Iron & Steel
Heat-Number Batch Traceability for Metals
The heat number is the batch passport key for metals: how it survives the route, how it is marked on the product and how it is encoded as a GS1 batch number
In steel and aluminium the natural granularity of the Digital Product Passport is the heat (or cast), not the item. A heat is a single mass of metal melted in the furnace at one time: one chemistry, one set of tests, one certificate. The real question is therefore not "at which level should the passport be kept" but "how does the heat number survive from the rolling mill to the service centre".
This article follows the number along the route: assignment, splitting and merging, on-product marking and GS1 encoding.
What the heat number ties together
The number is assigned when the furnace is tapped. The chemical analysis of the sample taken at that moment is written against it; tensile, impact and hardness tests after rolling are reported per heat and rolling lot. The inspection document gathers the results under this number. For turning the certificate into structured data see EN 10204 certificates going digital.
The heat number is therefore the batch passport's primary identifier. The chemistry, mechanical-property, scrap-share and carbon fields hang off it; for which fields to expect see steel DPP data fields. The general granularity framework is in choosing model, batch or item.
Splitting and merging along the route
A heat is one mass, but the product does not stay one. One slab becomes several coils, one coil dozens of slit strips, one billet hundreds of sections. Each step creates a new child lot; the rule is that the child lot carries the parent identifier.
| Process step | Identifier carried | Typical carrier |
|---|---|---|
| Melting and continuous casting (slab, billet) | Heat number | Hot stamp, stencil paint |
| Rolling (coil, plate, section) | Heat number + coil or rolling lot | Coil tag, stencil, Data Matrix |
| Slitting and cut-to-length | Parent coil number + child coil or bundle number | Bundle label, Data Matrix |
| Coating (galvanising, painting) | Input coil number + coating lot | Coil tag, RFID |
| Service centre and distributor | Bundle number mapped to heat number | Bundle label, QR |
| Finished-product manufacturer | Product batch + input heat numbers | Product passport link |
Merging is the harder case: if a bundle contains plates from two heats, the bundle record lists both numbers and the passport becomes a multi-heat batch. Chemistry and mechanical-property fields are kept per heat; a single averaged value breaks traceability.
Marking on the product
On slabs and billets the number is hot-stamped or stencilled; coils and bundles use hang tags; on plate and pipe, Data Matrix direct part marking (dot peen, laser) gives a permanent identity. On coils, RFID tags designed for metal surfaces automate reading at warehouse entry and exit. For choosing the method see Data Matrix and direct part marking and when NFC and RFID make sense.
The rule: the number must still be readable after surface treatment, and if the tag is torn off, the mark on the part itself must survive.
Encoding with GS1
In GS1 notation two identifiers work together. The GTIN identifies the trade item: a combination of grade, dimension and specification is one trade item. The batch number (AI 10) says which heat or coil that item came from. In a Digital Link URI the two form a path: /01/GTIN/10/heat-number. Where a per-coil serial is needed, the serial number (AI 21) is added.
The same QR or Data Matrix then works in the warehouse system and in the passport resolver alike. See GS1 Digital Link and, for unique-identifier rules, EN 18219; the standards as a whole are in the standards guide.
When a distributor re-bundles
Service centres and distributors repack material from different heats to match customer orders. Three things are needed: assigning their own bundle number, keeping a record that maps it to the input heat numbers, and linking the bundle passport to the parent heat passports. For facilities that want to record splits and merges as events, the EPCIS transformation event is the standard form of that mapping; see EPCIS 2.0 traceability.
An intermediary that does not keep this mapping breaks the chain; the passport then knows only the intermediary's bundle, not the heat. Adding "input heat numbers are preserved in the bundle record" to the supplier contract is the cheapest safeguard.
Frequently asked questions
Are heat number and lot number the same thing?
No. The heat number identifies the mass of metal that left the furnace; the lot number identifies the child unit produced at rolling, slitting or packing. One heat yields many lots, and every lot must carry the parent heat number.
Should a steel DPP be at item (serial) level?
For most products, no; heat or coil level is enough. Serial level makes sense where a single piece will be tracked for life, such as structural or pressure-equipment components.
What happens to the passport when a service centre splits a coil?
The parent coil's passport does not change; each child coil or bundle gets its own number and links to the parent coil's passport. Chemistry and test data are inherited from the parent, while dimension and packing data live in the child record.
