Iron and Steel Making Process
Terms Related To ‘IRON’
Iron : Iron is a base metal extracted from iron ore. Pure iron has melting point of 1530 Degree Centigrade and density of 7.86 gm/cc
Iron Making: Iron making is the process of Reduction of iron ore using the relevant reducing agent (Reductant).
Hot Metal (Liquid Iron) : It is the hot, liquid, metallic iron product obtained upon reduction of iron ore ( normally in Blast Furnace or in Corex Furnace). It contains about 93-94% Iron (Fe) and other elements/impurities like Carbon (4% ), Silicon (~1%), Manganese(+1%) Sulphur, Phosphorus etc. Hot metal is the primary input for production of steel in the Integrated Steel Plants.
Pig Iron : A product in solid (lumpy) form obtained upon solidification of Hot Metal in Pig Casting Machine. It is called Pig or Pig Iron because of its typical humpy shape. It is produced in 2 broad categories/grades:
a) Foundry Grade Pig Iron: Pig iron used in the Foundries for production of Cast Iron (CI) Castings using Cupola Furnace. This is the major use of pig iron.
b) Basic/Steel Making Grade Pig Iron: Pig iron (including hot metal) used for production of Steel.
Sponge Iron/ Direct Reduced Iron(DRI)/ Hot Briquetted Iron(HBI):
Direct Reduced Iron(DRI): Solid metallic iron product obtained upon Direct Reduction of high grade iron ore in solid state itself without being converted into liquid form like that in Blast Furnace.
Sponge Iron(SI): DRI is also known as Sponge Iron because of its spongy micro structure.
Hot Briquetted Iron(HBI): At times the DRI/SI coming out from the furnace is converted into a bigger compact mass i.e. Briquettes for ease in transportation/charging in steel making furnace, which are known as Hot Briquetted Iron.
NOTE: SI/ DRI/HBI is produced by reducing high quality iron ore lumps or iron ore pellets with the help of non-coking coal in Rotary Kiln (in Coal based Plants) or with the help of Natural Gas in Shaft Furnace (known as Gas based plants).
NOTE: SI/ DRI/HBI is primarily used for production of steel (as a substitute of steel melting scrap), in the Electric Furnaces like the Electric Arc Furnace (EAF) or the Induction Furnace (EIF). However, SOME COMPANIES is using it in their blast furnace as substitute for iron ore or/sinter
Terms Related To ‘STEEL’ and ‘STEEL PRODUCTS’
Steel is an iron based alloy containing Carbon, Silicon, Manganese etc.
Steel making: Steel making is the process of selective oxidation of impurities present in the charge material (Hot metal/Scrap/DRI) in the presence of suitable fluxes in the Steel Melting Shops (SMS).
Steel/Steel Products as per Form/shape/size:
Liquid Steel : The immediate hot molten steel product from Steel Melting Shop (LD Converter/Electric Arc Furnace/Electric Induction Furnace/Energy Optimising Furnace). It is further cast into ingots/Semis. The by-product from SMS is called SMS slag.
Ingot Steel (ingots): The primary solid product obtained upon solidification of liquid steel in conventional, vertical, Cast Iron Molds which are intended for rolling into intermediate/semi-finished products after re-heating.
NOTE: Ingots are normally very large and heavy weighing several tonnes (up to 15-20 tonnes). Pencil Ingots: Small ingots in Kgs produced in mini-steel plants.
Semi-Finished Steel Products (Semis):
Intermediate solid steel products obtained by Hot rolling/Forging of ingots (in conventional process) or by Continuous casting of liquid steel are known as Semis. These are called so since they are intended for further rolling/forging to produce Finished steel products. Various types of semis are as under:
Blooms: A Semi-finished product, usually in square (at times in rectangular) section of cross sectional size exceeding 5”x5” (125mm X 125mm). In some of the modern mills, the term bloom is used to cover such products of cross sectional size exceeding 8”x8”.These are inputs for producing Heavy sections and Sheet piling section normally by hot rolling. At times, like in VSP , blooms are used to produce billets by hot rolling in the Billet Mill.
Billets : A semi-finished product which are similar to blooms but of smaller cross sectional size (usually less than or 5’’x5’’/7’’x7’’. These are used as input material for production of Finished Steel long products viz bars & rods, light sections etc.
