Glossary of Terms used for Defining Steels
Glossary of Terms used for Defining Steels
Abrasion resistant steels – These are alloy steels suitable for applications where resistance to wear is a critical demand. Examples of such applications can include (i) resistance to hard particles grinding under a surface sliding over the top of the steel surface, (ii) resistance to impact from rocks and other hard and heavy materials, (iii) resistance to high velocity abrasive dust and other particles. Boron (B) , manganese (Mn), nickel (Ni) , and chromium (Cr) are the alloying elements used to make the steel it wear resistant.
Acid steel – It is the steel made by an acid process.
Advanced high strength steels – These are basically steels for auto body with very high strength to weight ratio. Their mechanical properties evolve from their unique processing and structure. Such steels are produced by controlling the cooling rate, from the austenite or austenite plus ferrite phase, either on the run out table of the hot rolling mill (for hot-rolled products) or in the cooling section of the continuous annealing furnace (continuously annealed or hot dip coated products).
Air hardening steels – These are alloy steels which can be hardened by cooling in air from a temperature above the transformation range. Such steels attain their martensitic structure without going through the quenching process. Additions of Cr, Ni, Mn, and Mo (molybdenum) are effective toward this end.
Aluminium killed steel – It is a type of steel which is produced when Al (aluminium) is used as a deoxidizing agent to remove O2 (oxygen) from steel during its production.
Alloy steels – Alloy or alloyed steels are defined by the ISO specification 4948/1. Alloy steels are those containing any element listed below in a quantity equal to or greater than the quantity for that listed element. The quantities are (i) Al – 0.10 %, (ii) B – 0.008 %, (iii) Bi (bismuth) – 0.10 %, (iv) Cr-0.30 %, (v) Co (cobalt) – 0.10 %, (vi) Cu (copper) – 0.40 %, (viii) Mn -1.65 %, (viii) Mo -0.06 %, (ix) Pb (lead) – 0.40 %, (x) Se (selenium) – 0.10 %, (xi) Si (silicon) – 0.50 %, (xii) Te (tellurium) – 0.10 %, (xiii) Ti (titanium) – 0.05 %, (xiv) W (tungsten) – 0.10 %, (xv) V (vanadium) – 0.10 %, and Zr (zirconium) – 0.05 %.
Alloy tool steels – The principle function of the alloying elements in tool steels is (i) to increase the hardenability, (ii) to form hard, wear resistant alloy carbides, and (iii) to increase resistance to softening on tempering. The alloy tool steels can be roughly classified as given below.
- Low alloy tool steels – These are having higher hardenability than that of the plain C (carbon) tool steels so that they can be hardened in heavier sections or with less drastic quenches and thereby have less distortion.
- Intermediate alloy tool steels – These steels normally contain elements such as W, Mo, or V which form hard and wear resistant carbides.
- High speed tool steels – These contain large amounts of the carbide forming elements which serve not only to furnish wear resisting carbides but also to promote secondary hardening and thereby to increase resistance to softening at elevated temperature.
Austenitic steels – These are steels which contain sufficient austenite stabilizing elements, such as Mn, Ni, Cr and N2 (nitrogen), so that the microstructure of these steels is austenitic at room temperature. The austenitic steels offer the most resistance to corrosion in the stainless group, owing to its substantial Ni content and higher levels of Cr. Such steels cannot be quenched or air hardened but can be work hardened rapidly. They are non magnetic.
Bake hardening steels – Bake hardening steels are cold-rolled, low-carbon sheet steel used for automotive body panel applications. They are so constituted that after press forming and baking through the paint curing process they age and has good stamping and strength characteristics. They have good formability which is combined with added stiffness in the finished component. This is desirable in an automotive body panel in which enhanced dent resistance is a requirement.
Bars – These are long steel products which are rolled from billets. Merchant bars and reinforcement bars (rebar) are two common categories of bars, where merchants include rounds, flats, angles, squares, and channels which are used by fabricators to produce a wide variety of products. Rebars are used to strengthen concrete used in construction work.
Basic steel – It is the steel made by the basic steelmaking process.
Billet – It is a semi-finished steel form which is used for ‘long’ products such as bars, channels, or other structural shapes. A billet has a square cross-section having a side ranging from 60 mm to 150 mm. Billets can be either rolled or cast in a continuous casting machine.
Black plate – It is a cold-reduced sheet steel, which serves as the substrate (raw material) to be coated with the tin (Sn).
Blank – A blank is a section of sheet which has the same outer dimensions as a specified part (such as a car door or hood), but which has not yet been stamped.
