Production of high-quality wire rod

Abstract

Currently, world wire-rod output exceeds 50 million t/yr, which is ~10% of the total rolled-metal output. To produce more competitive wire rod and hence increase sales, manufacturers need to better satisfy the requirements on the mechanical properties and structure of the steel, the dimensional precision, the bale size, and other characteristics. In the 1970s, the finishing groups of wire mills began to be replaced with finishing cell modules and two-stage cooling lines. In the next 20 years, the rolling rate of wire rod increased from 35 to 120 m/s, the bale mass reached 2.0‐2.5 t, and the dimensional accuracy of the wire rod increased from ± 0.5 mm to ± 0.10‐ 0.15 mm. Besides the structure of the wire rod, the mechanical properties and their uniform distribution over the bale length improved. The range of final products expanded [1‐3]. The mass-production of wire rod of 5.5-mm diameter was organized, without loss of productivity of the mills. There was an increase in the output of wire rod made from high-alloy and special steel and alloys and from continuous-cast billet. Reequipment of wire mills consumed considerable capital expenditure, especially in radical reconstruction. However, the investment was recouped in full, thanks to the improved quality and broader range of the wire rod. As a rule, after 10‐15 years of operation, mills are partially modernized, with the installation of up-todate equipment. Reequipment began in the Soviet Union in 1979, when a new 150 mill wire mill was introduced at Beloretsk Metallurgical Works (BMW). The 250-2 mill at Cherepovets Metallurgical Works was them reconstructed; mini mills were built in Moldavia and Belorussia with modern 320/150 small-rod and wire mills; and 150 wire mills went into operation at Makeevsk Metallurgical Plant (MMP), as well as 150 and 250/150 mills at Krivorozhstal works. In collaboration with plant specialists, researchers at the Institute of Ferrous Metallurgy (IFM) improved the design technology for a series of wire mills. As a result, high-quality wire rod went into production, including rod made from different grades of steel. For example, the rolling rate was increased at the BMW 150 mill, and metal consumption was reduced, with improvement in overall performance. In addition, rolling from lowertemperature billet reduced the metal losses on account of scale and also the gas consumption [4]. The water-cooling system for the wire rod was redesigned, and two-stage cooling was introduced, with improvement in the structure and properties of carbonand alloy-steel wire rod. This permitted simplification of the subsequent treatment and reduced metalware production costs [4‐6]. After a number of years, the BMW 150 mill and the 320/150 mill at Belorussian Metallurgical Plant (BMP) were reconstructed. At BMW, high-speed units with refined gear ratios from the electric drive to the rollers were introduced. The line for cooling wire rod in coils was reconstructed on the basis of research data from IFM, the All-Russian Scientific-Research Institute of Metallurgical Technology (ASIMT), and BMW; cooling by high-speed air fluxes was introduced. At BMP, the small-bar and wire mill was divided into a 320 small-bar mill and a 150 wire mill, with integration of the primary and secondary equipment [2]. The reconstruction costs for the BMP 320/150 mill (with the participation of foreign firms) were recouped within 2‐3 years of operation. Thanks to improvement in wire rod quality and performance, the manufacturing technology for metal cord was improved, and cord exports increased. Where necessary, high-speed air fluxes were used in cooling coils of high-carbon wire rod; this expanded the range of both 150 mills and improved the metal structure. The wire-rod output for the production of high-strength metal cord increased; the quality of cable and high-carbon wire rod for the manufacture of high-strength reinforcing wire was improved, thereby eliminating the need for one patenting operation in metalware production. The production of high-quality wire rod for cold bulk stamping increased; the structure and mechanical properties of the metal became more uniform over the length of the bales. At IFM, a mathematical model of continuous rolling in the finishing modules with a common cell drive has been developed. It may be used to determine and regulate the longitudinal stress in the steel between the cells, in the baseline (design) mode, as well as the rolling