. Whether the first machining operation locates on forged faces, and which ones.
- Unmachined surfaces. The permitted depth of scale pits and of decarburisation on faces that stay as forged, and whether they are shot blasted.
A forging with too little machining stock can look perfect until the cutter exposes a lap or a decarburised layer. Agree in advance who pays when that happens — the forge or the machine shop — especially if the two are different companies. Who pays for defects and delays in Vietnam covers how to write that down.
💬 We can turn a forging drawing into an enquiry that every Vietnamese forge reads the same way — tolerance standard, heat-treatment condition, testing and die terms — see sourcing from Vietnam.
Proving soundness: what to test and when
Forging defects such as laps, folds, cracks and internal bursts are not reliably visible after shot blasting, so decide which test proves soundness at first article and which tests continue in production.
The defects specific to forging come from the way metal flows in the die. A lap or fold forms when metal folds over itself and does not weld. Underfill leaves a corner short. Cracks can form at the flash line or from forging at too low a temperature. Internal bursts can appear in heavy sections. Grain flow that breaks out across a highly loaded fillet weakens the part even when nothing is cracked.
For steel forgings, the EN 10228 series sets out non-destructive testing methods and acceptance criteria:
| Part | Method | What it finds |
|---|---|---|
| EN 10228-1 | Magnetic particle testing | Surface and near-surface cracks and laps in ferromagnetic steel |
| EN 10228-2 | Penetrant testing | Surface-breaking discontinuities |
| EN 10228-3 | Ultrasonic testing, ferritic and martensitic steel | Internal discontinuities |
| EN 10228-4 | Ultrasonic testing, austenitic and duplex stainless steel | Internal discontinuities in stainless forgings |
Part 4 excludes closed-die forgings, so for a closed-die stainless part, agree the ultrasonic method and acceptance level separately. If your industry uses ASTM methods, name them instead; the point is to name a method and an acceptance level, not to write “NDT required”.
A practical sequence:
- At first article, section one forging and macro-etch it to show grain flow through the critical fillets, run magnetic particle testing on all surfaces, measure every dimension, and check hardness at the agreed locations. Record what was approved and keep a retained sample.
- Freeze what first article proved: the steel grade and source, the forging route, the die, the heat-treatment cycle and the machining datums cannot change without your written approval.
- In production, agree the sampling plan for hardness and crack testing per heat-treatment batch, and which lots get ultrasonic testing if internal soundness matters.
How first-article and pre-production samples are recorded is covered in sample approval stages, and sampling for visible defects in pre-shipment inspection and AQL.
What to look at in a Vietnamese forge
On a visit, follow one part from bar to packing and ask at each step who does it, where the record is and what happens to rejects.
- Bar stock. How bars are identified by heat number, and whether offcuts of different heats are kept apart.
- Heating and forging. How billet temperature is checked, and how dies are labelled and checked for wear.
- Heat treatment. In-house or subcontracted, and whether each batch has a chart.
- Inspection. Calibrated hardness testers, crack-testing equipment, and NDT operators qualified to a recognised scheme.
- Rework. How ground-out defects are recorded; weld repair of a forging should be prohibited unless you approve it in writing.
General points on a first visit are in what to check on a first visit to a Vietnamese factory.
The enquiry checklist for a forging
Attach these lines to the drawing; whatever does not fit on the drawing goes in a one-page specification.
| Item | What to write | What happens if it is missing |
|---|---|---|
| Route | Closed-die, open-die or cold forging | Quotations for different products |
| Steel | Grade, standard number, substitution rule | A “similar” grade from stock |
| Heat treatment | Condition, hardness range, scale and location | Correct steel, wrong properties |
| Test pieces | Prolongation, sacrificial forging or first article | Results that do not represent the part |
| Certificate | EN 10204 type, heat and batch traceability | Paper that does not prove your lot |
| Tolerances | EN 10243-1 grade or another named table | The forge’s own practice applies |
| Geometry | Parting line, flash, mismatch, draft, machining stock | Disputes after machining |
| Soundness | NDT method and acceptance level by stage | Cracks found by your machine shop |
| Rework | Grinding limits, weld repair prohibited or approved | Repaired parts that look sound |
| Packing | Rust protection, separation, marking by lot | Corrosion and mixed lots on arrival |
Unit prices, die costs and lead times depend on the shape, the steel, the route and each forge’s equipment. There is no market rate worth quoting; comparable quotations on identical terms are the only useful benchmark, and comparing Vietnamese supplier quotations shows how to line them up.
For customs, forgings are often classified by what they are — a part of a particular machine, a flange or a fitting — rather than as forgings as such. Confirm the code before relying on a preferential rate; proof of origin by destination is covered in Vietnam export proof of origin.
💬 Send us the drawing outline even before the checklist is complete. For each project we find, vet and manage the forge that fits the part, and arrange testing and export documents. Get in touch.
Frequently asked questions
1. Is a forging always stronger than a casting or a machined part?
Not automatically. A forging’s advantage comes from sound metal and grain flow that follows the shape, and both depend on the die design, the forging temperature and the heat treatment. Prove it at first article with a sectioned, macro-etched part and the agreed mechanical tests.
2. Can a Vietnamese forge supply EN or ASTM steel grades?
Many can source them, but JIS grades are often what is in stock. Write the standard number and grade, and require written approval for any substitute. Check the material certificate against the heat number on the bar.
3. Who should do the heat treatment?
Either the forge or a specialist heat-treatment shop can do it. What matters is that one party is responsible for the result, that each batch has a furnace record, and that the batch number follows the parts.
4. Which crack test should I ask for?
For ferromagnetic steel, magnetic particle testing finds surface cracks and laps; penetrant testing is the alternative for non-magnetic materials. Add ultrasonic testing where internal soundness matters. Name the method and the acceptance level in the order, for example by reference to the EN 10228 series.
5. Can I start with a small lot?
Yes, but a closed-die forging carries its die cost from the first piece, so a small first lot has a high unit cost. Open-die forging or machining from bar can bridge the gap until the design is stable; see negotiating minimum order quantities in Vietnam.
Sources: EN 10243-1 (steel die forgings, tolerances, drop and vertical press forgings) and EN 10243-2; EN 10228-1 to -4 (non-destructive testing of steel forgings); EN 10204. Checked on 19 October 2026.
More industrial sourcing guides: Fasteners and Springs From Vietnam: Classes, Coatings, Lots · Castings and Forgings From India: Clusters, Specs, Shipping · Steel Fabrication in Vietnam: Welding, Paint and Shipping Size. All guides by category are on the industrial sourcing page.