Cleaning and Coating(1)

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Cleaning and Coating(1)



Cleaning and Coating(1)

Messaggioda Aldebaran » 02/07/2010, 22:17

Cleaning and Coating
Mill scale is cleaned from steel wire rods by pickling or caustic cleaning followed by water rinsing, or by mechanical
means such as shot blasting with abrasive particles or reverse bending over sheaves. The chemical cleaning of steel wire
rods is always followed by a supplementary coating operation. Lime, borax, or phosphate coating is applied to provide a
carrier for the lubricant necessary for subsequent processing into wire. In lime coating, practices may be varied in order to
apply differing amounts of lime on the rods depending on the customer requirements. Phosphate-coated rods may have a
supplementary coating of lime, borax, or water-soluble soap. Mechanically descaled rods may be drawn without coating
using only wire drawing soaps, or may be coated in a fashion similar to that used for chemically cleaned rods.
Heat Treatment
The heat treatments commonly applied to steel wire rod, either before or during processing into wire, include annealing,
spheroidize annealing, patenting, and controlled cooling. Annealing commonly involves heating to a temperature near or
below the lower critical temperature and holding at that temperature for a sufficient period of time, followed by slow
cooling. This process softens the steel for further processing, but not to the same degree as does spheroidize annealing.
Spheroidize annealing involves prolonged heating at a temperature near or slightly below the lower critical temperature
(or thermal cycling at about the lower critical temperature), followed by slow cooling, with the object of changing the
shape of carbides in the microstructure to globular (spheroidal), which produces maximum softness.
Patenting is a heat treatment usually confined to medium-high-carbon and high-carbon steels. In this process, individual
strands of rod or wire are heated well above the upper critical temperature and then are cooled comparatively rapidly in
air, molten salt, molten lead, or a fluidized bed. The object of patenting is to develop a microstructure of homogeneous,
fine pearlite. This treatment generally is employed to prepare the material for subsequent wire drawing.
Controlled cooling is a heat treatment performed in modern rod mills in which the rate of cooling after hot rolling is
carefully controlled. The process imparts uniformity of properties and some degree of control over scale, grain size, and
Carbon Steel Rod
Carbon steels are those steels for which no minimum content is specified or required for chromium, nickel, molybdenum,
tungsten, vanadium, cobalt, niobium, titanium, zirconium, aluminum, or any other element added to obtain a desired
alloying effect; for which specified minimum copper content does not exceed 0.40%; for which specified maximum
manganese content does not exceed 1.65%; and for which specified maximum silicon or copper content does not exceed
0.60%. In all carbon steels, small quantities of certain residual elements, such as chromium, nickel, molybdenum, and
copper, are unavoidably retained from raw materials. These elements are considered incidental, although maximum limits
are commonly specified for specific end-uses.
Carbon steel rods are produced in various grades, or compositions:
Low-carbon steel wire rods (maximum carbon content ≤0.15%)

Medium-low-carbon steel wire rods (maximum carbon content >0.15%, but ≤0.23%)

Medium-high-carbon steel wire rods (maximum carbon content >0.23%, but ≤0.44%)

• High-carbon steel wire rods (maximum carbon content >0.44%)
Ordinarily, sulfur and phosphorus contents are kept within the usual limits for each grade of steel, while carbon,
manganese, and silicon contents are varied according to the mechanical properties desired. Occasionally, sulfur and/or
phosphorus may be added to the steel to improve the machinability.
Qualities and Commodities of Carbon Steel Rod
Rod for the manufacture of carbon steel wire is produced with manufacturing controls and inspection procedures intended
to ensure the degree of soundness and freedom from injurious surface imperfections necessary for specific applications.
The various quality descriptors and commodities applicable to carbon steel wire rod are described below.
Industrial quality rod is manufactured from low-carbon or medium-low-carbon steel and is intended primarily for
drawing into industrial quality wire. Rod of this quality is available in the as-rolled or heat-treated conditions. Practical
limitations for drawing are: low-carbon rod 5.6 mm ( in.) in diameter can be drawn without intermediate annealing to
2.0 mm (0.080 in.) by five conventional drafts; medium-low-carbon rod 5.6 mm ( in.) in diameter can be drawn
without intermediate annealing to 2.69 mm (0.106 in.) by four conventional drafts.
Chain Quality Rod. Rod for the manufacture of wire to be used for resistance welded chain is made from low-carbon
and medium-low-carbon steel produced by practices that ensure their suitability for drawing into wire for this end-use.
Good butt welding uniformity characteristics and internal soundness are essential for this application. Rod for the
manufacture of wire to be used for fusion welded chain can be produced from specially selected low-carbon rimmed steel,
but is more often made from continuous cast steel.
Fine wire quality rod is suitable for drawing into small-diameter wire either without intermediate annealing
treatments or with only one such treatment. Rod 5.6 mm ( in.) in diameter can be direct drawn into wire as fine as 0.9
mm (0.035 in.) without intermediate annealing. Wire finer than 0.9 mm (0.035 in.), for such products as insect-screen
wire, weaving wire, and florist wire, is usually drawn in two steps: reducing to an intermediate size no smaller than 0.9
mm (0.035 in.), followed by annealing and redrawing to final size.
Fine wire quality rod is generally rolled from steel of grade 1005 or 1006 produced using techniques to provide good
surface finish and internal cleanliness. In addition to these precautions, the producer may subject the rod to tests such as
fracture or macroetch tests.
Cold finishing quality rod is intended for drawing into cold finished bars; the manufacture of such rod is controlled to
ensure suitable surface conditions.
