Characteristics and Evolution of Inclusions in Hot Work Die Steel Produced by Electric Arc Furnace‐Ladle Furnace‐Vacuum Degassing‐Protective Electroslag Remelting

The characteristics and evolution mechanism of inclusions in the industrial high‐Mo hot work die steel produced by electric arc furnace‐ladle furnace‐vacuum degassing‐protective electroslag remelting (EAF‐LF‐VD‐PESR) are investigated through scanning electron microscope and energy‐dispersive spectrometer. The result shows that the constituent of the oxide inclusion changes with the contents of calcium and aluminum in molten steel during production. The MgO⋅Al 2 O 3 before LF is gradually transformed into high CaO‐containing MgO‐CaO‐Al 2 O 3 with the low‐melting‐temperature after vacuum treatment, and then into low CaO‐containing and low MgO‐containing MgO‐CaO‐Al 2 O 3 after casting of the electrode, and finally into Al 2 O 3 as the main oxide after PESR. It is found that Ca/Al ratio in steel has a positive influence on the CaO content in MgO‐CaO‐Al 2 O 3 , affecting the melting temperature of the oxide inclusion. There are the smallest average size of the inclusion and the lowest oxygen after vacuum treatment, for the flotation of the low‐melting‐temperature inclusions and strong ability to deoxidize by carbon in steel. Unexpectedly, the mean size of the inclusion increases to 4.3 μm after PESR. The investigation has revealed that the inclusion size is greatly affected by the oxygen content. Thermodynamic analysis is applied to expound the evolution of the oxide inclusion during production and the increase in oxygen after PESR.