Volume 01 - Properties and Selection Irons, Steels, and High-Performance Alloys Part 5 potx

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 Produ

and take their chances on occasional difficulties In conventional practice, depth of machining for hot-rolled bars is 1.6

mm ( 1

16 in.) for bars 38 to 76 mm (11

2 to 3 in.) in diameter, and 3.2 mm (1

8in.) for bars over 76 mm (3 in.) in diameter

Reference cited in this section

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

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 Hardness is a relatively simple property to measure, and it is closely related to tensile strength, as shown in Fig 1 When Fig 2 is used together with Fig 1, a simple hardness test can give an estimate of yield strength and elongation, as well as tensile strength

Fig 1 Relationship between hardness and tensile strength of steel Range up to 300 HB is applicable to the

hot-finished steel discussed in this article Source: Ref 2

Fig 2 Relation of tensile properties for hot-rolled carbon steel

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

Table 2 Lowest maximum hardness that can be expected for hot-rolled steel bars, billets, and slabs with ordinary mill annealing

Maximum hardness, HB(a)

(a) Specific microstructure requirements may necessitate modification of these hardness numbers

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 The minimum expected mechanical properties of commonly used grades of rolled carbon steel bars are shown in Fig 3

hot-Fig 3 Estimated minimum tensile properties of selected hot-rolled carbon steel bars

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 hot-rolled steel bar products and their characteristics are described in the following sections

Table 3 Typical ASTM specifications for structural quality steel bars and steel structural shapes

Covered in ASTM A 6

Specification Steel type and condition

Carbon steels

A 36(a)(b) Carbon steel plates, bars, and shapes

A 131(c) Carbon and HSLA steel plates, bars, shapes, and rivets for ships

A 529 Carbon steel plates, bars, shapes, and sheet piling with minimum yield strength of 290 MPa (42 ksi)

A 709 Carbon, alloy, and HSLA steel plates, bars, and shapes for bridges

Alloy steel

A 710 Age-hardening low-carbon Ni-Cu-Cr-Mo-Nb and Ni-Cu-Nb alloy steel plates, bars, and shapes

High-strength low-alloy (HSLA) steels

A 131(c) See above under Carbon Steel

A 242 HSLA steel plates, bars, and shapes

A 572 Nb-V HSLA steel plates, bars, shapes, and sheet piling

A 588 HSLA steel plates, bars, and shapes with minimum yield point of 345 MPa (50 Ksi)

A 633 Normalized HSLA steel plates, bars, and shapes

A 690 HSLA steel H-piles and sheet piling for use in marine environments

(a) This ASTM specification is also published by the American Society of Mechanical Engineers, which adds an S in front of the A

(b) See also Canadian Standards Association (CSA) specification G40.8

(c) See also Section 39 of the ABS specifications

Table 4 Typical ASTM specifications for hot-rolled steel bars

See Table 3 for ASTM specifications for structural quality bars and structural shapes

Specification Steel type and condition

Carbon steels

A 321(a) Quenched and tempered carbon steel bars

A 575(a) Merchant quality carbon steel bars

A 576(a) Special quality carbon steel bars

A 663(a) Merchant quality carbon steel bars subject to mechanical property requirements

A 675(a) Special quality carbon steel bars subject to mechanical property requirements

Alloy steels

A 295 Bearing quality high-carbon chromium steel billets, forgings, tube rounds, bars, rods, and tubes

A 304(a) Alloy steel bars subject to end-quench hardenability requirements

A 322(a) Alloy steel bars for regular constructional applications

A 434(a) Quenched and tempered alloy steel bars, hot rolled or cold finished

A 485 Bearing quality high-carbon chromium steel billets, tube rounds, bars, and tubes modified for high hardenability

A 534 Carburizing alloy steel billets, tube rounds, bars, rods, wire, and tubes of bearing quality

A 535 Special quality alloy steel billets, bars, tube rounds, rods, and tubes for the manufacture of antifriction bearings

(a) Covered in ASTM A 29

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:

• 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, half-rounds, octagons, and special bar-size shapes

Hot-rolled alloy steel bars are covered by several ASTM specifications (Tables 3 and 4) Many of the alloys covered in these specifications are standard AISI-SAE grades (Table 5)

Table 5 AISI-SAE grades of hot-rolled alloy steel bars in ASTM specifications

ASTM

specification

AISI-SAE grades

A 295 52100, 51100, 50100

A 304 All H grades except 4626H and 86B30H

A 322 All standard grades except 4032, 4042, 4135, 4422, 4427, 4617, 50B40, 5046, 5060, 5115, 5117, 50100, 8115,

