Hot-Rolled Steel Bars and Shapes

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Hot-Rolled Steel Bars and Shapes

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Hot-Rolled Steel Bars and Shapes

Messaggioda Aldebaran » 12/05/2010, 13:23

Introduction
HOT-ROLLED STEEL BARS and other hot-rolled steel shapes are produced from ingots, blooms, or billets converted
from ingots or from strand cast blooms or billets and comprise a variety of sizes and cross sections. Bars and shapes are
most often produced in straight lengths, but bars in some cross sections in smaller sizes are also produced in coils.
The term "bar" includes:
· Rounds, squares, hexagons, and similar cross sections 9.5 mm ( 3
8
in.) and greater across
· Flats greater than 5.16 mm (0.203 in.) in thickness and 152 mm (6 in.) and less in width, or 5.84 mm
(0.230 in.) and greater in thickness and 203 mm (8 in.) and less in width
· Small angles, channels, tees, and other standard shapes less than 76 mm (3 in.) across
· Concrete-reinforcing bars
The term "shape" includes structural shapes and special shapes. Structural shapes are flanged, are 76 mm (3 in.) or greater
in at least one cross-sectional dimension, and are used in structures such as bridges, buildings, ships, and railroad cars.
Special shapes are those designed by users for specific applications.
Dimensions and Tolerances
The nominal dimensions of hot-rolled steel bars and shapes are designated in inches or millimeters with applicable
tolerances, as shown in ASTM A 6 and A 29. Bars with certain quality descriptors have size limitations; these are covered
in discussions of individual product qualities later in this article.
Bars or shapes can be cut to length in the mill by a number of methods, such as hot or cold shearing or sawing. The
method used is determined by cross section, grade, and customer requirements. Some end distortion is to be expected
from most methods. When greater accuracy in length or freedom from distortion is required, bars of shapes can be cut
overlength, then recut on one or both ends by cold sawing or equivalent means.
If a bar or shape requires straightening, prior annealing is sometimes necessary, depending on the grade of steel and the
cross-sectional shape of the part. The processing necessary to meet straightness tolerances is not intended to improve
either the surface finish or accuracy of cross-sectional shape and may result in increased surface hardness. Length and
straightness tolerances for bars and shapes are found in ASTM A 6 and A 29.
Surface Imperfections
Most carbon steel and alloy steel hot-rolled bars and shapes contain surface imperfections with varying degrees of
severity. In virtually all cases, these defects are undesirable and may in some applications affect the integrity of the
finished product.
Included in the manufacturing process for hot-rolled bars and shapes are various steps designed to minimize or eliminate
surface defects. These steps include inspection of both the semifinished and the finished product and either subsequent
removal of the defects or rejection of the material if defect removal is not possible. Inspection techniques range from
visual inspection of the semifinished material to sophisticated electronic inspection of the finished product. Defects found
in the semifinished product can be removed by hot scarfing, grinding, or chipping. Defects in the finished products are
generally removed by grinding, turning, or peeling and, to a lesser degree, by chipping.
Currently, it is not technically feasible to produce defect-free hot-rolled bars. With the current demand for high-quality
bar products, it is becoming increasingly common to subject hot-rolled bars to a cold-finishing operation, such as turning
or grinding, coupled with a sensitive electronic inspection. With this process route, it becomes possible to significantly
reduce both the frequency and the severity of surface defects.
Seams, Laps, and Slivers
Seams, laps, and slivers are probably the most common defects in hot-rolled bars and shapes.
Seams are longitudinal defects that can vary greatly in length and depth. It is quite common for steel users to refer to any
longitudinal defect as a seam regardless of the true nature of the defect. However, there is a classical definition of a seam,
as follows. Gas comes out of the solution as the liquid steel solidifies. This gas is trapped as bubbles or blowholes by the
solidifying steel and appears as small holes under the surface of the steel. When the steel is reheated, some areas of the
surface may scale off, exposing and oxidizing the interior of these blowholes. This oxidation prevents the blowholes from
welding shut during rolling. This rolling then elongates the steel, resulting in a longitudinal surface discontinuity--a seam.
