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Mill Certificates, Heat Numbers and Traceability on Titanium Parts

On a titanium part the certificate can be the most expensive piece of paper in the job, and the one most often specified wrong. Here is what the documents are, what they prove and which one belongs on your RFQ.

What a mill certificate actually is

A mill test certificate, sometimes MTC or MTR, is the mill’s record of one heat of material. A heat is a single melt, identified by a heat number, and everything made from it shares that number.

A titanium mill certificate typically carries:

• The heat number and the mill that produced it.
• The chemical analysis: aluminium, vanadium, iron, oxygen, nitrogen, carbon, hydrogen and residuals.
• Mechanical test results: tensile strength, yield strength, elongation, sometimes reduction of area and hardness.
• The standard the material was made and tested to, for example ASTM B348, AMS 4928 or ASTM F136.
• The product form, size and quantity.
• Any heat treatment condition, such as annealed.

Note what it is not. It is a certificate for the material, not for your part. Your shop adds a certificate of conformity that ties its parts to that heat.

The EN 10204 types

EN 10204 is the standard that names the document types. It applies to metallic products generally, titanium included.

Type	Name	Who issues it	What it means
2.1	Declaration of compliance	Manufacturer	A statement that the material meets the order. No test results
2.2	Test report	Manufacturer	Results from non specific inspection, not necessarily your material
3.1	Inspection certificate 3.1	Manufacturer’s independent inspection representative	Actual results for your delivered heat, tied to the heat number
3.2	Inspection certificate 3.2	Manufacturer plus an independent inspector or the buyer’s representative	Same as 3.1, witnessed and countersigned by a third party

For machined titanium parts, 3.1 is the normal requirement. It is what mills issue as a matter of course, it ships with the material and it adds no lead time.

3.2 costs real money and real time, because somebody independent has to attend the testing. Ask for it only when a pressure code, a nuclear specification or a specific customer requirement says so. It is one of the more common cases of a requirement copied forward from an old drawing and never questioned.

Traceability inside the shop

The certificate is the easy half. The hard half is keeping the link from your finished part back to that heat, through every operation.

A shop with a working process does this:

1. Receiving. The heat number is recorded against the purchase order and the material is marked and segregated by grade and heat.
2. Transfer marking. Before any cut removes the original marking, the heat number is marked on each new piece. A QC inspector witnesses it, per the quality plan.
3. Work in progress identification. Every batch travels with a router that carries the heat number through machining, deburring and any outside process.
4. Outside processes. Anodizing, passivation and heat treatment all send parts away. The identity has to survive the trip, in both directions.
5. Final documentation. A certificate of conformity names the part number, the quantity, the heat number and references the original mill certificate, which is usually attached.

If any of those five steps is missing, the parts are not traceable, whatever the folder says. For aerospace and medical work that is not a paperwork failure, it is a scrap decision.

What to ask a shop

• Do you supply mill certificates to EN 10204 3.1 as standard?
• How do you transfer heat numbers when the original marking is machined away?
• How do you segregate grades in stores, and specifically Grade 5 from Grade 23?
• What identification travels with parts to an outside finisher?
• What does your certificate of conformity look like? Ask for a redacted example.

That last question is the shortcut. A shop that can send you a sample certificate within the hour has done this before.

What to put on the RFQ

Be exact. Vague requirements get priced defensively.

Material: Grade 5 Ti-6Al-4V bar to ASTM B348. Mill certificate to EN 10204 3.1 required, heat number to appear on the certificate of conformity. No third party witness required.

Four facts: grade, standard, certificate type, and an explicit statement that 3.2 is not needed. That last clause alone saves money and days on a surprising number of orders.

When you genuinely need more

Some cases justify going further than 3.1:

• Aerospace structural parts may require AMS 4928 material and an AS9102 first article inspection report.
• Implants require ASTM F136 or ISO 5832-3 material and full lot traceability under ISO 13485.
• Pressure equipment under some codes requires 3.2.
• Safety critical parts may require retained samples or additional testing.

All of these are legitimate. The point is that each one should trace back to a requirement somebody can name, not to a template.

Frequently asked questions

Keep reading

• Why Titanium Lead Time Is Usually About the Bar, Not the Machine
• Drilling Titanium: Speeds, Heat and Why Holes Fail First