86B45, 8650, 8660, 9310, and 94B15

A 434 By agreement

A 534 4023, 4118, 4320, 4620, 4720, 5120, 8620, E-3310, E-9310

A 535 3310, 4320, 4620, 4720, 4820, 52100, 52100 Mod 1, 52100 Mod 2, 52100 Mod 3, 52100 Mod 4, 8620, 9310

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 high-carbon 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 mm (100 in.) 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

Aircraft quality alloy steel bars are ordinarily made to Aerospace Material Specifications published by the Society of Automotive Engineers Typical examples of parts for aircraft engines and airframes made from bars covered by AMS specifications are given in Table 6

Table 6 Specifications and grades of alloy steel bars for aircraft parts

Bolts, studs, and nuts 6322 8740

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:

• 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 The nominal values for bar diameter, sectional area, and weight per unit length corresponding to these size numbers are given in Table 7 The nominal cross-sectional area and the nominal diameter of a deformed bar are the same as those of a plain bar of equal weight per foot

cross-Table 7 Dimensions of deformed and plain concrete-reinforcing bars of standard sizes

Nominal

diameter

Cross- sectional area

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

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

Cold-Finished Steel Bars

Revised by the ASM Committee on Cold-Finished Bars*

Introduction

COLD-FINISHED STEEL BARS are carbon and alloy steel bar products (round, square, hexagonal, flat, or special shapes) that are produced by cold finishing previous hot-wrought bars by means of cold drawing, cold forming, turning, grinding, or polishing (singly or in combination) to yield straight lengths or coils that are uniform throughout their length Not covered in this article are flat-rolled products such as sheet, strip, or plate, which are normally cold finished by cold rolling, or cold-drawn tubular products

Cold-finished bars fall into five classifications:

• Cold-drawn bars

• Turned and polished (after cold drawn or hot roll) bars

• Cold-drawn, ground, and polished (after cold draw) bars

• Turned, ground, and polished bars

• Cold-drawn, turned, ground, and polished bars

Cold-drawn bars represent the largest tonnage production and are widely used in the mass production of machined and other parts They have attractive combinations of mechanical and dimensional properties

Turned and polished bars have the mechanical properties of hot-rolled products but have greatly improved surface finish and dimensional accuracy These bars are available in sizes lager than those that can be cold drawn Turned bars are defect and decarb free

Cold-drawn, ground, and polished bars have the increased machinability, tensile strength, and yield strength of drawn bars together with very close size tolerances However, cold-drawn, ground, and polished bars are not guaranteed

cold-to be defect free

Turned, ground, and polished bars have superior surface finish, dimensional accuracy, and straightness These bars find application in precision shafting and in plating, where such factors are of primary importance

Cold-drawn, turned, ground, and polished bars have improved mechanical properties, close size tolerances, and a surface free of imperfections

Note

* K M Shupe, Bliss & Laughlin Steel Company; Richard B Smith, Stanadyne Western Steel; Steve Slavonic, Teledyne Columbia-Summerill; B F Leighton, Canadian Drawn Steel Company; W Gismondi, Union Drawn Steel Company, Ltd.; John R Stubbles, LTV Steel Company; Kurt W Boehm, Nucor Steel; Donald

M Keane, LaSalle Steel Company

Bar Sizes

Cold-finished steel bars are available in a wide variety of sizes and cross-sectional shapes Normally, they are furnished in straight lengths, but in some sizes and cross sections they may be furnished in coils Cold-finished steel bars are available with nominal dimensions designated in either inches or millimeters Cold-finished product is available in standard size increments, which vary by size range Special sizes can be negotiated depending on hot mill increments and cold-finish tooling The sizes in which they are commonly available in bar and coil form are given in Table 1

Table 1 Common commercially available sizes of cold-finished steel bars and coils

Bars (a)

Minimum thickness or diameter

Maximum thickness or diameter

Size increments Normal length

75 3.2-

152

32nds to 1 in., 16ths to 3 in., 8ths

to 6 in

3.0-3.7

or 7.3

0.125 thick × 0.25 wide

76 ×

371

3 thick ×

1458

wide

1.6-17 3.2-

44 6.4-

(c)

(a) Ref 1

(b) Ref 2

(c) Or other sections having cross-sectional areas ≤194 mm2 (≤0.30 in.2)