Bloom – It is a semi-finished steel form, with a rectangular cross-section which is 200 mm or higher. This large cast steel shape is rolled in the hot rolling mill to produce the structural sections. Blooms are rolled into billets and thus are a part of the high-quality bar manufacturing process since the reduction of a bloom to a much smaller cross-section can improve the quality of the steel.
Boiler quality steel – It is the steel used in boilers, pressure vessels and for steam application. It is a high tensile C steel with consistent quality and is designed to withstand high pressure.
Boron steels – These are steels which contain B normally in the range of 0.002 % to 0.003 %. B is added to increase the hardenability of the steel.
Capped steel – It is rimming steel in which the depth of the rim is controlled by arresting the rimming action at the appropriate time. The rimming action can be arrested mechanically by putting a heavy steel plate on the top of the surface of the ingot (mechanical capping) or can be stopped by killing by the addition of deoxidizers on the ingot top (chemical capping). The rimming action can also be stopped by spraying water on the top of the ingot.
Carbon steels – Steels containing only C as the specific alloying element are known as C steels. These steels can also contain upto 1.2 % Mn and 0.4 % Si. Residual elements such as Ni, Cr, Al, Mo, and Cu, which are unavoidably retained from raw materials, can be present in small quantities, in addition to impurities such as P (phosphorous), and S (sulphur).
Carbon manganese steels – These steels refer to a family of medium to high strength steels which through a combination of correct selection of chemical composition and hot rolling mill processing parameters produce products with enhanced formability and toughness. The Mn content in these steels is increased for the purpose of increasing depth of hardening and improving strength and toughness. C steels containing higher than 1.2 % and upto around 1.8 % Mn are referred to as carbon manganese steels.
Cast steel – This term is used for castings of steel.
Clean steels – These are steels which are obtained after secondary steelmaking and satisfy stringent requirements of surface, internal and micro cleanliness quality and of mechanical properties.
Cold heading quality steels – These are quality of steels used for making of fasteners by cold heading process. The steel is to be very clean and without any internal or external defects.
Cold rolled steels – These are sheet steels which have been pickled and run through a cold rolling mill. A cold rolled strip has a final product width of around 300 mm, while sheet can be more than 2000 mm wide. Cold-rolled sheet is considerably thinner and stronger than hot-rolled sheet.
Complex phase steels – Complex phase (CP) steels typify the transition to steel with very high ultimate tensile strengths. The microstructure of CP steels contains small amounts of martensite, retained austenite and pearlite within the ferrite/bainite matrix. An extreme grain refinement is created by retarded recrystallization or precipitation of micro alloying elements like Ti or Nb (niobium). In comparison with dual phase (DP) steels, CP steels show significantly higher yield strengths at equal tensile strengths of 800 MPa and higher. CP steels are characterized by high energy absorption and high residual deformation capacity.
Corten steels – These steels are distinguished by their high weather resistant properties. The alloying of steel with Cu and Cr ensures the formation of a firmly adhering protective layer of rust which protects the steel from corrosion in atmospheric condition. The protective layer of rust also makes an attractive appearance on the steel surface.
Dead soft steel – This steel is with C content less than 0.10 % and Mn content in the range of 0.20 % and 0.50 %. This steel is completely annealed.
Deep drawing steel – It is a high quality low C steel possessing high ductility and desirable grain size which permits deep drawing.
Die steels – These are steels which are used in die forging for making dies which work under heavy pressure and which produce a flow of metal compressing it into the desired form or shape. These steels are used for making crimping dies, embossing dies, heading dies, extrusion dies, and staking dies etc. These steels are properly heat treated to get the desired properties.
Drawing quality steels – These are flat rolled steel products which are produced either as rimmed steel or as aluminium killed steel. Special rolling and processing operations help in producing a product, which can stand extreme pressing, drawing or forming operations without creating defects.
Dual phase steel – The DP steels consist of a ferritic matrix containing a hard martensitic second phase in the form of islands. Increasing the volume fraction of hard second phases generally increases the strength. DP steels are produced by controlled cooling from the austenite phase (in hot-rolled products) or from the two phase ferrite plus austenite phase (for continuously annealed cold rolled and hot dip coated products) to transform some austenite to ferrite before a rapid cooling transforms the remaining austenite to martensite. Depending on the composition and process route, hot rolled steels requiring enhanced capability to resist stretching on a blanked edge (typically measured by hole expansion capacity) can have a micro-structure containing significant quantities of bainite.
