| With the advancement of global industrialization,the market demands for the performance and quality of steel materials continue to increase.As one of the critical important reasons affecting the quality and performance of steel,inclusions in steel restrict the application and life of steel.As a common harmful element in steel,sulfur easily combines with sulfide forming elements to form sulfides,especially MnS,which adversely affect many steel types.Therefore,an in-depth study of effective means and schemes for controlling the precipitation of MnS has important significance and value for industrial production.This paper was based on the principle of not introducing new inclusions,making inclusions harmless,and combining the precipitation of inclusions,thereby reducing production costs.It was proposed to use the deoxidation product?produced under the Al-Si deoxidation system?as the nucleation point of MnS to precipitate the composite of MnS and deoxidation products.Controlling the form and quantity of sulfides,and obtaining a new method for improving the properties of steel grades such as free-cutting steel and non-oriented silicon steel.The composite precipitation rule of MnS and SiO2-Al2O3 oxides was studied by designing a smelting test of the compound of sulfide and oxide.From the perspective of lattice mismatch and nucleation work,the influence mechanism of composite oxide composition on heterogeneous nucleation of MnS was analyzed,and the oxide type which is easy to composite sulfide was obtained.The specific scheme for controlling the formation of target oxides was proposed.The main research contents and conclusions are as follows:?1?Scanning electron microscopy and built-in spectrometer were used to detect the oxygen-sulfur composite inclusions in the smelted samples,and the precipitation ratio and precipitation morphology of MnS on the composite oxide were observed.The results showed that MnS could be partially precipitated on SiO2-Al2O3 or encapsulated with SiO2-Al2O3,and the MnS morphology of composite precipitation was mainly divided into two types:patch and shell.The precipitation ratio of MnS on SiO2-Al2O3oxide decreased with the increase of Al2O3 content.When the content of Al2O3 in composite oxide ranged from 1 wt.%to 10 wt.%,the composite precipitation ratio of MnS reached the maximum.?2?The ability of different SiO2/Al2O3 composite oxides to trigger MnS heterogeneous nucleation was analyzed by lattice mismatch theory.The calculation results showed that the SiO2-Al2O3 composite oxide can be used as the nucleation point of MnS.With the increase of Al2O3 content in the composite oxide,the mismatch between oxide and MnS increased.The mismatch of MnS and SiO2-Al2O3?Al2O3:140wt.%?oxides ranged from 1.71%to 3.44%,and the lattice mismatch with Al2O3?54SiO2oxide?Al2O3 content in the range of 110 wt.%?is the lowest,only 1.71%?3?Based on the Nishizawa interface energy model and the principle of energy and establishment of wetting angle model,the interface energy between MnS and each oxide was calculated,and then the corresponding nucleation work was calculated by classical heterogeneous nucleation theory.The results showed that the nucleation work of MnS on Al2O3 was 5.6×10-20 J·mol-3,and the nucleation work on SiO2 was 5.47×10-21 J·mol-3.As the content of Al2O3 in the composite oxide increased,the heterogeneous nucleation work of the MnS nucleation increased continuously.The nucleation work required for precipitation on SiO2-Al2O3?Al2O3:140 wt.%?oxide ranged from 2.6×10-21 J·mol-33 to 4.8×10-20 J·mol-3.SiO2-Al2O3?Al2O3:110 wt.%?had the lowest nucleation work,which was 2.6×10-21 J·mol-3.?4?The comprehensive analysis was applied between mismatch and nucleation work.The result showed that SiO2-Al2O3?Al2O3:140 wt.%?oxide was the most easily become the heterogeneous nucleation point of MnS,which created conditions for the composite precipitation of MnS.?5?The effects of deoxidation mode on the composition of composite SiO2-Al2O3inclusions were analyzed by thermodynamics.The results showed that when Si-Al-Fe alloy was used for deoxidation,the[Al]and[Si]of steel should be consistent with a certain proportion to form SiO2-Al2O3?Al2O3:140 wt.%?.For high-aluminum steel,a step-by-step deoxidation method of“Si/Al”was required.The added aluminum element can continue to deoxidize,and there was a possibility of forming an Si-Al-O composite inclusion. |
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