Abstract：The specification and quality of rack steel used for offshore drilling platforms have an important impact on the scope and life of offshore platforms. In order to inhibit the oxidative burn loss of B element in steel in the process of electroslag remelting (ESR), and ensure the prograde of the remelting process and low cost, the basic slag with qualified melting temperature was designed by combining the melting point of rack steel and the CaF2-CaO-Al2O3 phase diagram. The effects of MgO and B2O3 on the melting point, viscosity, and electrical conductivity of basic slag were studied using FactSage 8.2 software and relevant empirical formulas. The relationship between the content of MgO and B2O3 and the dissolved oxygen and the equilibrium B element content was analyzed by the mass action concentrations based on the coexistence theory of slag structure. The suitable electroslag remelting slag for remelting B-containing rack steel was obtained, and the viscosity of the slag was determined by high temperature test. The results show that the melting point range of suitable slag for remelting rack steel is 1 309-1 409 ℃, and MgO can reduce the electrical conductivity of slag and improve the viscosity, but MgO has almost no effect on the oxygen potential and activity of B2O3. With the increase of B2O3 content in the slag, both the turning point temperature and the precipitation amount of the high melting point phase decreases. The slag used for remelting B-containing rack steel with the best performance is 57.08%CaF2-20.83%CaO-22.09%Al2O3-4%MgO-5%B2O3.
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2023, Vol. 33 