Electrical steels – These are steels in which the composition and processing conditions are controlled carefully in order to give the steel specific magnetic properties, so that they can be used as core materials in electrical machines. They can be of a non oriented grain type, in which case their magnetic properties are similar both in the direction of rolling and in the transverse direction, or a grain oriented type, in which case the steel has preferred magnetic properties in the rolling direction. Typically steels of the latter type contain greater than 3 % Si and Mn in the range 0.05 % to 0.07%.
Electrode quality steels – These are low C, low Si, and controlled Mn steels used for making welding electrode rods.
Eutectoid steels –These are the steels representing the eutectoid composition of the iron-carbon system with around 0.80 % to 0.83 % C and the eutectoid temperature of around 723 deg C. Such steels in the annealed condition consist exclusively of pearlite. The presence of certain elements, such as Ni or Cr, lowers the eutectoid carbon content.
Extra deep drawing steel – It is a superior quality of low C deep drawing steel.
Ferritic bainitic steels – Ferritic bainitic (FB) steels are sometimes called ‘stretch flangeable’ (SF) or ’high hole expansion’ (HHE) steels because of their improved edge stretch capability. FB steels have a micro-structure of fine ferrite and bainite. Strengthening is obtained by both grain refinement and the second phase hardening with bainite. FB steels are available as hot-rolled products. The primary advantage of FB steels over HSLA (high strength low alloy) and DP steels is the improved stretchability of sheared edges as measured by the hole expansion test. Compared to HSLA steels with the same level of strength, FB steels also have a higher strain hardening exponent and increased total elongation. Because of their good weldability, FB steels are considered for tailored blank applications. These steels are characterized by both good crash performances and good fatigue properties
Flat rolled steels – These are the steel produced in flat rolling mills utilizing relatively smooth and cylindrical rolls. The width to thickness ratio of flat rolled products is normally fairly large. Examples of flat rolled steel are hot rolled plates, sheets and coils, cold rolled sheets and coils, and coated sheets and coils, and tin mill products etc.
Finish steels – These are steels which are ready for the dispatch without further work or treatment.
Forging quality steels – These are the steels which are used for open forging, die forging and upsetting operations. In these steels, gas content and inclusions are controlled.
Full hard cold rolled steel – It is a hot rolled pickled steel which has been cold reduced to a specified thickness and subject to no further processing (not annealed or temper rolled). The product is very stiff. It is not intended for flat work where deformation is very minimal. Full hard temper consists of full hard cold rolled steel produced to a Rockwell hardness of 84 and higher on the B scale.
Galvanized steels – These are steels coated with a thin layer of Zn (zinc) to provide corrosion resistance. These are normally used in under body auto parts, garbage cans, storage tanks, or fencing wire. Sheet steels are normally cold rolled prior to the galvanizing stage. Galvanized steels are produced either by hot dipping process or by electro-galvanizing process.
Galvalume steel – It is the steel sheet with a unique coating of 55 % Al and 45 % Zn which resists corrosion. The coating is applied in a continuous hot-dipped process, which improves the weather resistance of the steel.
Galvannealed steel – In this steel an extra tight coat of galvanizing metal (Zn) applied to a soft steel sheet, after which the sheet is passed through an oven at around 650 deg C. The resulting coat is dull gray without spangle especially suited for subsequent painting.
Hadfield steel – The original austenitic Mn steel, containing around 1.2 % C and 12 % Mn was invented by Sir Robert Hadfield in 1882. Hadfield steel is unique in that it combines high toughness and ductility with high work hardening capacity and it normally has good resistance to wear.
Heat resisting steels – These are steels required to operate at very high temperatures and hence they are to have one or more of these characteristics such as creep resistance, resistance to oxidation, or other forms of gaseous attack, and freedom from micro-structural changes which leads to their embrittlement. Because service conditions can vary greatly, a wide range of steel compositions come under the category of heat resisting steels with C-Mn or low alloy steels being used to 500 deg C – 525 deg C and the austenitic stainless steel grades containing around 25 % Cr and 20 % Ni being used for higher temperatures.
Hot rolled steel – it is the steel rolled on a hot rolling mill. Normally, hot rolled steels are further processed into other finished products.
High speed tool steels – Steels which are alloyed in such a way that they can be used as a cutting tool material to machine other metals at high speeds, and still retain its cutting ability, even though the tool tip is at a low red heat. The various grades of these steels contain 0.6 % or more of C, a combined content of 7 % or more of the elements like W, Mo, and V, 3 % to 6 % of Cr and in those required to operate at the highest temperatures additions of 4 % to 13 % of Co. These steels are widely used for the production of taps, dies, twist drills, reamers, saw blades and other cutting tools.
