Investigation of heredity of wire rod structure, manufactured by the rolling with shear technology, at following cold drawing
Quality of wire on the hardware plants is judged by the indexes of prepared products quality and by the indexes of expenditures on its processing. The high abruptness of wire is a principal reason of equipment outage at dragging. The low ductility of wire is the one of most widespread reasons of abruptness. It requires optimization of production technology with the purpose of the wire upgrading and conducting of research works. The size of maximal deformation is determining in the process of dragging. Maximal deformation is a size to which a metal becomes deformed without heat treatment. This size depends on the steel grade, method of material preparation to dragging, number of passage-ways and other factors. Ductility relies on the character of distribution structure. If dislocations in a structure are distributed more evenly and less fastened, ductility is higher.
The application of special methods of deformation allows to get materials with the row of structural features ?6-7?. They provide the high supply of ductility. The question is about rolling with a displacement (PS - technology). She is developed with the use of modern concepts of intensive plastic deformation with a displacement. Such technology allows to produce wire rod with small grain size (a 9-12 number); with the low compactness of defects and absence of anisotropy of characteristics in the transversal and longitudinal section of wire rod. It is provided by the receipt of equiaxial grains as a result of rolling. These characteristics lead to the considerable resource of ductility due to the differences of the metal internal structure which produced on PS technology, from a metal which is got on traditional technology on ISC “Mittal Steel Kryvy Rig”. This resource of wire rod ductility provides technological during production of small diameters of wire.
The study of structure and properties transformations of 08G2S steel wire at cold drawing in conditions of ISC “Mittal Steel Kryvy Rig” was the purpose of the work. The initial state of material was got after rolling on technology of rolling with a displacement.
9 tests of 9,0 mm circle of 08G2S steel were explored. They were selected from the beginning, middle and ends of two bundles. Bundles were rolled with a different temperature of winding. Temperature of bundle ¹1 winding makes 870 °Ñ, temperature of bundle ¹2 winding makes 920 °Ñ. Transversal macrosections and microsections from tests were prepared for research
Macrostructure of all tests metal is compact, the defects of contraction cavity are not present. It is adjusting as a result of investigations. Microanalysis showed that a structure at the surface of metal consisted of ferrite, perlite and bainite. Correlation of perlite + bainite / ferrite is estimated as 35/75% in the first bundle. This correlation makes 45/55% in the second bundle. The grain size on the section is estimated at ¹ 9 – 10. It is identical in all tests. Microstructure is characterized by the identical form and size of grain in the transversal and longitudinal section.
This situation is not standard. Anisotropy of grains is formed after the ordinary rolling along the axle of deformation. A grain must be extruded in the longitudinal section. PS is contributing in forming of equiaxial not anisotropy structure from action displacement components.
Obtained structure is characterized by the near values of quantitative descriptions of grain in transversal and longitudinal directions. The values of microhardness are considerable in different sections. It is explained forming substructure. Microhardness grows on all section of pieces with the increase of degree of deformation. Non-monotone change of microhardness is observed at some degrees of deformation. It indicates to development of recycled material processes in the process of the cold dragging. It is confirmed by data on determination of pieces closeness. A closeness changes also non-monotone depending on the extent of deformation.
Wire rod to be produced on the PS technology possesses greater ductility during further dragging. Such wire rod allowed to drag a wire to the diameter 2,6 mm without the intermediate annealing.
The conducted researches confirm that technology of the PS rolling takes large potential advantages thanks to the effective management by a structure and mechanical characteristics of materials. PS behaves to the charts of the combined plastic deformation, which allow in potential to pass to a new level of mechanical characteristics.