Heading, Cold Extrusion, or Cold Rolling Quality Rod. Rod used for the manufacture of heading, forging, cold
extrusion or cold rolling quality wire is produced by closely controlled manufacturing practices. It is subject to mill
testing and inspection to ensure internal soundness and freedom from injurious surface imperfections. Heat treatment as a
part of wire mill processing is very important in the higher carbon grades of steel. For common upsetting, represented by
the production of standard trimmed hexagon-head cap screws, 1016 to 1038 steel wire drawn from annealed rod is
suitable. Wire for moderate upsetting, also produced from 1016 to 1038 steel, should be drawn from spheroidize annealed
rod or should be in-process annealed. Wire for severe heading and forging, produced from rod of 1016 to 1541 steel,
should be spheroidize annealed in process or at finished size. Rod of this quality is not intended for recessed-head or
similar special-head applications.
In the production of rod for heading, forging, or cold extrusion is killed carbon steels with nominal carbon contents of
0.16% or more (AISI grades 1016 or higher), both austenitic grain size and decarburization should be controlled. Such
steels can be produced with either fine or coarse austenitic grains, depending on the type of heat treatment and end-use.
Wood screw quality rod includes low-carbon resulfurized and nonresulfurized wire rod for drawing into wire for the
manufacture of slotted-head screws only, not for recessed-head or other special-head screws.
Scrapless Nut Quality Rod. Rod to be drawn into wire for scrapless nuts is produced by specially controlled
manufacturing practices. It is subjected to mill tests and inspection designed to ensure internal soundness; freedom from
injurious segregation and injurious surface imperfections; and satisfactory performance during cold heading, cold
expanding, cold punching, and thread tapping.
Rod for scrapless nut wire commonly is made from low-carbon, resulfurized steels. Nonresulfurized steels are also used;
these steels ordinarily are furnished only in grades containing more carbon than the resulfurized grades and with
phosphorus content not exceeding 0.035% and sulfur content not exceeding 0.045% by heat analysis.
In making resulfurized steel for scrapless nut quality rod, either an ingot or continuous casting process can be used. In an
ingot manufacturing process, sometimes the sulfur content is obtained through delayed mold additions to a conventional
nonresulfurized rimming steel. The purpose of such a practice is to produce a steel consisting of a rim of low-sulfur steel
suitable for expansion during nut forming around a high-sulfur interior section suitable for the piercing and threading
operations involved in making scrapless nuts. When high sulfur content is secured through such mold additions, sulfur
analyses are made on the solid billets rather than by heat analysis. It is customary to produce these steels to a specified
sulfur range of either 0.08 to 0.13% or 0.04 to 0.09%. Because of the practice used in making the steel and the degree to
which sulfur segregates, the sulfur content at various locations in a billet may vary from the indicated range.
When a continuous casting process is used to make resulfurized steel, the sulfur content is typically more uniform than
the ingot process. However, continuous casting precludes the rimming practice described in the above paragraph.
Severe cold heading, severe cold extrusion, or severe scrapless nut quality rod is used for severe single-
step or multiple-step cold forming where intermediate heat treatment and inspection are not possible. Rod of this quality
is produced with carefully controlled manufacturing practices and rigid inspection practices to ensure the required degree
of internal soundness and freedom from surface imperfections. A fully killed fine-grain steel is usually required for the
most difficult operations. Normally, the wire made from this quality rod is spheroidize annealed, either in process or after
drawing finished sizes. Decarburization limits and the steels to which they apply are the same as those described in the
section "Heading, Cold Extrusion, or Cold Rolling Quality Rod" in this article.
Welding-quality rod is used to make wire for gas or electric-arc welding filler metal. Welding-quality rod can be made
from selected ingots or billets of low-carbon rimmed, capped, or killed steel, but is preferably made from continuous cast
steel. It is produced to several restricted ranges and limits to chemical composition; an example of the restricted ranges
and limits for low-carbon, arc welding wire rod is shown below:
Rod for welding-quality wire constitutes an exception to the general practice that rimmed or capped steel is not
commonly subject to product analysis. Experience to date has shown the necessity for close control of composition, and
therefore only billets from those portions of the ingot that conform to the applicable ranges and limits are used for
welding-quality rod. For the majority of welding-quality rod that is made from continuous cast steel, these product checks
may not be necessary.
Medium-high-carbon and high-carbon quality rod is wire rod intended for drawing into such products as strand
wire, lockwasher wire, tire bead wire, upholstery spring wire, rope wire, screen wire (for heavy aggregate screens),
aluminum cable steel reinforced core wire, and prestressed concrete wire.
These wire qualities are normally drawn directly from patented or control-cooled rod. When drawing to sizes finer than
2.0 mm (0.080 in.) (from 5.6 mm, or in., rod), it is customary to employ in-process heat treatment before drawing to
finish size. Medium-high-carbon and high-carbon quality rod is not intended for the manufacture of higher-quality wires
such as music wire or valve spring wire.
Rod for Special Purposes. In addition to the carbon steel rod commodities described above, which have specific
quality descriptors, several other commodities are produced, each having the characteristics necessary for a specific
application, but for which no specific quality descriptor exists. Some of these commodities are made to standard
specifications; the others are made to proprietary specifications that are mutually acceptable to both producer and user.
Rod for music wire, valve spring wire, and tire cord wire is rolled and conditioned to ensure the lowest possible incidence
of imperfections. Surface imperfections are objectionable because they lower the fatigue resistance that is important in
many of the end products made from these wires. Internal imperfections are objectionable because they make the rod
unsuitable for cold drawing to high strength levels and the extremely fine sizes required.
Rod for concrete reinforcement is nondeformed rod produced from steel chemical compositions selected to provide the
mechanical property requirements for grade 40 and grade 60, as described in ASTM A 615. This quality rod is produced
in coils.
