What is a heat number? Steel traceability from cast to customer

Ask anyone on a stockholder's shop floor what a heat number is and you get a quick, confident answer. Ask them to prove one, from a piece on the rack back to a certificate and forward to a customer, and it gets slower.

This article covers what a heat number is, where it lives, what it is tied to, and where stockholders lose it.

What a heat number is

A heat number identifies a single melt of steel. The mill melts a furnace charge, adjusts the chemistry, casts it, and gives that cast an identifier. Everything rolled or forged from it shares that number.

You will also hear "cast number" and "melt number". In everyday trade use they point at the same thing: the identity of the cast the material came from.

The heat matters because chemistry is set at the melt. The carbon, chromium, nickel and molybdenum in a 316L bar were fixed when it was cast. The heat number is how you connect a physical piece of steel to the analysis that describes it.

Where you find it

On the material, if the mill has done its job. Bar ends are commonly stamped, painted or tagged. Plate is usually stamped near the edge. Bundles carry a tag. Coil carries a label.

On the paperwork, in two places:

• The mill test certificate, which states the heat and the analysis for it.
• The mill's delivery documentation, which links the heat to what was shipped.

If the number on the steel and the number on the certificate do not agree, you have a problem before the material has even been unloaded. That check is the first reason the heat number earns its place.

What the heat number is tied to

Three things hang off it.

1. The certificate. The mill test certificate reports chemistry and, for most products, mechanical results, for that heat. It carries an EN 10204 type, which tells you who validated it. Our EN 10204 explainer covers 2.1 to 3.2.
2. The grade claim. A bar sold as 316L is 316L because the certificate for its heat says the chemistry falls within the standard's limits. Without the link, the grade is an assertion.
3. The customer's requirement. Many customers specify a minimum certificate type, or require the cert to travel with the delivery. The heat number is how you show the cert you send relates to the steel on the wagon.

Heat number, batch and lot are not the same

This is where confusion starts, and it matters once you hold stock.

A heat is the mill's unit. It is one melt. A single heat can be rolled into a lot of bar, and one delivery can include several heats. One certificate can cover several lengths of the same heat.

A batch, in your own books, is your unit. It is one receipt of one product with one location, weight and cost.

So the relationship is not one to one. A delivery of 20 bars might be one heat or three. Two deliveries a month apart might share a heat. Your records have to hold the heat on every batch and let several batches point at the same certificate.

Treating "heat" and "batch" as synonyms is how stock records end up unable to answer a simple question: which certificate belongs to this piece?

Where stockholders lose the thread

The mill gives you a clean heat number. Most of the damage is done afterwards, in four places.

Goods in. The delivery note says one thing, the cert says another, and somebody retypes a heat number from a PDF. One transposed digit and the batch is tied to the wrong certificate, or none. Nothing looks wrong until an audit.

Cutting. Take a 6 m bar of one heat and saw it into pieces. Every piece is the same cast, so every piece needs the same heat and certificate. If the cut pieces are only identified by a chalk mark and a job number, the heat is held by the memory of whoever cut them.

Offcuts. The remnant that goes back on the rack is the most exposed material in the building. It is certified steel with an unreliable label. We wrote about that in the remnant graveyard.

Outprocessing. Material goes out for polishing, machining or testing, and comes back with a subcontractor's paperwork and your own. Unless the heat travels with it, the return is steel with a history gap.

In each case the material is fine. The record is what fails.

What a clean audit trail looks like

Traceability sounds abstract until a customer's quality manager phones. The test is simple. Pick a piece of steel you delivered last year. Can you answer all of these in minutes?

• What heat was it?
• Which certificate covers that heat, and what type is it?
• Which receipt did the material come in on, and from which supplier?
• If it was cut, which parent did it come from, and what else came off the same parent?
• If it went out for processing, did it come back with the heat and cert intact?
• Which delivery note and invoice did it leave on?

Every one of those is a lookup if the heat has been carried correctly. If it has not, every one is a search through email, folders and people's heads.

How MetlSys carries the heat

MetlSys is built so the heat number is attached to the batch from the point of receipt and does not come off.

On goods in, you drop the delivery note and mill cert on the receipt. The extraction reads the heat number, grade, certificate type, chemistry and mechanicals and proposes them. A person checks them against the source PDF and confirms. Nothing posts until they do.

The certificate is stored as a record, with its reference, heat, type, grade, standard, chemistry and mechanicals alongside the PDF, and matched to batches by heat number. Loose certificates that arrive later can be matched by heat in one go. Anywhere you are offered a batch, one with no certificate linked is flagged.

When a batch is split or cut on a works order, every child inherits the parent's heat and certificate. When material goes to a subcontractor and returns, the return books in as a child batch with the certificate re-linked to it.

At despatch, MetlSys checks each line against the certificate requirement. It blocks when no certificate is linked, when the type is below what the customer or line requires, or when the cert's heat or grade does not match the batch or line. The certificate pack then goes out with the delivery note.

The result is that the question "which heat is this?" has one answer, held in one place, from the day it was booked in.

The practical test

Do this once, this week. Take three deliveries from the last quarter, one of them cut. Trace each from the customer's delivery note back to the mill certificate and the original receipt, and time it.

If it takes minutes, your heat numbers are doing their job. If it takes an afternoon, or one of them cannot be done, you have found the gap an auditor or a customer will find for you.

For how the heat number works through the rest of the stock process in a stainless operation, see MetlSys for stainless steel stockholders.

If you want to see your own heat numbers followed from receipt to despatch, request a demo.