As viewed in the cross section, seams are generally characterized as being perpendicular to the surface, completely
surrounded by decarburization, and associated with disperse oxides.
Laps are mechanical defects that occur during the hot rolling of both semifinished and finished material. Laps are
nothing more than a folding over of the material, resulting, for example, from gouging during the rolling process or
misalignment of the pass lines or rolls. As viewed in the cross section, laps are characterized as being at an angle from the
steel surface; they have decarburization on one side only of the defect and often contain entrapped scale.
Slivers usually appears as a scablike defect, adhering on one end to the surface of the hot-rolled steel. They are normally
pressed into the surface during hot rolling. They can originate from short, rolled out defects such as torn corners that are
not removed during conditioning. They can also result from conditioning gouges or mechanical gouges during rolling.
Although there is no specific metallographic definition of slivers, metallographic examination can be used to determine
the origin of these defects.
Decarburization
Another condition that could be considered a surface defect is decarburization. This condition is present to some degree
on all hot-rolled steel. Decarburization occurs at very high temperatures when the surface carbon of the steel reacts with
the oxygen in the furnace atmosphere. This loss of surface carbon results in a surface that is softer and unsuitable for any
application involving wear or fatigue. Because of the existence of this condition, steel ordered for critical applications can
be produced oversize and then ground to desired size.
Allowance for Surface Imperfections in Machining Applications
Experience has shown that when purchasers order hot-rolled or heat-treated bars that are to be machined, it is advisable
for the purchaser to make adequate allowances for the removal of surface imperfections and to specify the sizes
accordingly. These allowances depend on the way the surface metal is removed, the length and size of the bars, the
straightness, the size tolerance, and the out-of-round tolerance. Bars are generally straightened before machining. For
special quality carbon steel bars and regular quality alloy steel bars, either resulfurized or nonresulfurized (see the article
"Cold-Finished Steel Bars" in this Volume.
Surface Treatment
It is uncommon for hot-rolled steel bars and shapes to be descaled by the producer or protected from the weather during
transit. Most cleaning and coating operations are done either by the customer or by an intermediate processor.
Descaling of hot-rolled bars and shapes is generally done by either pickling or blasting, depending on the end use. There
are several subsequent coatings that can be used. Oil is both the simplest and the least expensive to use and acts as a
temporary rust preventive. Lime, in addition to serving as a rust preventive, can serve as a carrier for lubricants used
during cold drawing or cold forging. A more sophisticated system includes descaling, followed by a zinc phosphate
coating, coupled with a dry lubricant. This system provides some rust protection and serves as a lubricant for coldforming
operations.
Heat Treatment
Hot-rolled low-carbon and medium-carbon steel bars and shapes are often used in the as-rolled condition, but hot-rolled
bars of higher-carbon steel and most hot-rolled alloy steel bars must be heat treated in order to attain the hardness and
microstructure best suited for the final product or to make them suitable for processing. Such heat treatment consists of
one or more of the following: some form of annealing, stress relieving, normalizing, quenching, and tempering.
Ordinary annealing is the term generally applied to heat treatment used to soften steel. The steel is heated to a suitable
temperature, held there for some period of time, and then cooled; specific times, temperatures, and cooling rates vary.
Maximum hardness compatible with common practice can be specified.
Annealing for specified microstructures can be performed to obtain improved machinability or cold-forming
characteristics. The structures produced may consist of lamellar pearlite or spheroidized carbides. Special control of the
time and temperature cycles is necessary. A compatible maximum hardness can be specified.
Stress relieving involves heating to a sub-critical temperature and then cooling. For hot-rolled bars, the principal
reason for stress relieving is to minimize distortion in subsequent machining. It is used to relieve the stresses resulting
from cold-working operations, such as special machine straightening.
