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Encyclopedia > Carbon steel
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Iron alloy phases

Austenite (γ-iron; hard)
Bainite
Martensite
Cementite (iron carbide; Fe3C)
Ledeburite (ferrite - cementite eutectic, 4.3% carbon)
Ferrite (α-iron, δ-iron; soft)
Pearlite (88% ferrite, 12% cementite)
Spheroidite General Name, symbol, number iron, Fe, 26 Chemical series transition metals Group, period, block 8, 4, d Appearance lustrous metallic with a grayish tinge Standard atomic weight 55. ... For specification language, see Alloy Analyzer. ... Iron-carbon phase diagram, showing the conditions under which austenite (γ) is stable in carbon steel. ... Iron-carbon phase diagram, showing the eutectoid temperature and composition, at which bainite can form. ... Martensite in AISI 4140 steel 0. ... Cementite or iron carbide is a chemical compound with the formula Fe3C, and an orthorhombic crystal structure. ... Iron-carbon phase diagram, showing the iron-carbon phase diagram (near the lower left). ... Iron-carbon phase diagram, showing the conditions under which ferrite (α) is stable. ... Pearlite occurs at the eutectoid of the iron-carbon phase diagram (near the lower left). ... Wikipedia does not yet have an article with this exact name. ...

Types of Steel

Plain-carbon steel (up to 2.1% carbon)
Stainless steel (alloy with chromium)
HSLA steel (high strength low alloy)
Tool steel (very hard; heat-treated)
For other uses, see Steel (disambiguation). ... Plain-carbon steel is a metal alloy, a combination of two elements, iron and carbon, where other elements are present in quantities too small to affect the properties. ... The 630 foot high, stainless-clad (type 304L) Gateway Arch defines St. ... HSLA steel (high strength low alloy steel) is a type of steel alloy that provides many benefits over regular steel alloys. ... Tool steel refers to a variety of carbon and alloy steels that are particularly well-suited to be made into tools. ...

Other Iron-based materials

Cast iron (>2.1% carbon)
Wrought iron (almost no carbon)
Ductile iron
Cast iron usually refers to grey cast iron, but can mean any of a group of iron-based alloys containing more than 2% carbon (alloys with less carbon are carbon steel by definition). ... It has been suggested that Wrought iron furniture be merged into this article or section. ... -1...

Carbon steel,is very fun 2 play with also called plain carbon steel, is a metal alloy, a combination of two elements, iron and carbon, where other elements are present in quantities too small to affect the properties. The only other alloying elements allowed in plain-carbon steel are manganese (1.65% max), silicon (0.60% max), and copper (0.60% max). Steel with a low carbon content has the same properties as iron, soft but easily formed. As carbon content rises the metal becomes harder and stronger but less ductile and more difficult to weld. Higher carbon content lowers steel's melting point and its temperature resistance in general. This article does not cite any references or sources. ... For specification language, see Alloy Analyzer. ... General Name, symbol, number iron, Fe, 26 Chemical series transition metals Group, period, block 8, 4, d Appearance lustrous metallic with a grayish tinge Standard atomic weight 55. ... General Name, symbol, number carbon, C, 6 Chemical series nonmetals Group, period, block 14, 2, p Appearance black (graphite) colorless (diamond) Standard atomic weight 12. ... General Name, symbol, number manganese, Mn, 25 Chemical series transition metals Group, period, block 7, 4, d Appearance silvery metallic Standard atomic weight 54. ... General Name, Symbol, Number silicon, Si, 14 Chemical series metalloids Group, Period, Block 14, 3, p Appearance as coarse powder, dark grey with bluish tinge Standard atomic weight 28. ... For other uses, see Copper (disambiguation). ... For other uses, see Steel (disambiguation). ... Ductility is the physical property of being capable of sustaining large plastic deformations without fracture (in metals, such as being drawn into a wire). ... Welding is a fabrication process that joins materials, usually metals or thermoplastics, by causing coalescence. ...


Carbon content influences the yiestrength of steel because they fit into the interstitial crystal lattice sites of the body-centered cubic arrangement of the iron molecules. The interstitial carbon reduces the mobility of dislocations, which in turn has a hardening effect on the iron. To get dislocations to move, a high enough stress level must be applied in order for the dislocations to "break away". This is because the interstitial carbon atoms cause some of the iron BCC lattice cells to distort. Interstitials are a variety of crystallographic defects, i. ... In geometry and crystallography, a Bravais lattice, named after Auguste Bravais, is an infinite set of points generated by a set of discrete translation operations. ... The cubic crystal system is a crystal system where the unit cell is in the shape of a cube. ... In materials science, a dislocation is a crystallographic defect, or irregularity, within a crystal structure. ...

