Volume 01 - Properties and Selection Irons, Steels, and High-Performance Alloys Episode 4 doc

Steel is considered to be low-alloy steel when either of the following conditions is met: • The maximum of the range given for the content of alloying elements exceeds one or more of th

(a) Maximum

Low-Alloy Steel Plate Steel is considered to be low-alloy steel when either of the following conditions is met:

• The maximum of the range given for the content of alloying elements exceeds one or more of the following limits: 1.65% Mn, 0.60% Si, and 0.60% Cu

• Any definite range or definite minimum quantity of any of the following elements is specified or required within the limits of the recognized field of constructional alloy steels: aluminum, boron, chromium up to 3.99%, cobalt, niobium, molybdenum, nickel, titanium, tungsten, vanadium, zirconium,

or any other alloying element added to obtain the desired alloying effect

Alloying elements are added to hot-finished plates for various reasons, including improved corrosion resistance and/or improved mechanical properties at low or elevated temperatures Alloying elements are also used to improve the hardenability of quenched and tempered plate

Low-alloy steels generally require additional care throughout their manufacture They are more sensitive to thermal and mechanical operations, the control of which is complicated by the varying effects of different chemical compositions To secure the most satisfactory results, consumers normally consult with steel producers regarding the working, machining, heat treating, or other operations to be employed in fabricating the steel; mechanical operations to be employed in fabricating the steel; mechanical properties to be obtained; and the conditions of service for which the finished articles are intended

The chemical composition requirements of standard low-alloy steel plate are listed in Table 3 These low-alloy steels may

be suitable for some structural applications when furnished according to ASTM A 6 and A 829 The effect of residual alloying elements on the mechanical properties of hot-finished steel plate is discussed in the section "Mechanical Properties" in this article The effect of alloying elements on the hardenability and mechanical properties of quenched and tempered steels is discussed in the articles "Hardenable Carbon and Low-Alloy Steels" and "High-Strength Structural and High-Strength Low-Alloy Steels" in this Volume

Table 3 Composition ranges and limits for AISI-SAE standard low-alloy steel plate applicable for structural applications

Boron or lead can be added to these compositions Small quantities of certain elements not required may be found These elements are

to be considered incidental and are acceptable to the following maximum amounts: copper to 0.35%, nickel to 0.25%, chromium to 0.20%, and molybdenum to 0.06%

Heat composition ranges and limits, %(a) AISI-SAE

(b) Other silicon ranges may be negotiated Silicon is available in ranges of 0.10-0.20%, 0.20-0.30%, and 0.35% maximum (when carbon deoxidized) when so specified by the purchaser

(c) Prefix "E" indicates that the steel is made by the electric furnace process

(d) Contains 0.15% V minimum

In addition to the low-alloy steels listed in Table 3, other low-alloy steel plates are also classified according to more specific requirements in various ASTM specifications The chemical composition requirements and mechanical properties

of low-alloy steel plate in ASTM standards are discussed in the section "Steel Plate Quality" in this article

High-strength low-alloy steels offer higher mechanical properties and, in certain of these steels, greater resistance

to atmospheric corrosion than conventional carbon structural steels The HSLA steels are generally produced with emphasis on mechanical property requirements rather than the chemical composition limits They are not considered alloy steels as described in the American Iron and Steel Institute (AISI) steel products manuals, even though utilization of any intentionally added alloy content would technically qualify as such

There are two groups of compositions in this category:

• Vanadium and/or niobium steels, with a manganese content generally not exceeding 1.35% maximum and with the addition of 0.2% minimum copper when specified

• High-strength intermediate-manganese steels, with a manganese content in the range of 1.10 to 1.65% and with the addition of 0.2% minimum copper when specified

Other elements commonly added to HSLA steels to yield the desired properties include silicon, chromium, nickel, molybdenum, titanium, zirconium, boron, aluminum, and nitrogen The chemical compositions of ASTM structural quality and pressure vessel quality plates made of HSLA steel are listed in Table 4 More information on HSLA steels is provided in the article "High-Strength Structural and High-Strength Low-Alloy Steels" in this Volume

