Effect of holding time on inclusions in U75V heavy rail steel

doi:10.13251/j.issn.0254-6051.2022.06.006

Abstract

Abstract: U75V heavy rail steel was smelted in a vacuum induction furnace, then the steel specimens were heated to 1100 ℃ in a box-type resistance furnace and held for 30, 60, and 90 min respectively, and the inclusions were analyzed by scanning electron microscope. The results show that in the steel without heat treatment there are three main types of inclusions MnS, Al₂O₃ and MnS-Al₂O₃. The elongated MnS inclusions tend to split with the prolongation of holding time. The average circularity of the MnS inclusions is 1.86 when the holding time is 90 min, and the circularity decreases by 1.52 compared with the specimen without heat treatment. When held for 30 and 60 min, the morphology and size of the Al₂O₃ inclusions change little, but the quantity decreases. When held for 90 min, the sharp edges and corners of some Al₂O₃ inclusions are obtused, and the circularity slightly decreases. After heated at 1100 ℃, the number of composite inclusions increases. With the extension of holding time, the distributions of MnS and Al₂O₃ in the MnS-Al₂O₃ inclusions change, and the Al₂O₃ in the outer layer tends to move inward. The Al₂O₃ is enriched inside the inclusions, and the content of Al₂O₃ in the outer coating is extremely low. The MnS-Al₂O₃ inclusions gradually form composite inclusions with Al₂O₃ as the core and MnS as outer coating, thereby reducing the damage to the steel matrix.

Key words: U75V heavy rail steel, holding time, inclusions, MnS, Al₂O₃

CLC Number:

TG161

Fan Zhiming, Yang Jichun, Zhang Ying, Li Xiangchuan, Zhu Jun. Effect of holding time on inclusions in U75V heavy rail steel[J]. Heat Treatment of Metals, 2022, 47(6): 33-38.

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