Contents

Types of carbon steel

Typical compositions of carbon:

  • Mild (low carbon) steel: approximately 0.05–0.29% carbon content[1] (e.g. AISI 1018 steel). Mild steel has a relatively low tensile strength, but it is cheap and malleable; surface hardness can be increased through carburizing.[2]
  • Medium carbon steel: approximately 0.30–0.59% carbon content[1](e.g. AISI 1040 steel). Balances ductility and strength and has good wear resistance; used for large parts, forging and automotive components.[3]
  • High carbon steel: approximately 0.6–0.99% carbon content [1]. Very strong, used for springs and high-strength wires.[4]
  • Ultra-high carbon steel: approximately 1.0–2.0% carbon content [1]. Steels that can be tempered to great hardness. Used for special purposes like (non-industrial-purpose) knives, axles or punches. Most steels with more than 1.2% carbon content are made using powder metallurgy and usually fall in the category of high alloy carbon steels.

Steel can be heat-treated which allows parts to be fabricated in an easily-formable soft state. If enough carbon is present, the alloy can be hardened to increase strength, wear, and impact resistance. Steels are often wrought by cold-working methods, which is the shaping of metal through deformation at a low equilibrium or metastable temperature. blah Carburization (often referred to as carburizing) is the name of the process by which carbon is introduced into a metal. ... Powder metallurgy is a forming and fabrication technique consisting of three major processing stages. ... Cold Work is a quality imparted on a material as a result of plastic deformation. ...


Metallurgy

Mild steel is the most common form of steel as its price is relatively low while it provides material properties that are acceptable for many applications. Mild steel has a low carbon content (up to 0.3%) and is therefore neither extremely brittle nor ductile. It becomes malleable when heated, and so can be forged. It is also often used where large amounts of steel need to be formed, for example as structural steel. Density of this metal is 7,861.093 kg/m³ (0.284 lb/in³), the tensile strength is a maximum of 500 MPa (72,500 psi) and it has a Young's modulus of 210 GPa. For finery forges (making iron), see finery forge. ...


Carbon steels which can successfully undergo heat-treatment have a carbon content in the range of 0.30–1.70% by weight. Trace impurities of various other elements can have a significant effect on the quality of the resulting steel. Trace amounts of sulfur in particular make the steel red-short. Low alloy carbon steel, such as A36 grade, contains about 0.05% sulfur and melts around 1426–1538 °C (2600–2800 °F).[5] Manganese is often added to improve the hardenability of low carbon steels. These additions turn the material into a low alloy steel by some definitions, but AISI's definition of carbon steel allows up to 1.65% manganese by weight. The periodic table of the chemical elements A chemical element, or element, is a type of atom that is defined by its atomic number; that is, by the number of protons in its nucleus. ... General Name, Symbol, Number sulfur, S, 16 Chemical series nonmetals Group, Period, Block 16, 3, p Appearance lemon yellow Standard atomic weight 32. ... Red-short is the quality possessed by carbon steel that suffers from having too much sulfur as an impurity. ... A36 steel is a standard steel alloy which is the most common structural steel used in the United States. ... General Name, symbol, number manganese, Mn, 25 Chemical series transition metals Group, period, block 7, 4, d Appearance silvery metallic Standard atomic weight 54. ... Low alloy steel is steel alloyed with other elements, usually molybdenum, manganese, chromium, vanadium, silicon, boron or nickel, in amounts of up to 10% by weight to improve the hardenability of thick sections. ... The American Iron and Steel Institute (AISI) is an association of North American steel producers formed in 1855. ...


Hardened steel usually refers to quenched or quenched and tempered steel.