Table 4 Composition of high-strength low-alloy steel plate

Composition, %(a) ASTM

specification

Material grade

or type

Structural quality

42 0.21 1.35 0.04 0.05 0.40(d) (e) (e) (e)

45 0.22 1.35 0.04 0.05 0.40(d) (e) (e) (e)

50 0.23 1.35 0.04 0.05 0.40(d) (e) (e) (e)

60 0.26 1.35 0.04 0.05 0.40(d) (e) (e) (e)

0.40-0.40

0.25-0.40

0.10

0.50-0.50

0.20-0.40

0.10

0.30- 0.50

0.25- 0.25- 0.25- 0.50

0.20- 0.10

0.01- 0.01- 0.01-

0.10-0.20

1.25

0.75-0.04 0.05

0.50-0.90

0.90

0.50- 0.50- 0.50- 0.30 0.04 Zr,

0.15

0.01-3 0.18 1.65 0.025 0.035 0.60 0.08

0.005-0.15

N, 0.020

A 656

7 0.18 1.65 0.025 0.035 0.60

0.005-0.015(i)

0.015(i)

0.04-(g)

0.03

0.40-0.50

0.20-0.40

0.10

(a) Except as noted, when a single value is shown, it is a maximum limit

(b) Choice and amount of other alloying elements added to give the required mechanical properties and atmospheric corrosion resistance are made

by the producer and reported in the heat analysis

(c) Elements commonly added include silicon, chromium, nickel, vanadium, titanium, and zirconium

(d) Limiting values vary with plate thickness

(e) For type 1, 0.005-0.05% Nb; for type 2, 0.01-0.15% V; for type 3, 0.05% Nb max + V = (0.02-0.15%); for type 4, N (with V) 0.015% max

(f)

For plates under 13 mm (1

2 in.) thickness, the minimum niobium limit is waived

(g) Niobium may be present in the amount of 0.01-0.05%

(h) The minimum total aluminum content shall be 0.018% or the vanadium:nitrogen ratio shall be 4:1 minimum

(i) Niobium, or vanadium, or both, 0.005% min When both are added, the total shall be 0.20% max

(j) Applicable only when specified

(k) 0.05% max Nb may be present

Steel Plate Quality

Steel quality, as the term applies to steel plate, is indicative of many conditions, such as the degree of internal soundness, relative uniformity of mechanical properties and chemical composition, and relative freedom from injurious surface imperfections The various types of steel plate quality are indicated in Table 1

The three main quality descriptors used to describe steel plate are regular quality, structural quality, and pressure vessel quality Special qualities include cold-drawing quality, cold-pressing quality, cold-flanging quality, and forging quality carbon steel plate, along with drawing quality and aircraft quality alloy steel plate Quality descriptors that have been used

in the past include flange quality and firebox quality carbon and alloy steel plate and marine quality carbon steel plate However, use of these descriptors has been discontinued in favor of pressure vessel quality

Regular quality is the most common quality of carbon steel, which is applicable to plates with a maximum carbon

content of 0.33% Plates of this quality are not expected to have the same degree of chemical uniformity, internal soundness, or freedom from surface imperfections that is associated with structural quality or pressure vessel quality plate Regular quality is usually ordered to standard composition ranges and is not customarily produced to mechanical property requirements Regular quality is analogous to merchant quality for bars because there are normally no restrictions on deoxidation, grain size, check analysis, or other metallurgical factors Also, this quality plate can be satisfactorily used for applications similar to those of merchant quality bars, such as those involving mild cold bending, mild hot forming, punching, and welding for noncritical parts of machinery

Structural quality steel plate is intended for general structural applications such as bridges, buildings, transportation

equipment, and machined parts The various ASTM specifications for structural quality steel plate are given in Table 5 Most of the structural steel plate listed in Table 5 is furnished to both chemical composition limits (Table 6) and mechanical properties (Table 7) However, some structural steel plate (ASTM A 829 and A 830 in Table 5) is produced from the standard steels listed in Tables 2 and 3 These steels can be furnished only according to the chemical

compositions specified by SAE/AISI steel designations Factors affecting the mechanical properties of hot-finished carbon steel are discussed in the section "Mechanical Properties" in this article

Table 5 ASTM specifications for structural quality steel plate

General requirements for structural plate are covered in ASTM A 6

ASTM

specification (a)

