Heat Number Traceability in a Forging Shop
· 5 min read
A heat number identifies one batch of steel poured from a single melt. Forging shops trace it so that if a material problem is found later, every part made from that melt can be identified. Keeping the link intact means recording the heat at receiving and carrying it through every operation that transforms the material.
A heat number identifies one batch of steel poured from a single melt. Every bar in that batch shares the same chemistry and is covered by the same mill test report. That is why the heat number, not the bar and not the purchase order, is the unit that material properties are guaranteed against — and why it is the thing you have to be able to follow.
What a heat number actually identifies
When a mill melts a batch of steel, it assigns that melt a heat number and issues a mill test report against it: chemical composition, mechanical properties, and the tests performed. Every bar cut from that melt carries the same guarantee.
This matters because the guarantee does not survive being pooled. Two bars of the same grade from two different heats are not interchangeable from a traceability standpoint, even though they are metallurgically similar and will forge identically. If one of those heats is later found to be out of specification, you need to know which parts came from it.
Why forging shops are asked to trace it
The requirement almost always arrives from a customer rather than from a regulator. A shop supplying into aerospace, defense, oil and gas, or automotive safety components will be asked to demonstrate that it can identify, for any part it shipped, which heat the material came from.
The practical test is a question: if a mill notifies you tomorrow that heat 84213 was out of specification, which shipped parts are affected?
A shop with intact traceability answers with a list. A shop without it answers with a date range, and every part shipped in that range becomes suspect. The difference is the cost of a targeted recall versus a broad one — which is the entire commercial argument for tracking heats properly.
Where the link breaks
Traceability is not lost dramatically. It is lost quietly, at four predictable points.
Receiving. If the heat number is written on the paperwork but not into the system, the link is broken before the material reaches the floor. Everything downstream is then reconstruction from memory.
Pooling at stock level. This is the most common failure and the most damaging. If your inventory records say 4140 round bar, 3,200 lb on hand and that figure was built from three deliveries across three heats, the heat information is gone. Not hard to find — gone. No downstream record can recover which parts came from which melt.
Transformation. Cutting, forging, heat treatment and machining all consume one material and produce another. If the heat number is not carried across each of those operations, the chain breaks at the first stage that does not record it.
Partial consumption. A cut that consumes 400 lb from a 1,000 lb bar has to leave 600 lb still attributed to the same heat. If the remainder is written back to a generic pool, the link is lost mid-process.
What it takes to keep the link intact
The requirement is narrower than it first appears. Three things have to be true.
Record the heat at receiving, per line. Not per delivery — per line. One delivery frequently contains material from more than one heat, and a single heat field on the header silently merges them. Capture it alongside the test report number and the QC result, so the material identity and its acceptance status arrive together.
Make the heat number part of how stock is counted. This is the structural point, and it is what separates a system that traces heats from one that merely records them. If your on-hand quantity is stored per item and location only, then two heats of the same item in the same location are indistinguishable by construction. The heat number has to be part of the key that stock is bucketed by, so that 1,200 lb of heat A and 2,000 lb of heat B remain two balances rather than one figure of 3,200 lb.
Carry it through every transformation. When a cutting operation consumes material from a heat, the output must be attributed to the same heat. The same applies at forging, heat treatment and machining. Done consistently, the chain from receiving line to shipped part is continuous, and tracing it is a matter of following the records rather than reconstructing history.
What traceability does not give you
It is worth being clear about the boundary, because it is frequently oversold.
Heat number traceability tells you which material went where. It does not store your mill test reports, it does not certify your parts, and it does not satisfy a quality management standard on its own. AS9100, IATF 16949 and NADCAP all require document control, corrective action processes and audit evidence that no inventory system provides.
What traceability gives you is the factual backbone those processes need: an accurate, auditable answer to where a given heat ended up. The certificates, procedures and approvals remain a separate discipline.
How Ongoing Forge handles it
Ongoing Forge treats the heat number as part of the stock bucket rather than as a label on a document. Stock balances are keyed by item, location, process stage, heat number and trading partner, so material from two heats never collapses into one figure.
At receiving, each line captures the heat number, the supplier it came from, the test report number, a Jominy reference where hardenability matters, and the QC outcome including accepted and rejected quantity. Each subsequent stage — cutting, forging, heat treatment, machining, shipping — consumes from a specific heat's balance and posts its output against the same heat.
Because every movement is written to an append-only ledger, tracing a heat is a matter of reading the record: enter a heat number and see every document it touched, in order, with a running balance and the forward chain through to shipping.
To be explicit about the boundary described above: Ongoing Forge records the heat number and test report number, and traces the material. It does not store or generate the mill test report documents themselves.
Common questions
What is a heat number?
A heat number is an identifier assigned by the steel mill to one batch of metal poured from a single melt. Everything in that batch shares the same chemistry and the same mill test report, so the heat number is the unit that material properties are guaranteed against.
Why do forging shops need heat number traceability?
Because material properties are guaranteed per heat, not per bar. If a customer or a mill later reports a problem with a heat, a shop that has traced it can identify exactly which parts were made from that material. A shop that has not must treat every part shipped in that period as suspect.
How long do I need to keep heat number records?
Retention is set by your customer contracts and by the standards your customers hold you to, not by a single universal rule. Aerospace and defense work commonly requires far longer retention than general industrial work. Confirm the requirement with each customer rather than assuming a default.
What breaks heat number traceability most often?
Mixing material from two heats into one inventory figure. Once two heats are pooled into a single on-hand quantity, no downstream record can say which parts came from which melt, and the link is unrecoverable without a physical segregation and re-identification.