Silver steel or high-carbon bright steel, gets its name from its appearance, due to the high carbon content. It is a very-high carbon steel, or can be thought of as some of the best high-carbon steel. It is defined under the steel specification standards BS-1407. It is a 1%-carbon tool steel which can be ground to close tolerances. Usually the range of carbon is minimum 1.10% but as high as 1.20%. It also contains trace elements of 0.35% Mn (range 0.30–0.40%), 0.40% Cr (range 0.4–0.5%), 0.30% Si (range 0.1–0.3%), and also sometimes sulfur (max 0.035%) and phosphorus (max 0.035%). Silver steel is sometimes used for making straight razors, due to its ability to produce and hold a micro-fine edge, as those made by the French company Thiers-Issard. blah A straight razor Straight razor is the name given to a reusable knife blade used for shaving facial hair. ...


Heat treatments

Iron-carbon phase diagram, showing the temperature and carbon ranges for certain types of heat treatments.

The purpose of heat treating plain-carbon steel is to change the mechanical properties of steel, usually ductility, hardness, yield strength, and impact resistance. Note that the electrical and thermal conductivity are slightly altered. As with most strengthening techniques for steel, the modulus of elasticity (Young's modulus) is never affected. Steel has a higher solid solubility for carbon in the austenite phase, therefore all heat treatments, except spheroidizing and process annealing, start by heating to an austenitic phase. The rate at which the steel is cooled through the eutectoid reaction affects the rate at which carbon diffuses out of austenite. Generally speaking, cooling quickly will give a finer pearlite (until the martensite critical temperature is reached) and cooling slowly will give a coarser pearlite. Cooling a hypoeutectoid (less than 0.8 wt% C) steel results in a pearlitic structure with α-ferrite at the grain boundaries. If it is hypereutectoid (more than 0.8 wt% C) steel then the structure is full pearlite with small grains of cementite scattered throughout. The relative amounts of constituents are found using the lever rule. Here is a list of the types of heat treatments possible: Image File history File links Heat_transfer_steel_diag2. ... Image File history File links Heat_transfer_steel_diag2. ... In physical chemistry, mineralogy, and materials science, a phase diagram is a type of graph used to show the equilibrium conditions between the thermodynamically-distinct phases. ... In solid mechanics, Youngs modulus (E) is a measure of the stiffness of a given material. ... Iron-carbon phase diagram, showing the conditions under which austenite (γ) is stable in carbon steel. ... Eutectoid transformation occurs when a solid solution decomposes into a fixed two solid constituents at a fixed temperature. ... Pearlite occurs at the eutectoid of the iron-carbon phase diagram (near the lower left). ... Martensite in AISI 4140 steel 0. ... Iron-carbon phase diagram, showing the conditions under which ferrite (α) is stable. ... Cementite or iron carbide is a chemical compound with the formula Fe3C, and an orthorhombic crystal structure. ... In metallurgy the Lever rule is a mathematical expression whereby the relative phase amounts in a two-phase alloy at equilibrium may be computed. ...

