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 may include resistance to hard particles grinding under a surface sliding over the top of the steel surface, or resistance to impact from rocks and other hard and heavy materials, or resistance to high velocity abrasive dust and other particles. Boron, Manganese, Nickel, and Chromium are the alloying elements used to make 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 may 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 chromium, nickel, molybdenum and manganese are effective toward this end.
Aluminum killed steel – It is a type of steel which is produced when aluminum is used as a deoxidizing agent to remove oxygen from steel during its manufacture.
Alloy Steels – Alloy or alloyed steels are defined by the ISO specification 4948/1 in the following manner. Alloy steels are those containing any element listed below in a quantity equal to or greater than the quantity for that listed element.
Al-0.10%, B-0.008%, Bi-0.10%, Cr-0.30%, Co-0.10%, Cu-0.40%, Mn-1.65%, Mo-0.06%, Pb-0.40%, Se-0.10%, Si-0.50%, Te-0.10%, Ti-0.05%, W-0.10%, V-0.10%, Zr-0.05%,
Alloy Tool Steels – The principle function of the alloying elements in tool steels is to increase the hardenability; to form hard, wear resistant alloy carbides and to increase resistance to softening on tempering. The alloy tool steels may be roughly classified as follows:
1. Low alloy tools steels – These are having higher hardenability than that of the plain carbon tool steels so that they may be hardened in heavier sections or with less drastic quenches and thereby have less distortion.
2. Intermediate alloy tool steels – These steels usually contain elements such as tungsten, molybdenum or vanadium which form hard wear resistant carbides.
3. 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 that contain sufficient austenite stabilizing elements, such as Mn, Ni, Cr and N, so that the micro structure of these steels is austenitic at room temperature. Such steels cannot be quenched or air hardened but will work hardened rapidly. They are non magnetic.
Bake hardening steels – Bake hardening steels are so constituted that after press forming and baking through the paint curing process they age, i.e. they increase in strength. In this way, good formability 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.
Basic Steel – It is the steel made by the basic process of steel making.
Boiler quality steel – It is the steel used in boilers, pressure vessels and for steam application. It is a high tensile carbon steel with consistent quality and is designed to withstand high pressure.
Boron steels – These are steels which contain boron normally in the range of 0.002 % – 0.003 %. Boron 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 carbon as the specific alloying element are known as carbon steels. These steels can also contain up to 1.2% manganese and 0.4% silicon. Residual elements such as nickel, chromium, aluminium, molybdenum and copper, which are unavoidably retained from raw materials, may be present in small quantities, in addition to impurities such as phosphorous and sulphur.
Carbon manganese steels – Carbon manganese 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 manganese content in these steels is increased for the purpose of increasing depth of hardening and improving strength and toughness. Carbon steels containing over 1.2% up to approximately 1.8% manganese 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 steel making 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 steels produced after cold rolling.
Complex phase (CP) steels – Complex phase 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 Cb. In comparison with DP steels, CP steels show significantly higher yield strengths at equal tensile strengths of 800 MPa and greater. CP steels are characterized by high energy absorption and high residual deformation capacity.
Corten steels – It is distinguished by its high weather resistant properties. The alloying of steel with copper and chromium ensures the formation of a firmly adhering protective layer of rust which protects it from corrosion in atmospheric condition. The protective layer of rust also makes an attractive appearance on the steel surface.
Dead soft steel – These are steels with carbon less than 0.10% and manganese in the 0.20-0.50% range and completely annealed.
Deep Drawing Steel – It is a high quality low carbon 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 that work under heavy pressure and that 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 aid in producing a product, which can stand extreme pressing, drawing or forming operations without creating defects.
Dual phase (DP) steel – These 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. Dual Phase (ferrite plus martensite) 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 microstructure 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 0.05-0.07%.
Electrode quality steels – These are low carbon low silicon and controlled manganese steels used for making welding electrode rods.
Eutectoid steels –These are the steels representing the eutectoid composition of the iron carbon system with about 0.80% to 0.83% carbon and the eutectoid temperature of around 723 degree centigrade. Such steels in the annealed condition consist exclusively of pearlite. The presence of certain elements, such as nickel or chromium, lowers the eutectoid carbon content.
Extra deep drawing steel – It is a superior quality of low carbon deep drawing steel.
Ferritic bainitic (FB) steels – 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 microstructure 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 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 (n) 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 usually fairly large. Examples of flat rolled steel are hot rolled, cold rolled, and coated sheets and coils and tin mill products etc.
Finish steels – These are steels which are ready for the market 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.
Galvanized steels – These are steels coated with a thin layer of zinc to provide corrosion resistance. These are normally used in under body auto parts, garbage cans, storage tanks, or fencing wire. Sheet steels normally must be cold rolled prior to the galvanizing stage.
Hadfield steel – The original austenitic manganese steel, containing about 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 usually it has good resistance to wear.
