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With implementation of new criteria for AH36, 16MnR and other steel categories, provisions on Sulphur content in steel has been stricter. Restricted by various factors, many small and medium-sized converter steelmaking plants (with a capacity of less than 50t) have no molten iron pretreatment process in front of the converter, which makes it difficult to control the sulphur content in converter production and fall short of the new standard.

1.    Ratio of magnesium in cored wire. Desulfurate the molten steel with magnesium powder has proved that magnesium is a good desulfurizer which the maximum desulfurization rate is up to 64.5%. With unit consumption of magnesium increased, desulfurization rate shows a downward trend because with the addition of magnesium powder increased, a large splash appeared in molten steel, magnesium yield reduced significantly.

2.    Desulfuration and deoxygenation. For processing molten steel with magnesium contained cored wire, controlling oxygen content in steel is the precondition of effective desulfuration.

3.    Wire feeding depth. In order to improve alloy utilization rate as much as possible and to protect the ladle bottom, wire feeding depth should be properly controlled.

4.    Wire feeding speed for cored wire of different specifications. It is very important to determine suitable parameters of wire feeding speed. When wire feeding speed is high, reaction of core wire fed into depth of the steel ladle to lead to molten steel splashing. When wire feeding speed is low, cored wire is likely to burn on the surface of the molten steel to affect metallurgical effect.

5.    Argon blowing and wire feeding. It is generally considered that bottom argon blowing and stirring whilst wire feeding can accelerate flow of molten steel to provide good dynamic conditions for desulfuration, but actually, results of multiple melts are contrary to the above viewpoint. In some experiment melts for bottom argon blowing whilst wire feeding, sharp fluctuations appeared, which impacted on production operation and desulfuration effect.

6.    Desulfurization rate and temperature drop. Production results show that, by using this process, content of sulfur w[S] can be reduced from approximately 0.035% prior to steel tapping with converter to less than 0.020%. Desulfurization rate is high and low. Melt is of low desulfurization because amount of slag is large in the process of steel tapping and a great deal with converter final slag was brought in that leads to high content of steel ladle top slag w (FeO) and motel steel w[O] to impact on desulfuration effect.

7.    Social benefit and application prospect. Analyzing from desulfurization thermodynamics, pre-desulfuration of molten iron in front of furnace is more economic and feasible than that of molten steel, but after molten iron wire feeding desulfuration, slagging-off must be done, otherwise, serious resulfurization will appear under high oxygenation atmosphere. Undoubtedly, increasing slagging-off and corresponding facilities is a burden for small and medium-sized converter plants and it is also not in line with the national policy orientation of limiting the development of small and medium-sized converter in the long run. 

• [Editor:張德眾]