Effect of Erbium on Inclusions and Mechanical Properties of a High Sulfur Steel
摘要
In order to enhance the performance of the high sulfur steel, the rare-earth element erbium (Er) was introduced during smelting, and the effects of varying total erbium (T.Er) contents on the characteristics of inclusions, the microstructure, and the mechanical performance were systematically investigated. As the T.Er content increased from 0 to 270 ppm, inclusions evolved sequentially from MnS→MnS-Er2O2S→Er2O2S-Er2S3→Er2S3. Long strip-like MnS inclusions were progressively modified into uniformly distributed spherical Er-bearing inclusions. After Er addition, the formation of Er2O2S and Er2S3 consumed sulfur, thereby suppressing MnS precipitation. These Er-bearing inclusions exhibited spherical morphologies and higher hardness than MnS, which enhanced the deformation resistance of inclusions. With the rise in T.Er content, the proportion of inclusions exhibiting an aspect ratio below 3 rose from 34.47 to 99.08 pct, while the number density decreased from 210.8 to 53.1 #/mm2. The steel microstructure consisted mainly of lamellar pearlite and network ferrite. Due to the combined effects of reduced carbon content, austenite grain refinement and the presence of Er-bearing inclusions, the ferrite fraction reached a maximum of 37.04 pct at 140 ppm T.Er. Correspondingly, the hardness of the high sulfur steel rose from 14.2 HRC (0 ppm) to 22.3 HRC (270 ppm). Mechanical testing showed that yield strength and impact energy varied with T.Er content. At 0, 52, 94, 140, and 270 ppm, yield strengths were 494.8, 488.6, 465.5, 498.0, and 520.6 MPa, while impact energies were 34.35, 60.55, 60.25, 67.45, and 49.45 J, respectively. Overall, Er addition effectively modified MnS inclusions, refined austenite grain, and improved both strength and toughness, demonstrating its potential to enhance the performance of sulfur-containing steels.