Normalizing involves heating to a temperature above the critical temperature range and then cooling in air. A
compatible maximum hardness can be specified.
Hardening by quenching consists of heating steel to the correct austenitizing temperature, holding at that temperature
for a sufficient time to produce homogeneous austenite, and quenching in a suitable medium (water, oil, synthetic oil or
polymer, molten salts, or low-melting metals) depending on chemical composition and section thickness.
Tempering is an operation performed on normalized or quenched steel bars. In this technique, the bars are reheated to a
predetermined temperature below the critical range and then cooled under suitable conditions.
When a hardness requirement is specified for normalized and tempered bars, the bars are ordinarily produced to a range
of hardnesses equivalent to a 0.4 mm range of Brinell impression diameters. Quenched and tempered bars are ordinarily
produced to a 0.3 mm range of Brinell impression diameters. Quenched and tempered bars can also be produced to
minimum mechanical property requirements.
Product Requirements
Hot-rolled steel bars and shapes can be produced to chemical composition ranges or limits, mechanical property
requirements, or both. The mechanical testing of hot-rolled steel bars and shapes can include tensile, Brinell or Rockwell
hardness, bend, Charpy impact, fracture toughness, and short-time elevated-temperature tests, as well as test for elastic
limit, proportional limit, and offset yield strength, which require the use of an extensometer or plotting of a stress-strain
curve. These tests are covered by ASTM A 370 and other ASTM standards.
Other tests sometimes required include the measurement of grain size and hardenability. Austenitic grain size is
determined by the McQuaid-Ehn test, which is described in ASTM E 112. This test involves metallographic examination
of a carburized specimen to observe prior austenitic grain boundaries. Hardenability can be measured by several methods,
the most common beingthe Jominy end-quench test, as described in ASTM A 255 (see the article "Hardenability of
Carbon and Low-Alloy Steels" in this Volume).
Soundness and homogeneity can be evaluated by fracturing. The fracture test is commonly applied only to high-carbon
bearing quality steel. Location of samples, number of tests, details of testing technique, and acceptance limits based on
the test should be established in each instance.
Testing for nonmetallic inclusions consists of careful microscopic examination (at 100×) of prepared and polished
specimens. The specimens should be taken on a longitudinal plane midway between the center and surface of the product.
Location of specimens, number of tests, and interpretation of results should be established in each instance. Typical
testing procedures are described in ASTM E 45. Nonmetallic inclusion content can also be measured on the macroscopic
scale by magnetic particle tests such as those described in AMS 2300 and 2301. These tests involve the measurement of
inclusion frequency and severity in a sampling scheme that represents the interior of the material.
Surface and subsurface nonuniformities are revealed by magnetic particle testing. This test was developed for, and is used
on, fully machined or ground surfaces of finished parts. When the magnetic particle test is to be applied to bar stock,
short-length samples should be heat treated and completely machined or ground.
Tensile and hardness tests are the most common mechanical tests performed on hot-rolled steel bars and shapes.
It is not practicable to set definite limitations on tensile strength or hardness for carbon or alloy steel bars in the as-rolled
condition. For mill-annealed steel bars, there is a maximum tensile strength or a maximum hardness (Table 2) that can be
expected for each grade of steel. For steel bars in the normalized condition, maximum hardness, maximum tensile
strength, minimum hardness, or minimum tensile strength can be specified. For normalized and tempered bars and for
quenched and tempered bars, either maximum and minimum hardness or maximum and minimum tensile strength can be
specified; for either property, the range that can be specified varies with tensile strength and is equivalent to a 0.4 mm
range of Brinell indentation diameters at any specified location for normalized and tempered bars and to a 0.3 mm range
for quenched and tempered bars.