  • Spheroidizing: Spheroidite forms when carbon steel is heated to approximately 700 °C for over 30 hours. Spheroidite can form at lower temperatures but the time needed drastically increases, as this is a diffusion controlled process. The result is a structure of rods or spheres of cementite within primary structure (ferrite or pearlite, depending on which side of the eutectoid you are on). The purpose is to soften higher carbon steels and allow more formability. This is the softest and most ductile form of steel. The image to the right shows where spheroidizing usually occurs.
  • Full annealing: Plain-carbon steel is heated to approximately 40 °C above Ac3 or Ac1 for 1 hour; this assures all the ferrite transforms into austenite (although cementite still might exist if the carbon content is greater than the eutectoid). The steel must then be cooled slowly, in the realm of 38 °C (100 °F) per hour. Usually it is just furnace cooled, where the furnace is turned off with the steel still inside. This results in a coarse pearlitic °structure, which means the "bands" of pearlite are thick. Fully annealed steel is soft and ductile, with no internal stresses, which is often necessary for cost-effective forming. Only spheroidized steel is softer and more ductile.
  • Process annealing: A process used to relieve stress in a cold-worked plain-carbon steel with less than 0.3 wt% C. The steel is usually heated up to 550–650 °C for 1 hour, but sometimes temperatures as high as 700 °C. The image to the right shows the area where process annealing occurs.
  • Isothermal Annealing:It is a process in which hypo eutectoid steel is heated above the upper critical temperature and this temperature is maintained for a period of time and then the temperature is brought down below lower critical temperature and is again maintained. Then finally it is cooled at room temperature. This method helps in eliminating any temperature gradient.
  • Normalizing: Plain-carbon steel is heated to approximately 55 °C above Ac3 or Acm for 1 hour; this assures the steel completely transforms to austenite. The steel is then air cooled, which is a cooling rate of approximately 38 °C (100 °F) per minute. This results in a fine pearlitic structure, and a more uniform structure. Normalized steel has a higher strength than annealed steel; it has a relatively high strength and ductility.
  • Quenching: Plain-carbon steel with at least 0.4 wt% C is heated to normalizing temperatures and then rapidly cooled (quenched) in water, brine, or oil to the critical temperature. The critical temperature is dependent on the carbon content, but as a general rule is lower as the carbon content increases. This results in a martensitic structure; a form of steel that possesses a super-saturated carbon content in a deformed body-centered cubic (BCC) crystalline structure, properly termed body-centered tetragonal (BCT). This crystalline structure has a very high amount of internal stress. Due to these internal stress quenched steel is extremely hard but brittle, usually too brittle for practical purposes. These internal stresses cause stress cracks on the surface. Quenched steel is approximately three (lower carbon content) to four (high carbon content) times harder than normalized steel.
  • Martempering (Marquenching): Martempering is not actually a tempering procedure, hence the term "Marquenching." It is a form of isothermal heat treatment applied after an initial quench of typically in an oil or brine solution at a temperature right above the "martensite start temperature". At this temperature, residual stresses within the material are relieved and some bainite may be formed from the retained ferrite which did not have time to transform into anything else. In industry, this is a process used to control the ductility and hardness of a material. With longer marquenching time, the ductility increases with a minimal loss in strength; the steel is held in this solution until the center and surface temperatures equalize. Then the steel is cooled at a moderate speed to keep the temperature gradient minimal. Not only does this process reduce internal stresses and stress cracks, but it also increases the impact resistance.
  • Quench and tempering: This is the most common heat treatment encountered, because the final properties can be precisely determined by the temperature and time of the tempering. Tempering involves reheating quenched steel to a temperature below the eutectoid temperature then cooling. The elevated temperature allows very small amounts of spheroidite to form, which restore ductility, but reduces hardness. Actual temperatures and times are carefully chosen for each composition.
  • Austempering: The austempering process is the same as martempering, except the steel is held in the brine solution through the bainite transformation temperatures, and then moderately cooled. The resulting bainite steel has a greater ductility, higher impact resistance, and less distortion. The disadvantage of austempering is it can only be used on a few steels, and it requires a special brine solution.

Annealing, in metallurgy and materials science, is a heat treatment wherein a material is altered, causing changes in its properties such as strength and hardness. ... Ferrite may refer to: Ferrite (magnet)s (e. ... Iron-carbon phase diagram, showing the conditions under which austenite (γ) is stable in carbon steel. ... Cementite or iron carbide is a chemical compound with the formula Fe3C, and an orthorhombic crystal structure. ... Pearlite occurs at the eutectoid of the iron-carbon phase diagram (near the lower left). ... Ductility is the physical property of being capable of sustaining large plastic deformations without fracture (in metals, such as being drawn into a wire). ... Quenching is a general term for non-radiative de-excitation. ... A material is brittle if it is subject to fracture when subjected to stress i. ... Tempering is a heat treatment technique for metals and alloys. ... Eutectoid transformation occurs when a solid solution decomposes into a fixed two solid constituents at a fixed temperature. ...

Case hardening

Only the exterior of the steel part is hardened, creating a hard, wear resistant skin, but preserving a tough and ductile interior.

