Guide
How do you read a mill test report and trace it to your finished parts?
A mill test report is the document a metal producer issues for one heat or lot of material, stating the specification it was made to, the heat number, the measured chemistry, the measured mechanical properties and a signed statement that the material conforms. Read correctly, it tells you whether the metal in your parts is the metal on your drawing; read carelessly, it is just a page that came in the box.
By Saola Manufacturing engineering team · Published · Updated
Buyers usually meet the MTR (also called a mill test certificate, material test report or, in Europe, an EN 10204 inspection document) when parts arrive and someone in receiving asks whether the paperwork is right. This guide walks through the report in the order an experienced engineer reads it: the governing specification first, then the heat number, then chemistry, then mechanicals, and finally the chain of documents that links that heat to the parts you are holding. It closes with the drawing note and RFQ wording that make the whole check possible.
On this page
What is on a mill test report, block by block?
Every mill test report has the same five working parts: an identification block, the governing specification, the heat or lot number, the test results and the conformance statement. Layouts vary by mill, but if any of those five is missing, the document cannot do its job.
The identification block names the producing mill and its location, the purchaser and purchase order, and the product: alloy or grade, form (round bar, hex, plate, tube), size and condition or temper. The specification block lists the standards the material was made and tested to, ideally with the edition year, for example ASTM A108 for cold-finished carbon steel bar or ASTM B211/B211M for rolled or cold-finished aluminum bar. Many mills list several specifications at once (an ASTM, an ASME and an EN grade), which means the mill is stating that the material meets every one of them, in practice the strictest limit of each, not that any one of them is optional.
The results block is where most readers start, and should not. It holds the chemical analysis (usually labeled heat analysis or ladle analysis), the tensile results, and any extra tests the specification or the order called for, such as hardness, grain size, ultrasonic inspection or, for stainless, an intergranular corrosion test. The last block is the conformance statement and signature, often with the EN 10204 document type (2.2 or 3.1), the country of melt and, sometimes, the country of manufacture.
What is a heat number, and why does it matter more than anything else on the page?
A heat number identifies one melt of metal, the batch poured from one furnace charge, and it is the only field that ties the test results to a physical bar. Every other value on the report is only as trustworthy as the link between that number and your parts.
Steel mills test chemistry on the melt itself. ASTM A751 separates heat analysis, which the producer reports as representative of the whole heat, from product analysis, made later on the semi-finished or finished product, usually by a purchaser checking conformance. Aluminum producers usually report a cast or lot number instead of a heat number, and the logic is the same: one number, one batch, one set of results.
The heat number has to survive every step after the mill. It is stenciled or tagged on bar bundles, carried onto the service center’s cut tickets, written on the machine shop’s receiving log and job traveler, and finally quoted on the certificate of conformance or packing list for your lot. If the number on the MTR appears nowhere else in the paperwork you receive, you have a report about some metal, not about your parts.
Two practical checks catch most problems. First, confirm the product on the MTR covers the stock that was actually used: a report for one bar diameter does not cover parts turned from another diameter, even in the same grade. Second, confirm the dates are plausible: a report dated after your parts shipped, or a heat melted long after the parts were machined, needs an explanation.
How do you check the chemistry against the specification?
Take each element the specification limits and compare the reported value with the limit, element by element, including the “others” rows. A report passes only if every limited element is reported and inside its range, so a missing element is a finding, not a pass.
Get the limits from the specification or registration the drawing names, not from a supplier datasheet. For wrought aluminum the composition limits are registered by the Aluminum Association in its Teal Sheets, and ASTM B211 states that the Teal Sheets limits govern if its own composition table ever differs. For carbon and alloy steel bar, grade chemistries and the general rules for reporting them sit in ASTM A29/A29M, which A108 builds on. The table below is a worked check of a 6061-T6 bar report; the “example reading” column is illustrative, not data from a real heat.
