Influence of RH degassing on cleanness and fatigue life of 60Si2MnA spring steel

¹ State Key Laboratory of Advanced Metallurgy, University of Science and Technology Beijing, Beijing 100083, P.R. China
e-mail: 13401162963@163.com
² Henan Jiyuan Iron and Steel Group Co., Ltd, Henan Jiyuan 459000, P.R. China

Received: 29 December 2015
Accepted: 23 September 2016

Abstract

Plant trials of Al killed 60Si2MnA spring steel were performed under two different processes (LF + calcium treatment, LF + RH + calcium treatment). The T.[O] (total oxygen) contents, inclusions during the two processes and the fatigue lifes of finished steels were compared. Results showed the non-liquid and liquid Al₂O₃-SiO₂-CaO-MgO inclusions in steel both decreased with the RH time, the removal ratio of inclusions reached 46% after 20 min treatment. The liquid inclusions decreased steadily throughout all the RH time, but the non-liquid inclusions quickly decreased at 10 min, then showed down due to the possibly bad interfacial parameters. The average size of inclusions increased firstly and then decreased due to the collision and coagulation of the abundant inclusions (1–5μm) in the first 10 min. As a result, RH degassing decreased the T.[O] content, as well as the number and size of inclusions in finished steel from 13 ppm, 5.2 per mm² and 3.5 μm to 6 ppm, 4.6 per mm² and 2.4 μm and encouraged the inclusions to transform from Al₂O₃-SiO₂-CaO-MgO to Al₂O₃-SiO₂-CaO-MgO-CaS completely, then reduced the formations of voids between inclusions and steel matrix. Finally, the fatigue life was raised obviously from 9.8 × 10⁴ cycles to 1.5 × 10⁷ cycles.