It is essential that the purchaser specify the positions at which hardness readings are to be taken. When both hardness and
tensile strength are specified at the same position, the limits should be consistent with each other. When hardness limits
are specified as surface values, they may be inconsistent with tensile-test values, which of necessity are properties of the
bulk metal; the inconsistency will vary according to the size of the bar and the hardenability of the steel. The purchaser
should specify limits that take this inconsistency into account.
If the locations of hardness readings are not specified on the purchaser's order or specification, the hardness values are
applicable to the bar surface after removal of decarburization. Hardness correction factors for bars of various diameters as
described in ASTM E 18 should be employed if a flat area is not available on the bar tested.
Generally, yield strength, elongation, and reduction in area are specified as minimums for steel only in the quenched and
tempered or the normalized and tempered condition, and they should be consistent with ultimate tensile strength or
hardness. When quenched and tempered bars are cold worked by cold straightening, stress relieving may be required to
restore elastic properties and to improve ductility.
Reference cited in this section
2. Materials, Vol 1, 1989 SAE Handbook, Society of Automotive Engineers, 1989
Product Categories
Hot-rolled carbon steel bars are produced to two primary quality levels: merchant quality and special quality. Merchant
quality is the lower quality level and is not suitable for any operation in which internal soundness or freedom from surface
imperfections is of primary importance. Special, quality includes all bar categories with end-use-related and restrictive
quality requirements.
The mechanical properties of hot-rolled carbon steel bars in the as-rolled condition are influenced by:
· Chemical composition
· Thickness or cross-sectional area
· Variables in mill design and mill practice
Carbon content is the dominant factor.
Quality descriptors for hot-rolled alloy steel bars are related to suitability for specific applications. Characteristics
considered include inclusion content, uniformity of chemical composition, and freedom from surface imperfections.
Carbon steel and alloy steel structural shapes and special shapes do not have specific quality descriptors but are covered
by several ASTM specifications (Table 3). In most cases, these same specifications also cover structural quality steel bars.
The ASTM specifications covering other qualities of hot-rolled bars are listed in Table 4. The various categories of hotrolled
steel bar products and their characteristics are described in the following sections.
Merchant Quality Bars
Merchant quality is the least restrictive descriptor for hot-rolled carbon steel bars. Merchant quality bars are used in the
production of noncritical parts of bridges, buildings, ships, agricultural implements, road-building equipment, railway
equipment, and general machinery. These applications require only mild cold bending, mild hot forming, punching, and
welding. Mild cold bending is bending in which a generous bend radius is used and in which the axis of the bend is at
right angles to the direction of rolling.
Merchant quality bars should be free from visible pipe; however, they may contain pronounced chemical segregation, and
for this reason, product analysis tolerances are not appropriate. Internal porosity, surface seams, and other surface
irregularities may be present and are generally expected in bars of this quality. Consequently, merchant quality bars are
not suitable for applications that involve forging, heat treating, or other operations in which internal soundness or freedom
from surface imperfections is of primary importance.
Grades. Merchant quality bars can be produced to meet both chemical composition (heat analysis only) and mechanical
properties. These steels can be supplied to chemical compositions within the ranges of 0.50% C (max), 0.60% Mn (max),
0.04% P (max), and 0.05% S (max), but are not produced to meet any specific silicon content, grain size, or any other
requirement that would dictate the type of steel produced.
Merchant quality steel bars do not require the chemical ranges typical of standard steels. They are produced to wider
carbon and manganese ranges and are designated by the prefix "M."
When ordering merchant quality bars to meet mechanical properties, the following strength ranges are to be used up to a
maximum of 655 MPa (95 ksi):
· 70 MPa (10 ksi) for minimums up to but not including 415 MPa (60 ksi)
· 80 MPa (12 ksi) for minimums from 415 MPa (60 ksi) up to but not including 460 MPa (67 ksi)
· 100 MPa (15 ksi) for minimums from 460 to 550 MPa (67 to 80 ksi)
Specification ASTM A 663 defines the requirements for hot-wrought merchant quality carbon steel bars and bar-size
shapes intended for noncritical constructional applications.