High strength low alloy steels – HSLA steels are designed to provide better mechanical properties than conventional C steels. These steels are designed to meet specific mechanical properties rather than a chemical composition. The chemical composition of specific HSLA steel can vary for different product thickness to meet mechanical property requirements. The HSLA steels have low C contents (0.05 % to around 0.25 % C) in order to produce adequate formability and weldability and they have Mn contents up to 2 % percent. Small quantities of Cr, Ni, Mo, Cu, N2, V, Nb, Ti, and Zr are used in various combinations.
Hot formed steels – Optimized part geometries with intricate shapes and no spring back issues are being accomplished by hot forming quench hardening steels at temperatures above the austenitic range (900 deg C to 950 deg C). During processing, the following three states with different mechanical properties are important.
- State 1- Tensile strengths upto 600 MPa at room temperature is to be considered for the design of blanking dies.
- State 2 – High elongations (more than 50 %) and low strengths at deformation temperatures allow forming of complex shapes. A special coating based on Al and Si is recommended to avoid surface oxidation of the product after forming.
- State 3 – Following forming, strengths above 1300 MPa are achieved after quenching in the die. Special processes are to be taken into account when finishing the product (no additional forming, special cutting and trimming devices etc.).
Typical cycle time is 20 seconds to 30 seconds for each press cycle. However, several parts can be stamped at the same time so that 2 or more parts can be obtained per cycle. Hot forming B steels are most commonly used for safety and structural parts.
Hot rolled steels – These steels are produced either by hot rolling or by hot rolling followed by on line heat treatment.
Hypo eutectoid steels – These are steels are having less than eutectoid % of C.
Hyper eutectoid steels – These are steels having more than the eutectoid % of C.
Ingot steel – It is a form of semi-finished steel. Liquid steel is teemed (poured) into ingot moulds, where it slowly solidifies. Once the steel is solid, the mould is stripped, and the ingot is then ready for subsequent rolling or forging.
Interstitial free steel – Interstitial free (IF) steel is a sheet steel product with very low C levels. IF steel is used primarily in automotive deep drawing applications. The improved ductility (drawing ability) of IF steels is made possible by vacuum degassing.
Killed steels – Killed steels are made by complete deoxidation of the liquid steel before it is cast so that no gas evolution occurs during solidification. These are the steels to which generally Al, silico-manganese, ferro-silicon, or ferro-manganese is added as deoxidizing agents. Properly killed steel is more uniform in analysis and is comparatively free from aging. However for the same C and Mn content killed steels are harder than rimmed steels. Generally all steels above 0.25 % C are killed. Also all forging grades of steels, structural steels from 0.15 % to 0.25 % C and some special steels in the low C range are killed. Only killed steels can be cast in continuous casting machines.
Leaded steels– These are steels to which Pb, in amounts ranging from 0.15 % to 0.35 %, is normally added along with S to improve the machinability of the steel product.
Light gauge steel – This steel is in the form of very thin steel sheet that has been temper rolled or passed through a cold rolling mill. Light gauge steel normally is plated with Sn or Cr for making cans to be used as food containers.
Long product steel – This steel is used for rolling long products. As per the classification of steel products bar, rod and structural products are the long products.
Low alloy steels – Many attempts have been made to differentiate low alloy steels from high alloy steels but the definition of low alloy steel vary from country to country and between the standard setting organisations. As a general indication, low alloy steels can be regarded as alloy steels (by the ISO definition) containing more than 1 % and less than 5 % of alloying elements deliberately added for the purpose of modifying properties.
Low temperature steels – These are steels which are especially suited for extremely cold climates and for the handling of liquefied gases such as O2, N2, propane (C3H8), anhydrous ammonia (NH3), carbon dioxide (CO2), and ethane (C2H6).
Magnet steels – These are normally alloy electrical steels. The outstanding property of these steels is their ability to retain magnetism. Co, Cr, and W are the alloying elements normally used to enhance this characteristic.
Maraging steels – These steels are high Ni steels with not less than 18 % Ni and are characterized by extreme high strength and toughness. Ni normally encourages the formation of austenite in steels as opposed to carbides. Because of this, under the proper conditions high strength can be obtained by the transformation of austenite into martensitic type structures. The advantage of maraging steels is that this change is achieved as a result of a simple heat treatment which means that the problems of distortion normally associated with high temperature heat treatments are avoided. A typical heat treatment can involve heating to 820 deg C grade followed by air cooling (This avoids distortion which is associated with a faster rate cooling). The process is completed by ageing at a temperature in the range 450 deg C to 510 deg C.
