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Glossary of Terms - Steel

The Carmeuse Lime & Stone glossary of terms is a great resource for our customers and visitors. Here you can find definitions for many industry terms and acronyms regarding the multiple uses of lime. You'll find this section to be a useful supplement to the research papers and case studies available through our website. Locate a definition in the immediate display of general terms or choose an industry from the list to find terms specific to their application.

 

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Acid Steel

Steel produced in a furnace with an acid lining, i.e. consisting of a siliceous refractory and under a siliceous slag. With an acid slag, carbon, silicon and manganese only are removed so that the pig iron must not contain sulfur and phosphorus in percentages exceeding those permissible for the specification being made. Most steel manufactured today is in furnaces with basic linings.

Active oxygen

The free oxygen in liquid iron or steel which is in the form of FeO. It is normally measured using an oxygen probe.

Alloy Steel

A steel to which one or more alloying elements other than carbon have been deliberately added (e.g. chromium, nickel, molybdenum) to achieve a particular physical property.

Alumina Inclusion

Inclusion formed by the addition of aluminum to deoxidize the liquid steel (drive the gaseous oxygen out)

Annealing

Heating steel to, and holding at a suitable temperature, followed by relatively slow cooling. The purpose of annealing may be to remove stresses, to soften the steel, to improve machinability, to improve cold working properties, to obtain a desired structure. The annealing process usually involves allowing the steel to cool slowly in the furnace.

Arc Furnace

A steel melting furnace in which heat is generated by an arc between graphite electrodes and the metal. Both carbon and alloy steels are produced in electric arc furnaces and scrap rather than molten metal is used as the base material. Furnaces with capacities up to 200 tonnes are now in use.

Argon Stirring/Rinsing

Used for several purposes, including rapid and uniform mixing of alloys, temperature homogenization, adjustment of chemical composition and partial removal of non-metallic inclusions. This accomplished by the blowing of argon through porous refractory plugs inserted in the bottom of refractory lined ladles or in a refractory rod.

Argon-Oxygen Decarburization (AOD)

Process for further refinement of stainless steel through reduction of carbon content. The amount of carbon in stainless must be lower than that in carbon steel or lower alloy steel. After melting in the EAF the steel is transferred to the vessel and a mixture of argon and oxygen is blown from the bottom of the vessel.

Austempering

Quenching from a temperature above the transformation range to a temperature above the upper limit of martensite formation, and holding at this temperature until the austenite is completely transformed to the desired intermediate structure, for the purpose of conferring certain mechanical properties.

Austenite

The solid solution of carbon in gamma (face centered cubic) iron.

Austenitic Steels

Steels containing high percentages of certain alloying elements such as manganese and nickel which are austenitic at room temperature and cannot be hardened by normal heat-treatment but do work harden. They are also non-magnetic. Typical examples of austenitic steels include the 18/8 stainless steels and 14% manganese steel.

 

Bainite

An acicular aggregate of ferrite and carbide particles formed when austenite is transformed on cooling at temperatures in the intermediate (200-450°C) range, i.e. above the martensite and below the pearlite range.

Bars

Long steel products that are rolled from billets or blooms. Merchant bars, rebar, rounds, flats, angles, squares, and channels are common forms.

Basic Steel

Steel produced in a furnace in which the hearth consists of a basic refractory such as dolomite or magnesite, as opposed to steel melted in a furnace with an acid lining. The basic process permits the removal of sulfur and phosphorous and in this respect is superior. Present day BOS and electric arc furnaces use basic linings.

Bend Test

Bending tests are carried out to ensure that a metal has sufficient ductility to stand bending without fracturing. A standard specimen is bent through a specified arc and in the case of strip, the direction of grain flow is noted and whether the bend is with or across the grain.

Billet

Steel in a semi-finished stage in the form of a square cross section with rounded corners and having a length several times greater than their maximum cross sectional area. Sizes range from 2"x2" to under 10"x10".

Blast Furnace

A tall, cylindrical, refractory lined furnace for the production of pig iron or hot metal for direct conversion into steel.