Sizes. Merchant quality steel rounds are not produced in diameters greater than 76 mm (3 in.).
Special Quality Bars
Special quality bars are employed when end use, method of fabrication, or subsequent processing treatment requires
characteristics not available in merchant quality bars. Typical applications, including many structural uses, require hot
forging, heat treating, cold drawing, cold forming, and machining.
Special quality bars are required to be free from visible pipe and excessive chemical segregation. Also, they are rolled
from billets that have been inspected and conditioned, as necessary, to minimize surface imperfections. Frequency and
degree of surface imperfections are influenced by chemical composition, type of steel, and bar size. Resulfurized grades,
certain low-carbon killed steels, and boron-treated steels are most susceptible to surface imperfections.
Some end uses or fabricating procedures can necessitate one or more extra requirements. These requirements include
special hardenability, internal soundness, nonmetallic inclusion rating, and surface condition and are described in the
AISI manual covering hot-rolled bars. The quality descriptorfor bars to which only one of these special requirements is
applied is Restrictive Requirement Quality A. When a single special restriction other than the four mentioned above is
applied, the quality descriptor is Restrictive Requirement Quality B. Multiple Restrictive Requirement Quality bars are
those to which two or more restrictive requirements are applied.
Special quality steel bars can be produced using rimmed, capped, semikilled, or killed deoxidation practice. The
appropriate type is dependent on chemical composition, quality, and customer specifications. Killed steels can be
produced to coarse or fine austenitic grain size.
Special quality steel bars are produced to product chemical composition tolerances and can be purchased on the basis of
heat composition. Special quality steel bars can also be produced to meet mechanical property requirements. The tensile
strength ranges are identical to those presented in the section "Merchant Quality Bars" in this article. Additional
information on mechanical property requirements and test frequencies is available in the appropriate ASTM
specifications.
Sizes. Special quality steel bars are commonly produced in the following sizes:
· Rounds: 6.4 to 254 mm ( 1
4
to 10 in.)
· Squares: 6.4 to 154 mm ( 1
4
to 6 1
16
in.)
· Round-cornered squares: 9.5 to 203 mm ( 3
8
to 8 in.)
· Hexagons: 9.5 to 103 mm ( 3
8
to 4 1
16
in.)
· Flats: greater than 5.16 mm (0.203 in.) in thickness and 152 mm (6 in.) and less in width, or 5.84 mm
(0.230 in.) and greater in thickness and 203 mm (8 in.) and less in width
Common size ranges have not been established for special quality bars of other shapes, including bar-size shapes, ovals,
half-ovals, half-rounds, octagons, and special bar-size shapes.
Carbon Steel Bars for Specific Applications
Cold-working quality is the descriptor (replacing the older terminology of scrapless nut, cold forging, cold heading,
and cold extrusion qualities) for hot-rolled bars used in the production of solid or hollow shapes by means of severe cold
plastic deformation, such as (but not limited to) upsetting, heading, forging, and forward or backward extrusion involving
movement of metal by expansion and/or compression. Such processing normally involves special inspection standards
and requires sound steel of special surface quality and uniform chemical composition. If steel of the type or chemical
composition specified does not have adequate cold-forming characteristics in the as-rolled condition, a suitable heat
treatment, such as annealing or spheroidize annealing, may be necessary.
Axle Shaft Quality. Bars of axle shaft quality are produced for the manufacture of power-driven axle shafts for cars,
trucks, and other vehicles. Because of their design or method of manufacture, these axles either are not machined all over
or undergo less than the recommended amount of stock removal for proper cleanup of normal surface imperfections.
Therefore, it is necessary to minimize the presence of injurious surface imperfections in bars of axle shaft quality through
the use of special rolling practices, special billet and bar conditioning, and selective inspection.