Martensitic steels – To create martensitic (MS) steels, the austenite which exists during hot rolling or annealing is transformed almost entirely to martensite during quenching on the run out table or in the cooling section of the continuous annealing line. The MS steels are characterized by a martensitic matrix containing small amounts of ferrite and/or bainite. Within the group of multi-phase steels, MS steels show the highest tensile strength level. This structure can also be developed with post forming heat treatment. MS steels provide the highest strengths, up to 1700 MPa ultimate tensile strength. MS steels are often subjected to post quench tempering to improve ductility, and can provide adequate formability even at extremely high strengths.
Merchant bar – It is a group of commodity steel shapes which consist of rounds, squares, flats, strips, angles, and channels, which are cut, bent, and shape into products. Merchant products require more specialized processing than reinforcing bar.
Micro alloyed steels – These are C-Mn steels containing deliberately added alloying elements totalling in the range of 0.05 % to 0.10 %. Alloying elements which are effective in modifying steel properties when present in such small amounts include B, V, and Nb. A major advantage of these steels is that in the case of forgings, careful control of forge processing temperatures can eliminate subsequent heat treatment. Mechanical properties developed by controlled hot working conditions are similar to those developed by conventional hardening and tempering treatments for components where strength and toughness are required.
Nickel steels – These are the steels which contain Ni as an alloying element. Different amounts of Ni are added to increase the strength in the normalized condition to enable hardening to be performed in oil or air instead of water.
Nitriding steels – These steels are normally suited for the nitriding process. These steels form a very hard and adherent surface upon proper nitriding process (heating in a partially dissociated atmosphere of NH3 gas). These steels have a composition normally containing of C in the range of 0.20 % to 0.40 %, Cr in the range of 0.90 % to 1.50 %, Mo in the range of 0.15 % to 1.00 %, and Al in the range of 0.85 % to 1.20.
Non magnetic steels – These are steels which have a stable fully austenitic microstructure.
Oil hardening steel – This steel is adaptable to hardening by heat treatment and quenching in oil than in place of any other medium.
Piling – It is also known as sheet piling. It is a structural steel product with edges designed to interlock. It is used in the construction of cofferdams or riverbank reinforcement.
Plain carbon steel – It is steel where the main alloying constituent is C. Steel is considered to be plain C steel where minimum content is not specified or required for Cr, Co, Mo, Nb, Ni, W, V, or Zr, or any other element to be added to obtain a desired alloying effect or when the specified minimum for Cu does not exceed 0.40 % or when the maximum content specified for Mn and Si does not exceed 1.65 % and 0.60 % respectively. The plain C steels are classified based on carbon percentage as given below.
- Ultra low carbon steels – These steels contain very low C normally less than 0.10 %. These steels also contain very low Mn and very low Sin. These steels are having extra deep drawing properties and usually produced in the form of flat and wire rod products.
- Low carbon steels – Steels with less than 0.005 % and upto 0.10 % carbon are called low carbon steels. They are more ductile (malleable). The largest category of this type of steel is flat rolled products (sheet or strip) normally cold rolled and annealed condition. It is capable of being drawn out or rolled thin for use in automotive body applications. C is removed from the steel bath through vacuum degassing.
- Mild steels – These are ordinary weldable non alloy steels with normal strength. The term mild steel is used to describe standard C steels used for structural purposes. It is also applied commercially to C steels not covered by standard specifications. C content of these steels can vary from levels of 0.10 % upto around 0.3 %. Generally mild steel is readily weldable and have reasonable cold bending properties.
- Medium carbon steels – These steels are similar to low carbon steels except that the C content ranges from 0.35 % to 0.60 % and the Mn content from 0.60 % to 1.65 %. Increasing the C content to around 0.5 % with an accompanying increase in Mn content allows medium C steels to be used in the quenched and tempered condition. These steels balance ductility and strength and have good wear resistance.
- High carbon steels – These steels have C content ranging from 0.61 % to 1 % with Mn content ranging from 0.30 % to 0.90 %. The more C which is dissolved in the iron, the less formable and the tougher the steel becomes. Hardness of the high C steel makes it suitable for plough blades, shovels, bedsprings, cutting edges, or other high-wear applications. The use of high C steels also includes pre stressed concrete wires, springs, and high strength wires etc.
- Ultra high carbon steels – These steels contain C in the range of 1 % to 1.2 %. These steels can be tempered to high hardness. These steels are made by powder metallurgy technique and are used for special purpose such as knives, axles or punches etc.
