A mill certificate for steel bar should identify the heat number, the grade and its chemical analysis, the mechanical properties tested, the delivered condition, the size and quantity covered, the producing mill and the date of issue. It should also name the specification the bar was made to and confirm that the recorded results belong to that heat.
What does a mill certificate for steel bar contain?
A mill certificate is written per heat, not per order. A heat is one cast of steel, so the certificate describes the chemistry of that cast and the results of the tests carried out on it. The minimum set a buyer should expect is the heat number, the grade and the specification it was made to, the heat analysis, the mechanical test results for the properties named on the order, the delivery condition, the diameter and length, the quantity or mass covered, the producing mill, the issue date and an authorized signature or stamp.
The delivery condition matters as much as the grade. The same grade supplied as-rolled and supplied quenched and tempered does not behave the same way in a machined part, so the certificate should state which condition was shipped. If the order also called for a particular test, such as hardness, the certificate is where the result should appear.
For Yixin Precision Machinery (Changzhou) orders, the standard document set includes a mill certificate, and the heat analysis is on the steel mill certificate, forwarded unaltered. Where a delivery is drawn from more than one heat, ask for the heat numbers to be listed against the bundle references on the packing list, so each certificate can be matched to the bundles it covers.
Which certificate fields should you check first?
Check the heat number first, then the grade and its chemistry, then the mechanical results and the condition. Those four fields decide whether the rest of the document is worth reading.
| Field | What it should show | Why you check it |
|---|---|---|
| Heat number | One number for the cast, repeated on the certificate and on the bundle or bar marking | Connects the bars in front of you to the document |
| Grade and specification | The grade ordered and the specification it was made to | Confirms the grade you specified is the grade shipped |
| Chemical composition | Heat analysis for the elements the grade covers | Lets you compare values against grade limits instead of a trade name |
| Mechanical properties | Results of the tests named on the order, such as tensile strength, yield strength, elongation or hardness | Describes the properties of the shipped condition, not only the chemistry |
| Delivery condition | As-rolled, normalized, quenched and tempered, or annealed | The same grade in two conditions behaves differently in the finished part |
| Size, length and quantity | Diameter, length, and the quantity or mass the certificate covers | A certificate is issued per heat and may cover only part of a shipment |
| Mill, date and signature | Producing mill, issue date, authorized signature or stamp | Makes the document traceable in your quality file |
Do not stop at the grade name. Foreign grade names are a starting point for discussion, not a certificate check: C45, S45C and SAE 1045 are comparable with 45 steel, for reference only, and the chemistry limits differ between standards. Read the analysis against the grade and the specification you actually ordered.
Does a mill certificate cover chrome plating, grinding or heat treatment?
A mill certificate covers the steel as it left the mill. Chrome layer thickness, chrome hardness, ground surface finish, straightness and cut length are finishing results, and they belong on the finishing supplier's inspection records, not on the mill certificate.
For a chrome-plated bar, keep two sets of documents. The mill certificate carries the base steel: heat number, chemistry and the properties of the bar as supplied to the finisher. The finishing record carries what was done afterwards. On Yixin chrome-plated bars, hard chrome is specified at 10–50 μm per side, chosen per order, with chrome hardness HV800+. Yixin re-checks chrome thickness, diameter and surface when the bars come back from the partner plant.
Heat treatment performed after the mill also falls outside the mill certificate. The 45 Steel Q&T Ground Round Bar from Yixin is quenched and tempered after the mill, with surface hardness of HRC25–28 or HRC28–32 chosen per order. Because grade 45 has limited hardenability, the core is softer, so that surface range should not be read as uniform hardness through the section, and it will not appear on the steel mill certificate. The 40Cr Q&T Ground Round Bar is supplied at HRC28–35, and the 42CrMo Q&T Chrome-Plated Bar at HRC30–38 before plating, made to order.
How do you match the certificate to the bars delivered?
Match the heat number on the certificate with the heat number marked on the bundle tag, the packing list or the bar marking, then check that size, quantity and condition on the certificate match the order. A certificate that cannot be tied to a bundle is a document without a subject.
A certificate is issued per heat, so a shipment built from several heats needs several certificates, and a single certificate may cover only part of what arrives. That is why the packing list, not the certificate, is the practical tool for splitting a delivery by heat. If you need heat traceability after the bars are cut to length, transfer the heat number to your own traveler or job record at goods in, because the certificate follows the bundle, not the individual cut piece.
For Yixin orders the standard document set is a commercial invoice, a packing list and a mill certificate. A certificate of origin is arranged per order, and third-party inspection is arranged on request rather than applied to every shipment.
What to put in your RFQ
- The grade and the specification the mill certificate must be issued against, plus the delivery condition you want shipped.
- A certificate for each heat, and whether it must be forwarded unaltered rather than re-typed.
- Whether you also need a certificate of origin, which is arranged per order.
- Whether you need third-party inspection, which is arranged on request.
- Diameter, length, quantity and tolerance, so the certificate and packing list can be checked against the delivery.
- Where hardness matters, the surface hardness range required and the location on the bar where it should be measured.
- Whether chrome plating is part of the order or done downstream, so the finishing records are issued for the right operation.
Summary
A mill certificate for steel bar is a heat document: heat number, grade and specification, chemical analysis, mechanical results, delivery condition, size and quantity, mill and issue date. Check those fields against what you ordered, keep the heat number with your goods-in record, and treat finishing separately, because chrome thickness, chrome hardness, surface finish and any heat treatment after the mill are not part of the mill certificate. For Yixin orders, the standard set is a commercial invoice, a packing list and a mill certificate, with a certificate of origin arranged per order and third-party inspection arranged on request.