Bloom

A large square section of steel intermediate in the rolling process between an ingot and a billet. Blooms are now also being produced by the continuous casting process eliminating the necessity of first producing an ingot. Sizes are greater than 10"x10"

BOP/BOF

Basic Oxygen Process/Basic Oxygen Furnace: Modern steel making process employing the use of high purity oxygen blowing onto the surface of the bath in a basic lined vessel by a cooled vertical pipe or lance inserted into the mouth of the vessel.

Boron Steels

The addition of boron in the range 0.0005- 0.005% to certain steels increases the hardenability. A range of boron steels is now listed in the current BS 970 and are widely used for the production of cold headed fastenings.

 

Calcium

In the form of calcium silicide acts as a deoxidizer and degasifier when added to steel. Recent developments have found that carbon and alloy steels modified with small amounts of calcium show improved machinability and longer tool life. Transverse ductility and toughness are also enhanced.

Carbon

Carbon is an essential element in steel, it is added in specific amounts to control the hardness and strength of the material. In general, increased carbon content reduces ductility but increases tensile strength and the ability of the steel to harden when cooled rapidly from elevated temperatures. This can be in the form of anthracite coal or petroleum coke.

Carbon Steel

A steel whose properties are determined primarily by the amount of carbon present. Apart from iron and carbon, manganese up to 1.5% may be present as well as residual amounts of alloying elements such as nickel, chromium, molybdenum, etc. It is when one or more alloying elements are added in sufficient amount that it is classed as an alloy steel.

Cast Iron

A definition can be applied that Cast Iron is an alloy of iron and carbon in which the carbon is in excess of the amount that can be retained in solid solution in austenite at the eutectic temperature. Carbon is usually present in the range of 1.8% to 4.5%, in addition, silicon, manganese, sulfur and phosphorus are contained in varying amounts. Various types of cast iron are covered by a British Standard classification and includes grey, malleable and white irons. Elements such as nickel, chromium, molybdenum, vanadium can be added to produce alloy cast irons.

Charge buckets

A container used for holding, transporting and dumping scrap and other raw materials into a furnace.

Coefficient of Expansion

The ratio of change in length, area, or volume per degree to the corresponding value at a standard temperature.

Coils

Steel sheet that has been wound. A slab, once rolled in a hot-strip mill, is more than one quarter mile long; coils are the most efficient way to store and transport sheet steel.

Cold Drawing

The process of reducing the cross sectional area of wire, bar or tube by drawing the material through a die without any pre-heating. Cold drawing is used for the production of bright steel bar in round square, hexagonal and flat section. The process changes the mechanical properties of the steel and the finished product is accurate to size, free from scale with a bright surface finish.

Cold Working

Altering the shape or size of a metal by plastic deformation. Processes include rolling, drawing, pressing, spinning, extruding and heading, it is carried out below the recrystallization point usually at room temperature. Hardness and tensile strength are increased with the degree of cold work whilst ductility and impact values are lowered. The cold rolling and cold drawing of steel significantly improves surface finish.

Continuous Casting

A method of producing blooms, billets and slabs in long lengths using water cooled molds. The castings are continuously withdrawn through the bottom of the caster whilst the teeming of the metal is proceeding. The need for primary and intermediate mills and the storage and use of large numbers of ingot molds is eliminated. The continuous casting process is also used in the production of cast iron, aluminium and copper alloys.

Critical Temperature

The temperature at which some phase change occurs in a metal during heating or cooling, i.e. the temperature at which an arrest or critical point is shown on heating or cooling curves.

 

Dead-burned dolomite

A highly sintered form of dolomitic quicklime which is used primarily as a basic refractory material.

Decarburization

The loss of carbon from the surface of steel as a result of heating in a carbon weak atmosphere. During the rolling of steel hot surfaces are exposed to the decarburizing effects of oxygen in the atmosphere and as a result the surface is depleted of carbon. In steels where the components are to be subsequently heat treated it is necessary to remove the decarburized surface by machining.

Deoxidation

Elements such as silicon and aluminium when added to molten steel react to form stable oxides and reduce the amount of dissolved oxygen. The solubility of oxygen in steel is reduced as temperature is lowered during solidification and the excess oxygen combines to form carbon monoxide. If the molten metal is not deoxidized the effervescence produced by the evolution of carbon monoxide during solidification would result in blow holes and porosity. Steel treated in this way is termed, "Killed Steel".