Plate – It is a flat steel product with a width of more than 200 mm, with a thickness ranging from 6 mm to more than 100 mm.
Post forming heat treatable steel -Post-forming heat treatment (PFHT) is a general method to develop an alternative higher strength steel. The major issue holding back widespread implementation of high strength steel (HSS) typically has been maintaining part geometry during and after the heat treatment process. Fixturing the part and then heating (furnace or induction) and immediate quenching appear to be a solution with production applications. In addition, the stamping is formed at a lower strength and then raised to a much higher strength by heat treatment.
One process is water quenching of inexpensive steels with chemistries which allow in part strengths in the range of 900 MPa to 1,400 MPa of tensile strength. In addition, some Zn coatings can survive the heat treating cycle since the time at temperature is very short. The wide assortment of chemistries to meet specific part specifications needs extra special coordination with the steel supplier.
Another process is air-hardening of alloyed tempering steels which feature very good forming properties in the soft-state (deep-drawing properties) and high strength after heat treatment (air-hardening). Apart from direct application as sheet material, air hardening steels are suitable for tube welding. These tubes are excellent for hydroforming applications. The components can be heat treated in the furnace in a protective gas atmosphere (austenitized) and then hardened and tempered during natural cooling in air or a protective gas. The very good hardenability and resistance to tempering is achieved by adding, in addition to C and Mn, other alloying elements such as Cr, Mo, V, B, and Ti. The steel is very easy to weld in both its soft and air-hardened states, as well as in the combination of soft/air-hardened. This steel responds well to coating using standard coating methods (conventional batch galvanizing and high-temperature batch galvanizing.
Rail steel – The rail steel is having a pearlitic structure based on its C-Mn composition. It is wear resistant pearlite consists of alternating lamellae of soft iron and very hard iron carbide (also known as cementite). The smaller the spacing between cementite layers, the harder and more wear resistant the rail steel is. Rails not only wear, they also break. Their inherent toughness is poor as a result of the presence of the brittle carbide phase. Fracture can occur from relatively minor stress-concentrating features inside the rail, or on the surface, as a result of manufacture or subsequent handling damage. Pearlitic rails have been developed almost to their limit. Now rails are also being made of a carbide free bainitic steel which is a tough rail steel with excellent wear resistance.
Reinforcement bar (Rebar) – It is a commodity-grade steel used to strengthen concrete in civil construction work.
Rimming steels – These are steels possessing a rim of purer material (with maximum freedom from surface defects) and is associated with evolution of CO (carbon monoxide) gas occurring due to the interaction of dissolved iron oxide and C during the solidification of low C and low Mn steel made under controlled deoxidation. The composition and extent of the rim can be varied and, if required, by arresting the rimming action after sometime. This steel can be produced with an outer layer of very pure iron which gives rise to a sheet product with excellent surface and good formability. The widespread adoption of the continuous casting process has resulted in rimming steels generally being replaced by killed steels.
Rod – It is round, thin semi-finished steel length which is rolled from a billet and coiled for further processing. Rod is normally drawn into wire products or used to make bolts and nails.
Secondary steels – Steels which do not meet the original customer’s specifications because of a defect in its chemistry, gauge or surface quality are called secondary steels.
Semi finished steels – Steel shapes such as blooms, billets or slabs which are later rolled into finished products such as beams, bars or sheet are called semi finished steels.
Semi killed steels – Steels which are incompletely deoxidized and which permit evolution of sufficient CO to offset solidification shrinkage are semi killed steels.
Silicon electrical steels – These are specialty steels created by Si during the steel making process. These electrical steel shows certain magnetic properties (such as greatly increased electrical resistivity, high permeability and greatly reduced core losses), which make it optimum for use in transformers, power generators and electric motors. They are of two types as given below.
- Grain oriented – The metal’s grain runs parallel within the steel, permitting easy magnetization along the length of the steel. Although grain oriented steel can be twice as expensive to produce, its magnetic directional characteristics enable power transformers, made from this steel, to absorb less energy during operation.
- Non grain oriented – Since there is no preferential direction for magnetization, non grain oriented steel is best used in rotating apparatus such as electric motors.
Special steels – These are the steels where during the production special care is to be taken so as to attain the desired cleanliness, surface quality and mechanical properties.
Specialty steels – These are the types of steels which needs restricted or specific chemical composition or mechanical or metallurgical properties.
Spring steels – These steels are used for the manufacturer of springs. Depending on the type and application of the spring, the steel composition can vary from a plain C type, to C-Si type, to any of a range of alloy steels and if necessary to the use of a martensitic or austenitic stainless steel grade.