Steel type and condition

Carbon steel

A 36(b) Carbon steel shapes, plates, and bars of structural quality

A 131(c) Structural steel shapes, plates, bars, and rivets for use in ship construction (ordinary strength)

A 283(b) Low and intermediate tensile strength carbon steel plates

A 284 Low and intermediate tensile strength carbon-silicon steel plates for machine parts and general construction

A 529(d) Structural steel with 290 MPa (42 ksi) minimum yield point

A 573 Structural quality carbon-manganese-silicon steel plates with improved toughness

A 678 Quenched and tempered carbon and HSLA plates for structural applications

A 709 Carbon and HSLA steel structural shapes, plates, and bars, and quenched and tempered alloy steel for use in

bridges

A 827(e) Carbon steel plates for forging applications

A 830(e) Structural quality carbon steel plates furnished to chemical requirements

Low-alloy steel

A 514 Structural quality quenched and tempered alloy steel plates for use in welded bridges and other structures

A 709 See above under "Carbon steel"

A 710 Low-carbon age-hardening Ni-Cu-Cr-Mo-Nb, Ni-Cu-Nb, and Ni-Cu-Mn-No-Nb alloy steel plates, shapes, and

bars for general applications

A 829(e)(f) Structural quality alloy plates specified to chemical composition requirements

HSLA steel

A 13 Structural steel shapes, plates, bars, and rivets for use in ship construction (higher strength)

A 242 HSLA structural steel shapes, plates, and bars for welded, riveted, or bolted construction

A 441(g) Mn-V HSLA steel plates, bars, and shapes

A 572 HSLA structural Nb-V steel shapes, plates, sheet piling, and bars for riveted, bolted, or welded construction

of bridges, buildings, and other structures

A 588(h) HSLA structural steel shapes, plates, and bars for welded, riveted, or bolted construction for use in bridges

and buildings with atmospheric corrosion resistance approximately two times that of carbon steel with copper

A 633 Normalized HSLA structural steel for welded, riveted, or bolted construction suited for service at low

ambient temperatures of -45 °C (-50 °F) or higher

A 656 Hot-rolled HSLA structural steel with improved formability for use in truck frames, brackets, crane booms,

rail cars, and similar applications

A 678 See above under "Carbon steel"

A 709 See above under "Carbon steel"

A 808 Hot-rolled HSLA Mn-V-Nb structural steel plate with improved notch toughness

A 852 Quenched and tempered HSLA structural steel plate for welded, riveted, or bolted construction for use in

bridges and buildings with atmospheric corrosion resistance approximately two times that of carbon steel with copper

A 871 HSLA structural steel plate in the as-rolled, normalized, or quenched and tempered condition with

atmospheric corrosion resistance approximately two times that of carbon steel with copper

(a) Also designated with the suffix "M" when the specification covers metric equivalents

(b) This specification is also published by the American Society of Mechanical Engineers, which uses the prefix "S" (for example, SA36)

(c) See also Section 43 of the American Bureau of Shipping specifications and MIL-S-22698 (SH)

(d)

13 mm (1

2 in.) maximum thickness

(e) See also Ref 1

(f) Tensile properties may also be specified when compatible

(g) Discontinued in 1989 and replaced by A 572

(h) Minimum yield point 345 MPa (50 ksi) to 100 mm (4 in.) Lower minimum yield points for thicker sections

Table 6 ASTM specifications of chemical composition for structural plate made of low-alloy steel or carbon steel