Rod for telephone and telegraph wire is produced by practices and to chemical compositions intended for the manufacture
of wire having electrical and mechanical properties that will meet the requirements of the various grades of this type of
Special Requirements for Carbon Steel Rod
Some of the quality descriptors discussed above imply special requirements for the manufacture and testing of wire rod. A
few of the more common requirements are listed below. For some applications, it may be appropriate to add one or more
special requirements to those implied by the quality descriptor.
Macroetch testing is deep-etch testing to evaluate internal soundness. A representative cross section is etched in a hot
acid solution.
Fracture Testing. In fracture testing, a specimen is fractured to evaluate soundness and homogeneity.
Austenitic Grain Size Requirements. For applications involving carburizing or heat treatment, austenitic grain size
for killed steels may be specified as either coarse (grain size 1 through 5) or fine (grain size 5 through 8 inclusive), in
accordance with ASTM E 112.
Heat-Treating Requirements. When heat-treating requirements must be met in the purchaser's end product, all heat
treatment procedures and mechanical property requirements should be clearly specified.
Nonmetallic inclusion testing comprises a microscopic examination of longitudinal sections of the rod to determine
the nature and frequency of nonmetallic inclusions. Methods B or C of ASTM E 45 are commonly used.
Decarburization limits are specified for special applications when required. A specimen is polished so that the entire
cross-sectional area is in a single plane, with no rounded edges. After etching with a suitable etchant, the specimen is
examined microscopically (usually to 100 diameters), and the results are reported in hundredths of a millimeter or
thousandths of an inch. The examination includes the entire periphery, and the results reported should include the amount
of free ferrite and the total depth of decarburization. Further details of this microscopic method are contained in SAE
Recommended Practice J419,
Mechanical Properties of Carbon Steel Rod
In the older mills, where rod was coiled hot, there was considerable variation within each coil because of the effect of
varying cooling rates from the center to the periphery of the coil. Therefore, as-hot-rolled rod was seldom sold to specific
mechanical properties because of the inherent variations of such properties. These properties for a given grade of steel
varied from mill to mill and were influenced by both the type of mill and the source of steel being rolled.
In new rod mills, which are equipped with controlled cooling facilities, this intracoil variation is kept to a minimum. In
such mills, finishing temperature, cooling of water, cooling air, and conveyor speed all are balanced to produce rod with
the desired scale and microstructure. This structure, in turn, is reflected in the mechanical properties of the rod and
permits the rod to be drawn directly for all but the most demanding applications. The primary source of intracoil variation
on these new mills is the overlapping of the coiled rings on the conveyor. These overlapped areas cool at a slower rate
than the majority of the ring.
Alloy Steel Rod
Alloy steels are those steels for which maximum specified manganese content exceeds 1.65% or maximum specified
silicon or copper content exceeds 0.60%; or for which a definite range or definite minimum quantity of any other element
is specified in order to obtain desired effects on properties. Detailed information on composition ranges and limits of alloy
steels can be found in the article "Classification and Designation of Carbon and Low-Alloy Steels" in this Volume.
Qualities and Commodities for Alloy Steel Rod
The various qualities of alloy steel wire rod possess characteristics that are adapted to the particular conditions typically
encountered during fabrication or service. Manufacture of these steels normally includes careful selection of raw
materials for melting, exacting steelmaking practices, selective discard (when the steel is produced in ingots), extensive
billet preparation, and extensive testing and inspection.
Occasionally, alloy steel of a special quality is specified for the manufacture of wire rod. Aircraft quality alloy steel may
be specified for wire rods intended for processing into critical or highly stressed aircraft parts or for similar purposes.
Bearing quality alloy steel may be specified for wire rods intended for processing into balls and rollers for antifriction
bearings. Bearing quality alloy steel is usually specified when purchasing the standard carburizing grades, such as 4118,
4320, 4620, 4720, and 8620, or the through-hardening, high-carbon chromium grades such as E51100 and E52100. The
various standard qualities and commodities available in alloy steel wire rod are described below.
Cold heading quality alloy steel rod is used for the manufacture of wire for applications involving cold plastic
deformation by such operations as upsetting, heading, forging, or extrusion. Typical parts are fasteners (cap screws, bolts,
eyebolts), studs, anchor pins, and balls and rollers for antifriction bearings.
Special cold heading quality alloy steel rod is used for wire for applications involving severe cold plastic
deformation. Surface quality requirements are more critical than for cold heading quality. Steel with very uniform
chemical composition and internal soundness, as well as special surface preparation of the semifinished steel, are
required. Typical applications are ball joint suspension studs, socket head screws, recessed-head screws, and valves.
Welding quality alloy steel rod is used for the manufacture of wire used as filler metal in electric arc welding or for
building up hard wearing surfaces of parts subjected to wear. The heat analysis limits give below for phosphorus and
sulfur apply to this quality rod:
Special Requirements for Alloy Steel Rod
Alloy steel rod can be produced with special requirements in addition to those implied by the quality descriptors
discussed above. These special requirements include those given below.
Special surface entails a product with minimal frequency and severity of seams and other surface imperfections.
Decarburization limits can be specified for special applications. An example of such limits are those shown in the
table below for alloy steel rod for wire for heading, forging, roll threading, extrusion, lockwasher, and screwdriver
applications. Listed below are the maximum allowable amounts of decarburization as defined by the average value for the
depth of the layer of free ferrite plus the layer of partial decarburization (the total affected depth) and the average depth of
the layer of free ferrite alone:
When limits closer than those given above are required for the end product, it is sometimes appropriate to incorporate
carbon restoration in the fabrication process. For some applications, the rod producer can include carbon restoration in the
mill heat treatment. The method of measuring decarburization is the same as that described for carbon steel rods.
Heat-Treating Requirements. When the end product must be heat treated, the heat treatment and mechanical
properties should be clearly defined.
Hardenability requirements are customarily specified by H-steel designations and hardenability bands. These steels
and hardenability bands are discussed in the article "Hardenability of Carbon and Low-Alloy Steels" in this Volume.
