What’s The Difference Between Sponge Iron And Pig Iron?

There are a number of products that are made from the same material but have different features or purposes. When you see sponge iron and pig iron, then it might be difficult to understand their differences without getting any help from experts. So this blog is going to explain the difference between sponge iron and pig iron in a very simple way. Let’s find out.

Sponge Iron, also referred to as Direct Reduced Iron (DRI), is produced from the direct reduction of iron ore (in the form of lumps, pellets, or fines) into iron by a reducing gas or elemental carbon produced from natural gas or coal. Many ores are suitable for direct reduction.

Direct reduction refers to solid-state processes which reduce iron oxides to metallic iron at temperatures below the melting point of iron. Reduced iron derives its name from these processes, one example being heating iron ore in a furnace at a high temperature of 800 to 1200° C (1470 to 2190° F) in the presence of the reducing synthetic gas, a mixture of hydrogen and carbon monoxide.

Pig iron, also known as crude iron, is an intermediate product of the iron industry within the production of steel which is obtained by smelting iron ore in a blast furnace. Pig iron has very high carbon content, typically 3.8–4.7%, together with silica and other constituents of dross, which makes it very brittle and not useful directly as a material except for limited applications.

The traditional shape of the molds used for pig iron ingots is a branching structure formed in sand, with many individual ingots at right angles to a central channel or “runner”, resembling a litter of piglets being nursed by a sow. When the metal had cooled and hardened, the smaller ingots (the “pigs”) were simply broken from the runner (the “sow”), hence the name “pig iron”. As pig iron is intended for re-melting, the uneven size of the ingots and therefore the inclusion of small amounts of sand cause only insignificant problems considering the ease of casting and handling them.

Traditional Manufacturing Process

• Sponge Iron is often processed to create wrought iron or steel. The sponge is removed from the furnace, called a bloomery, and repeatedly beaten with heavy hammers and folded over to get rid of the slag, oxidize any carbon or carbide, and weld the iron together. This treatment usually creates wrought iron with about three percent slag and a fraction of a percent of other impurities. Further treatment may add controlled amounts of carbon, allowing various sorts of heat treatment (e.g. “steeling”).
• Pig Iron was typically poured directly out of the underside of the blast furnace through a trough into a ladle car for transfer to the steel mill in mostly liquid form; in this state, the pig iron was referred to as hot metal. The hot metal was then poured into a steelmaking vessel to produce steel, typically an electric arc furnace, induction furnace or basic oxygen furnace, where the surplus carbon is burned off and the alloy composition controlled. Earlier processes for this included the finery forge, the puddling furnace, the Bessemer process, and the open hearth furnace.

Modern Manufacturing Process

• Sponge Iron: Today, sponge iron is produced by reducing iron ore without melting it. This makes for an energy-efficient feedstock for specialty steel manufacturers which used to rely upon scrap metal.
• Pig Iron: Modern steel mills and direct-reduction iron plants transfer the molten iron to a ladle for immediate use in the steel making furnaces or cast it into pigs on a pig-casting machine for reuse or resale. Modern pig casting machines produce stick pigs, which break into smaller 4-10 kg piglets at discharge.

Applications of Sponge Iron:

• Sponge iron is a pivotal material used for the production of various steel items like best quality TMT bars, DI pipes and so on.
• The steel melting scrap is extremely useful for mini steel plants as it acts as a feed material. It also can be used as a coolant in LD converters of the integrated steel plants.

Applications of Pig Iron:

• Pig iron is used for steel making, foundries, alloy making, in automotive castings and other iron based castings.

• Pig Iron comprises three main types:  BASIC PIG IRON which used mainly in electric arc steelmaking, FOUNDRY PIG IRON used in mainly in the manufacture of gray iron castings in cupola furnaces, and NODULAR PIG IRON (SG GRADE), used in the manufacture of ductile iron castings. 

Although being similar sorts of iron, both sponge iron and pig iron have different properties. They are different from each other in terms of their use and the way they are produced. 

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