Development of Rolled Steel Products from 3 t Ingot of Grade 8620 for Railway Axle Box Bearings

Abstract

Based on the current quality situation of ESR bearing steel for passenger railway and wagons in China， the grade 8620 steel bars with diameters between 60 mm and 120 mm are produced with the process as follows：70 t EAF（HotMetal+Scrap）→LF→RH→3 t steel ingot→soaking pit →1350+750/650 rolling mill， whose chemical composition are （%）：0. 18-0. 22 C，0. 15-0. 30 Si，0. 75-0. 95 Mn，0. 45-0. 65 Cr，0. 45-0. 70 Ni，0. 15-0. 25 Mo，≤0. 020 P，≤0. 015 S， 0. 020-0. 050 Al. By taking technological measures such as steel and slag retention operation，slag formation and alloy ad⁃ dition during tapping， vacuum holding time ≥25 min and soft argon blowing， superheat control， full process Argon protec⁃ tion casting and automatic pouring as well as controlling cooling after rolling etc， to keep 8620 steel bars conform to all technical specification requirements， especially， macro-inclusions of finished bars less than 10 mm/dm³， grain size class 8-8. 5， and the density being 7. 854 g/cm³.

Keywords

• 3 t steel ingot； grade 8620 steel； automatic ingot casting， macro-inclusion； density