Study On Evolution Of Non-metallic Inclusions In Production Of 92Si Steel For Bridge Cable

With the rapid development of bridge construction in China,high carbon steel wire rod products such as steel for bridge cable are developing towards the direction of high strength and continuous improvement of fatigue performance.At present,the high carbon steel wire rod produced in our country has many serious problems,such as unstable mechanical properties and the breakage of the wire during drawing.The brittle inclusions and large-size inclusions in steel are one of the main reasons for the breakage of the wire during drawing.Even if the breakage of the wires is not caused by brittle and large-size inclusions during drawing process,the remaining in steel products will eventually do harm to the performance of products.In this paper,the industrial trails of 92 Si steel for bridge cable is carried out and samples are systematically sampled at the whole process of converter tapping,refining(LF+VD),tundish,continuous casting slab and hot rolling wire rod,and the composition,number,morphology and size of inclusions in 92Si steel for bridge cable produced by BOF-LF-VD-CC process are analyzed by means of manual analysis(SEM-EDS)and automatic statistics(ASPEX Explorer)are studied systematically.During the process of deoxidization and alloying in converter tapping,the influence of[Al]content in molten steel on the formation of deoxidizing products and the distribution of inclusions in actual samples were studied.It is found that the deoxidation products are in the low melting point region of the ternary phase diagram of MnO-SiO2-Al2O3 system when the mass fraction of Al2O3 in the inclusions of MnO-SiO2-Al2O3 system is in the range of 0-25%.During the LF refining process,combined with the component activity diagram of CaOSiO2-Al2O3 ternary system,the composition of refining slag system was designed in the low melting point region of the inclusion phase diagram of CaO-SiO2-Al2O3 ternary system.After the reasonable adjustment of refining slag system,the number density of large-size inclusions of 5-10 ?m decreased,at the same time,the adjustment of refining slag system realized the movement of inclusion composition distribution in the inclusion phase diagram of CaO-SiO2Al2O3 ternary system to the low melting point area.During the process of Ca treatment in VD furnace,in order to realize the modification of MgO·Al2O3 system hard inclusions with high melting point,the corresponding relationship between different initial[S]content in molten steel and the most appropriate Ca addition interval is calculated.At the same time,the unmodified MgO·Al2O3 system inclusions and CaO-Al2O3-MgO system inclusions in the samples after Ca treatment are statistically analyzed.When the content of T.Ca in the samples is in the range of 8-10 ppm,the effect of modification on MgO·AlO3 inclusion is the best.Finally,the deformation behavior of different types of inclusions in the process of fabrication is studied.It is found that the composite inclusions formed by Al2O3 hard core wrapped with MnS inclusions can achieve the cooperative deformation with steel matrix to a certain extent.However,TiN hard inclusions basically do not deform in the process of rolling,while MnS inclusions can achieve the cooperative deformation with steel matrix very well.The research on the deformation ability of different types of inclusions provides a new idea for the follow-up research on non-metallic inclusions in 92Si steel for bridge cable.