References cited in this section

1 J.G Bralla, Handbook of Product Design for Manufacturing, McGraw-Hill, 1986

2 Alloy, Carbon, and High Strength Low Alloy Steels, Semifinished for Forging; Hot Rolled Bars; Cold Finished Steel Bars; Hot Rolled Deformed and Plain Concrete Reinforcing Bars, AISI Steel Products

Manual, American Iron and Steel Institute, 1986

Product Types

In the manufacture of cold-finished bars, the steel is first hot rolled oversize to appropriate shape and is then subjected to mechanical operations (other than those intended primarily for scale removal) that affect is machinability, straightness, and end-cut properties The two common methods of cold finishing bars are:

• Removal of surface material by turning or grinding, singly or in combination

• Drawing the material through a die of suitable configuration

Pickling or blasting to remove scale may precede turning or grinding and must always precede drawing For bar products, cold rolling has been almost superseded by cold drawing Nevertheless, cold-finished bars and special shapes are sometimes incorrectly described as cold rolled

Commercial Grades. Any grade of carbon or alloy steel that can be hot rolled can also be cold finished The choice of grade is based on the attainable cold-finished and/or hardenability and tempering characteristics necessary to obtain the required mechanical properties

Production methods vary widely among cold-finished cold-drawn suppliers For example, one supplier currently anneals and cold draws grades 1070, 1090, and 5160, and in the future plans to do the same with grade 9254 Grade 1070 is a high-volume item, and cold drawing is required for precision sizing and subsequent nondestructive testing of the bar, using a rotating-probe eddy current device (see the articles "Eddy Current Inspection," "Remote-Field Eddy Current

Inspection," and "Steel Bar, Wire, and Billets" in Nondestructive Evaluation and Quality Control, Volume 17 of ASM

Handbook, formerly 9th Edition Metals Handbook) for detecting surface seams Cold drawing is also necessary because

the smallest hot-rolled size typically available for some applications is not small enough for customer use Thus, a supplier whose smallest hot-rolled bar size is 11.1 mm (0.437 in.) cold draws this diameter to as small as 9.98 mm (0.393 in.)

Carbon steels containing more than 0.55% C must be annealed prior to being cold drawn so that the hardness will be sufficiently low to facilitate the cold-drawing operation For carbon steels containing up to 0.65% C, this will normally be

a lamellar pearlitic anneal; for carbon steels containing more than 0.65% C, a spheroidize anneal is required The type of structure required is normally reached by agreement between the steel producer and the customer

Alloy steels containing more than 0.38% C are usually annealed before cold drawing

Machined Bars. Bar products that are cold finished by stock removal can be:

• Turned and polished

• Turned, ground, and polished

• Cold drawn, ground, and polished

• Cold drawn, turned, and polished

• Cold drawn, turned, ground, and polished

Turning is done in special machines with cutting tools mounted in rotating heads, thus eliminating the problem of having

to support long bars as in a lathe Grinding is done in centerless machines Polishing can be done in a roll straightener of the crossed-axis (Medart) type with polished rolls to provide a smooth finish Polishing by grinding with an organic wheel

or with a belt is of increasing interest (see the article "Grinding Equipment and Processes" in Machining, Volume 16 of

ASM Handbook, formerly 9th Edition Metals Handbook) because it is cost effective to grind and polish the bars on the

same machine simply by using grinding wheels or belts of different grit size Grinding produces a smoother finish than turning; polishing improves the surface produced by either technique Turned, ground, and polished rounds represent the highest degree of overall accuracy, concentricity, straightness, and surface perfection attainable in commercial practice (Ref 3)

The surface finish desired is specified by using the process names given above because the industry has not developed standard numerical values for roughness, such as microinch or root mean square (rms) numbers However, surface finish with respect to rms (root mean square deviation from the mean surface) as determined with a profilometer can be negotiated between the producer and a customer This could be done for such critical-finish applications as turned and polished bars used to produce shafting as well as stock used to produce machined parts of which a superior finish is required on surfaces not machined

The published range of diameters both for turned and for turned and ground bars is 13 to 229 mm (1

2 to 9 in.) inclusive; for cold-drawn and ground bars, it is 3.2 to 102 mm (1

8 to 4 in.) inclusive These are composites of size ranges throughout the industry; an individual producer may be unable to furnish a full range of sizes