Stainless steel – Steel is known as stainless steel when it contains 4 % or more Cr. Stainless steel resists corrosion, maintains its strength at high temperatures, and is easily maintained. By the addition of other alloying elements to this basic steel, such as Ni, C, N2 and Mo, a variety of different grades of stainless steel, namely ferritic, austenitic, martensitic, duplex and precipitation hardened type can be produced.
- Ferritic – It has a body centred cubic structure. Ferritic stainless steels are plain Cr steels with low C level and with no significant Ni content. The lack of Ni results in lower corrosion resistance than the austenitic stainless steels (Cr-Ni stainless steels). These steels are the second-largest class of stainless steel, constituting around 25 % of stainless production. Ferritic stainless steels are best suited for general and high temperature corrosion applications rather than services requiring high strength. They can be hardened primarily by cold working, although some will harden slightly by heat treating. Ferritic stainless steels are work harden much slower than austenitic stainless steels. Two of the most common grades are type 430 (general-purpose grade for many applications, including decorative ones) and type 409 (low-cost grade well suited to withstanding high temperatures).
- Austenitic – These steels contain a maximum of 0.15 % C, a minimum of 16 % Cr and sufficient Ni and/or Mn to retain an austenitic structure at all temperatures from the cryogenic region to the melting point of the alloy. A typical composition consists of 18 % Cr and 8 % Ni, normally known as 18/8 stainless steel. Super austenitic stainless steels show great resistance to chloride pitting and crevice corrosion due to high Mo content ( higher than 6 %) and N2 additions, and the higher Ni content ensures better resistance to stress corrosion cracking. The higher alloy content of super austenitic steels makes them more expensive. Other austenitic steels can give similar performance at lower cost and are preferred in certain applications.
- Martensitic – These stainless steels have a body centered tetragonal structure. They work harden slowly in the annealed condition but can be heat treated to very high tensile strengths. These are not as corrosion resistant as the other stainless steels but are extremely strong and tough as well as highly machineable. These stainless steels are magnetic in nature, can be hardened by heat treatment for strength and hardness and have poor welding characteristics. Martensitic stainless steels contain Cr in the range of 11.5 % to 18 %, Mo in the range of 0.2 % to 1.0 %, Ni in the range of 0 % to 2 % and C in the range of 0.15 % to 1.2 %. The steel can be quenched. The main uses for this type of stainless steels are knife blades, surgical instruments, fasteners, shafts and springs etc.
- Precipitation hardening type stainless steels – These steels have corrosion resistance comparable to austenitic stainless steels and can be precipitation hardened to higher strength than other martensitic grades.
- Duplex stainless steels – These steels consist of a category of stainless steel with high amounts of Cr (19 % to 28 %), Mo (upto 5 %), and moderate Ni content. These have a mixed micro-structure of austenite and ferrite.The duplex steel is so named since it is a mixture of austenitic (Cr-Ni stainless class) and ferritic (plain Cr stainless class) structures. This combination provides more strength than either of those stainless steels. Duplex stainless steels provide high resistance to stress corrosion cracking (formation of cracks caused by a combination of corrosion and stress). These have improved strength over austenitic stainless steels and also improved resistance to localized corrosion specially pitting, crevice corrosion and stress corrosion cracking. These steels are suitable for heat exchangers, desalination plants, and marine applications.
Steel – Steel is an iron base alloy generally suitable for working to the required shape in the solid state. Steel is normally defined as an alloy of iron and carbon with the C content ranging between a few hundred of a percent upto around 2 %. Other alloying elements can amount in total to around 5 % in low-alloy steels and higher in more highly alloyed steels such as tool steels and stainless steels. A limited number of high alloyed steels can have more than 2 % C but 2 % is the usual dividing into between steel and cast iron.Steels can show a wide variety of properties depending on composition as well as the phases and micro constituents present, which in turn depend on the heat treatment. Heat treatment of steel is governed by iron-carbon phase diagram (Fig 1).
Fig 1 Iron- carbon phase diagram
Structural quality steel – It is steel applicable to the different classes of structures, indicated by the standard specifications, which is suitable for the different mechanical operations employed for the fabrication of such structures. Structural quality steel represents the quality of steel produced under regular or normal manufacturing conditions.
Steel strapping – It is the banding and packaging material which is used to close and reinforce shipping units, such as bales, boxes, cartons, coils, crates, and skids etc.
