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Steel Terms Glossary

From alloy steel and annealing to vacuum arc degassing and yield strength, this steel terms glossary gives you a handy guide to terminology common in the steel industry – and unique to TimkenSteel. Two main categories for this information are alloying elements such as aluminum, carbon, sulfur, and vanadium, as well as standard mill technology.


    Used to deoxidize steel and control grain size with additions up to around 0.05 wt. percent. Grain size control is accomplished by the formation of a fine dispersion of aluminum nitride precipitates, which restricts austenite grain growth. Aluminum can be added at higher levels as an effective nitride former in nitriding steels.


    A treatment consisting of heating uniformly to a temperature, within or above the critical range, and cooling at a controlled rate to a temperature under the critical range. This treatment is used to produce a definite microstructure, usually one designed for best machinability, and/or to remove stresses, induce softness, and alter ductility, toughness or other mechanical properties.


    A solid semifinished round or square that has been hot worked usually smaller than a bloom. Also, a general term for wrought starting stock for forgings or extrusions.


    As-cast or wrought semifinished long steel products destined for further hot working processing into final form. Blooms are generally rectangular in cross-section and are larger than billets, which are usually square or round. The size differentiation is somewhat arbitrary.

    A semifinished hot rolled rectangular product. The width of the bloom is no more than twice the thickness and the cross-sectional area is usually not less than 36 square inches.

  • BORON - B

    Usually added between 0.0005-0.003 wt. percent to significantly increase the hardenability, especially for low carbon alloys. It does not affect the strength of ferrite, and therefore has little effect on ductility, formability or machinability in the annealed or soft state.

  • CALCIUM - Ca

    Used in certain steels to control the composition, type, shape, size and distribution of oxide and/or sulfide inclusions. Benefits may include improved ductility, impact strength and/or machinability. Ca can also be added to improve castability.


    A type of steel similar to rimmed steel, usually cast in a bottle top ingot, in which the application of a mechanical or chemical cap renders the rimming action incomplete by causing the top metal to solidify.

  • CARBON - C

    The most important alloying element which is essential for the formation of cementite, graphite, pearlite, spheriodite, bainite, and iron-carbon martensite. Strength, hardness, hardenability, and ductile-to-brittle transition temperature are increased with increasing carbon content up to approximately 0.60 percent. Toughness and ductility of steels are decreased with increasing carbon content. The maximum achievable hardness level of a martensitic steel is a function of carbon content only, with hardness level increasing with carbon content.


    Used in alloy steels to increase 1) resistance to corrosion and oxidation, 2) high temperature strength, 3) hardenability, and 4) abrasion resistance in high carbon alloys. Straight chromium steels are susceptible to temper embrittlement and can be brittle.


    A solidification process in which refined liquid steel is continuously fed through a bottomless water-cooled copper mold. A solidified shell forms supporting the remaining liquid steel within. Heat extraction and continued solidification of the steel strand proceeds below the mold via water cooling and radiation, until the entire strand cross-section is fully solidified, at which point sections of the steel strand are cut to desired lengths.

  • COPPER - Cu

    Detrimental to hot workability and subsequent surface quality, and is normally restricted to residual levels. It is used in certain steels to improve resistance to atmospheric corrosion.

  • DI Ideal Diameter

    The diameter of a round steel bar that will harden at the center to a given percent of martensite when subjected to an ideal quench (i.e., Grossman quench severity H=infinity).


    In tensile testing, the increase in gage length, measured after the fracture of a specimen within the gage length, usually expressed as a percentage of the original gage length.


    A laboratory procedure for determining the hardenability of a steel or other ferrous alloy. Hardenability is determined by heating a standard specimen above the upper critical temperature, placing the hot specimen in a fixture so that a stream of cold water impinges on one end, and, after cooling to room temperature is completed, measuring the hardness near the surface of the specimen at regularly spaced intervals along its length. The data are normally plotted as hardness versus distance from the quenched end.


    Resistance of a metal to plastic deformation, usually by indentation. However, this may also refer to stiffness or temper, or to resistance to scratching, abrasion, or cutting.


    This is the standard process of air-cooling the steel immediately following the rolling operation. We transfer the steel to a special table or hot bed that continuously advances the product across the bed. Steel that is hot bed cooled may require additional thermal treatment to obtain optimum machinability or required mechanical properties.


    A test to determine the behavior of materials when subjected to high rates of loading, usually in bending, tension or torsion. The quantity measured is the energy absorbed in breaking the specimen by a single blow, as in the Charpy or Izod tests.


    A casting of a simple shape that can be used for hot working or remelting.

  • LAP

    A surface imperfection that appears as a seam. It is caused by the folding over of hot metal, fins, or sharp corners and then rolling or forging them into the surface but not welding them. Laps on tubes can form from seams on piercing mill billets.

  • LEAD - Pb

    Can be added to improve machinability. It does not dissolve in the steel matrix but remains as secondary particles. Environmental concerns are resulting in a decreased usage of lead in the steel industry.