Desulfurization

Operation that injects a chemical mixture of lime base products into a ladle of hot metal prior to its charging into the BOF. In the EAF process, lime fluxes are added to the ladle after tapping and the slag is deoxidized with calcium carbide or metallic deoxidants and stirred to reduce the sulfur content in the steel.

Dolomite

A natural carbonate of calcium and magnesium generally used as a flux in furnaces to prevent erosion of refractory. Dead-burned dolomite a highly sintered form of dolomitic quicklime which is used primarily as a basic refractory material.

Ductility

The property of metal which permits it to be reduced in cross sectional area without fracture. In a tensile test, ductile metals show considerable elongation eventually failing by necking, with consequent rapid increase in local stresses.

 

Elasticity

The property which enables a material to return to its original shape and dimension.

Electric Arc Furnace

Steelmaking furnace where scrap is generally 100% of the charge. Heat is supplied from electricity that arcs from graphite electrodes to the metal bath. Furnaces may be either an alternating current (AC) or direct current (DC). Use primarily for just melting and very little refining is done in the furnace.

Electrical Steels

Steels which are characterized by their magnetic properties and are intended for the manufacture of electrical circuits. They are supplied in the form of cold rolled sheet or strip, generally less than 2mm thick and up to 1500mm wide. Grain orientated steels have preferential magnetic properties in the direction of rolling and non-grain orientated steels have similar magnetic properties both transversely and in the direction of rolling.

Elongation

A test to measure the ductility of steel. When a material is tested for tensile strength it elongates a certain amount before fracture takes place. The two pieces are placed together and the amount of extension is measured against marks made before starting the test and is expressed as a percentage of the original gauge length.

Equiaxed Crystals

Crystals, each of which has axes approximately equal in length. These are normally present in the centre of a steel ingot.

Equilibrium

A diagram constructed from thermal and other data showing the limits of composition and temperature within which the various constituents or phases of alloys are stable.

Etching

Treatment of a prepared metal surface with acid or other chemical reagent which, by differential attack, reveals the structure.

Eutectic

A mixture of two or more constituents which solidify simultaneously out of the liquid at a minimum freezing point.

Eutectoid

A mixture of two or more constituents which forms on cooling from a solid solution and transforms on heating at a constant minimum temperature. A eutectoid steel contains approximately 0.83.

 

Ferrite

The solid solution of carbon in body-centered cubic iron, a constituent of carbon steels.

Ferritic Steel

A term usually applied to a group of stainless steels with a chromium content in the range of 12-18° and whose structure consists largely of ferrite. Such steels possess good ductility and are easily worked but do not respond to any hardening or tempering processes. Types of applications include automotive trim and architectural cladding.

Ferro Alloys

Alloys of iron with chromium, manganese, silicon, tungsten, molybdenum or vanadium. Used in steelmaking as a means of introducing these alloying elements into the cast or as deoxidizers.

Flux

An agent that is normally a blended lime based product utilizing fluidizers that will speed up the dissolution of the material so that it can collect impurities in the steel making process during gas stirring in the ladle or vessel. It is utilized to influence the reduction of active oxygen in the slag and steel.

Freecutting Steels

Steels which have had additions made to improve machinability. The most common additives are sulfur and lead, other elements used include tellurium, selenium and bismuth.

 

Grain Size Measurement

Grain size is normally quantified by a numbering system. Coarse 1-5 and fine 5-8. The number is derived from the formula N=2n-1 where n is the number of grains per square inch at a magnification of 100 diameters. Grain size has an important effect on physical properties. For service at ordinary temperatures it is generally considered that fine grained steels give a better combination of strength and toughness, whereas coarse grained steels have better machinability.

 

Heat

In steel making terms this is often used to define the batch or cast produced from a single melting operation.

Heat Treatment

A process where solid steel or components manufactured from steel are subject to treatment by heating to obtain required properties, e.g. softening, normalizing, stress relieving, hardening. Heating for the purpose of hot-working as in the case of rolling or forging is excluded from this definition.

 

Inclusion Count

A method of assessing the number and size of non-metallic inclusions present in metal.

Inclusions

Usually non-metallic particles contained in metal. In steel they may consist of simple or complex oxides, sulfides, silicates and sometimes nitrides of iron, manganese, silicon, aluminium and other elements. In general they are detrimental to mechanical properties but much depends on the number, their size, shape and distribution.

