The product requiring stretching for spring steel C67S cold-rolled steel strip

Spring steel C67S is a grade in the European standard, as specified in EN 10132-4:2000, which covers the delivery conditions for cold-rolled narrow strip for heat treatment – Part 4: Spring steels and other applications. C67S is primarily used in the state of cold-rolled steel strips, with minimal direct use of hot-rolled raw materials. For the C67S grade, 'C' stands for carbon, and 'S' indicates its suitability for springs. The number '67' signifies a nominal carbon content of 0.67%, with an actual range between 0.65% and 0.73%. This carbon content range is relatively close to the Chinese national standard GB 70 steel.

For high-carbon steels with a carbon content exceeding 0.60%, the general hardness of hot-rolled raw materials is around HRB100. Commonly used 65Mn cold-rolled steel strips typically have a factory hardness of around HRB110. Manufacturers often avoid direct stamping production for such hardness, as it can damage molds easily and is not conducive to complex processes like punching holes in products.

Recently, a customer approached us with an order requesting the use of S67C, 1.2mm hot-rolled carbon steel, to produce a sleeve-type product with bent teeth. The customer faced difficulties in sourcing 1.2mm hot-rolled steel and contacted us to check for availability and if we could produce such a product.

The main difference between hot-rolled and cold-rolled lies in the surface. The debate over 1.2mm hot-rolled versus cold-rolled is unnecessary, especially considering that after sample production, surface coating and rust prevention treatments are still required. After discussion, the customer decided to use cold-rolled for the initial sample, although for a product of this nature, a stretch of approximately 19mm is needed, which is uncommon in high-carbon steel. Taking an approach of testing first and solving problems later, we customized a 1.2 * 180mm C67S cold-rolled steel strip sample for the customer. The finished product's hardness is controlled between HRB58 and HRB63, utilizing a spheroidizing annealing process to achieve a high spheroidization rate. These process adjustments ensure that the C67S cold-rolled steel strip produced exhibits excellent forming performance. Currently, production of this sample is underway.

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