Strip – It is thin, flat steel which resembles hot-rolled sheet, but it is normally narrower (upto 300 mm wide) and produced to more closely controlled thicknesses. Strip can also be cut from steel sheet coil by a slitting machine.
Structurals – These are steel product group which includes I-beams, H-beams, wide-flange beams, and sheet piling. These products are used in the construction of multi-story buildings, industrial buildings, bridge trusses, vertical highway supports, and riverbank reinforcement.
Substrate – It is the raw material used as an input for steel processing: For example, hot-rolled steel is the substrate for cold-rolling operations.
Super alloy – It is an alloy, usually based on Ni, Co, or Fe (iron), developed for high temperature service where relatively severe mechanical stressing is encountered and where high surface stability is frequently needed.
Super stainless steel – Stainless steel alloys with significant additions of Cr, Ni, Mo, and Cu. Super stainless steel is used in chemical processing, petroleum refining, marine, heat treating, pollution, and waste control industries where there are requirements for extra corrosion protection, strength, or heat resistance.
Terne – It is sheet steel coated with a mixture of Pb, and Sn. Terne principally is used in the manufacture of gasoline tanks, although it also can be found in chemical containers, oil filters, and television chassis
Tin free steel – It is single or double reduced black plate having a thin coating of Cr and chromium oxide applied electrolytically. Because it is used in food cans just like tin plate, it ironically is classified as a tin mill product. Tin free steel is easier to recycle because tin contaminates scrap steel in even small concentrations.
Tin plate – It is thin sheet steel with a very thin coating of metallic Sn. Tin plate is used primarily in food can making.
Transformation induced plasticity (TRIP) steel – The microstructure of TRIP steels is retained austenite embedded in a primary matrix of ferrite. In addition to a minimum of 5 volume percent of retained austenite, hard phases such as martensite and bainite are present in varying amounts. TRIP steels typically need the use of an isothermal hold at an intermediate temperature, which produces some bainite. The higher Si and C content of TRIP steels also result in significant volume fractions of retained austenite in the final microstructure. During deformation, the dispersion of hard second phases in soft ferrite creates a high work hardening rate, as observed in the DP steels. However, in TRIP steels the retained austenite also progressively transforms to martensite with increasing strain, thereby increasing the work hardening rate at higher strain levels. The TRIP steel has a lower initial work hardening rate than the DP steel, but the hardening rate persists at higher strains where work hardening of the DP begins to diminish. The work hardening rates of TRIP steels are substantially higher than for conventional HSS, providing significant stretch forming. This is particularly useful when designers take advantage of the high work hardening rate (and increased bake hardening effect) to design a part utilizing the as formed mechanical properties. The high work hardening rate persists to higher strains in TRIP steels, providing a slight advantage over DP in the most severe stretch forming applications.
Tool steels – Tool steels refer to a variety of C and alloy steels which are well suited for making of tools. The suitability is due to their distinctive hardness, resistance to abrasion, ability to hold a cutting edge and resistance to deformation at higher temperatures (red hardness). Tool steels are normally used after heat treatment. Tool steels are having C content in the range of 0.7 % to 1.4 % and need care and fully controlled condition during its production. The Mn content is kept low to avoid cracking during water quenching.
Twinning induced plasticity (TWIP) steel – TWIP steels have high Mn content (17 % to 24 %) which causes the steel to be fully austenitic at room temperatures. This causes the principal deformation mode to be twinning inside the grains. The twinning causes a high value of the instantaneous hardening rate (n value) as the micro-structure becomes finer and finer. The resultant twin boundaries act like grain boundaries and strengthen the steel. TWIP steels combine extremely high strength with extremely high formability. The ‘n’ value increases to a value of 0.4 at an approximate engineering strain of 30 % and then remains constant until a total elongation around 50 %. The tensile strength is higher than 1000 Mpa.
Weathering steel – It is a high strength, low alloy steel which forms a corrosion resistant oxide patina that eliminates the need for paint or other protective coatings. Weathering steels are self protecting, durable and attractive, so they are ideally suited to a whole range of outdoor applications for structures in exposed locations. The corrosion retarding effect of the protective layer is produced by the particular distribution and concentration of the alloying elements in it. The layer protecting the surface develops and regenerates continuously when subjected to the influence of the weather.
Wear resistant steels – Wear resistant special structural steels are, as a rule, quenched or quenched and tempered, and have a fine martensitic or martensitic-bainitic microstructure. They are produced in thicknesses up to 120 mm.
Wire – It is a long product which is from 0.76 mm to 6 mm in diameter, in round, square, octagonal, or hexagonal cross-sections.