Why is the Chemical Composition of the Charge Important in Electric Arc Furnace Smelting?

Why is the Chemical Composition of the Charge Important in Electric Arc Furnace Smelting?

Because the charge contains various alloying elements, we must also have specific requirements for each element.

Carbon: When determining the carbon content, three factors are generally considered: carbon loss during the melting phase, decarburization during the oxidation phase, and recarburization of the molten steel by alloy and slag additions during the reduction phase.

In order to utilize decarburization boiling to remove gases and non-metallic inclusions from the molten steel, the carbon content should meet these requirements.

Silicon: Generally, silicon is present in the charge. It is generally not artificially added during oxidation smelting. In the oxidation process, if the silicon content of the molten steel exceeds 0.3%, it will slow boiling time, so the addition of silicon scrap should be limited. In the return process, adding some high-silicon scrap to the charge can increase the yield of other alloying elements, but the silicon content should not exceed 1.0%.

Manganese: For steels smelted using the oxidation process, if the manganese specification is relatively wide, its addition is generally not considered during charge mixing. For materials with narrow manganese specifications or low manganese content, such as carbon tool steel, some alloy tool steels, and chromium bearing steel, careful consideration should be taken when batching the materials. The manganese content of the clear steel should be below 0.2%. For some alloy structural steels used in critical applications, the manganese content of the clear steel should be at least 0.2% to facilitate the removal of non-metallic inclusions, but it should not be too high to prevent the boiling of the melt pool.

When using the return method, the manganese content should not exceed the upper limit of the steel grade specification.

Chromium: When using the oxidation method, the chromium content in the charge should be as low as possible, even for chromium structural steels, as some chromium will oxidize during the oxidation process and enter the slag. Furthermore, chromium oxides thicken the slag, hindering the dephosphorization reaction and prolonging the smelting time.

When smelting high-chromium steel, the chromium content should be within the lower-middle limit for the charging method and below the lower limit for the return oxygen blowing method.

For elements such as nickel, molybdenum, and tungsten, if the steel grade requires higher content, the content should be within the lower-middle limit of the specification and charged with the charge. Nickel in tool steel and molybdenum in spring steel are particularly detrimental to steel properties and should be strictly controlled to the lowest possible level. Nickel content in the charge for nickel-free steels should not exceed 0.20%.

In addition, the potential recovery of the steel from the previous smelting process should be considered when assigning the charge.

The lower the sulfur and phosphorus content in the charge, the better, but the rarity of such charge materials (scrap, pig iron, and soft iron) should be considered. Generally speaking, the sulfur and phosphorus levels in the oxidation process of electric arc furnace can be adjusted based on the source material; the lower the better. In the return process, the phosphorus content must be strictly controlled to below 0.005% of the final product's phosphorus content.