Mill Test Report
Also known as: MTR, Material Test Report, Mill Certificate, Material Certificate
A mill test report is the certificate a steel mill issues for one heat, recording the chemical composition and mechanical test results for that melt. It is the document a forging shop's own traceability records point at — the heat number identifies the material, and the mill test report says what the material is.
A mill test report is the certificate a steel mill issues for one heat. It records the chemical composition of that melt and the results of the mechanical tests the governing specification requires.
It is the other half of a heat number. The heat number identifies which material you are holding; the mill test report says what that material actually is. Neither is much use without the other, which is why traceability systems record them as a pair.
What it contains
The contents are set by the specification the material was produced to, but a report that cannot support traceability is missing one of these:
- The heat number, which is what links the certificate to physical material.
- The grade and specification — for example AISI 4140 to ASTM A29 — including the revision where the specification has them.
- Chemical composition, element by element, as measured for that heat.
- Mechanical properties where the specification requires them: tensile strength, yield, elongation, hardness, impact values.
- The mill's identity, without which the heat number is ambiguous.
Why forging shops are asked for them
A forging shop is rarely the last stop. Its customer often has to satisfy its own customer, and somewhere up that chain is a requirement to show the material's provenance. The mill test report is what gets passed along, sometimes several times, which is why customers care about the document itself and not simply the shop's assurance that the material was correct.
Two things follow from that. First, the report has to remain associated with the material through every operation, which is a records problem rather than a filing problem. Second, the values on it can matter directly to processing — a heat near the low end of its carbon range may behave differently in heat treatment than one near the top.
What it does not do
A mill test report describes material as it left the mill. It says nothing about what has happened since. Forging, heat treatment and machining all change mechanical properties, so a certificate showing acceptable properties in bar form is not evidence about the finished part. Process records cover that, and the two are complementary rather than interchangeable.
It is also worth being clear that holding the document is not the same as controlling it. Storing and issuing certificates, with revision control and approved-signatory rules, is a distinct capability from recording which heat a part came from. Plenty of shops need both and buy them separately.
Common questions
What is on a mill test report?
At minimum the heat number, the grade and specification the material was produced to, the chemical composition by element, and the results of whatever mechanical tests the specification calls for. Most also carry the mill's identity, the product form and size, and a statement of the standard the certificate itself is issued under.
Is a mill test report the same as a certificate of conformance?
No. A mill test report contains actual measured values for a specific heat. A certificate of conformance only states that the material meets a specification, without reporting the numbers. A customer asking for an MTR is asking for the data, not the assurance.
Who is responsible for keeping mill test reports?
Whoever the contract says, which in practice usually means everyone in the chain keeps their own copies. Retention periods are set by customer requirements and the standards they hold you to rather than by one universal rule, so confirm the period per customer.
Related terms
- Heat Number — The identifier a steel mill assigns to one batch of metal poured from a single melt, and the unit material properties are guaranteed against.
- EN 10204 Inspection Documents — The four types of inspection document defined by EN 10204:2004 — 2.1, 2.2, 3.1 and 3.2 — and what distinguishes specific from non-specific inspection.
- Country of Melt and Pour — Where raw steel was first melted and poured into its first solid shape, why US importers must report it, and what that means for a forging shop's records.