For example, one well-known producer supplies turned rounds from 13 to 229 mm (1

2 to 9 in.), another from 29 to 203

mm (11

8 to 8 in.) all finished sizes Yet another producer supplies sizes up to and including 152 mm (6 in.) that are turned on special turning machines and ground on centerless grinders; larger sizes are lathe turned and ground on centers Because turning and grinding do not alter the mechanical properties of the hot-rolled bar, this product can be machined asymmetrically with practically no danger of warpage (Ref 3)

Stock removal is usually dependent on American Iron and Steel Institute (AISI) seam allowances (Ref 2) Stock removal

in turning, or turning and grinding, measured on the diameter, is normally 1.6 mm ( 1

16 in.) for sizes up to 38 mm (11

2in.), 3.2 mm (1

8 in.) for the 38 to 76 mm (11

2 to 3 in.) range, 4.8 mm ( 3

16 in.) for the 76 to 127 mm (3 to 5 in.) range, and 6.4 mm (1

4 in.) for 127 mm (5 in.) diameter and larger

Cold-drawn round bars are available in a range of diameters from 3.2 to 152 mm (1

8 to 6 in.) The maximum diameters available from individual producers, however, may vary from 76 to 152 mm (3 to 6 in.) The reduction in diameter in cold drawing, called draft, is commonly 0.79 mm ( 1

32 in.) for finished sizes up to 9.5 mm (3

8 in.) and 1.6 mm ( 1

16 in.) for sizes over 9.5 mm (3

8 in.) Some special processes use heavier drafts followed by stress relieving One producer employs heavy drafting at elevated temperature With this exception, drawing operations are begun with the material at room temperature to start, and the only elevated temperature involved is that developed in the bar as a result of drawing; this temperature rise is small and of little significance

Originally, cold finishing, whether by turning or by cold rolling, was employed only for sizing to produce a bar with closer dimensional tolerances and a smoother surface As cold-finished bar products were developed and improved, increased attention was paid to the substantial enhancement of mechanical properties that could be obtained by cold working This additional advantage is now more fully appreciated, as evidenced by the fact that increased mechanical properties are an important consideration in about 40% of the applications In approximately half of these applications, or 20% of the total, cold drawing is used only to increase strength; in the other 20%, close tolerances and better surface finish are desired in addition to increased strength

As-rolled microalloyed high-strength low-alloy (HSLA) steels or microalloyed HSLA steels in various combinations of controlled drafting and furnace treatment provide an extension of property attainment A high percentage of free-machining steels are cold drawn for the combination of size accuracy and improved machinability Recent developments

in microalloyed steels provide hot-rolled turned bars, under certain circumstances, having mechanical properties similar

to cold-drawn nonmicroalloyed steels

An appreciable fraction of all applications of cold finishing to carbon steel bars utilizes cold drawing to improve mechanical properties For alloy steel, however, cold finishing is commonly used to improve surface finish and dimensional accuracy, and not for additional mechanical strength When additional mechanical strength is desired, alloy steel bars may be heat treated (quenched and tempered) and then cold drawn and stress relieved Elevated-temperature or warm-drawn steels are also available with increased mechanical strength and improved machinability

Heavily drafted and strain-tempered carbon and alloy steels subjected to induction hardening of the surface provide many additional property combinations The extra cost of using alloy steel in cold-finished bars can be justified only when heat treatment (quenching and tempering) is necessary for meeting the required strength level Because work-hardening effects are removed during heating prior to quenching, the benefit of increased mechanical strength due to cold finishing is eliminated from the finished product

Turning Versus Cold Drawing. Basic differences exist between bars finished by turning and those finished by cold drawing First, it is obvious that turning and centerless grinding are applicable only to round bars, while drawing can be applied to a variety of shapes Drawing, therefore, is more versatile than turning

Second, there is a difference in the number and severity of the surface imperfections that may be present Because stock is removed in turning and grinding, shallow surface imperfections and decarburization may be completely eliminated When material is drawn, stock is only displaced, and surface imperfections are only reduced in depth (in the ratio of the change

in bar diameter or section thickness) The length of these imperfections may be slightly increased because in the drawing operation an increase in length accompanies the reduction in cross section

Cold-drawn bars can approach the freedom from surface imperfections obtained in turned or turned and ground bars if the hot-rolled bars from which they are produced are rolled from specially conditioned billets Quality conditions such as cold-working quality are available from producers of hot-rolled bars The depth limits of the surface imperfections are as agreed to between the producer and the customer However, if maximum freedom from surface imperfections is the controlling factor, turned bars have an advantage