Cold-Shearing Quality. There are limits to the sizes of hot-rolled steel bars that can normally be cold sheared without
specially controlled production procedures. When the cold shearing of larger bars is desirable, it is recommended that
cold-shearing quality bars be ordered. Bars of this quality have characteristics that prevent cracking even in these larger
sizes. Cold-shearing quality bars are not produced to specific requirements such as hardness, microstructure, shear life, or
productivity. Maximum size (cross-sectional area) limitations for the cold shearing of hot-rolled steel bars without the
specially controlled production procedures, and of cold-shearing quality bars, are given in the AISI manual that covers
hot-rolled bars. If even larger bars are to be cold sheared, cold-shearing behavior can be further improved by suitable
prior heat treatment.
Structural quality is the descriptor for hot-rolled bars used in the construction of bridges and buildings by riveting,
bolting, or welding and for general structural purposes. The general requirements for bars of this quality are given in
ASTM A 6; individual ASTM specifications are listed in Table 3.
Additional qualities of carbon steel bars are available for specific requirements. Such qualities are related to
application and processing. They include:
· File quality
· Gun barrel quality
· Gun receiver quality
· Shell steel quality A
· Shell steel quality B
· Shell steel quality C
· Shell steel quality D
Alloy Steel Bars
Hot-rolled alloy steel bars are commonly produced in the same size as special quality steel bars. Common size ranges
have not been established for other shapes of hot-rolled alloy steel bar, including bar-size shapes, ovals, half-ovals, halfrounds,
octagons, and special bar-size shapes.
Hot-rolled alloy steel bars are also covered by several quality descriptors, which are discussed below. As with all quality
descriptors, these descriptors differentiate bars on the basis of characteristic properties required to meet the particular
conditions encountered during fabrication or use.
Regular quality is the basic or standard quality for hot-rolled alloy steel bars, such as those covered by ASTM A 322.
Steel for this quality are killed, are usually produced to fine grain size, and are melted to chemical composition limits.
Bars of this quality are inspected, conditioned, and tested to meet the normal requirements for regular construction
applications for which alloy steel is used.
Axle Shaft Quality. Alloy steel bars of axle shaft quality are similar to carbon steel bars of the same quality (see the
discussion of axle shaft quality bars in the section "Carbon Steel Bars for Specific Applications" in this article).
Ball and roller bearing quality and bearing quality apply to alloy steel bars intended for antifriction bearings.
These bars are usually made from steels of the AISI-SAE standard alloy carburizing grades and the AISI-SAE highcarbon
chromium series. These steels can be produced in accordance with ASTM A 534, A 535, A 295, or A 485 (Table
4). Bearing quality steel bars require restricted melting and special teeming, heating, rolling, cooling, and conditioning
practices to meet rigid quality standards. Steelmaking practices may include vacuum treatment. The foregoing
requirements include thorough examination for internal imperfections by one or more of the following methods:
macroetch testing, microscopic examination for nonmetallic inclusions, ultrasonic inspection, and fracture testing.
It is not practical to furnish bearing quality steel bars in sizes exceeding 64,500 mm2 (100 in.2) in cross-sectional area to
the same rigid requirements as those for bars in smaller sizes because of insufficient hot working in the larger bars.
Usually, bars over 102 mm (4 in.) in thickness are forged to 102 mm (4 in.) square or smaller for testing.
Cold-Shearing Quality. Alloy steel bars of cold-shearing quality are similar to carbon steel bars of the same quality
(see the discussion of cold-shearing quality bars in the section "Carbon Steel Bars for Specific Applications" in this
article).
Cold-working quality, which replaces the older terminologies cold-heading quality and special cold-heading quality,
is the descriptor for hot-rolled bars used in the production of solid or hollow shapes by means of severe cold plastic
deformation, such as (but not limited to) upsetting, heading, forging, and forward or backward extrusion involving
movement of metal by expansion and/or compression. Such processing normally involves special inspection standards
and requires sound steel of special surface quality and uniform chemical composition. If steel of the type or chemical
composition specified does not have adequate cold-forming characteristics in the as-rolled condition, a suitable heat
treatment, such as annealing or spheroidize annealing, may be necessary.