Slabs : A semi-finished Rectangular, wide, semi-finished steel product intended for production of finished Hot Rolled Flat products viz Plates, sheets, Strips etc. They are normally of width 150-250mm wherein width is at-least 3 or 4 times of thickness. Thin Slabs : In modern thin slab casting machine, liquid steel is continuously cast into much thinner slabs of 35-50mm directly which are used for production of Finished Hot Rolled Flat products upon heating on-line.
Finished Steel :
Products obtained upon hot rolling/forging of Semi-finished steel (blooms/billets/slabs) . These cover 2 broad categories of products, namely Long Products and Flat Products:
a) Long Products: Finished steel products produced normally by hot rolling/forging of Bloom/billets/pencil ingots into useable shape/sizes. These are normally supplied in straight length/ cut length except Wire rods which are supplied in ir-regularly wound coils. Different types of long products are :
Bars & Rods : Long steel products obtained normally by hot rolling/forging of billets/blooms. They include Rounds, Flats (flat bars), Squares, Hexagons, Octagons etc. which find direct use in in a wide variety of products in Engg, & Agricultural, House hold, Furniture sector etc. with/without further processing.
CTD (Cold-worked Twisted & Deformed)/ TMT (Thermo Mechanically Treated)Bar &
Rods: Hot rolled round bars/rods with indentations/ribs normally supplied in straight length or in folded bundles. Used directly in civil construction.
Wire Rod : Hot rolled plain bar/rods (i.e without indentation) in Coil Form, normally used to produce Steel Wires and at times Steel Bright Bars.
Angles, Shapes & Section : Hot rolled Structural Sections obtained by hot rolling of blooms/billets. They include Angles, Channels, Girders, Joist, I Beams, H Beams etc used in civil/mechanical construction.
Rails : Hot rolled Rail Sections obtained upon hot rolling of Blooms/Billets. Used in rail ways/tram ways, on which rail/tram moves .
Wires: Wires are produced by cold drawing of wire rod through a die. They are normally supplied in coils.
Bright Bars : There are cold drawn/ ground/ Peeled plain bars produced from hot rolled plain bars/wire rods. (Does not fall under the purview of MOS but under D/o IP&P).
Flat Products (Flat Rolled Products)
Finished steel thin flat products, produced from slabs/thin slabs in rolling mills using flat rolls. These are supplied in Hot Rolled (HR), Cold Rolled (CR) or in Coated condition depending upon the requirement. Different types of flat products are :
Plate : Thick flat finished product of width: +500mm & Thickness: (+)5mm which are supplied in cut/straight length. Plates are normally produced/supplied in as hot rolled condition with or without specific heat treatments.
Sheet : Thin flat finished steel products, Width: +500MM, Thickness: (-) 5mm, Supplied in cut/straight length. Sheets are produced/ supplied in hot rolled /cold rolled/coated condition and accordingly, known as Hot Rolled (HR) Sheets or Cold Rolled (CR) Sheets or Coated Sheets.
Strips : Hot/cold/coated Flat rolled products, supplied in regularly wound coils of super imposed layers. Accordingly, known as HR Strips or CR Strips or Coated Strips. Depending upon width, strips are sub-classified as wide strip or narrow strip as under :
a) Wide Strips : Strips of widths 600mm & above. Also known as Coils in India and Wide Coils in Europe etc. Accordingly, the terms HR Coils/Wide Coils or CR Coils/ Wide Coils etc. are commonly used.
b)Narrow Strips : Strips of widths less than 600mm. Hot Rolled (HR) flat products are produced by re-rolling of slabs/thin slabs at high temperature (above 1000 Degree C) in Plate Mills (which produce plates) or in Hot Strip Mills (which produce strips) . Hot Rolled Strips are cut into straight length to produce HR Sheets or Thin Plates. Cold Rolled(CR) Strips are produced by cold rolling of HR Strips in Cold Rolling Mills (normally at room temperature). CR Strips are cut to produce CR sheet. CR Strips/sheets are characterised by lower thickness, better/bright finish, closer dimensional tolerance and specific
mechanical/metallurgical properties. They are directly used in automobiles (cars/ scooters, motorcycles etc.), white goods, consumer durable etc. or for production of coated sheet products. Cold Rolled Sheets/Strips are supplied in as rolled condition (CRFH- Cold Rolled Full Hard) or in closed annealed (CRCA –Cold Rolled Close Annealed) condition or in closed annealed & skin passed/temper passed condition, depending upon the requirement of the end users.