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The chemical composition and mechanical properties of the raw materials for cold heading should comply with relevant standards for multi-station automatic cold heading machines.
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The raw materials must undergo spheroidizing annealing treatment, with a metallographic structure of spheroidized pearlite at levels 4-6.
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In terms of hardness, to minimize the tendency of material cracking and enhance die service life, cold drawn materials should have as low hardness as possible to improve plasticity. Generally, the hardness of raw materials should range from HB110 to 170 (HRB62-88).
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The precision of cold drawn material’s dimensions should generally be determined based on the specific requirements of the product and technological circumstances. For multi-station cold heading machines, the requirements for reduction in diameter and forceful reduction are generally lower.
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The surface quality of cold drawn materials is required to have a lubricating film that is dark without gloss. Additionally, the surface should not have any scratches, folds, cracks, pull lines, rusting, oxidation or recesses and pitted surface defects.
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It is required that the total thickness of the decarburized layer in the radial direction of cold drawn material does not exceed 1-1.5% of the raw material’s diameter, but specific circumstances depend on the requirements of each manufacturer.
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In order to ensure the cut-off quality during cold forming, it is required that cold drawn material has a relatively hard surface and a softer core.
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Cold drawn material should undergo a cold heading forging test. At the same time, it is required that the material is as insensitive as possible to work hardening in order to reduce the deformation resistance increase during the deformation process.