Austenitic Grain Size Determination. Most alloy steels are produced using fine-grain practice. Fine-grain steels are
useful in carburized parts, especially when direct quenching is involved, and are less sensitive than coarse-grain steels to
variations in heat-treating practices. Coarse-grain steels are deeper hardening and are generally considered more
machinable. Austenitic grain size is specified as either coarse (grain sizes 1 through 5) or fine (grain sizes 5 through 8),
determined in accordance with ASTM E 112.
Nonmetallic-Inclusion Testing. When the nonmetallic-inclusion test is specified, it is commonly done on billets.
Prepared and polished specimens are examined microscopically at 100 diameters. Sample locations, number of tests, and
limits of acceptability should be established in each instance. Test procedures are described in ASTM E 45.
Magnetic-Particle Inspection. For alloy steel rod and wire products subject to magnetic-particle inspection, it is
customary for the producer to test the product in a semi-finished form, such as billets (using specimens properly machined
from billets), to ensure that the heat conforms to the magnetic-particle inspection requirements, prior to further
The method of inspection consists of suitably magnetizing the steel and applying a prepared magnetic powder, either dry
or suspended in a suitable liquid, that adheres to the steel along lines of flux leakage. On properly magnetized steel, flux
leakage develops along surface or subsurface discontinuities. The results of the inspection will vary with the degree of
magnetization, the inspection procedure (including such conditions as relative location of surfaces tested), the method and
sequence of magnetizing and applying the powder, and the interpretation. The testing procedure and standards of
acceptance for magnetic-particle inspection are described in Aerospace Materials Specification 2301.
Macroetch Testing. Soundness and homogeneity of alloy steel rod are sometimes evaluated macroscopically by
examining a properly prepared cross section of the product after it has been immersed in a hot acid solution. It is
customary to use hydrochloric acid for this purpose.
Steel Wire
Revised by Allan B. Dove, Consultant
WIRE can be cold drawn from any of the types of carbon steel or alloy steel rod described in the article "Steel Wire Rod"
in this Volume. For convenience, the various grades of carbon steel wire can be divided into the same four classes used
for carbon steel rod. Based on carbon content, these classes are:
• Low-carbon steel wire (0.15% C max)
• Medium-low-carbon steel wire (>0.15 to 0.23% C)
• Medium-high-carbon steel wire (>0.23 to 0.44% C)
• High-carbon steel wire (>0.44% C)
The conventional four-digit or five-digit American Iron and Steel Institute--Society of Automotive Engineers (AISI-SAE)
designation is used to specify the carbon or alloy steel used to make the wire. Carbon and alloy steel wire can be produced
in qualities suitable for cold rolling, cold drawing, cold heading, cold upsetting, cold extrusion, cold forging, hot forging,
cold coiling, heat treatment, or carburizing and for a wide variety of fabricated products.
The contributions of the following individuals were critical in the preparation of this article. T.A. Heuss, LTV Steel Bar
Division; Bill Schuld, Seneca Wire and Manufacturing Company; and Walter Facer, American Spring Wire Company.
Wire Configurations and Sizes
Shapes of Wires. Although wire is ordinarily thought of as being only round, it may have any one of an infinite
number of sectional shapes, as required by end use. After ordinary round wire, the most common shapes are square,
hexagonal, octagonal, oval, half-oval, half-round, triangular, keystone, and flat. In addition to these regular (symmetrical)
shapes, wire is also made in various odd and irregular shapes for specific purposes.
Flat wire, as defined by AISI, is wire that has been cold rolled or drawn, has a prepared edge, is rectangular in shape, 25
mm (1 in.) or less in width, and less than 9.5 mm ( in.) in thickness. Flat wire is generally produced from hot-rolled
rods or specially prepared round wire by one or more cold-rolling operations intended primarily for the purpose of
obtaining the size and section desired and for improving surface finish, dimensional accuracy, and mechanical properties.
Low-carbon steel flat wire can also be produced by slitting cold-rolled flat sheet or strip steel to the desired width. The
width-to-thickness ratio and the specified type of edge generally determine the process that will be necessary to produce a
specific flat wire item. The edges, finishes, and tempers obtainable in flat wire are similar to those furnished in cold-rolled
strip. It should be noted that a product having an approximately rectangular section, rolled from carbon steel round wire
of selected size, without edge, is also known as carbon steel flat wire.
Sizes of Wire. The size limits for the product commonly known as wire range from approximately 0.13 mm (0.005 in.)
to (but not including) 25.4 mm (1 in.) for round sections and from a few tenths of a millimeter to approximately 16 mm
( in.) for square sections. Larger rounds and squares (if passed through a die or rolled) and all sizes of hexagonal and
octagonal sections are commonly known as cold-drawn bars.
The size (diameter) of round wire is expressed in decimal units or by gage numbers. In the United States, the conventional
unit is the inch, and wire diameter is determined with micrometers capable of making measurements accurate to at least
one thousandth of an inch. Sizes specified are expressed in ten thousandths of an inch, which should be followed by the
metric dimension in brackets to two decimal places. There are several different systems of gage numbers that can be used
for the measurement of wire, but in general these systems have fallen into disuse and have been replaced by sizes in
thousandths of an inch or by metric dimensions. The size of music wire is usually expressed in music wire gage (MWG),
which is the standard for this wire application. For iron and steel telephone and telegraph wire, the standard is the
Birmingham wire gage (BWG) system. The system commonly used by manufacturers of steel wire (other than the
exceptions noted) is the United States steel wire gage (USSWG) or, more commonly, the steel wire gage (SWG) system,
and all unidentified gage numbers used in this article will refer to this system. The use of gage numbers for steel wire
measurements is falling from favor, and the use of absolute units is gaining acceptance. Table 1 lists decimal equivalents
in inches and millimeters for steel wire gage numbers from 7/0 (12.45 mm, or 0.490 in.) to 50 (0.112 mm, or 0.0044 in.).