Different size tolerances are applicable to cold-finished products, depending on shape, carbon content, and heat treatment Listed in Tables 2, 3, and 4 are the tolerances for cold-finished carbon and alloy steel bars published in ASTM A 29 These tables include cold-drawn bars; turned and polished rounds; cold-drawn, ground, and polished rounds; and turned, ground, and polished rounds From the data in Tables 2, 3, and 4, certain generalizations can be stated The tolerances for cold-drawn and for turned and polished rounds, for example, are the same for sizes up to and including 102 mm (4 in.) There are differences, however, between the tolerances that apply to carbon steel and those that apply to alloy steels Tolerances for several finishes also vary with certain levels of carbon content Broader tolerances are applicable to bars that have been heat treated before cold finishing In contrast, tolerances are closer when bars are ground, and these tolerances are independent of carbon content

Table 2 Size tolerances for cold-finished carbon steel bars, cold drawn or turned and polished

This table includes tolerances for bars that have been annealed, spheroidize annealed, normalized, normalized and tempered, or quenched and tempered before cold finishing This table does not include tolerances for bars that are annealed, spheroidize annealed, normalized, normalized and tempered, or quenched and tempered after cold finishing; the producer should be consulted for tolerances for such bars

finishing

C > 0.55

All grades quenched and tempered

or normalized

before cold finishing

mm in mm in mm in mm in mm in mm in

Rounds cold drawn (to 102 mm, or 4 in., in size) or turned and polished

To 38 inclusive

To 1 1

2inclusive

0.05

0.002

0.08 -0.003 -0.10 -0.004

-0.13

0.005

inclusive

0.08

0.003

0.10 -0.004 -0.13 -0.005

-0.15

0.006

0.004

0.13 -0.005 -0.15 -0.006

-0.18

0.007

0.15 -0.006 -0.18 -0.007

-0.20

0.008

0.18 -0.007 -0.20 -0.008

-0.23

0.009

0.20 -0.008 -0.23 -0.009

-0.25

0.010

0.002

0.08 -0.003 -0.10 -0.004

-0.15

0.006

0.003

0.10 -0.004 -0.13 -0.005

-0.18

0.007

inclusive

0.10

0.004

0.13 -0.005 -0.15 -0.006

-0.20

0.008

0.20 -0.008

64-80 inclusive

>21

2-3

18

inclusive

0.13

0.005

0.15 -0.006 -0.18 -0.007

-0.23

0.009

0.005

0.002

0.10 -0.004 -0.13 -0.005

-0.18

0.007

0.003

0.13 -0.005 -0.15 -0.006

-0.20

0.008

inclusive

0.10

0.004

0.15 -0.006 -0.18 -0.007

-0.23

0.009

0.006

0.20 -0.008 -0.23 -0.009

-0.28

0.011

0.003

0.10 -0.004 -0.15 -0.006

-0.20

0.008

0.004

0.13 -0.005 -0.20 -0.008

-0.25

0.010

0.005

0.15 -0.006 -0.25 -0.010

-0.30

0.012

0.20 -0.008 -0.28 -0.011

-0.40

0.016

0.25 -0.010 -0.30 -0.012

-0.50

0.020

0.50 -0.020

>152 >6

-0.33

0.013

0.38 -0.015

Source: Ref 4

(a) Tolerances can be ordered all plus, or distributed plus and minus with the sum equivalent to the tolerances listed

(b) Width governs the tolerance for both width and thickness of flats, for example, when the maximum of carbon range is 0.28% or less for a flat

50 mm (2 in.) wide and 25 mm (1 in.) thick The width tolerance is 0.13 mm (0.005 in.), and the thickness is the same, nearly 0.13 mm (0.005 in.)

Table 3 Size tolerances for cold-finished alloy steel bars, cold drawn or turned and polished

This table includes tolerances for bars that have been annealed, spheroidize annealed, normalized, normalized and tempered, or quenched and tempered before cold finishing This table does not include tolerances for bars that are annealed, spheroidize annealed, normalized, normalized and tempered, or quenched and tempered after cold finishing; the producer should be consulted for tolerances for such bars

C > 0.55 with

or without stress relieving or annealing after cold finishing

All carbons quenched and tempered (heat treated) or normalized and tempered before

cold finishing

Rounds cold drawn (to 102 mm, or 4 in., in size) or turned and polished

(a) Width governs the tolerance for both width and thickness of flats, for example, when the maximum of carbon range is 0.28% or less for a flat

50 mm (2 in.) wide and 25 mm (1 in.) thick The width tolerance is 0.13 mm (0.005 in.), and the thickness is the same, nearly 0.13 mm (0.005 in.)