Ingot

The mass of metal that results from casting molten steel into a mold. An ingot is usually rectangular in shape and is subsequently rolled into blooms and billets for rods, bars and sections and slabs for plates, sheet and strip. With the increasing use of the continuous casting process the ingot route is less used as the molten steel is now directly cast into a bloom or billet.

Ingot Mold

The receptacle into which molten steel is poured to form an ingot. After solidification the steel is suitable for subsequent working, i.e. rolling or forging.

Integrated Mills

These facilities make steel by processing iron ore and other raw materials in blast furnaces. Technically, only the hot end differentiates integrated mills from mini-mills. Nearly all domestic integrated mills specialize in flat rolled steel.

Iron

The term iron, as used in the chemical or scientific sense of the word, refers to the chemical element iron or pure iron and is the chief constituent of all commercial iron and steel.

 

Killed Steel

The term indicates that the steel has been completely deoxidized by the addition of an agent such as silicon or aluminum, before casting, so that there is practically no evolution of gas during solidification. Killed steels are characterized by a high degree of chemical homogeneity and freedom from porosity.

 

Ladle Metallurgy Furnace (LMF)

An intermediate steel processing unit that furthers refines the chemistry and temperature of molten steel while it is still in the ladle. The ladle metallurgy step comes after the steel is melted in the electric arc or basic oxygen furnace, but before the steel is sent to the continuous caster or teeming ailse.

Leaded Steels

When added to steel, lead does not go into solution but exists in a very finely divided state along the grain boundaries. It greatly assists machinability as it acts as a lubricant between the steel and the tool face. Lead is normally added in amounts between 0.15-0.35% and when combined with similar amounts of sulfur, optimum machinability is attained as in such steel as BS 970 230M07 Pb.

Long Products

Classification of steel products that includes bar products, rod and structural products. Long products are traditional products of mini-mills.

 

Macrostructure

The general crystalline structure of a metal and the distribution of impurities seen on a polished or etched surface by either the naked eye or under low magnification of less than x10.

Martensite

The hard constituent produced when steel is cooled from the hardening temperature at a speed greater than its critical cooling rate. Martensite is an acicular phase when seen in the microstructure of steel.

Matrix

The mass or principal constituent (e.g. iron in the case of steel) in which other constituents are embedded.

Melting Point

The temperature at which a solid begins to liquefy.

Microstructure

The structure that is observed when a polished and etched specimen of metal is viewed in an optical microscope at magnifications in range of approximately x25 to x1500.

Mini-Mills

Normally defined as a steel mill melts scrap metal to produce commodity products. Although the mini-mills are subject to the same steel processing requirements after the caster as the integrated steel companies, they differ greatly in regard to their minimum efficient size, labor relations, product markets and management styles.

 

Non Destructive Testing

Those forms of testing that do not result in permanent damage or deformation to the part being tested. Typical examples are magnetic crack detection, ultrasonic inspection, X-Ray inspection and gamma radiography.

Non Magnetic Steels

Austenitic steels such as the 14% manganese steels and the 303 type 18/8% chromium-nickel stainless steels.

Normalizing

A heat treatment process that has the object of relieving internal stresses, refining the grain size and improving the mechanical properties. The steel is heated to 800-900°C according to analysis, held at temperature to allow a full soak and cooled in still air.

 

Oxidation

A common form of chemical reaction which is the combining of oxygen with various elements and compounds. The corrosion of metals is a form of oxidation, rust on iron for example is iron oxide.

Oxygen

Oxygen is one of the chief constituents of the atmosphere of which it forms approximately one fifth. It is odorless and invisible. Although oxygen itself does not burn it is extremely efficient in supporting combustion, nearly all other chemical elements combine with it under evolution of heat. It has many uses in industry and is essential to the BOS (Basic Oxygen Steel making Process).

 

Pig Iron

The product of the blast furnace. The term was derived from the method of casting the bars of the pig iron in depressions or molds formed in the sand floor adjacent to the furnace. These were connected to a runner (known as a sow) and when filled with metal the runner and the numerous smaller molds were supposed to resemble a litter of suckling pigs, hence the term pig iron.