    This is a generic term for describing the ability of a material to be machined. To be meaningful, machinability must be qualified in terms of tool wear, tool life, chip control, and/or surface finish and integrity. Overall machining performance is affected by a myriad of variables relating to the machining operation and the workpiece. An overall review is provided in the ASM Metals Handbook: Machinability, Ninth Edition, Volume 16, 1989.


    A common alloying element used in most steels because it deoxidizes the melt, facilitates hot working of the steel by reducing the susceptibility to hot shortness due to sulfur content and adds to hardenability. Mn also partially combines with sulfur to form MnS inclusions, which are commonly used to increase machinability. Mn also improves pearlitic strength in the non-hardened state, and is a major element used in micro-alloy steels.


     This is a controlled cooling of the steel immediately following rolling. In some low and medium carbon alloy grades, this method produces the optimum hardness and microstructure for machinability.


    Increases hardenability of steels and helps maintain a specified hardenability. It increases high temperature tensile and creep strengths. Molybdenum hardened steels require higher tempering temperatures for softening purposes.

  • NICKEL - Ni

    Used in low alloy steels to reduce the sensitivity of the steel to variations in heat treatment and distortion and cracking on quenching. It also improves low temperature toughness and hardenability.

  • NIOBIUM - Nb (Columbium - Cb)

    Lowers transition temperature and raises the strength of low carbon steel. Niobium increases strength at elevated temperatures, results in finer grain size and forms stable carbides, lowering the hardenability of the steel.


    Increases the strength, hardness and machinability of steel, but it decreases the ductility and toughness. In aluminum-killed steels, nitrogen combines with the aluminum to provide grain size control, thereby improving both toughness and strength. Nitrogen can reduce the effect of boron on the hardenability of steels.


    A treatment consisting of heating uniformly to temperature at least 100°F above the critical range and cooling in still air at room temperature. The treatment produces a recrystallization and refinement of the grain structure and gives uniformity in hardness and structure to the product.


    Generally restricted to below 0.04 weight percent to minimize its detrimental effect on ductility and toughness. Certain steels may contain higher levels to enhance machinability, strength and/or atmospheric corrosion resistance.


    An operation by which surface oxide (scale) is removed by chemical action. Sulfuric acid is typically used for carbon and low-alloy steels. After the acid bath, the steel is rinsed in water.


    A treatment consisting of heating uniformly to a predetermined temperature and cooling rapidly in air or liquid medium to produce a desired crystalline structure.


    The difference, expressed as a percentage of original area, between the original cross-sectional area of a tensile test specimen and the minimum cross-sectional area measured after complete separation.

  • SCAB

    An imperfection that is a flat piece of metal rolled into the steel surface.

  • SEAM

    A defect on the surface of a metal that appears as a crack. Experience indicates that most seams are created during the cooling or reheating of cast structures.

  • SILICON - Si

    One of the principal deoxidizers with the amount used dependent on the deoxidization practice. It slightly increases the strength of ferrite without a serious loss of ductility. In larger quantities, it aids the resistance to scaling up to 500°F in air and decreases magnetic hysteresis loss.


    A special type of annealing that requires an extremely long cycle. This treatment is used to produce globular carbides and maximum softness for best machinability in some analyses, or to improve cold formability.


    A thermal treatment to restore elastic properties and to minimize distortion on subsequent machining or hardening operations. This treatment is usually applied to material that has been heat treated (quenched and tempered). Normal practice would be to heat to a temperature 100°F lower than the tempering temperatures used to establish mechanical properties and hardness. Ordinarily, no straightening is performed after the stress relieve temper.

  • SULFUR - S

    Detrimental to transverse strength and impact resistance. It affects longitudinal properties to a lesser degree. Existing primarily in the form of manganese sulfide stringers, sulfur is typically added to improve machinability.


    Added to steel to modify sulfide-type inclusion size, morphology and distribution. The resulting sulfide-type inclusions are finer and remain ellipsoidal in shape following hot working, thereby improving transverse properties.


    A treatment consisting of heating uniformly to some predetermined temperature under the critical range, holding at that temperature a designated period of time and cooling in air or liquid. This treatment is used to produce one or more of the following end results: A) to soften material for subsequent machining or cold working, B) to improve ductility and relieve stresses resulting from prior treatment or cold working, and C) to produce the desired mechanical properties or structure in the second step of a double treatment.


    In tensile testing, the ratio of maximum load to original cross-sectional area.


    Added to boron steels because it combines with oxygen and nitrogen, thus increasing the effectiveness of boron. Titanium, as titanium nitride, also provides grain size control at elevated temperatures in micro-alloy steels. In excess, titanium is detrimental to machinability and internal cleanness.


    Inhibits grain growth during heat-treating while improving strength and toughness of hardened and tempered steels. Additions up to 0.05 percent increase hardenability whereas larger amounts tend to reduce hardenability because of carbide formation. Vanadium is also utilized in ferrite/pearlite micro-alloy steels to increase hardness through carbonitride precipitation strengthening of the matrix.


    The first stress in a material, usually less than the maximum attainable stress, at which an increase in strain occurs without an increase in stress. If there is a decrease in stress after yielding, a distinction may be made between upper and lower yield points.


    The stress at which a material exhibits a specified deviation from proportionality of stress and strain. An offset of 0.2 percent is commonly used.


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