  • Flame hardening and induction hardening: The surface of the steel is heated to high temperature then cooling rapidly through the use of localized heating mechanisms and water cooling. The purpose is to create a "case" of martensite on the surface where wear resistance is needed. A carbon content of 0.4–0.6 wt% C is needed for this type of hardening. Typical uses are for the shackle of a lock, where the outer layer is hardened to be file resistant, and mechanical gears where hard gear mesh surfaces are needed to maintain a long service life while toughness is required to maintain durability and resistance to catastrophic failure.
See main article, Carburization
  • Carburizing: A process used to case harden steel with a carbon content between 0.1 and 0.3 wt% C. In this process steel is introduced to a carbon rich environment and elevated temperatures for a certain amount of time. Because this is a diffusion controlled process, the longer the steel is held in this environment greater the carbon penetration will be and the higher the carbon content in these areas. The part is then quenched so that the carbon is locked in the structure. The hardness is moderately increased, but it can be hardened again through flame or induction hardening. It's possible to carburize only a portion of the part by covering it in copper plating or coating it with a commercial paste. The following are some examples of carburizing processes:
  • Pack carburizing: Packing low carbon steel parts with a carbonaceous material and heating for some time diffuses carbon into the outer layers. A heating period of a few hours might form a high-carbon layer about one millimeter thick.
  • Liquid carburizing: This method involves heating the part in a bath of molten barium cyanide or sodium cyanide. The surface absorbs both sodium and carbon this way.
  • Gas carburization: Parts placed into a furnace at 927 °C (1700 °F) containing a partial methane or carbon monoxide atmosphere. The parts are then quenched.
  • Carburization may also be accomplished with an acetylene torch set with a fuel rich flame and heating and quenching repeatedly in a carbon rich fluid (oil).
  • Nitriding: This process heats the steel part to 482–621 °C (900–1150 °F) in an atmosphere of ammonia gas and dissociated ammonia. The time the part spends in this environment dictates the depth of the case. The hardness is achieved by the formation of nitrides. Nitride forming elements must be present for this method to work; these elements include chromium, molybdenum, and aluminum. The advantage of this process is it causes little distortion, so the part can be case hardened after being quench and tempered and machined.
  • Cyaniding: This process heats the part in a bath of sodium cyanide to a temperature in the austenitic phase and then is quenched. This creates a very hard, yet thin case.
  • Carbonitriding: This process is similar to cyaniding except a gaseous atmosphere of ammonia and hydrocarbons is used instead of sodium cyanide. If the part is to be quenched then the part is heated to 775–885 °C (1425–1625 °F); if not then the part is heated to 649–788 °C (1200–1450 °F). Trade names for the process include Tenifer, Melonite, Sursulf, Arcor, Tufftride, and Koline.

A limitation of plain carbon steel is the very rapid rate of cooling needed to produce hardening. In large pieces it is not possible to cool the inside rapidly enough and so only the surfaces can be hardened. This can be improved with the addition of other elements resulting in alloy steel. A semiconductor induction heater with a small inductor Induction heating is the process of heating a metal object by electromagnetic induction, where eddy currents are generated within the metal and resistance leads to Joule heating of the metal. ... Martensite in AISI 4140 steel 0. ... Carburization (often referred to as carburizing) is the name of the process by which carbon is introduced into a metal. ... Carburization is the name of the process by which carbon is introduced into a metal. ... Nitridization, also known as nitriding, is a process which introduces nitrogen in the surface of a material. ... General Name, symbol, number chromium, Cr, 24 Chemical series transition metals Group, period, block 6, 4, d Appearance silvery metallic Standard atomic weight 51. ... General Name, Symbol, Number molybdenum, Mo, 42 Chemical series transition metals Group, Period, Block 6, 5, d Appearance gray metallic Standard atomic weight 95. ... Aluminum is a soft and lightweight metal with a dull silvery appearance, due to a thin layer of oxidation that forms quickly when it is exposed to air. ... Tenifer is a trademarked name for the end result of a chemical bath nitriding process that embeds nitrogen into an iron-containing alloy to create a corrosion-resistant finish that is a dull grey in color and extremely hard. ...


See also

For other uses, see Steel (disambiguation). ... Heat treatment is a method used to alter the physical, and sometimes chemical, properties of a material. ... Cold Work is a quality imparted on a material as a result of plastic deformation. ... The American Iron and Steel Institute standardizes numbered AISI steel grades, including the following: // Carbon Steel and Low Alloy Steel Carbon steels and low alloy steels are designated by a four digit number, where the first two digits indicate the alloying elements and the last two digits indicate the amount...

References

  • Oberg, E. et al., (1996). "Machinery's Handbook", 25th ed., Industrial Press Inc.
  • Smith, W.F. & Hashemi, J. (2006). "Foundations of Materials Science and Engineering", 4th ed., McGraw-Hill.

Notes

  1. ^ a b c d Classification of Carbon and Low-Alloy Steels
  2. ^ Engineering fundamentals page on low-carbon steel
  3. ^ Engineering fundamentals page on medium-carbon steel
  4. ^ Engineering fundamentals page on high-carbon steel
  5. ^ Ameristeel article on carbon steel

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