Deoxidation during electroslag remelting of S136 die steel was experimentally studied. The characteristics of inclusions in the electrode and ESR ingots were determined by image analyzer and SEM-EDS. The results show that the oxygen content can be reduced from 89 ppm in the electrode to the lowest (12 ppm) in the ingot only when protective Ar gas remelting in combination with specially designed slag deoxidation treatment were employed simultaneously. The proportion of the oxygen combined as oxide inclusions increases with decreasing the total oxygen content in ESR ingot. The original inclusions in the electrode are mainly large (Mn,Cr)S and the large inclusions in the form of Al 2 O 3 core surrounded by an outer sulfide layer, besides a few pure Al 2 O 3 inclusions. After ESR process, while only pure Al 2 O 3 inclusions with the size of about 1 mm were observed in ESR ingots. The large inclusions in the electrode were removed during ESR process. With higher oxygen content in the ingot, the contents of inclusions and large inclusions would be relatively higher. The results from industrial experiments have confirmed the availability of the present oxygen control technique. The mechanisms of oxygen behavior and control as well as inclusion evolution during ESR process were proposed based on experimental results along with thermodynamic analysis.

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Abstract:The properties of carbides, such as morphology, size, and type, in H13 hot work die steel were studied with optical microscopy, transmission electron microscopy, electron diffraction, and energy dispersive X-ray analysis; their size distribution and quantity after tempering, at different positions within the ingot, were analyzed using Image-Pro Plus software. Thermodynamic calculations were also performed for these carbides. The microstructures near the ingot surface were homogeneous and had slender martensite laths. Two kinds of carbide precipitates have been detected in H13: (1) MC and M 6 C, generally smaller than 200 nm; and (2) M 23 C 6 , usually larger than 200 nm. MC and M 6 C play the key role in precipitation hardening. These are the most frequent carbides precipitating at the halfway point from the center of the ingot, and the least frequent at the surface. From the center of the ingot to its surface, the size and volume fraction of the carbides decrease, and the toughness improves, while the contribution of the carbides to the yield strength increases.

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