Wire 20 gage and smaller in size is usually regarded as fine; wire of these sizes is normally drawn and coiled on 203 mm
(8 in.) diam blocks. Larger blocks are used as finished wire diameter increases. For example, 2.34 or 0.092 in. (13 gage)
wire is generally drawn on 559 mm (22 in.) blocks. Table 2 indicates the usual block sizes by gages for wires between
0.889 and 12.70 mm (0.035 and 0.500 in.).
Wiremaking Practices
Wiredrawing. Steel wire is produced from coils of wire rod, after removal of scale, by one or more cold reduction
processes intended primarily for the purpose of obtaining the desired size. Wiredrawing, which improves surface finish
and dimensional accuracy, is the most common cold reduction process. A natural result of cold drawing is that the
resultant wire develops mechanical and physical properties different from those of hot-rolled steel of like composition. By
varying the amount of cold reduction and other wire mill practices, including thermal treatment, a wide variety of
properties and finishes can be obtained.
The mechanical characteristics of steel wire (tensile strength, stiffness, ductility, hardness, and so on) result from wire
mill treatment as well as from chemical composition; therefore, the mechanical properties of wire are less dependent on
chemical composition than those of other steel mill forms. In most cases, the purchaser of wire is interested in suitable
mechanical properties for a given application rather than in chemical composition.
Prior to drawing, the scale is removed from the material by acid pickling or mechanical descaling. If chemically cleaned,
the coil is then rinsed with water, dipped in a vat containing lime in suspension or other material in solution, and in some
cases baked to dry the coating and to liberate the mobile hydrogen that may have been absorbed by the steel during
In the cold drawing of wire, coiled rod or bar is drawn through the tapered hole of a die or through a series of dies; the
number of dies used depends on the finished diameter required. In the past, the smallest rod section used was 5.6 mm (
in.), but a few rod producers now provide 4 mm (0.157 in.) material. To begin drawing, one end of the rod is swaged to a
point, inserted through the die, and attached to a power-driven reel (block). The block then pulls the material through the
die and coils the drawn wire.
The common design of a wiredrawing die (Fig. 1) consists of a supporting ring of steel encasing a hard, wear-resistant
nib. The nib consists of one or more carbides (such as tungsten, tantalum, or titanium) mixed with a bonding agent (such
as cobalt), pressed into the desired shape, and sintered into its hardened rough form, after which it is mounted, sized, and
polished. Diamond dies are sometimes used instead of carbide dies for special fine wire applications. The finest sizes, less
than 0.51 mm (0.020 in.) in diameter, are generally drawn in diamond dies.
The amount of reduction during drawing is expressed as a
percentage of the original cross-sectional area and is
known as the overall draft or total reduction. When a rod
has been reduced by cold reduction (or drawing), it is
called a wire, even though many more reductions (drafts)
may be necessary to reduce it to final size. This usually
requires a thermal treatment between drafts. Wire
produced by the single-draft drawing method refers to rod
that is drawn through one die at a time, with the wire
being removed from the block after each draft, until the
desired diameter is achieved. Continuous drawing, which
is more widely used, designates wire that is drawn through
a series of dies with power-driven blocks between dies.
The drawing speed increases with each draft. The wire is
coiled on the last block as in single-draft drawing or it
may be taken up on a spool. With either single-draft or
continuous drawing, the term direct drawing is used when
the wire is drawn from acid-cleaned or mechanically
descaled rod directly to finished size without thermal
Lubricants. In the drawing operation, various materials
are used as lubricants to produce different finishes on the
surface of the wire and to minimize die wear. Drawing
can be done either with dry lubricants or wet lubricants. In
dry drawing, the base for lubrication is lime, borax,
Fig. 1 Typical wiredrawing die phosphate, or a combination of these, applied to the
surface of the cleaned rod or wire. The lubricant, soap,
grease, or oil is applied in the die box or die container at the time of drawing.
Wet drawing is used for manufacturing some classes of fine wire, for the light drafting of coarse wire, and for
producing special finishes. The rod is generally dry drawn to a suitable size before wet drawing. The wire, with or without
a preparatory heat treatment, is then cleaned and immersed in a solution of copper phosphate, iron or zinc phosphate, or a
combination of these salts, depending on the finish desired. The wire thus prepared is drawn wet using a liquid lubricant.
Welds. In the continuous drawing of wire, industry practice is to weld rod coils together prior to the first draft.
Ordinarily, the welds are difficult to identify unless indicated by painting, and the indicator paint can be removed from the
finished wire if the customer so specifies. The welded joints will have mechanical properties that differ somewhat from
those of the unaffected base metal. Therefore, samples taken for testing should not contain welds. If a test specimen is
found to contain a weld, the specimen should be discarded as nonrepresentative of the wire coil and a new sample taken
to establish compliance with the properties specified. If a variation in properties characteristic of welded joints between
coils is objectionable, weld-free wire should be specified. It should be recognized that this restriction may limit finished
wire coil weight based on the weight of the initial rod coil applied.
Finishes. The following finishes are specified to obtain smooth and clean surfaces, which may be required for functional
or cosmetic reasons.
Common dry-drawn finish, sometimes referred to as bright finish, is ordinarily obtained by conventional dry-
drawing practice. Many wiredrawing lubricants available in powder or viscous form consist primarily of calcium or
sodium stearates.
Clean bright wire finish, which applies to low-carbon and medium-low-carbon dry-drawn wire, is a finish that is
sufficiently clean and bright to ensure satisfactory performance in applications requiring spot welding and painting.