Table 4 Size tolerances for cold-finished carbon and alloy steel round bars cold drawn, ground, and polished or turned, ground, and polished

Size

Cold drawn, ground, and polished Turned, ground, and polished

Tolerances from specified size

>76-102 incl >3-4 incl >76-102 incl >3-4 incl -0.08 -0.003

>102-152 incl >4-6 incl -0.10(a) -0.004 (a)

Table 5 Straightness tolerances for cold-finished carbon and alloy steel bars

All grades quenched and tempered or normalized and tempered to HB 302 before cold finishing; all grades stress relieved or annealed after cold finishing Straightness tolerances are not applicable to bars having Brinell hardness exceeding 302 The tolerances are based on the following method of measuring straightness Departure from straightness is measured by placing the bar on a level table so that the arc or departure from straightness is horizontal, and the depth of the arc is measured with a feeler gage and a straightedge

It should be recognized that straightness is a perishable quality and may be altered by mishandling The preservation of straightness in cold-finished bars requires the utmost care in subsequent handling Specific straightness tolerances are sometimes required for carbon and alloy steels, in which case the purchaser should inform the manufacturer of the straightness tolerances and the methods to be used

in checking the straightness

Straightness tolerances (maximum deviation) from straightness

in any 3 m (10 ft) portion of the bar

Carbon range, ≤0.28% Carbon range >0.28% and

all grades thermally treated

Size Length

Rounds Squares,

hexagons, and octagons

Table 6 Minimum stock removal for cold-finished steel bars subject to magnetic particle inspection

For turned and polished alloy steel bars subject to magnetic particle inspection, the recommended minimum total stock removal from the surface (the amount removed by the producer plus the amount removed by the purchaser) is based on the hot-rolled alloy steel bar size used by the producer

Cold-finished size Minimum

stock removal from the surface(a)

(a) For example, the minimum reduction in diameter of rounds is twice the minimum stock removal from the surface

References cited in this section

2 Alloy, Carbon, and High Strength Low Alloy Steels, Semifinished for Forging; Hot Rolled Bars; Cold Finished Steel Bars; Hot Rolled Deformed and Plain Concrete Reinforcing Bars, AISI Steel Products

Manual, American Iron and Steel Institute, 1986

3 Handbook of Machining Data for Cold Finished Steel Bars, LTV Steel Flat Rolled and Bar Company, 1985

4 Steel Bars, Forgings, Bearing, Chain, Springs, Vol 1.05, Annual Book of ASTM Standards, American

Society for Testing and Materials, 1989

Product Quality Descriptors

The term quality relates to the suitability of a mill product to become an acceptable part When used to identify finished steel bars, the various quality descriptors are indicative of many characteristics, such as degree of internal soundness, relative uniformity of chemical composition, and relative freedom from detrimental surface imperfections

cold-Because of the characteristic surface finish of cold-drawn bars, close visual inspection cannot identify detrimental surface imperfections Therefore, for applications that do not allow surface imperfections on the finished surfaces of standard quality cold-drawn carbon steel bars and regular quality cold-drawn alloy steel bars, the user should recognize that some stock removal is necessary to eliminate such imperfections as seams The recommended stock removal per side for all nonresulfurized grades is 0.025 mm (0.001 in.) per 1.6 mm ( 1

16 in.) of cross section, or 0.25 mm (0.010 in.), whichever is greater For example, for a 25 mm (1 in.) bar, recommended stock removal is 0.41 mm (0.016 in.) per side For the resulfurized grades, recommended stock removal is 0.038 mm (0.0015 in.) per 1.6 mm ( 1

16 in.), or 0.38 mm (0.015 in.), whichever is greater Therefore, for a 25 mm (1 in.) bar, recommended stock removal is 0.61 mm (0.024 in.) per side

Occasionally, some bars in a shipment may have imperfections that exceed the recommended stock removal limits Therefore, for critical applications, inspection of finished parts is recommended, or more restrictive quality and/or additional inspection methods can be specified by agreement of both supplier and customer

To minimize pitting, the recommended stock removal per side for cold-drawn bars that are to be decorative chromium plated is as follows:

Size, mm (in.) Stock removal

per side, mm (in.)