Pipe

A defect that arises during the solidification of steel in the ingot mold. As steel contracts on solidification a central cavity forms in the upper portion of the ingot, if this is not completely removed before rolling into bars a central defect known as "pipe" results. The risk of piping is considerably reduced on continuously cast steel due to molten steel being available to fill any shrinkage cavity.

Plate

Sheet steel with a width of more than eight inches, with a thickness ranging from one quarter of an inch to more than one foot.

 

Quenching

Rapid cooling from a high temperature by immersion in a liquid bath of oil or water. Molten salts may also be used.

 

Re-crystallization

The re-arrangement of crystals in cold worked metal brought about by heating so that the deformed crystals are absorbed by newly-formed crystals and the effects of work hardening are removed. Also occurs when steel is heated through the transformation range and when steel is hot worked.

Reduction of area

The percentage decrease in the cross-sectional area of a tensile test piece caused by wasting or necking of the specimen. It is expressed as a percentage of the original area of the test piece and is a measure of ductility.

Refining

(a) The removal of impurities and metallic oxides from the molten bath by the reaction of the slag and other additions. (b) A heat treatment process with the object of refining or making the grain size of the steel uniform.

Residuals

The impurities in mini-mill steel as the result of the mix of metals entering the process dissolved in obsolete scrap. Residuals are key concerns regarding the mini-mills recent entry into the flat-rolled market, where high residuals can leave sheet steel too brittle for the customer use. Typically these are Cu, Sn, Cr, and Ni.

Rod

Round, thin semi-finished steel length that is rolled from a billet or bloom and coiled for further processing. Rod is commonly drawn into wire products or used to make bolts and nails. Rod mills can run as fast as 20,000 ft/min. (200 mph).

Rolling

The process of shaping metal by passing it between rolls revolving at the same peripheral speed and in opposite directions. In steel there are a number of different types of rolling mill for processing the ingot to its finished shape. These are variously known as Cogging mills, Slabbing mills, Billet mills, Bar mills and Strip mills, which produce plate, sections, bars, sheet and strip. Cold rolling of previously hot rolled strip is carried out to produce strip that is accurate to size and with a smooth bright polished surface.

 

Scale

The oxidized surface of steel produced during hot working, as in rolling, and by exposure to air or steam at elevated temperature.

Scrap

It forms the basic raw material for making steel by the electric arc process. Steel offers ecological advantages as it can be recycled enabling the discarded car of today to appear as part of a new model tomorrow. Scrap is sorted and graded before use and the necessary elements are added during the steel making process to achieve the desired specifications.

Scrap substitutes

Feedstock that can be charged in place of scrap in the EAF and BOF to help lower residuals. These substitutes include Direct Reduced Iron (DRI), Hot Briquetted Iron (HBI), iron carbide and pig iron.

Segregation

A term applied to the concentration and partial separation of one or more elements from solution during solidification of liquid steel in an ingot mold. Sulfur and phosphorus tend to segregate to a greater extent than other elements which can have a particular adverse effect on machinability in high sulfur free-cutting steels. Modern steel making and continuous casting have largely overcome this problem.

Sheet steel

Thin, flat-rolled steel. Coiled sheet steel accounts for nearly one-half of all steel shipped domestically and is created in a hot-strip mill by rolling a cast slab.

Slab

The most common type of semi-finished steel. Traditional slabs measure ten inches thick and 30-85 inches wide and average 20 feet long. Recent "thin slab" casting machines cast approximately 2 inches thick and then are sent to the hot-strip mill to be rolled into coiled sheet.

Slag

Slag is a combination of metallic and non-metallic oxides, usually molten, that floats on a pool of iron or steel. The slags comes from fluxes such as lime, dolomitic lime, fluorspar, calcium aluminate, dissolved refractories from the furnace, and metallic elements in the melted scrap. Because slag is less dense it floats on top of the liquid steel.

Special Bar Quality (SBQ)

This represents a wide variety of high quality carbon and alloy bars that are used in forging, machining and cold-drawing industries.

Spring Steel

The steels used for spring making depend on the application and type of spring. They range from plain carbon grades in the range 0.5% to 1.00% C. to Chromium, Chromium-Vanadium, Nickel-Chromium-Molybdenum, Silico-Manganese and Silicon-Manganese-Chromium-Molybdenum types. Full details can be found in BS5770.