Composition, %(b) ASTM

specification

Material grade or type

0.80-0.035 0.04

0.40-0.80

0.80

0.70-0.035 0.04

0.20-0.35

0.65

0.40- 0.40- 0.40-

0.15-0.25

V, 0.03-0.08; Ti,

0.01-0.03; B, 0.0005-0.005

0.10-0.20

1.50

0.40-0.035 0.04

0.20-0.40

2.00

0.0.60-0.035 0.04

0.15-0.35

0.65

0.40- 1.00

0.70- 0.60

0.40- 0.50

0.15-V, 0.03-0.08; B, 0.0005-0.006

0.12-0.21

1.30

0.95-0.035 0.04

0.20-0.35

0.65

0.40- 0.70

0.30- 0.30

0.45- 0.45- 0.45- B, 0.001-0.005

0.12-0.21

0.70

0.45-0.035 0.04

0.20-0.35

1.20

0.85- 1.50

1.20- 0.60

0.95-0.035 0.04

0.15-0.35

1.50

1.00- 1.50

1.20- 0.6

0.40- 0.40- 0.40- V, 0.03-0.08

R

0.15-0.80

1.15

0.85-0.035 0.04

0.20-0.35

0.65

0.35- 1.10

90- 0.25

0.15- 0.15- 0.15- V, 0.03-0.08

0.10-0.20

1.50

0.70- 0.25

0.15- 1.30

0.15- 1.30

A 827 (e) (See Table 11.)

A 830 (e) (See Table 2.)

(a) Note: See Table 4 for the compositions of structural plate made of HSLA steel

(b) When a single value is shown, it is a maximum limit, except for copper, for which a single value denotes a minimum limit

(c) Vanadium can be substituted for part or all of the titanium on a one-for-one basis

(d) Titanium may be present in levels up to 0.06% to protect the boron additions

(e) Specification covers many AISI/SAE grades and chemistries

(f) Limiting values vary with plate thickness

(g) Minimum value applicable only if copper-bearing steel is specified

(h)

Plates over 13 mm (1

2 in.) in thickness shall have a minimum manganese content not less than 2.5 times carbon content

(i) The upper limit of manganese may be exceeded provided C + 1/6 Mn does not exceed 0.40% based on heat analysis

Table 7 ASTM specifications of mechanical properties for structural plate made of carbon steel, low-alloy steel, and HSLA steel

Tensile strength (a) Yield strength (a)

ASTM

specification

Material grade or type

Minimum elongation (b)

in 200 mm (8 in.), %

Minimum elongation(b)

(a) Where a single value is shown, it is a minimum

(b) Minimum and/or maximum values depend on plate width and/or thickness

(c) Specification does not specify mechanical properties

(d) Includes several AISI/SAE grades

Pressure Vessel Plate Steel plate intended for fabrication into pressure vessels must conform to specifications

different from those of similar plate intended for structural applications The major differences between the two groups of specifications are that pressure vessel plate must meet requirements for notch toughness and has more stringent limits for allowable surface and edge imperfections

Table 8 lists the various ASTM specifications for pressure vessel steel plate All of these steel plate specifications are furnished according to both chemical composition limits and mechanical properties

Table 8 ASTM specifications for pressure vessel quality steel plate

General requirements for pressure vessel plate are covered in ASTM A 20

Specification Steel type and condition

Carbon steel

A 285(a) Carbon steel plates of low or intermediate tensile strength

A 299(a) Carbon-manganese-silicon steel plates

A 442(b) Carbon steel plates for applications requiring low transition temperature

A 455(a) Carbon-manganese steel plates of high tensile strength

A 515(a) Carbon-silicon steel plates for intermediate-and higher-temperature service

A 516(a) Carbon steel plates for moderate and lower-temperature service

A 537(a) Heat-treated carbon-manganese-silicon steel plates

A 562 Titanium-bearing carbon steel plates for glass or diffused metallic coatings

A 612(a) Carbon steel plates of high tensile strength for moderate-and lower-temperature service

A 662(a) Carbon-manganese steel plates for moderate-and lower-temperature service

A 724 Quenched and tempered carbon steel plates for layered pressure vessels not subject to postweld heat treatment

A 738(a) Heat-treated carbon manganese-silicon steel plates for moderate-and lower-temperature service

Low-alloy steel

A 202(a) Cr-Mn-Si alloy steel plates

A 203(a) Nickel alloy steel plates

A 204(a) Molybdenum alloy steel plates

A 225(a) Mn-V alloy steel plates

A 302(a) Mn-Mo and Mn-Mo-Ni alloy steel plates

A 353(a) Double normalized and tempered 9% Ni alloy steel plates for cryogenic service