Aircraft quality and magnaflux quality are the descriptors used for alloy steel bars for critical or highly stressed
parts of aircraft and for other similar or corresponding purposes involving additional stringent requirements such as
magnetic particle inspection, additional discard, macroetch tests, and hardenability control. To meet these requirements,
exacting steelmaking, rolling, and testing practices must be employed. These practices are designed to minimize
detrimental inclusions and porosity. Phosphorus and sulfur are usually limited to 0.025% maximum each.
Many parts for aircraft, missiles, and rockets require aircraft quality alloy steel bars. Magnetic particle testing as in AMS
2301 is sometimes specified for such applications. Some very critical aircraft, missile, and rocket applications require
alloy steel bars of a quality attained only by vacuum melting or by an equivalent process. The requirements of AMS 2300
are sometimes specified for such applications.
Structural quality is the descriptor for hot-rolled bars used in the construction of bridges and buildings by riveting,
bolting, or welding and for general structural purposes. The general requirements for bars of this quality are given in
ASTM A 6; the only individual ASTM specification referred to in A 6 that pertains to alloy steel bars is A 710.
Additional Qualities. The quality designations shown below apply to alloy steel bars intended for rifles, guns, shell,
shot, and similar applications. They may involve requirements for amount of discard, macroetch testing, surface quality,
or magnetic particle testing, as indicated in the product specification:
· AP shot quality
· AP shot magnaflux quality
· Gun quality
· Rifle barrel quality
· Shell quality
· Shell magnaflux quality
High-Strength Low-Alloy Steel Bars
In addition to the carbon steel and alloy steel bars of structural quality discussed in preceding sections of this article,
ASTM A 6 also lists several specifications covering high-strength low-alloy (HSLA) steel bars of structural quality
(Table 3). High-strength low-alloy steel bars are also covered in SAE J 1442.
Bars of these steels offer higher strength than that of carbon steel bars and are frequently selected for applications in
which weight saving is important. They also offer increased durability, and many offer increased resistance to
atmospheric corrosion. Additional information on HSLA steels is available in the articles "High-Strength Structural and
High-Strength Low-Alloy Steels," "High-Strength Low-Alloy Steel Forgings" and "Bulk Formability of Steels" in this
Volume.
Microalloyed steel bars constitute a class of special quality carbon steels to which small amounts of alloying
elements such as vanadium, niobium, or titanium have been added. Microalloyed steels in the as-hot-rolled condition are
capable of developing strengths higher than those of the base carbon grades through precipitation hardening. In some
cases, strength properties comparable to those of the quenched and tempered base grade can be attained. These steels are
finding increased application in shafting and automotive forgings.
Concrete-Reinforcing Bars
Concrete-reinforcing bars are available as either plain rounds or deformed rounds. Deformed reinforcing bars are used
almost exclusively in the construction industry to furnish tensile strength to concrete structures. The surface of the
deformed bar is provided with lugs, or protrusions, which inhibit longitudinal movement relative to the surrounding
concrete. The lugs are hot formed in the final roll pass by passing the bars between rolls into which patterns have been
cut. Plain reinforcing bars are used more often for dowels, spirals, structural ties, and supports than as substitutes for
deformed bars. Concrete-reinforcing bars are supplied either straight and cut to proper length, or bent or curved in
accordance with plans and specifications.
Grades. Deformed and plain concrete-reinforcing bars rolled from billet steel are produced to the requirements of
ASTM A 615 or A 706. For special applications that require deformed bars with a combination of strength, weldability,
ductility, and improved bending properties, ASTM A 706 is specified, which is an HSLA steel. Deformed and plain
concrete-reinforcing bars are also available rolled from railroad rails (ASTM A 616) and from axles for railroad cars
(ASTM A 617), Specification ASTM A 722 covers deformed and plain uncoated high-strength steel bars for prestressing
concrete structures.
