Research On New Smelting Process And Properties Optimization Of High Carbon Hard Wire Steel

High carbon hard wire which belongs to superior quality carbon structural steel is also called high carbon wire rod. SWRH82B is a representative kind of high carbon hard wire, it is used in the production of high-strength (low relaxation) prestressed wire and steel strand which with high technology content and high value-added. Because SWRH82B requires good cooperation with strength and toughness, it is very difficult to be produced. The quality of domestic 82B is not stable, it appear brittle fracture easily when drawing it. For this reason, users use imported raw materials more. In order to replace hot-rolled import hard wire, it is urgent thing to improve and stabilize the properties of hard wire. So it makes important significance to our country's sustainable development of economy and society.This paper's main contents are industrial test of low aluminum deoxidizing, micro alloying test of Cr and V, and making curve of CCT. It starts with improving smelting process, adjusting the chemical composition of 82B steel and controlled rolling and cooling.The factors which affecting the product's quality such as steelmaking, rolling, cooling, aging, drawing, the chemical composition of rod and alloying element are considered. The problems of the drawing brittle fracture of SWRH82B are analyzed by means of metallographic microscope, SEM, EDS mechanical properties test and so on. And its properties are optimized ultimately. The conclusions are as follows: The forms of drawing brittle fracture of SWRH82B which be produced by the company of group of Baotou iron and steel are penpoint and splitting shape. The fracture apperance is cleavage or quasi cleavage, and there is no obvious neckingdown. The analysis showed that, most penpoint fracture is caused by the large brittle inclusion Al₂O₃ in the center of base materials, and the minority is caused by central network cementite and central hole; and splitting fracture is mainly caused by central martensite combined with surface defect.Deoxidizing methods with low aluminum addition process (SiCaBaMg) can makes the aluminum inclusion content between 0.004% and 0.006%, the average content of Al₂O₃ is 31.12×10^-4%. There are three kinds of oxide inclusion: Al₂O₃-MgO-SiO₂-CaO, Al₂O₃-MgO and sulfide compound inclusion. The two formers like micro round sphere, the latter likes the fisheye. As a result, the incidence of fracture is reduced greatly, and the quality of the wire rod be improved.Adding Cr and V in 82B steel can improve its strength, make its C curve to shift right, and improve its hardenability. When the content of Cr between 0.32% and 0.36%, Mn between 0.75% and 0.90% in the large gauge 82B(Cr) steel, the casting blank that the contents of Cr and Mn are higher are easy to happen central segregation, thus induce the central martensite. When the content of Cr between 0.24% and 0.28%, Mn between 0.73% and 0.82% in that steel, the central segregation be reduced greatly. Therefore, it can avoid the central martensite.When the measure that combines with low aluminum deoxidizing, micro alloying and controlled rolling and cooling is taken, the strength of the hard wire rod can be improved and its plasticity can be maintained very well. As a result, it has high strength and toughness. The mechanical properties and drawing performances of the wire rod are improved greatly.