A 387(a) Cr-Mo alloy steel plates for elevated-temperature service

A 517(a) Quenched and tempered alloy steel plates of high tensile strength

A 533(a) Quenched and tempered Mn-Mo and Mn-Mo-Ni alloy steel plates

A 542(a) Quenched and tempered Cr-Mo alloy steel plates

A 543(a) Quenched and tempered Ni-Cr-Mo alloy steel plates

A 553(a) Quenched and tempered 8% and 9% Ni alloy steel plates

A 645(a) Specially heat treated 5% Ni alloy steel plates for low-or cryogenic-temperature service

A 734 Quenched and tempered alloy and HSLA steel plates for low-temperature service

A 735 Low-carbon Mn-Mo-Nb alloy steel plates for moderate-and lower-temperature service

A 736 Age-hardening low-carbon Ni-Cu-Cr-Mo-Nb alloy steel plates

A 782 Quenched and tempered Mn-Cr-Mo-Si-Zr alloy pressure vessel steel plates

A 832 Cr-Mo-V-Ti-B alloy pressure vessel steel plates

A 844 9% Ni alloy pressure vessel steel plates produced by the direct-quenching process

HSLA steel

A 734 See under "Alloy steel"

A 737(a) HSLA steel plates for applications requiring high strength and toughness

A 841 Steel pressure vessel plate produced by the thermomechanical control processes

(a) This specification is also published by the American Society of Mechanical Engineers, which adds an "S" in front of the "A" (for example, SA285)

(b) Discontinued in 1991

(c)

The chemical composition limits of pressure vessel steel plate include a maximum phosphorus content of 0.035% and a maximum sulfur content of 0.040% by product analysis The chemical compositions of various types of pressure vessel steel plate are given in Table 9

Table 9 ASTM specification of chemical composition for pressure vessel plate made of carbon and alloy steel

low-See Table 4 for the compositions of pressure vessel plate made of HSLA steel The maximum limits per ASTM A 20 on unspecified elements are 0.40% Cu, 0.40% Ni, 0.30% Cr, 0.12% Mo, 0.03% V, and 0.02% Nb

Composition, % (a) ASTM

specification

Material grade

0.30-0.020 0.010

0.20-0.50

9.50

8.00-0.40

0.85-1.05

V, 0.18-0.25;

Nb,0.06-0.10; N,

0.03-0.07; Al, 0.04

0.15-0.21

1.10

0.80-0.035 0.040

0.40-0.80

0.80

0.70-0.035 0.040

0.20-0.35

0.65

0.40-0.035 0.040

0.20-0.35

2.00

0.60-0.035 0.040

0.15-0.35

0.65

0.40- 1.00

0.70- 0.60

0.40- 0.40- 0.40- B,0.0005-0.006

0.12-0.21

1.30

0.95-0.035 0.040

0.20-0.35

0.65

0.40- 0.70

0.30- 0.30

0.20- 0.20- 0.20- B,0.0005

0.12-0.21

0.70

0.45- 0.45- 0.45- B, 0.001-0.005

0.12-0.21

0.70

0.45-0.035 0.040

0.20-0.35

1.20

0.85- 1.50

1.20- 0.60

0.45- 0.45- 0.45- B, 0.001-0.005

0.14-0.21

1.30

0.95-0.035 0.040

0.15-0.35

1.50

1.00- 1.50

1.20- 0.60

0.40- 0.40- 0.40- V, 0.03-0.08

0.10-0.20

1.50

0.45- 0.45- 0.45-

B 0.23 0.40 0.035 0.040

0.20-0.40

2.00

1.50- 3.25(b)

2.60- 0.60

1.20- 3.25(b)

2.25- 0.60

0.90- 0.40

0.70- 0.25

0.15- 1.30

0.15- 1.30

(a) When a single value is shown, it is a maximum limit, except where specified as a minimum limit

(b) Limiting values may vary with plate thickness

(c) When specified

Mechanical tests of pressure vessel steel plate involve a minimum of one tensile test for each as-rolled plate or a minimum of two tensile tests for quenched and tempered plates The mechanical property requirements given in ASTM specifications for pressure vessel steel plate are listed in Table 10

Table 10 ASTM specifications of mechanical properties for pressure vessel plate made of carbon steel, HSLA steel, or low-alloy steel

Tensile strength (a) Yield strength (a)

