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 Al2 O3 -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 (1–5μ m) 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 μ m to 6 ppm, 4.6 per mm2 and 2.4 μ m and encouraged the inclusions to transform from Al2 O3 -SiO2 -CaO-MgO to Al2 O3 -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.
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