Heat number markings through scale formation to mild steel

Traceability in the steel industry is crucial for the high-quality requirements that assure safety of the finished products. For example, a heat number is required by industry standards for identifying the batch of mild steel. Without proper identification, the steel cannot be used or delivered anywhere.

The challenge with processing mild steel is to maintain the heat number on the material through different circumstances. The steel material might be stored at different conditions, or further processed, e.g. quenched, but the heat number marking must stay readable on the material.

Problems with disappearing traceability markings

A global steel company was searching for a way to create permanent heat number markings for internal traceability throughout the production and testing processes within a steel mill. For testing purposes, they take a sample piece of each rolled steel plate, and this sample needs a traceability marking.

The samples are processed in inhouse laboratories, where the strength of the steel is tested. Strength tests are especially important when the steel is used in structural applications such as bridges that require high-strength steel. If the traceability marking vanishes, the whole steel plate has to be melted again, which is an expensive process. The sample piece marking includes data about the type of the required impact test and at what temperature the sample needs to be tested.

Depending on the used production processes, some steel batches might have scale formation on their surface. The traceability markings need to be made in a way that the marking is in the basic material underneath the possible scale. When cutting the steel plate, the heat of the process separates the scale from the surface of the steel plate, and with it the marking might vanish.

Engraved machine-readable markings

Up until now, the traceability markings have been made with die cutting, but it doesn’t produce machine-readable marking. A method was needed that could engrave the marking to the basic material, that would endure the cutting process and is visible also after that. Integrable solution Cajo Tailor was the perfect choice. Using the same amount of time than die cutting marking, Cajo’s laser solution can mark much more information, for example a 2D code and several lines of text.


Do you have problems with poor readability of the markings, challenging material (corrosion, material is painted or coated, size of the material) or are you having issues with integrating the marking process into the overall production process? We have created in cooperation with our clients and partners several dedicated solutions for different business areas. Cajo solutions are widely used in various stages of finished and unfinished metal and wire products, automotive, shipping, and infrastructure industries, as well as marking end products, e.g. consumer electronics.
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