ASTM

specification

Material grade or type

Minimum elongation (b)

in 200 mm (8 in.),%

Minimum elongation(b)in

(a) Where a single value is shown, it is a minimum

(b) Minimum and/or maximum values depend on plate thickness

(c) As-rolled class 1 plate is limited to 25 mm (1 in.) thickness

(d) As-rolled and aged class 2 plate is limited to 25 mm (1 in.) thickness

Aircraft quality plates are used for important or highly stressed parts of aircraft, missiles, and other applications

involving stringent requirements Plates of this quality require exacting steelmaking, conditioning, and process controls and are generally furnished from electric furnace steels in order to meet the internal cleanliness requirements outlined in

Aerospace Materials Specifications AMS-2301 The primary requirements of this quality are a high degree of internal soundness, good uniformity of chemical composition, good degree of cleanliness, and a fine austenitic grain size Aircraft quality plates can be supplied in the hot-rolled or thermally treated condition

Forging quality plates are intended for forging, quenching and tempering, or similar purposes or when uniformity of

composition and freedom from injurious imperfections are important (see ASTM A 827) Plates of this quality are produced from killed steel and are ordinarily furnished with the phosphorus content limited to 0.035% maximum and the sulfur content limited to 0.040% maximum by heat analysis Table 11 lists some AISI/SAE steels suitable for forging quality plate Plates of this quality can be produced to chemical ranges and limits and mechanical properties When mechanical properties are specified, two tension tests from each heat are taken from the same locations at tests for structural quality Factors affecting mechanical properties are discussed in the section "Mechanical Properties" in this article

Table 11 Compositions of forging quality steel plate specified in ASTM A 827

Reference cited in this section

1 Plates; Rolled Floor Plates: Carbon, High Strength Low Alloy, and Alloy Steel, AISI Steel Products Manual,

American Iron and Steel Institute, 1985

Mechanical Properties

Of the various mechanical properties normally determined for steel plate, yield strength is an important design criterion in structural applications Tensile strength is also an important design consideration in many design codes in the United States, but is useful primarily as an indication of fatigue properties Yield strength is a design criterion in most design codes when the ratio of yield to tensile strength is less than 0.5 Ductility, as measured by tensile elongation and reduction

in area, is seldom in itself a valuable design criterion, but is sometimes used as an indication of toughness and suitability for certain applications

The mechanical properties of steel plate in the hot-finished condition are influenced by several variables, of which chemical composition is the most influential Other factors include deoxidation practice, finishing temperature, plate thickness, and the presence of residual elements such as nickel, chromium, and molybdenum For steels used in the hot-

finished condition (such as plate), carbon content is the single most important factor in determining mechanical properties

The static tensile properties of the various grades, types, and classes of steel plate covered by ASTM specifications

are listed in Tables 7 and 10 It should be noted that some of these values vary with plate thickness and/or width An example of the variation of tensile strength and elongation with thickness is shown in Fig 1, which presents the minimum expected values for 0.20% C steel plate from 13 to 125 mm (1

2 to 5 in.) thick Plate under 13 mm (1

2 in.) thick would show even slightly higher tensile strength and lower elongation because of the increased amount of hot working during rolling and the faster cooling rates after rolling

Fig 1 Effect of thickness on tensile properties of 0.20% C steel plate

The distribution of the tensile properties obtained for a larger number of heats of A 285, A 515, and A 516 steel plate is illustrated in Fig 2, which also shows the distribution of the carbon and manganese content The use of the carbon and manganese contents to control mechanical properties is clearly shown in Fig 2; higher carbon and manganese contents accompany higher yield strengths

Fig 2 Distribution of tensile properties and chemical composition of carbon steel plate Data represent all the

Fig 3 Distribution of tensile properties and chemical composition of ASTM A 285, grade C, carbon steel plate

Data represent all the as-hot-rolled plate (224 heats from 6 mills) purchased to this specification by one fabricator during a period of 8 years

The common mechanical properties of hot-finished steel, including plate, reliably related to each other, and this relation is relatively free from influence of composition for most of these properties Figure 4 shows the relationship between yield strength, elongation, and tensile strength over a wide range of tensile strengths for various hot-rolled carbon steels

