Most incoming inspection departments check that a mill test certificate is present and file it. That satisfies the paperwork and misses the point. The certificate is the only objective evidence you have about what the steel actually is, and reading it properly takes about two minutes.
The heat number — the part that matters most
The heat number identifies the specific melt the steel was cast from. Everything else on the certificate describes that melt. If the heat number on the certificate cannot be matched to a number physically on the material you received, the certificate is describing steel you cannot prove you have.
This is the check most often skipped, and it is the one an auditor will ask about. Every bundle we despatch carries its heat number on a QR tag, and the same number is printed on the delivery challan — so the match can be made at the gate, not reconstructed later.
Chemical composition
The certificate lists actual measured percentages, element by element, for that heat. Compare them against the specification range for the grade you ordered — not against the previous certificate, and not against a memory of the grade.
Where a value matters, know why. For a carburising grade, manganese and chromium drive hardenability. For a free cutting grade, sulphur drives machinability. For a part that will be welded, carbon is the number that decides whether it can be.
Mechanical properties
Tensile strength, yield strength, elongation and hardness, measured on test pieces from that heat. Two cautions. First, check the condition the values were measured in — hot rolled, cold drawn, annealed and hardened-and-tempered give quite different numbers for the same steel. Second, these are properties of the test piece, not of your finished part after your own processing.
Hardenability data, where applicable
For H grades such as 16MnCr5H, the certificate should carry Jominy end-quench data — hardness values at defined distances from the quenched end. This is the certified property you are paying for. A certificate for an H grade without Jominy data is not certifying the thing that makes it an H grade.
Three checks worth making every time
- Does the heat number on the certificate match the number physically on the material?
- Does every listed element fall inside the specification range for the grade you ordered?
- Do the mechanical values correspond to the condition the material was supplied in?
If your own customer works to IATF 16949, there is a fourth: can you retrieve, for any batch of finished parts, the certificate for the heat it was made from? That is a question about your supplier's traceability as much as your own record keeping.
Written by the technical team at Kalika Enterprises, Waluj MIDC. Guidance here is general; the values that govern your part are those on the test certificate supplied with your consignment.