Carbon Steel Quality Descriptors

Standard quality is the descriptor applied to the basic quality level to which cold-finished carbon steel bars are produced Standard quality cold-finished bars are produced from hot-rolled carbon steel of special quality (the standard quality for hot-rolled bars for cold finishing) Steel bars of standard quality must be free from visible pipe and excessive chemical segregation They may contain surface imperfections In general, the size of surface imperfections increases with bar size

Restrictive requirement quality A (RRA) incorporates all the features of standard quality carbon steel bars described above, plus any one of the following restrictive requirements

Special surface bars are produced with special surface preparation to minimize the frequency and size of seams and other surface imperfections These bars are used for applications in which machining allowances do not allow sufficient surface removal to clean up the detrimental imperfections that occur in standard quality bars

Special internal soundness bars have greater freedom from chemical segregation and porosity than standard quality bars

Special hardenability bars are produced to hardenability requirements other than those of standard H-steels

Cold-finished carbon steel bars are also produced to inclusion ratings as determined by standard nonmetallic inclusion testing

Restrictive requirement quality B (RRB) incorporates all the features of standard quality carbon steel bars, plus any one of the following

Special discard is specified when minimized chemical segregation, special steel cleanliness, or internal soundness requirements dictate that the product be selected from certain positions in the ingot

Minimized decarburization is specified whenever decarburization is important, as in heat treating for surface hardness requirements

Single restrictions other than those noted above, such as special chemical limitations, special processing techniques, and other special characteristics not previously anticipated, are also covered by this quality level

Multiple restrictive requirement quality (MRR) applies when two or more of the above-described restrictive requirements are involved

Cold-forging quality A and cold-extrusion quality A apply to cold-finished carbon steel bars used in the production of solid or hollow shapes by means of cold plastic deformation involving the movement of metal by compression with no expansion of the surface and not requiring special inspection standards For an individual application, if the type of steel or chemical composition specified does not provide adequate cold-forming characteristics

in the as-drawn condition, a suitable heat treatment to provide proper hardness or microstructure may be necessary

Cold-heading quality, cold-extrusion quality B, cold-upsetting quality, and cold-expansion quality

apply to cold-finished carbon steel bars used in production of solid or hollow shapes by means of severe cold plastic deformation by cold heading, cold extrusion, cold upsetting, or cold expansion involving movement of metal by expansion and/or compression Such bars are obtained from steel produced by closely controlled steelmaking practices and are subject to special inspection standards for internal soundness and surface quality and uniform chemical composition For grades of steel with a maximum specified carbon content of 0.30% or more, an anneal or spheroidize anneal heat treatment may be required to obtain the proper hardness and microstructure for cold working

Restrictive cold-working quality applies to cold-finished carbon steel bars used in the production of solid or hollow shapes by means of very severe cold plastic deformation involving cold working by expansion and/or compression This degree of cold working normally involves restrictive inspection standards and requires steel that is exceptionally sound, of uniform chemical composition, and virtually free of detrimental surface imperfections Such severe cold-forming operations normally require suitable heat treatment to obtain proper hardness and microstructure for cold working

Other Carbon Steel Qualities. The quality descriptors listed below are some of those that apply to cold-finished carbon steel bars intended for specific requirements and applications They may have requirements for surface quality, amount of discard, macroetch tests, mechanical properties, or chemical uniformity as indicated in product specifications:

• Axle shaft quality

• Shell steel quality A

• Shell steel quality C

• Rifle barrel quality

• Spark plug quality

Alloy Steel Quality Descriptors

Regular quality is the descriptor applied to the basic, or standard, quality level to which cold-finished alloy steel bars are produced Steels for this quality are killed and are usually produced to a fine grain size They are melted to chemical ranges and limits and are inspected and tested to meet normal requirements for regular constructional alloy steel applications Regular quality cold-finished alloy steel bars may contain surface imperfections to the depths mentioned in the opening paragraphs of the section "Product Quality Descriptors" in this article In general, the size of detrimental surface imperfections increases with bar size

