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.
Ingots are normally very large and heavy weighing several tonnes (up to 15-20 tonnes).
PENCIL INGOTS: mall 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:
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 irregularly 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 a wide variety of products in Engineering & 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 flat products are 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 :
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.
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.
D/DD/IF STEEL:
Specific variety of Cold Rolled Sheets/ Strips with specific chemical composition used in Tin Mills are known as Tin Mill Black Plate (TMBP).
COATED PRODUCTS: There are cold rolled products coated with metals or organic chemicals as under:
GALVANISED PLAIN/ CORRUGATED (GP/GC) SHEETS: These are Cold Rolled Sheets/Strips coated with zinc metal. Process is known as Galvanising. Used in roofing, paneling etc. GP sheets are normally produced by Hot Deep Galvanising of CR Sheets/Strips in liquid zinc bath. GC sheets are obtained upon corrugating of GP sheets in corrugating machine.GP sheets are also produced by electroplating of zinc on CR sheets/strips when the process is known as Electro-Galvanising. Galvanised sheets are used mainly in roofing, paneling, automobile bodies, Trunks/Boxes etc.
TINPLATE: TMBP coated with tin metal. Used for manufacture of containers.
TIN FREE STEEL: TMBP sheet/strips coated with chromium metal and chromium oxide.
COLOUR COATED PRODUCTS: Cold Rolled/ galvanised steel sheets/strips coated with PVC/ plastics or any other organic material. Process known as Colour Coating. Used for manufacture of furniture, auto bodies, roofing, paneling etc.
TERNI PLATE: Cold rolled steel sheets/strips coated with an alloy of tin and lead, used in manufacture of Petrol Tanks for automobiles. Not produced in India.
GALFAN ALLOY COATED SHEETS: These are CR Sheets/Strips coated with an Zinc- Aluminum alloy comprising of 95% zinc and 5% aluminum. Uses are similar to GP/GC sheets but it has better life and better corrosion properties.
GALVALUME ALLOY COATED SHEETS: These are CR Sheets/ Strips coated with an alloy comprising of approx. 55% aluminum and approx. 45% zinc with nominal amount of silicon. Uses are similar to that of GP/GC sheets but it has better life and much better high temperature performance.
CRUDE STEEL:
The term is internationally used to mean the 1st solid steel product upon solidification of liquid steel. In other words, it includes Ingots (in conventional mills) and Semis (in modern mills with continuous casting facility).
According to International Iron & Steel Institute (IISI), for statistical purpose, crude steel also includes liquid steel which goes into production of steel castings.
SALEABLE STEEL:
The term is used to designate various types of solid steel products, which are sold to outside customers for further processing or for direct use/consumption. Therefore, it includes ingots and/or semis and/or finished steel products. (Liquid steel is normally not traded).
STEEL AS PER COMPOSITION
ALLOY STEEL :
Steel which is produced with intended amount of one or more alloying elements in specified proportions to impart specific physical, mechanical, metallurgical and electrical properties.
Common alloying elements are manganese, silicon, nickel, lead, copper, chromium, tungsten, molybdenum, niobium, vanadium etc. Some of the common examples of alloy steels are:
STAINLESS STEEL: which essentially contains chromium (normally more than 10.5% with/without nickel or other alloying elements. As the name implies, stainless Steel resist staining/corrosion and maintains strength at high temperatures. Used widely in Utensils, architectures and in Industrial applications viz automotive & food processing products as well as medical & health equipment.
Commonly used grades of stainless steels (SS) are:
TYPE 304: Chrome - Nickel Austenitic S S accounting for more than half of SS produced in the world. 18: 8 SS used for utensils are the most common example.
TYPE 316: Chrome - Nickel (Austenitic) SS containing 2-3% Molybdenum , intended for specific industrial use.
TYPE 410: Plain Chromium (Martensitic) S S with exceptional strength. It is a low cost, heat treatable grade suitable for non-corrosive applications.
TYPE 430: Plain Chrome (Ferritic) S S, offering general purpose corrosion resistance, often in decorative applications.
TYPE 201/202 ETC. : Low Nickel Austenitic S S containing 2-5% Nickel . Used as cheaper substitute of Type 304 grade for production of utensils.
SILICON-ELECTRICAL STEEL: which usually contains 0.6 - 6% silicon and exhibit certain magnetic properties, which make it suitable for use in transformers, power generators, and electric motors. They are normally supplied in 2 categories:
CRGO: Cold Rolled Grain Oriented Silicon-electrical steel sheets/strips, normally recommended for use in transformers and generators.
CRNO/ CRNGO: Cold Rolled Non-Grain Oriented Silicon-electrical steel sheets/strips, normally recommended for use in rotating machines such as electric motors.
HIGH SPEED STEEL: Alloy steel containing tungsten, vanadium, chromium, cobalt and other metals. Depending upon composition, they are classified as Cobalt Grade and Non-Cobalt Grade. Used for manufacture of cutting tools.
NON-ALLOY /CARBON STEEL/PLAIN CARBON /UN-ALLOYED STEEL :
These steels by definition do not contain any alloying element in specified proportions (i.e. beyond those normally present in commercially produced steel in industry). Non- alloy steel is divided into 3 categories namely
Low carbon steel or Mild steel (normally containing up to 0.3% carbon) Medium carbon steel (normally containing 0.3 - 0.6% carbon) and High carbon steel (normally containing more than 0.6% carbon).
Non-alloy steel constitutes approx. 90% of total steel production, of which, mild steel takes the lion's share.
SPECIAL STEEL :
Steel, in production of which special care has to be taken so as to attain the special/desired properties, such as, cleanliness, surface qualities and mechanical/ metallurgical properties.
In layman's language, all steel other than mild steel fall under the category of special steel. But metallurgically, even mild steel/low carbon steel i.e containing less than 0.25%/0.30% carbon, may still fall under the category of special steel if any special properties is specified in the steel. Examples are DD/ EDD steel, Forging Quality steel, Free Cutting steel etc.
