Influence of billet enthalpy on the temperature field of the product in high-speed rolling

45 A typical setup in high-speed (up to 100 m/s) wire mills consists of a continuous roughing and intermediate group of cells, a finishing module, and two-stage cooling lines for the wire rod. The 150 mill at the Belorussian Metallurgical Plant is of this type. Continuous-cast billet (cross section 125 × 125 mm; length 10‐12 m) is heated in a stepping-floor furnace, with simultaneous turning in the heating zone. The equipment of the 150 mill includes a five-cell continuous roughing group of horizontal cells, in which the rolled metal is turned after cells 1, 3, and 5. These are very rigid cells of modern design, with short-barrel rollers. The first and second intermediate groups include six and four cantilever cells, respectively. The disk rollers of cells 7‐10 are made of special steel; those of cells 11‐16 are made of hard alloys. Beyond cell 16, there are water-cooling sections. Between cell 16 and the tencell finishing module, the direction of motion of the rolled product turns through 180 ° . The configuration, characteristics, and structure of the equipment in the mill may be found, together with the production technology for carbon-steel and alloy-steel wire rod, in [1]. The maximum rolling speed is 100 m/s. In modern wire and rod‐wire mills, the production of wire rod and circular billet generally involves both plastic and thermal treatment of the metal, i.e., the influence of structural defects of the heated and deformed steel on its structure properties during cooling and heat treatment is put to use [2]. Modification of the structure and properties by combined heat treatment and deformation is widely employed [3‐6]. The potential of particular methods depends on the chemical composition of the steel and its required properties, the configuration and characteristics of the equipment, the size range of the products, the strain, and so on. The effectiveness of heat treatment and deformation in changing the structure and properties of wire rod will depend on the possibility of regulating the temperature over the length of the mill and the final temperature of the rolled steel. Other important factors are the parameters of postdeformational treatment and the range of possible cooling rates. According to the global classification, three types of treatment are employed at modern rolling mills: hightemperature deformational treatment; normalizing rolling; and thermomechanical treatment. In all cases, after the rolled steel leaves the last cell, heat treatment continues, with certain stipulations on the temperature conditions and the cooling rate before and during γ α transformation. In high-temperature deformation, rolling ends at a temperature that is at least 150 ° C higher than the initial temperature of structural transformation (point Ar 3 ), depending on the quantity of carbon and alloying elements in the steel. In high-temperature deformation, the load on the technological equipment is reduced and its performance is improved. However, fairly large austenite grains are formed in the metal. The dominant mechanism is dynamic recrystallization in the course of rolling, at high temperature and critical strain. Therefore, at the end of deformation, all the grains may be regarded as newly formed. Repeated deformation and recrystallization reduces the austenite grain size; on entering the finishing module, it is 20‐25 µ m. With further cooling at a specified rate in the second stage of the Stelmor process, the required structural transformation occurs.