Three traps show up again and again. The first is the element nobody reported: a free-machining steel such as 12L14 contains added lead, and if your product falls under a restricted-substance regime the lead value matters even when the MTR omits it. The second is confusing heat and product analysis: a check analysis on a finished bar is allowed to stray slightly outside the heat limits, per ASTM A29 product-analysis tolerances, so a small difference between the MTR and an independent lab is not automatically a nonconformance. The third is the dual grade: a report showing that one heat meets both 304 and 304L is normal and legitimate, but it does not make every 304 report acceptable where your drawing says 304L.
| Line on the report | Requirement | Example reading | Result |
|---|---|---|---|
| Silicon, wt % | 0.40 to 0.8 | 0.62 | Within range |
| Iron, wt % | 0.7 max | 0.41 | Within limit |
| Copper, wt % | 0.15 to 0.40 | 0.27 | Within range |
| Manganese, wt % | 0.15 max | 0.08 | Within limit |
| Magnesium, wt % | 0.8 to 1.2 | 0.94 | Within range |
| Chromium, wt % | 0.04 to 0.35 | 0.19 | Within range |
| Zinc, wt % | 0.25 max | 0.05 | Within limit |
| Titanium, wt % | 0.15 max | 0.03 | Within limit |
| Others, each / total, wt % | 0.05 / 0.15 max | Not reported | Finding: ask the mill |
| Tensile strength, ksi | 42 min | 45.6 | Above minimum |
| Yield strength, ksi | 35 min | 40.9 | Above minimum |
| Elongation in 2 in. or 4D, % | 10 min | 14 | Above minimum |
How do you read the mechanical test results?
Compare tensile strength, yield strength and elongation with the minimums for the exact temper and size range on your drawing, and confirm the test was run in the condition the material was delivered in. A strong number in the wrong temper or size range proves nothing about your parts.
Tensile results come from a specimen pulled to failure under ASTM E8/E8M, or under ASTM A370 for steel products. Yield strength is normally the 0.2 % offset value, found by the offset method per ASTM E8, and elongation depends on the gauge length used, so check that the report states it before comparing two reports from different mills. Many specifications set different minimums for different size ranges, which is another reason the bar diameter on the MTR must match what was machined.
Watch the units. Reports from mills outside North America often give strength in MPa and the drawing in ksi, and a typical receiving error is comparing the two without converting. Watch the temper as well: a report for 6061-T6 and a report for 6061-T651 can show similar strength, but only one of them confirms the stress-relieving stretch your drawing may require (see the T6 versus T651 guide). And remember that the mechanicals describe the material as it left the mill. If anyone heat treats, welds or plates the parts afterward, the MTR no longer describes the final condition, and the drawing should say what test, if any, applies to the finished part.
Which specification governs, and what if the report does not match your drawing?
The drawing and purchase order govern; the mill test report is evidence that the material meets them. If the report cites a different specification, grade or edition than the drawing calls for, treat it as a nonconformance to be resolved in writing, not as a close-enough match.
Mismatches come in a few predictable forms. An equivalent grade from another system (an EN or JIS number where the drawing says an ASTM or SAE grade) may be close in chemistry but not identical in limits, tests or tolerances, so equivalence is an engineering decision for the design owner, not for receiving. A product specification for a different form, such as a plate or extrusion standard on a report for parts the drawing says come from rolled bar, changes the tests and minimums that applied. An older edition is usually harmless but occasionally is not, which is why the drawing should name the edition or say “latest revision at time of order.”
A clean material callout removes most of this. A typical example for a turned aluminum part reads: MATERIAL: ALUMINUM ALLOY 6061-T6 PER ASTM B211/B211M. MILL TEST REPORT REQUIRED, EN 10204 TYPE 3.1, TRACEABLE BY HEAT OR LOT NUMBER TO EACH LOT SHIPPED. For a steel part, name the grade, the product specification (for example ASTM A108) and the condition, such as cold drawn. The difference between a type 3.1 report, with results from the delivered material, and a type 2.2 report, with results typical of production, is covered in the EN 10204 3.1 vs 2.2 guide.
How do you trace a mill test report to the finished parts in your box?
Follow the heat number through every document between the mill and your dock: the distributor’s cut ticket, the machine shop’s receiving record and job traveler, and the certificate of conformance or packing list for your lot. If the number appears in each, the chain is intact.
Most machined parts are not cut from metal bought directly from a mill. A service center buys mill bundles, cuts them to length and ships them with either a copy of the mill report or its own certificate that quotes the mill heat number. Either is acceptable if the heat number carries through and the distributor’s document does not change the material description. A distributor certificate that lists a grade but no mill heat number is a break in the chain.
At the machine shop, the heat number should be recorded when the bar is received and again on the traveler or routing for each production lot. Good practice is one heat per shipped lot; where a lot has to span two heats, the shipping documents should list both and, if the drawing requires it, the parts should be segregated by heat. For parts where the stakes justify it, ask for a sample of the receiving record itself, not only the MTR.
