Abstract: The cleanliness problem of SCX400 wheel steel plates was checked by SEM and the results showed that the dot-line macro-inclusions inside the steel plates shaped from the big CaO-MgO-Al₂O₃ inclusions during rolling process, and those inclusions oriented form refining and casting process, not floating up into slag, consequently kept inside of slabs. Base on this study, actions were implemented to change inclusion into solid classes before RH process as Al₂O₃, MgO-Al₂O₃ or high melting point CaO-MgO-Al₂O₃ who have better tendency to float upon, and then global Al₂O₃-MgO-CaS inclusions, with high melting point. After that, inclusions were tested as Al₂O₃ or Al₂O₃-CaO cores coated by CaS inside the plate. The single-test qualified rate increased from previous 90 % to current 95.4 %, whilst cracking defect rate in production decreased to 0.5 %-1.0 % and the fatigue lifetime of wheels stabilized beyound million times.

Key words: wheel steel, calcium treatment, nonmetallic inclusion, B type inclusion, fatigue crack