Carbon steel manufacturing

The manufacturing process of carbon steel can be divided into three main stages: primary steelmaking, secondary steelmaking and casting. Each stage is followed by a series of finishing techniques that have a direct impact on the characteristics of the final product.

First, let's look at the primary steelmaking stage. At this stage, steel can be made from 100% recycled materials or from a combination of recycled materials and raw steel. Raw steel is made from iron ore, coke (produced from coal) and lime in blast furnaces. Raw materials are added to the top of the furnace, which operates at 3000°F. As the iron ore melts and mixes with the burning coke, the carbon is released into the molten product. Impurities are absorbed by the lime into the surface slag, which can be skimmed from the molten steel. The product at this stage contains about 4% carbon, and there are still some impurities. The melted raw steel is transferred to an alkaline oxygen furnace (BOF) that already contains recycled scrap metal. Pure oxygen is blown through molten steel to oxidize excess carbon, creating a finished product with up to 1.5% carbon content.

The recovered scrap can be reprocessed without adding the original steel to the EAF. High-power arcs melt metals at temperatures up to 3000°F. As the scrap melts, more batches of scrap can be added to the furnace up to its capacity. Once a flat bath of molten steel is obtained, oxygen is blown through in the same way as BOF. In both cases, the molten steel is removed from the furnace to the ladle or steel tank for further processing while the surface slag containing impurities is removed.

Next comes the secondary steelmaking stage. The market demand for higher quality steel products and consistent performance has driven the development of secondary steelmaking processes. At this stage, the composition of the steel can be changed by adding or removing individual components or by controlling the temperature. For example, electric arc furnaces can be used to change the composition of steel. In addition, electromagnetic fields can be used to generate turbulence in the ladle to separate non-metallic inclusions that float to the surface and ensure a uniform mixture and composition of the steel.

In the secondary steelmaking stage, ladle furnaces can also be used for precise temperature control and measurement injection of alloy composition. The inert gas can be injected into the bottom of the steel tank, and as the gas heats up and rises through the molten steel, the stirring effect is achieved. In addition, various technologies can be used to remove hydrogen, oxygen and nitrogen while reducing the sulfur content of the product. These technologies include vacuum, inert gas injection, and temperature control.

Finally, the casting stage. Traditional casting methods involve lifting ladles with a crane in order to inject molten steel into a single mold mounted on a rail car. The ingot mold is slightly tapered to facilitate the removal of the ingot after solidification. The ingot is transferred to a soaking pit where they are reheated for hot rolling.

In addition, a casting machine can be used to continuously cast molten steel into a shape more suitable for downstream processing. The ladles are raised to an elevated platform where they discharge the molten steel into a tundish that feeds the casting machine. The molten steel is fed from the tundish into a water-cooled mold with a removable base plate. As the steel skin solidifies, the steel plate slowly descends, allowing more molten steel to enter the mold. The steel is formed as slab, slab or billet in a continuous casting machine. The cured product is pulled by rollers before the end of the machine is straightened and cut. This process can continue for days or weeks without interruption.