Heat resisting steels – These are steels required to operate at very high temperatures and therefore they may require one or more of these characteristics such as creep resistance, resistance to oxidation, or other forms of gaseous attack, and freedom from microstructural changes that would lead 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 500-525°C and the austenitic stainless steel grades containing around 25% Cr and 20% Ni being used for higher temperatures.
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 carbon, a combined content of 7% or more of the elements like tungsten, molybdenum and vanadium, 3-6% of chromium and in those required to operate at the highest temperatures additions of 4-13% of cobalt. These steels are widely used for the manufacture of taps, dies, twist drills, reamers, saw blades and other cutting tools.
High strength low alloy (HSLA) steels – These steels are designed to provide better mechanical properties than conventional carbon steels. They are designed to meet specific mechanical properties rather than a chemical composition. The chemical composition of specific HSLA steel may vary for different product thickness to meet mechanical property requirements. The HSLA steels have low carbon contents (0.05 to ~0.25 weight percent C) in order to produce adequate formability and weldability and they have manganese contents up to 2.0 weight percent. Small quantities of chromium, nickel, molybdenum, copper, nitrogen, vanadium, niobium, titanium, and zirconium 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 region (900- 950º C). During processing, three states with different mechanical properties are important.
1. State 1- Tensile strengths up to 600 MPa at room temperature must be considered for the design of blanking dies.
2. State 2 – High elongations (more than 50%) and low strengths at deformation temperatures allow forming of complex shapes. A special coating based on aluminium and silicium is recommended to avoid surface oxidation of the product after forming.
3. State 3 – Following forming, strengths above 1300 MPa are achieved after quenching in the die. Special processes must be taken into account when finishing the product (no additional forming, special cutting and trimming devices, etc.).
Typical cycle time is 20 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 boron 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 with less than eutectoid percentage of carbon.
Hyper eutectoid steels – These are steels having more than the eutectoid percentage of carbon.
Interstitial free steel – It is a recently developed sheet steel product with very low carbon levels that is used primarily in automotive deep drawing applications. Interstitial free steel’s improved ductility (drawing ability) is made possible by vacuum degassing.
Killed steels – Killed steels are made by complete deoxidation of the molten steel before it is cast so that no gas evolution occurs during solidification. These are the steels to which generally aluminium, ferrosilicon or ferromanganese is added as deoxidizing agents. Properly killed steel is more uniform in analysis and is comparatively free from aging. However for the same carbon and manganese content killed steels are harder than rimmed steels. Generally all steels above 0.25% carbon are killed. Also all forging grades of steels, structural steels from 0.15% to 0.25% carbon and some special steels in the low carbon range are killed.
Leaded steels– These are steels to which lead, in amounts between 0.15% – 0.35%, is normally added along with sulphur 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 reduction mill. Light gauge steel normally is plated with tin or chrome for making cans to be used as food containers.
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 oxygen, nitrogen, propane, anhydrous ammonia, carbon dioxide and ethane.
Magnet steels – These are normally alloy electrical steels. The outstanding property of these steels is their ability to retain magnetism. Cobalt, chromium, and tungsten are the alloying elements commonly used to enhance this characteristic.
Maraging steels – These steels are high nickel steels with not less than 18% Ni and are characterised by extreme high strength and toughness. Nickel 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 might 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 450-510 deg C.
Martensitic (MS) steels – To create MS steels, the austenite that exists during hot rolling or annealing is transformed almost entirely to martensite during quenching on the runout 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 multiphase 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.
Micro alloyed steels – These are carbon manganese 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 boron, vanadium and niobium. 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 nickel as an alloying element. Different amounts of nickel 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. They will form a very hard and adherent surface upon proper nitriding process (heating in a partially dissociated atmosphere of ammonia gas). These steels have a composition range usually of 0.20% – 0.40% carbon, 0.90% – 1.50% chromium, 0.15% – 1.00% molybdenum, and 0.85% – 1.20% aluminium.
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.
Plain carbon steel – It is steel where the main alloying constituent is carbon. Steel is considered to be plain carbon steel where minimum content is not specified or required for chromium, cobalt, columbium [niobium], molybdenum, nickel, titanium, tungsten, vanadium or zirconium, or any other element to be added to obtain a desired alloying effect or when the specified minimum for copper does not exceed 0.40 per cent or when the maximum content specified for manganese and silicon does not exceed 1.65% and 0.60% respectively. The plain carbon steels are classified based on carbon percentage.
1. Low carbon steels – Steels with less than 0.005% up to 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) usually cold rolled and annealed condition. It is capable of being drawn out or rolled thin for use in automotive body applications. Carbon is removed from the steel bath through vacuum degassing.
2. Mild steels – These are ordinary weldable non alloy steels with normal strength. The term mild steel is used to describe standard carbon steels used for structural purposes. It is also applied commercially to carbon steels not covered by standard specifications. Carbon content of these steels may vary from levels of 0.10% up to approximately 0.3%. Generally mild steel is readily weldable and have reasonable cold bending properties.
