Formation of the Structure and Mechanical Properties of Rolled Products for Cold Heading of Bolted Metal Products

Products with a high level of physical and mechanical properties can be obtained either through the use of new materials, or through the development of new technological processes for their production. In this regard, increasingly higher requirements are imposed on metals and alloys as the main structural materials in terms of strength and plastic properties, formability, corrosion resistance and service life, as well as special and new functional characteristics. At the same time, there is a growing need to reduce labor costs, to save solutions to increasingly acute environmental problems. A widely spread and most productive way to obtain finished metal articles with high structural and mechanical properties are methods of cold heading out of rolled metal, which must have a certain quality - the required plasticity, uniform structure and process parameters along the full length, as well as soundness. In conditions of fierce competition in order to improve the quality of the upset metal articles, the enterprises are forced to find reserves at all the points of the process chain for transformation of the original rolled metal. The greatest effect is achieved by the excluding of energy-consuming and labor-intensive annealing in protective gas furnaces and control of surface defects by etching or mechanical operations. This paper is presenting an economical and environment-friendly technology for structural and mechanical maintenance of high quality of rolled stock for upsetting of metal articles. It is shown that drawing with rational degrees at each of the three stages of reduction after annealing with heating by high-frequency currents ensures the absence of mill scale and ellipticity. The minor oxide layer present was removed in the pickling baths within a few seconds. The rolled steel prepared by this technology has a highly dispersed equally spaced structure without a decarburized layer with increased plasticity, which enables to reduce the number of transitions in the process of upsetting of metal articles and to increase the tools service life. At the same time, there are no harmful emissions from annealing furnaces for rolled products and pickling solutions are less often refreshed.