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Improving the production quality of steel

Siemens improves the production quality of steel manufacturers in India. These companies process scrap iron and sponge iron in induction furnaces.

Partly due to fluctuations in the quality of the source materials, this steel contains high levels of phosphorus. Because this makes the steel brittle, the Bureau of Indian Standards (BIS) has established new specifications for the maximum phosphorus content that is allowed in structural steel.

The usual methods for removing phosphorus from steel cannot be used with induction furnaces. Siemens has developed a method for separating the phosphorus from the steel in a second processing stage.

The first facility using this method will be delivered to the Indian steel manufacturer Vandana Global and is scheduled to go into operation at the beginning of 2014.

Normally, lime is introduced into the steel furnace in order to bind with the phosphorus that is contained in the pig iron. This material is then removed together with the slag.

However, this method doesn't work in induction furnaces. These furnaces consist of a crucible surrounded by a coil. This coil induces an electric current in the iron and heats it up. In this type of crucible, it isn't possible to produce enough additional slag to remove the phosphorus from the steel.

What's more, the processing of sponge iron in particular generates a large amount of slag. Sponge iron is obtained from iron ore using direct reduction – in other words, without a smelting process.

In order to enable induction furnace operators to meet the new BIS specifications, Siemens moved the removal of phosphorus to the second step in the process. There the liquid steel is poured into ladles and treated using metallurgical processes to produce alloys.

Lime can be blown in to bind with the phosphorus while the liquid steel is in these ladles, and it can then be removed with the slag.

Siemens developed the entire dephosphorisation stand, including the ladle car and assorted blowing lance units for introducing the lime. The system for Vandana is designed to handle up to 15 tons of liquid steel.

Each induction furnace operator in India currently manufactures several hundred thousand tons of steel per year. Altogether, these companies account for one fifth of the country's total steel production.

By using this new process, these producers will be able to conform to the new quality specifications and will have access to the markets for higher-grade steel.

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