Although not requiring additional drafting, clean bright wire finish does require special care in processing to provide a
surface free of excess lime and lubricant. For some applications, further cleaning by the user or wire manufacturer may be
Extra smooth clean bright wire finish applies to low-carbon and medium-low-carbon wire given an especially
smooth, clean, bright surface by dry drawing from rod selected with respect to surface characteristics and by varying
lubrication and drafting practices. This finish is intended for use where a smooth, clean surface is of primary importance
in some subsequent operation, such as electroplating. A special wiredrawing practice, which requires additional
inspection, selection, and, in some cases, additional draft, is necessary to produce this finish.
Coppered finish and liquor finishes are obtained by drawing rod or wire that has been immersed in a copper sulfate
solution or a copper-tin sulfate solution. The solution selected depends on whether copper-colored finish, straw- or brass-
colored finish, or white liquor finish is required. Coppered finish and liquor finishes can be produced by dry or wet
drawing. Extra coppered finish and extra liquor finishes are normally produced with an extra smooth clean finish.
Coppered finish and liquor finishes are extremely thin. Because of the nature and thinness of these finishes, they do not
provide protection against corrosion. The coppered and liquor finishes are intended for appearance and for smooth clean
surfaces only. Even handling with bare hands can cause discoloration; cotton gloves should be worn. Copper or brass
finishes with heavier or more resistant coatings can be provided by electroplating. Prior to drafting, it is necessary to
remove the iron oxide scale from the rod. There are two common techniques used: chemical cleaning and mechanical
Cleaning and Coating. In chemical cleaning, scale and other surface contaminants are cleaned from steel wire by acid
pickling followed by water rinsing. Cleaning is always followed by a supplementary coating operation (lime, borax,
phosphate, or combinations of these).
Mechanical descaling by bending, wet abrasive blasting, or shotblasting can be used. This can be followed by coating
with lime, borax, or soap solution, but the coating must be dry before reaching the drawing lubricant.
Lime, borax, and phosphate coating operations are performed to provide a carrier for the lubricant necessary for
subsequent processing. In lime coating, practices can be varied to apply differing amounts of lime, depending on the end
use. Phosphate-coated wire may have a supplementary coating of lime, borax, or a water-soluble soap. Wire is frequently
cleaned and coated as a final operation, particularly where the wire has been thermally treated at finished size.
Thermal treatments for steel wire include stress relief, annealing, normalizing, patenting, and oil tempering. All
thermal treatment of ferrous material involves time and temperature to provide the three phases: recovery,
recrystallization, and grain growth.
Annealing is the general term applied to a variety of heat treatments for the purpose of softening the wire. Annealing
commonly involves heating to a temperature above, near, or below the upper critical temperature, Ac3 or Accm. A number
of processes are employed, all of which influence the surface finish obtained. If a particular finish is required on wire
annealed at finish size, the producer should be consulted. Specific annealing processes are described below:
• Regular annealing (black annealing) is performed by heating coils of wire in a furnace, followed by
slow cooling, without attempting to produce a specific microstructure or a specific surface finish
• Salt annealing is performed by immersing coils of wire in a molten salt bath, holding at the required
temperature for a predetermined time, cooling in air, and removing the salt. Salt-annealed wire is not as
soft as regular annealed wire and is used when maximum softness is not required or when wire slightly
stiffer than regular annealed wire is desired. Salt annealing can be used as an intermediate procedure
before final drawing
• Strand annealing is performed by passing wire in single strands through a bath of molten lead (lead
annealing), a fluidized bed, or through open-fired furnaces (some with controlled atmospheres),
followed by air cooling. Strand-annealed wire is not as soft as regular annealed wire and is used for
products requiring greater strength or stiffness or as an in-process procedure in continuous operations
such as wire galvanizing.
• Bright annealing of coppered finished and liquor finished wire is performed by heating and cooling the
wire in a controlled atmosphere to minimize oxidation
• Lime bright annealing is performed by heating and cooling bright dry-drawn wire in a controlled
atmosphere to minimize oxidation
• Spheroidize annealing involves prolonged heating at a temperature near or slightly below the lower
critical temperature, Acl, followed by very slow cooling, with the object of making the carbide particles
in the microstructure globular (spheroidal) in order to obtain maximum softness
Annealing in-process is performed on dry low-, medium-, and high-carbon steel wire. There are two primary levels of
annealing in this type: spheroidized anneal in-process and annealed in-process. The differentiation is based on a
metallographic examination of grain structure after thermal treatment. If 80% or more of the grains are spheroid, then the
product is designated spheroidized in-process. This requires a longer furnace time than annealed in-process.
In producing annealed in-process wire, an annealing heat treatment (followed by a separate cleaning and coating
operation) is performed at an intermediate stage of wire-drawing to produce a softer wire for applications in which direct-
drawn wire would be too hard or too stiff. Annealing in-process can also be used when controlled mechanical properties
are required for a specific application.
It should be noted that it is normal to clean scaled rod or wire before thermal treatment in order to avoid difficult-to-
remove secondary scale formation. Such practices employ cleaned lime-coated wire and rod.
Patenting is a thermal treatment that is usually confined to medium-high-carbon and high-carbon steels. In this process,
individual strands of rod or wire are heated well above the upper critical temperature (generally accepted as 900 °C, or
1650 °F) rapidly in air, molten salt, fluidized beds, or molten lead. This treatment is generally used to produce a fine
pearlitic grain structure to enhance the tensile properties in subsequent wiredrawing. Patenting can be used in a
continuous line in which the material is cleaned and coated.
