Research On Lead Patenting Process And Properties Of High Carbon Steel Wires

The quality of steel wires is closely related to wire rods, plastic deformation and heat treatment. Heat treatment is a key part in the production process of steel wires. Lead patenting has been widely used in steel wire products industry. However, the relationships of lead patenting process, microstructure and properties of steel wires have not been reported in detail. Metallographic microscope and scanning electron microscope were used to observe the microstructure of 70 high carbon steel wires. Microcomputer control electron universal testing machine, wire torsion testing machine and digital micro hardness tester were used to investigate mechanical properties of steel wires. The quality of wire rods produced by different manufacturers was compared. The changes of microstructure and properties influenced by drawing deformation were initially explored. The impacts of lead patenting on microstructure and properties of steel wires were mainly studied. The experimental results are as follows:The comparisons of rolling quality of wire rods produced by two manufacturers indicate that the size precision of two wire rods can satisfy the C-class precision standard requirements. However, the chemical compositions of two rods are different. The tensile strength of No.1 wire rod is higher, but its reduction of area is lower. Meanwhile, its discrete degrees of both tensile strength and reduction of area are larger, which are associated with its large range of chemical composition.The microstructure observation and mechanical property test in the drawing process of pearlitic steel wires show that the greater drawing deformation of steel wires, the finer their microstructure, the more obvious their fibrous morphology, and the higher their tensile strength.Researches on the relationships of microstructure, tensile strength and heating time of different diameter steel wires in the patenting process of heating transformation indicate that heat transformation process of steel wires in lead patenting is distributed into four stages. With the extension of heating time (0s-154s), steel wires go through strain aging and recovery, recrystallization and pearlite spheroidization, austenitic formation, austenitic composition homogenization and grain growth. When steel wires are heated to austenitize completely, their tensile strengths are maximum.Results of regression analysis exhibit that the heating time required to austenitize completely (Y) and the diameters of steel wires (X) have a linear relationship of Y=A+B*X (B>0). Based on the experimental studies, the heating time in practical production of steel wires was adjusted. It was found that the small diameter steel wire using shorter heating time and the large diameter steel wire using longer heating time would have the better properties.The effects of lead patenting temperature on the properties and microstructure of different diameter steel wires were studied during the patenting process of cooling transformation. The results demonstrate that the cooling transformation regularity of steel wires in lead patenting conforms to the isothermal transformation curve C:as the isothermal temperature drops, austenite transforms into pearlite, sorbite, austenite and upper bainite in sequence. Sorbite formed at the specific lead patenting temperature has excellent comprehensive mechanical properties, which is benefit for subsequent steel wires drawing. When lead patenting temperature range is 503℃-518℃, Φ2.70mm-Φ5.50mm steel wires have more sorbite and smaller interlamellar spacing, which have the better cooperation of tensile strength and plasticity.