3. Medium carbon steels – These steels are similar to low carbon steels except that the carbon ranges from 0.35% to 0.60% and the manganese from 0.60% to 1.65%. Increasing the carbon content to approximately 0.5% with an accompanying increase in manganese allows medium carbon steels to be used in the quenched and tempered condition. These steels balance ductility and strength and have good wear resistance.
4. High carbon steels – These steels contain carbon ranging from 0.60% to 1.00% with manganese contents ranging from 0.65% to 0.90%. These steels are very strong and are used for springs, high strength wires and other applications.
5. Ultra high carbon steels – These steels contain carbon in the range of 1.05 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.
Post forming heat treatable (PFHT) steel -Post-forming heat treatment is a general method to develop an alternative higher strength steel. The major issue holding back widespread implementation of 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 that allow in part strengths between 900 and 1,400 MPa tensile strength. In addition, some zinc coatings can survive the heat treating cycle because the time at temperature is very short. The wide assortment of chemistries to meet specific part specifications requires extra special coordination with the steel supplier.
Another process is air-hardening of alloyed tempering steels that 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 carbon and manganese, other alloying elements such as chrome, molybdenum, vanadium, boron, and titanium. 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 carbon manganese 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.
Rimming steels – These are steels possessing a rim of purer material (with maximum freedom from surface defects) and is associated with evolution of carbon monoxide gas occurring due to the interaction of dissolved iron oxide and carbon during the solidification of low carbon and low manganese steel made under controlled deoxidation. The composition and extent of the rim can be varied and, if required, the rimming action can be arrested after sometime By 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.
Secondary steels – Steels that do not meet the original customer’s specifications because of a defect in its chemistry, gauge or surface quality are secondary steels. Mills search to find another customer (that can accept the lower quality) to take the off spec steel at a discount.
Semi finished steels – Steel shapes such as blooms, billets or slabs—that later are 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 carbon monoxide to offset solidification shrinkage are semi killed steels.
Silicon electrical steels – These are specialty steels created by introducing silicon during the steel making process. Electrical steel exhibits 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:
1. Grain oriented – The metal’s grain runs parallel within the steel, permitting easy magnetization along the length of the steel. Although grain oriented steel may be twice as expensive to produce, its magnetic directional characteristics enable power transformers, made from this metal, to absorb less energy during operation.
2. Non grain oriented – Because 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 – Types of steels that needs restricted or specific chemical composition or mechanical or metallurgical properties are called speciality steels.
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 carbon type, to C-Si, 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 chromium. 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, N and Mo, a variety of different grades of stainless steel, namely ferritic, austenitic, martensitic, duplex and precipitation hardened type can be produced.
1. Ferritic – It has a body centred cubic structure. Ferritic stainless steels are plain chromium steels with low carbon level and with no significant nickel content. The lack of nickel results in lower corrosion resistance than the austenitic stainless steels (chromium- nickel stainless steels). 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.
2. Austenitic – These steels contain a maximum of 0.15% carbon, a minimum of 16% chromium and sufficient nickel and/or manganese 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% chromium and 8% nickel, commonly known as 18/8 stainless. Super austenitic stainless steels such as alloy AL-6XN and 254SMO, exhibit great resistance to chloride pitting and crevice corrosion due to high molybdenum content (>6%) and nitrogen additions, and the higher nickel 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.
3. 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 can be hardened by heat treatment. Martensitic stainless steels contain chromium in the range of 12%-14%, molybdenum in the range of 0.2% to 1.0%, nickel in the range of 0%- 2and carbon in the range of 0.1% to 1.0%. The steel can be quenched and is magnetic.
4. Precipitation hardening type stainless steels – These steels have corrosin resistance comparable to austenitic stainless steels and can be precipitation hardened to higher strength than other martensitic grades.
5. Duplex stainless steels – These have a mixed microstructure of austenite and ferrite. These have improved strength over austenitic stainless steels and also improved resistance to localized corrosion specially pitting, crevice corrosion and stress corrosion cracking. They have high chromium (19% – 28%) and molybdenum ( up to 5%) and low nickel contents than austenitic grades.
Steel – Steel is an iron base alloy generally suitable for working to the required shape in the solid state having carbon content generally less than its solubility limit in austenite and containing varying amounts of other elements. A limited number of high alloyed steels may have more than 2 % carbon but 2 % is the usual dividing into between steel and cast iron.
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.
Tin free steel – It is single or double reduced black plate having a thin coating of chromium 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 will contaminate scrap steel in even small concentrations.
Tin plate – It is thin sheet steel with a very thin coating of metallic tin. 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 require the use of an isothermal hold at an intermediate temperature, which produces some bainite. The higher silicon and carbon 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 carbon and alloy steels that 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 carbon in the range of 0.7% to 1.4% and need care fully controlled condition during manufacturer. The manganese content is kept low to avoid cracking during water quenching.
Twinning induced plasticity (TWIP) steel – TWIP steels have high manganese content (17% – 24%) that 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 microstructure 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 that 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.