Oil tempering is a heat treatment for high-carbon steel wire in which strands of the wire at finished size are
continuously heated to an appropriate temperature above the critical temperature range, oil quenched, and subsequently
passed through a stress-relieving bath. Oil tempering is used in the production of such commodities as oil-tempered
spring wire, which is used in certain types of mechanical springs that are not subjected to a final heat treatment after
forming. Oil-tempered wire is intended primarily for the manufacture of products that are required to withstand stresses
close to the limit of the elastic range of the wire. The mechanical propertiesof oil-tempered wire provide resistance to
permanent set under repeated and continuous stress. Oil-tempered wire is also used in applications that require abrasion
resistance, such as sieves and screens.
An oxide coating of controlled thickness can be developed during the tempering of spring wire. This coating is normally
left on the wire to help retain oil-base rust preventives on the surface of the wire. It also serves to prevent metal-to-metal
contact during coiling or forming.
Specification Wire
There are some applications for low-carbon and medium-low-carbon steel wire that involve special requirements, such as
specific tensile strength ranges or hardness limitations, the attainment of which involves special selection of steel and
modification of conventional wire mill practices and/or thermal treatment (for example, annealed in-process wire). Such
wire is commonly designated specification wire.
A standard specification that covers the general requirements for coarse, carbon steel round wire is ASTM A 510 (Table
5). Specification wire can be furnished with special finishes for subsequent processing, such as spot welding,
electroplating, and tinning.
Metallic Coated Wire
Metallic coatings can be applied to wire by various methods, including hot dip processes, the electrolytic process, and
metal cladding by rolling metallic strip over the wire.
Aluminized wire (aluminum-coated wire) is produced by passing fluxed strands of wire through a bath of molten
aluminum or aluminum alloy. The material is then rapidly cooled. This may, depending on the analysis, increase or
decrease the tensile values.
Brass-plated wire is produced by passing strands or wire through an electrolytic cell containing a solution of both
copper and zinc salts. Typical applications for this product are steel cord used for reinforcing automobile tires and rubber
hoses and when a pleasing appearance is important. Brass-plated wire is not intended for applications requiring corrosion
Bronze-coated wire, used for tire bead reinforcement around the rim area of the tire, is produced in continuous lines
by passing wires through thermal treatment to adjust physical properties, acid cleaning, and tin-copper solutions.
Galvanized wire (zinc-coated wire) is produced by passing strands of wire through a bath of molten zinc (hot dip
galvanized) or through an electrolytic cell containing a solution of a zinc salt (electrogalvanized). Galvanizing gives
corrosion protection to wire. The wire is usually annealed in the same operation by being passed through molten lead,
molten salt, or a fluidized bed, followed by cleaning or pickling, prior to galvanizing. The general requirements for
galvanized carbon steel wire are given in ASTM A 641.
The term temper as applied to galvanized wire is a reference to stiffness or resistance to bending, not to thermal treatment.
It is customarily expressed as soft, medium, or hard. Tensile strengths corresponding to these three tempers are given in
Table 6.
Because the wire is generally strand annealed prior to zinc coating, the temper of the wire can be controlled by using
different strand-annealing temperatures. Different properties can also be obtained by varying the chemical composition
for a given annealing practice. The user of galvanized wire should ensure that the manufacturer has a thorough
understanding of the properties, including both tensile strength and ductility, required by the end use of the wire.
The coating weights given in Tables 7(a) and 7(b) apply to ordinary galvanized wire only; heavier coatings are applied to
wire for structural applications, such as bridge wire, strand wire, and concrete-reinforcing wire. Size tolerances for
galvanized wire are given in Tables 4(a), 4(b), and 4(c). Tests for coating adherence are performed by wrapping the wire
on a mandrel of diameter indicated in Tables 7(a) and 7(b).
Tinned wire is produced by passing strands of wire continuously through a molten tin bath and then through tightly
compressed wipes as the strands emerge from the bath. Tinned wire is commonly manufactured in three tempers: soft,
medium hard, and hard. These three tempers are obtained by using the following techniques:
• Soft tinned wire is tinned after being annealed at or near finished size
• Medium-hard tinned wire is produced from thermal-treated wire
• Hard tinned wire is obtained by tinning wire that has been cold drawn to final size, usually without
intermediate thermal treatment
Quality Descriptions and Commodities
Many types of steel wire have been developed for specific components of machines and equipment and for particular end
uses. The unique properties of each of these types of wire are obtained by employing a specific combination of steel
composition, steel quality, process thermal treatment, and cold-drawing practice.
These wires are normally grouped into broad usage categories. These categories, as well as some items in each category,
are described in the following sections under their quality descriptions or commodity names.
Low-Carbon Steel Wire for General Usage
Low-carbon steel wire forms for general usage include industrial or standard-quality wire, annealed low-carbon
manufacturers' wire, and merchant wire.
Industrial or standard-quality wire is produced from low- or medium-low-carbon steel, manufactured under close
control in steelmaking procedures to provide internal soundness and freedom from detrimental surface imperfections for
industrial applications. It is usually drawn directly from hot-rolled rod. Applications may involve specific chemical
composition, but do not require specific tempers or tensile or softness limitations. The terms industrial or standard-quality
wire should not be confused with or used in connection with commodity descriptions that apply to types of wire that have
been developed for specific applications. Some of these are described in the AISI Steel Products Manual.
Annealed low-carbon manufacturers' wire, either black annealed or lime bright annealed, has the typical
properties given in Table 8.
Merchant wire is annealed or soft galvanized low-carbon steel wire supplied in coils of exact weights. Black annealed
wire can be supplied oiled and wiped for short-term corrosion protection.
Wire for Packaging and Container Applications
Included in wires for packaging and container applications are those designed for tying bags, baling hay and straw,
binding and stapling boxes, and strapping and reinforcing shipping packages.
Baling wire for use on automatic haybaling machines is 1.93 mm (0.076 in.) or 14 gage, diam wire made from
annealed low-carbon or annealed medium-low-carbon steel. The tensile strength of baling wire is 345 to 485 MPa (50 to
70 ksi), and minimum elongation is 12% in 250 mm (10 in.). The wire is commonly produced as rewound coils having an
oil-base protective coating that will not harden or become gummy when applied to the wire at the time of rewinding.