Cold-heading quality applies to cold-finished alloy steel bars intended for applications involving cold plastic deformation by such operations as upsetting, heading, or forging Bars are supplied from steel produced by closely controlled steelmaking practices and are subject to mill testing and inspection designed to ensure internal soundness, uniformity of chemical composition, and freedom from detrimental surface imperfections Proper control of hardness and microstructure by heat treatment and cold working is important for cold forming Most cold-heading quality alloy steels are low- and medium-carbon grades Typical low-carbon alloy steel parts, made by cold heading, include fasteners (cap screws, bolts, eyebolts), studs, anchor pins, and rollers for bearings Examples of medium-carbon alloy steel cold-headed parts are bolts, studs, and hexagon-headed cap screws

Special cold-heading quality applies to cold-finished alloy steel bars for applications involving severe cold plastic deformation when slight surface imperfections may cause splitting of a part Bars of this quality are produced by closely controlled steelmaking practices to provide uniform chemical composition and internal soundness Also, special processing (such as grinding) is applied at intermediate stages to remove detrimental surface imperfections Proper control of hardness and microstructure by heat treatment and cold working is important for cold forming Typical applications of alloy steel bars of this quality are front suspension studs, socket screws, and some valves

Axle shaft quality applies to cold-finished alloy steel bars intended for the manufacture of automotive or truck-type, power-driven axle shafts, which by their design or method of manufacture are either not machined all over or undergo less than the recommended amount of stock removal for proper cleanup of normal surface imperfections Axle shaft quality bars require special rolling practices, special billet and bar conditioning, and selective inspection techniques

Ball and roller bearing quality and bearing quality apply to cold-finished alloy steel bars used for the manufacture of antifriction bearings Such bars are usually produced from alloy steels of the AISI-SAE standard alloy carburizing grades and the AISI-SAE high-carbon chromium series These steels can be produced in accordance with ASTM A 534, A 295, and A 485 Bearing quality steels are subjected to restricted melting and special teeming, heating, rolling, cooling, and conditioning practices to meet rigid quality requirements The steelmaking operations may include vacuum treatment The foregoing requirements include thorough examination for internal imperfections by one or more

of the following methods: macroetch testing, microscopic or ultrasonic examination for nonmetallic inclusions, and fracture testing

Aircraft quality and magnaflux quality apply to cold-finished alloy steel bars for important 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 The 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 There are many aircraft parts and many parts for missiles and other rockets that require aircraft quality steel The magnetic particle testing requirements given in AMS 2301 are sometimes specified for such applications

Other Alloy Steel Qualities. The quality descriptors listed below apply to cold-finished alloy steel bars intended for rifles, guns, shell, shot, and similar applications They may have requirements for amount of discard, macroetch testing, surface requirements, or magnetic particle testing as indicated in the product specifications:

• Armor-piercing (AP) shot quality

• AP shot magnaflux quality

in percentage of reduction of cross section for bars drawn with normal commercial drafts of 0.8 and 1.6 mm ( 1

32 and 1

16in.) and with heavy drafts of 3.2 and 4.8 mm (1

8 and 3

16in.) are shown in Fig 3 Normal reductions seldom exceed 20% and are usually less than 12% According to Fig 2, the more pronounced changes in significant tensile properties occur within this range of reductions (up to about 15%)

Fig 1 Effect of cold work on the tensile stress-strain curve for low-carbon steel bars

Fig 2 Effect of cold drawing on the tensile properties of steel bars Data are for bars up to 25 mm (1 in.) in

cross section having a tensile strength of 690 MPa (100 ksi) or less before cold drawing

Fig 3 Effect of draft on reduction of cross section of steel bars

The minimum mechanical properties of several cold-drawn carbon steel bars in a range of sizes are presented in Table 7

In addition, the effects of both low- and high-temperature stress relief on the as-cold-drawn mechanical properties are noted The mechanical property ranges and average values for one of the steels listed in Table 7 (1137 resulfurized steel) are presented in Fig 4, which also shows the advantage in strength of cold-drawn over hot-rolled material

Table 7 Estimated minimum mechanical properties of cold-drawn carbon steel rounds, squares, and hexagons

Estiminated minimum mechanical properties for sizes under 16 mm (5

8 in.) can be obtained from individual producers The data in this table are not applicable to turned and polished or turned and ground bars, which have mechanical properties corresponding to those of hot-rolled steel bars of the same size and grade The size of a square or hexagon is the distance between opposite sides

low-temperature stress relief

Cold drawn followed by

high-temperature stress relief

Steel designation

and size range

mm in MPa ksi MPa ksi

Elongation

in

50 mm (2 in.), %

%

Reduction

in area,

%

Reduction

in area,

%

Reduction

in area,