Sizes. Numbers indicating sizes of reinforcing bars correspond to nominal bar diameter in eighths of an inch for sizes 3
through 8; this relationship is approximate for sizes 9, 10, 11, 14, and 18.
Structural Shapes
Structural shapes, as stated previously, are flanged shapes 76 mm (3 in.) and greater in at least one cross-sectional
dimension (smaller shapes are referred to as bar-size shapes) and are used in the construction of structures such as
bridges, buildings, ships, and railroad cars. Included in this product category are regular structural shapes (see ASTM A
6), such as standard beams, wide-flange beams, columns, light beams, joists, stanchions and bearing piles, and certain
tees, along with special structural shapes, which are those designed for specialized applications and that have dimensions
and/or values of weight per foot that do not conform to regular shapes. Bar-size structural shapes (angles, channels, tees,
and zees with greatest cross-sectional dimension less than 76 mm, or 3 in.) are considered to be in the merchant quality
bar category rather than the structural shape category.
The common method of designating sizes of structural shapes is as follows:
· Beams and channels: By depth of cross section and weight per foot.
· Angles: By length of legs and thickness in fractions of an inch or, more commonly, by length of legs and
weight per foot. The longer leg of an unequal angle is commonly stated first
· Tees: By width of flange, overall depth of stem, and weight per foot, in that order
· Zees: By depth, width of flanges, and thickness in fractions of an inch or by depth, flange width, and
weight per foot
· Wide-flange shapes: By depth, width across flange, and weight per foot, in that order
Most structural shapes are produced to meet specific standard specifications, such as those listed in Table 3. Structural
shapes are generally furnished to chemical composition limits and mechanical property requirements.
Special requirements are sometimes specified for structural shapes to adapt them to conditions they will encounter during
fabrication or service. These requirements may include specific deoxidation practices, additional mechanical tests, or
nondestructive testing.
Special Shapes
Special shapes are hot-rolled steel shapes made with cross-sectional configurations uniquely suited to specific
applications. Examples of custom-designed shapes are track shoes for tractors or tanks and sign-post standards.
The only type of standard shape in high production that falls in this classification is rail. Railroad rails of the standard
American tee rail shape are produced from carbon steel to the dimensional, chemical, and other requirements of the
American Railway Engineering Association (AREA). The sizes of railroad rails are designated in pounds per yard of
length; rails are furnished in 40 to 64 kg (90 to 140 lb) sizes. The most common sizes are 52, 60, 62, and 64 kg (115, 132,
136, and 140 lb). The ordinary length of railroad rails is 12 m (39ft). Carbon steel tee rails for railway track are covered
by ASTM A 1; rail-joint bars and tie plates are covered in ASTM A 3, A 4, A 5, A 49, A 67, and A 241.
Light rails are available for light duty, such as in mines and amusement park rides, in sizes from 6.8 to 39 kg (15 to 85 lb).
Light rails are covered by specifications of the American Society of Civil Engineers (ASCE).
Crane rails generally have heavier heads and webs than those of railroad rails in order to withstand the heavy loads
imposed on them in service. Crane rails in sizes from 18 to 79 kg (40 to 175 lb) are furnished to ASCE, ASTM, and
producers' specifications.
References
1. Alloy, Carbon and High Strength Low Alloy Steels: Semifinished for Forging; Hot Rolled Bars, Cold
Finished Bars; Hot Rolled Deformed and Plain Concrete Reinforcing Bars, AISI Steel Products Manual,
American Iron and Steel Institute, 1986
2. Materials, Vol 1, 1989 SAE Handbook, Society of Automotive Engineers, 1989
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Aldebaran
 
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