Fig 4 Relation of tensile properties for hot-rolled carbon steel

Residual alloying elements generally have a minor strengthening effect on hot-finished steels, such as plate This effect cannot be considered in design because residuals vary greatly among the different steel producing plants This influence is shown in Fig 5, which demonstrates that the effect is minor

Fig 5 Effect of carbon and amount of residuals on tensile properties of hot-finished carbon steel Curves

marked high residuals represent steel containing 0.06 to 0.12% Ni, 0.06 to 0.13% Cr, and 0.08 to 0.13% Mo Curves marked low residuals represent steel containing 0.05% Ni max, 0.05% Cr max, and 0.04% Mo max Total of 58 heats tested

Hardness is a relatively simply test to perform and is closely related to tensile strength, as shown in Fig 6 A simple hardness test, used in conjunction with the data in Fig 4, can be used to estimate yield strength, elongation, and tensile strength

Fig 6 Relation between hardness and tensile strength of steel Range up to 300 HB is applicable to the

hot-finished steel discussed in this article

Fatigue Strength The high-cycle (>1 million) fatigue properties of hot-finished steel, often called the fatigue limit, are

more or less directly related to tensile strength and are greatly affected by the surface condition The fatigue limit of machined specimens is about 40% of the tensile strength, depending on the surface finish In contrast, unmachined hot-rolled steel, when loaded so that fatigue stresses are concentrated at the surface, will have a considerably lower fatigue limit because of decarburization, surface roughness, and other surface imperfections For this reason, the location of maximum fatigue stresses should be carefully considered; for structural members designed in hot-finished steel, the surface should be machined off from critically stressed areas or an allowance made for the weakness of the hot-finished surface

The presence of inclusions in hot-finished steel may also have an adverse effect on the fatigue limit Large inclusions are considered harmful under the dynamic stresses of impact or fatigue, and the effect is greater in the harder steels

Low-Temperature Impact Energy When notch toughness is an important consideration, satisfactory service

performance can be ensured by proper selection of the steel that will behave in a tough manner at its lower operating temperature The Charpy V-notch tests and crack-starter drop-weight tests provide a fairly reliable indication of the tendency toward brittle fracture in service The transition temperatures of hot-finished steels are controlled principally by their chemical composition and ferrite grain size For the steels considered in this article, carbon is of primary importance because of its effect is raising the transition temperature, lowering the maximum energy values, and widening the temperature range between completely tough and completely brittle behavior

Manganese (up to about 1.5%) improves low-temperature properties Also, as mentioned previously, the transition temperature is affected by the deoxidation practice used The transition temperature decreases and the energy absorption before fracture at normal temperatures increases in the order of rimmed, capped, semikilled, and killed steels In addition, killed steels contain larger amounts of silicon or aluminum than semikilled steels, and these elements improve low-temperature toughness and ductility Because of variations in finishing temperatures and cooling rates, plate thickness influences the grain size and therefore the transition temperature Extensive data on the impact properties of hot-finished steel are given in the article "Notch Toughness of Steels" in this Volume

Elevated-Temperature Properties The steel plate used in pressure vessel applications is often subjected to

long-term elevated temperatures Of the carbon and low-alloy steels used for pressure vessel plate, the behavior of 2.25Cr-1Mo steel (ASTM A 387, Class 22, in Table 9) at elevated temperatures has been studied more thoroughly than any other steel and has become the reference for comparing the elevated-temperature properties of low-alloy steels Further information

on the elevated-temperature properties of 2.25Cr-1Mo steel can be found in the article "Elevated-Temperature Properties

of Ferritic Steels" in this Volume

Directional Properties An important characteristics of steel plate, known as directionality or fibering, must be

considered During the rolling operations, many inclusions, which are in a plastic condition at rolling temperatures, are elongated in the direction of rolling At the same time, localized chemical segregates that have formed during solidification of the steel are also elongated These effects reduce the ductility and impact properties transverse to the rolling direction, but have little or no effect on strength

Fabrication Considerations

Formability The cold formability of steel plate is directly related to the yield strength and ductility of the material The

lower the yield strength, the smaller the load required to produce permanent deformation; high ductility allows large deformation without fracture Therefore, the lower-carbon grades are most easily formed