Strapping wire, sometimes called tying wire, is used for strapping and reinforcing packages such as boxes, crates, and
cartons. Commonly, it is annealed wire, coppered wire, or galvanized wire. It is made to specified tensile strength
requirements and must have sufficient ductility and toughness to withstand severe crimping or twisting without breaking.
Wire for Structural Applications Other Than Prestressed Concrete
This classification includes galvanized bridge wire, zinc-coated or aluminum-coated steel strand wires, and concrete-
reinforcing wire.
Galvanized bridge wire is used as a component in the fabrication of strands or ropes for bridge cables, building
structures, and guys. The wire is drawn from high-carbon steel wire rods with closely controlled composition ranges to
achieve the desired properties. Wire size is dependent on the size of the strand or rope to be produced. Coating weight for
galvanized bridge wire is class A, B, or C. These coating weights are greater than those for the corresponding
designations for ordinary galvanized wire. The mechanical properties of galvanized bridge wire are given in Tables 9(a),
and 9(b).
Zinc-coated strand wire is used in the manufacture of galvanized steel wire strand for guy, messenger, and ground
wires and for similar applications. Zinc-coated steel strand wire is commonly produced to the specified tensile strength,
elongation, and weight properties of zinc coating. Each grade of strand wire is intended for use in one of the five grades
of strand covered in ASTM A 475 and A 363 or in equivalent specifications.
Aluminum-coated wire is similar to zinc-coated steel strand wire except for the coating, and it is used for similar
purposes. It is manufactured in conformance with ASTM A 474.
Concrete-reinforcing wire (plain, not deformed) is used either as wire or for fabrication into welded wire fabric.
Generally, this wire is produced to conform to ASTM A 82, which covers mechanical property requirements, tolerances,
and test procedures. Mechanical property requirements include tensile strength, yield strength, reduction in area, and bend
testing. Concrete-reinforcing wire is generally furnished with a clean bright finish suitable for spot welding, except that
fine wire for welded fabric is galvanized (regular coating weight) after drawing to final size. Sizes are designated by W
numbers related to sectional areas.
The surface deformation lines in deformed concrete-reinforcing wire provide a mechanical anchorage in concrete,
conforming to ASTM A 496. Sizes are designated by D numbers related to the average cross-sectional areas of the wires
between 6.45 to 200 mm2 (0.01 and 0.31 in.2).
Wire for Prestressed Concrete
Two types of uncoated round high-carbon steel wire are produced for prestressed concrete applications: cold drawn and
cold drawn/stress relieved. The wire is used for linear or circular pretensioning or posttensioning concrete structural
members. The stress-relieved product can be applied as a single wire or as a strand that has been stress relieved after
This product is described in American Society for Testing and Materials (ASTM) specifications as follows:
• A 648--Wire for prestressed concrete pipe
• A 416--Wire for stress-relieved strand
• A 421--Wire uncoated for linear prestressing
In North America, wires for direct linear prestressing are stress relieved.
Stress-relieved uncoated high-carbon wire is commonly used for the linear prestressing of concrete structures. It
is produced in diameters of 4.88, 4.98, 6.35, and 7.01 mm (0.192, 0.196, 0.250, and 0.276 in.) to tensile strengths of 1620
to 1725 MPa (235 to 250 ksi). This wire can also be made in a low-relaxation grade. Full requirements are given in
ASTM A 421. Full requirements for the stranded product are given in ASTM A 416.
After stress relieving, the inside diameters of coils are generally larger than those of drawn wire in order to prevent stress
set or reintroduction of coil stress. Coil inside diameters may be as large as 200 times the wire diameter.
High-carbon wire for mechanical tensioning is commonly used for circular prestressing in the manufacture of
concrete pressure pipe. Its chemical composition, tensile strength requirements, and specified wrap tests are indicated in
Tables 10, 11, and 12. Full requirements are given in ASTM A 648.
Wire for Electrical or Conductor Applications
Aluminum conductor steel reinforced wire, support wire, and telephone/telegraph wire are wires designed for electrical or
conductor applications.
Aluminum conductor steel reinforced wire is a special commodity for the steel reinforcement of aluminum
conductor cable. It is used either as a single center wire or as a multiple-wire strand and is supplied in diameters ranging
from 1.27 to 4.83 mm (0.050 to 0.190 in.). This commodity is produced from either aluminum coated (ASTM B 341) or
galvanized (ASTM B 498). Minimum tensile strength requirements range from 1140 to 1450 MPa (165 to 210 ksi),
depending on the type and class of coating specified. Minimum yield strength and elongation, minimum coating weight,
and mandrel wrap testing are additional requirements.
Support wire is a high-strength zinc-coated steel wire with a class A coating. This wire is used to support telegraph and
telephone distribution lines. It is usually furnished in diameters of 2.77 to 3.76 mm (0.109 to 0.148 in.). Physical
requirements are minimum tensile strength of 1310 MPa (190 ksi), minimum elongation of 2% in 250 mm (10 in.), and
wrap test for ductility and adherence.
Telephone and telegraph wire is galvanized wire for signal transmission purposes. It is manufactured in several
grades, for example, grades EBB and BB (ASTM A 111) and grades 85, 135, and 195 (ASTM A 326). The designations
EBB and BB are abbreviations of the long-standing trade terms Extra Best Best and Best Best, which are applied to
galvanized telephone and telegraph wire. All these grade designations, however, are now associated with definite values
of strength and electrical resistivity. For example, EBB designates the steel wire with the lowest resistivity considered
appropriate for signal transmission lines, and BB designates the steel wire with resistivity in the middle of the range
appropriate for this purpose.
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