Characteristics analysis of inclusion of 60Si2Mn-Cr spring steel via experiments and thermodynamic calculations

摘要

A plant trial of the production of 60Si2Mn-Cr spring steel using silicon-manganese combined with aluminium to deoxidise was performed, and the characteristics of inclusions during ladle furnace refining, calcium treatment and in billets were investigated by scanning electron microscope-energy dispersive spectroscopy and thermodynamic calculations. The formation mechanisms of oxide and CaS inclusions are discussed. The experimental observation and thermodynamic analysis showed that calcium treatment cannot entirely modify large-size MgO center dot Al2O3 spinel inclusions into homogeneous CaO-MgO-Al2O3 inclusions, but formed a liquid xCaO center dot yAl(2)O(3) layer on its surface. When the Al content was 0.05 mass%, [Mg], [Ca] and [O] in molten steel could be controlled at 2.7 similar to 5 ppm, 2.5 similar to 8 ppm and 4.1 similar to 5.2 ppm, respectively, to achieve inclusions in the low melting point region. A large amount of CaS was generated in the present process due to a higher sulphur concentration in the molten steel and an excessive amount of Ca-Si wire. To avoid/reduce its formation, the sulphur concentration should be controlled to below 70 ppm.