A Heat Number (also called Melt Number, Cast Number, or Heat Code) is a unique alphanumeric identifier assigned to a single batch of molten steel produced in one furnace cycle (one "melt" or "heat"). It is the fundamental unit of material traceability.
What it covers: All material originating from that specific melt, which may later be processed into different product forms (blooms, billets, bars, forgings) and sizes.
Critical Importance:
Full Traceability: It links the final product (e.g., a machined shaft) back to the original steelmaking process. The manufacturer's mill test certificate will be issued per Heat Number, documenting the chemical analysis from a sample of that specific melt.
Quality Consistency: It allows verification that the material meets the ordered specification. If a component fails, the Heat Number enables investigation into whether the issue is isolated to one melt or is more widespread.
Regulatory & Safety Compliance: In regulated industries (aerospace, automotive, energy), maintaining heat number traceability through the entire manufacturing chain is often a contractual and legal requirement.
The Heat Number is typically stamped on the end of each bar or on a tag attached to bundles.