Red flags worth a phone call: a report whose company name, logo or layout differs from the producing mill with no distributor document alongside; results that are identical across different heats; values printed as ranges instead of measurements on a report described as type 3.1; missing signatures or edition years; and any sign that the PDF has been edited. None of these proves fraud, but each one means the report alone is not enough evidence.
What should you put on the RFQ and purchase order?
State the material specification with grade, temper and edition, the report type you need, and the traceability you expect, before the supplier buys any metal. Material bought before those requirements are known often cannot be traced back after the fact.
A complete material clause covers six points: the material callout exactly as on the drawing; the report type (EN 10204 3.1, or a mill test report with actual results); traceability by heat or lot number to each shipped lot; the language and units of the report; whether country of melt must be stated; and whether you will commission an independent check analysis. A buyer who needs a product analysis should name the laboratory and the method, such as ASTM E1019 for carbon and sulfur in steel, rather than leaving the choice open. Calibration traceability for the labs involved is a separate question; NIST’s traceability policy explains what that term does and does not mean.
On a Saola order, the material trail is carried by the documents listed on our quality page: material certification on request, giving a traceable material source for the alloy or steel grade used; a process routing sheet per part number, also on request; and a dimensional inspection record with every lot. That page does not list in-house chemical or tensile testing, so if you need a check analysis, put it on the purchase order as a third-party test. The bar and tube grades running on our CNC turning line are listed on that page, including 12L14, C1117 and 52100 steel, 2011-T3 and 6061-T6 aluminum, silicon bronze and ASTM A513 DOM tube. Ask for the material certification when you send the drawing for a quote, so the requirement is in place before the metal is bought.
Frequently asked
Is a mill test report the same as a certificate of conformance?
No. The mill test report comes from the metal producer and covers the raw material: its chemistry and mechanical properties for one heat or lot. A certificate of conformance comes from the part supplier and states that the finished parts meet the drawing and purchase order. A good certificate of conformance quotes the heat number from the MTR, which is what links the two.
Can a distributor’s certificate replace the mill’s report?
It can, if your purchase order allows it and the distributor’s document quotes the original mill heat number and the same specification and grade. If the order calls for the original mill report, say so; many buyers ask for the distributor certificate and a copy of the mill report together.
What if a value on the report sits right at the specification limit?
A value at the limit is a conforming value. Whether it is acceptable for your design is a separate question; if your part relies on margin above the specification minimum, the drawing should state the higher requirement, because the mill only owes you the specification.
When is it worth paying for an independent check analysis?
When the material is safety-critical, when the supply chain has several intermediaries, when a report shows any of the red flags above, or on the first lot from a new supplier. Compare the result with the product-analysis tolerances in the governing specification, not with the heat limits alone.
Does machining or plating change what the MTR certifies?
Machining removes material but does not change the alloy, so the MTR still describes it. Heat treatment, welding or any thermal process after the mill changes the mechanical condition, and plating can add its own requirements, such as an embrittlement relief bake on high-strength steel. In those cases the drawing should name the test that applies to the finished part.
Sources
- ASTM A751, Standard Test Methods and Practices for Chemical Analysis of Steel Products, ASTM International, accessed October 2026
- ASTM A29/A29M-23, General Requirements for Steel Bars, Carbon and Alloy, Hot-Wrought, ASTM International, 2023
- ASTM A108-24, Steel Bar, Carbon and Alloy, Cold-Finished, ASTM International, 2024
- ASTM B211/B211M-19, Aluminum and Aluminum-Alloy Rolled or Cold Finished Bar, Rod, and Wire, ASTM International, 2019 (since revised as B211/B211M-23; check the current edition before ordering)
- International Alloy Designations and Chemical Composition Limits for Wrought Aluminum and Wrought Aluminum Alloys (Teal Sheets), The Aluminum Association, revised August 2025
- ASTM E8/E8M, Standard Test Methods for Tension Testing of Metallic Materials, ASTM International, accessed October 2026
- ASTM A370, Standard Test Methods and Definitions for Mechanical Testing of Steel Products, ASTM International, accessed October 2026
- ASTM E1019, Determination of Carbon, Sulfur, Nitrogen, and Oxygen in Steel, Iron, Nickel, and Cobalt Alloys by Combustion and Inert Gas Fusion Techniques, ASTM International, accessed October 2026
- BS EN 10204:2004, Metallic products. Types of inspection documents, BSI, published October 2004
- NIST Policy on Metrological Traceability, National Institute of Standards and Technology, accessed October 2026