Stainless Steel

Can be defined as a group of corrosion resisting steels containing a minimum 10% chromium and in which varying amounts of nickel, molybdenum, titanium, niobium as well as other elements may be present. An Englishman, Harry Brearley, is generally acknowledged to be the pioneer who developed stainless steels for commercial use.

Steel

Generally defined as a metallic product whose principal element is iron and where the carbon content is not more than 2%. (The presence of large quantities of carbide forming elements may modify the upper limit of the carbon content.)

Strain Ageing

The gradual changes in physical and mechanical properties, in particular hardness and tensile strength, which takes place following cold rolling or deformation. At atmospheric temperatures, this may take place over a number of weeks but can be accelerated by heating.

Strain Hardening

The loss of ductility and gain in hardness resulting from strain ageing.

Stress Relieving

A heat treatment including heating and soaking at a suitable temperature (e.g. 600-650°C) followed by cooling at an appropriate rate in order to reduce internal stresses without substantially modifying the steel's structure. This treatment may be used to relieve stresses induced by machining, quenching, welding or cold working.

Structural steels

Product group that includes I-beams, H-beams, wide-flange beams and sheet piling. These are used in the construction of multi-story buildings, bridge trusses, vertical highway supports and riverbank reinforcement.

Sulfur

One of the elements present in varying quantities in coal that contributes to environmental degradation when coal is burned. EIA classifies coal, in terms of pounds of sulfur per million Btu as low (less than or equal to 0.60 pounds of sulfur), medium (between 0.61 ad 1.67 pounds of sulfur), and high (greater than or equal to 1.68 pounds of sulfur). When coal is sampled, sulfur content is measured as a percent by weight of coal on an "as received" or "dry" (moisture-free) basis. Sulfur occurs in coal in three forms: (1) iron sulfides (pyrite and marcasite), (2) secondary sulfates (gypsum and hydrous ferrous sulfate), and (3) organic sulfur chemically bonded to the coal forming plant material.

 

Tap-to-tap time

The time lapse between tapping the furnace and the next tap.

Temper

A term to which a number of definitions can be applied. These include: a) The operation of tempering; b) The degree of hardness left in a steel bar after quenching and tempering; c) The grading of the hardness of low carbon cold rolled strip, e.g. Hard, Half Hard, Quarter Hard, Skin Passed, Soft; d) An indication of the amount of carbon present in a tool steel, e.g. razor temper, file temper, die temper, etc.

Tensile Strength

The maximum load applied in breaking a tensile test piece divided by the original cross-sectional area of the test piece. Originally quoted as tons/sq.in. it is now measured as Newtons/sq.mm. Also termed Maximum Stress and Ultimate Tensile Stress.

Tool Steel

A generic term applied to a wide range of steels, both plain carbon and alloy. It includes steels suitable for various types of cutting tools, press tools, hot and cold heading dies, molds for plastics and die-casting, extrusion tools, hand tools, etc.

Transformation Range

The temperature range within which austenite forms and ferrite or carbide progressively dissolves while ferrous alloys are being heated. Also the temperature range within which austenite decomposes to form ferrite and carbide on cooling.

Transformation Temperature

The temperature at which a change in phase occurs or the limiting temperature of a transformation range. These critical points are denoted by symbols, e.g. Ac1; the temperature at which austenite begins to form on heating. There are 12 principal temperatures to which symbols are applied.

TTT Curve

An abbreviation of Time Temperature Transformation Curve

Tundish

A refractory-lined vessel on top of the molds of a continuous caster that receives liquid steel from the ladle, during casting and acts as a distributor to regulate flow of metal into multiple water cooled molds to produce a slab, billet or bloom.

 

Unkilled Steel

Steel which has been insufficiently deoxidized and evolves gas during solidification with the formation of blow-holes.

 

Vacuum Degassing

A ladle of molten metal is placed within a chamber which is then evacuated. This reduces the gas content, particularly hydrogen, as well as reducing non-metallic inclusions. Modern secondary steel making processes using Vacuum Arc Degassing units that include automated stirring and control of temperature and chemical analysis, ensure a consistent and high quality product.

 

Yield Strength

The stress at which general plastic elongation of the test piece takes place. This point is well defined in hardened and tempered or annealed structures but can be ill defined in "as drawn" structures.

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