Effect of High‐Frequency Pulsed Direct‐Current Power Supply on the Cleanliness of 9Cr18Mo Stainless Steel During Electroslag Remelting

Pulse frequency, duty cycle, and slag composition were compared during laboratory electroslag remelting of 9Cr18Mo high‐carbon martensitic stainless steel using high‐frequency pulsed direct current. Gas analysis, automated inclusion analysis, and scanning electron microscopy with energy‐dispersive X‐ray spectroscopy characterized steel cleanliness. With 60% CaF ₂ –20% Al ₂ O ₃ –20% CaO slag (mass percentages), oxygen content and inclusion count varied nonmonotonically with frequency and duty cycle. At 90% duty cycle, 1000 Hz gave the lowest values among the tested pulsed frequencies. At 2000 Hz, increasing duty cycle from 90% to 95% reduced final total oxygen from 53.11 to 19.67 parts per million (ppm) and inclusion count from 11 168 to 3392. Both remained above the same‐slag 50 Hz alternating‐current reference (18.84 ppm; 2490 inclusions). At 2000 Hz and 90% duty cycle, the maximum projected inclusion area was smaller than under alternating current (62.23 vs. 205.76 μm ² ), despite higher oxygen and count. At this pulsed setting, replacing 15 wt% Al ₂ O ₃ with CaO at fixed 70 wt% CaF ₂ was associated with lower oxygen (51.31 to 46.02 ppm). These contrasting responses require joint evaluation of oxygen content, inclusion abundance, and particle size when selecting pulse and slag conditions.