Operations such as shearing and blanking are usually limited by the lack of the available facilities as the plate thickness increases This also applies to bending operations Of course, an adequate bend radius must be used to avoid fracture Because of fibering effects, the direction of bend is also important; when the axis of a bend is parallel to the direction of rolling, small bend radii are usually difficult to form because of the danger of cracking

Machinability Machining operations are usually performed with little difficulty on most plate steels up to about 0.50%

C Higher-carbon steels can be annealed for softening Steels with low carbon and manganese content, such as 1015, with large quantities of free ferrite in the microstructure may be too soft and gummy for good machining Increasing the carbon content (to a steel such as 1025) improves the machinability

Machining characteristics can be improved by factors that break up the chip as it is removed This is usually accomplished by the introduction of large numbers of inclusions such as manganese sulfides or complex oxysulfides These "free-machining" steels are somewhat more expensive, but are cost-effective when extensive machining is involved

Weldability is a relative term that describes the ease with which sound welds possessing good mechanical properties

can be produced in a material The chief weldability factors are composition, heat input, and rate of cooling These factors produce various effects, such as grain growth, phase changes, expansion, and contraction, which in turn determine weldability Heat input and cooling rate are characteristics of the specific process and technique used and the thickness of the metal part being welded Therefore, weldability ratings should state the conditions under which the rating was determined and the properties and soundness obtained

For carbon steels, the carbon and manganese contents are the primary elements of the composition factor that determine the effect of the steel of given heating and cooling conditions The great tonnage of steel used for welded applications consists of low-carbon steel, up to 0.30% C

Generally, steels with a carbon content less than 0.15% are readily weldable by any method Steel with a carbon range of 0.15 to 0.30% can usually be welded satisfactorily without preheating, postheating, or special electrodes For rather thick sections (>25 mm, or 1 in.), however, special precautions such as 40 °C (100 °F) minimum preheat, 40 °C (100 °F) minimum temperature between weld passes, and a 540 to 675 °C (1000 to 1250 °F) stress relief may be necessary

Higher-carbon and higher-manganese grades can often be welded satisfactorily if preheating, special welding techniques, and postheating and peening are used In the absence of such precautions to control the rate of cooling and to eliminate high stress gradients, cracks may occur in the weld and base metal In addition, base metal properties such as strength, ductility, and toughness may be greatly reduced

All comments about the effect of carbon and manganese on weldability must be qualified in terms of section size because

of its relationship to heat input and cooling rate In welding thicker sections, such as plate, the relatively cold base metal serves to greatly accelerate the cooling rate after welding with the result that plate thickness is a very important

consideration Figure 7 shows the effect of plate thickness and carbon equivalent on weldability as expressed in terms of a notch bend test

Fig 7 Ratio (welded to unwelded) of bend angle for normalized steel plate A high value of the ratio indicates

high weldability Source: Ref 2

Reference cited in this section

2 Weldability of Steels, Welding Research Council, 1953

References

1 Plates; Rolled Floor Plates: Carbon, High Strength Low Alloy, and Alloy Steel, AISI Steel Products Manual,

American Iron and Steel Institute, 1985

2 Weldability of Steels, Welding Research Council, 1953

Hot-Rolled Steel Bars and Shapes

Revised by Timothy E Moss, J.M Hambright, and T.E Murphy, Inland Bar and Structural, Division of Inland Steel Company;and J.A Schmidt, Joseph T Ryerson and Sons, Inc

Introduction

HOT-ROLLED STEEL BARS and other hot-rolled steel shapes are produced from ingots, blooms, or billets converted from ingots or from strand cast blooms or billets and comprise a variety of sizes and cross sections Bars and shapes are most often produced in straight lengths, but bars in some cross sections in smaller sizes are also produced in coils

The term "bar" includes:

• Rounds, squares, hexagons, and similar cross sections 9.5 mm (3

8 in.) and greater across

• Flats greater than 5.16 mm (0.203 in.) in thickness and 152 mm (6 in.) and less in width, or 5.84 mm

(0.230 in.) and greater in thickness and 203 mm (8 in.) and less in width

• Small angles, channels, tees, and other standard shapes less than 76 mm (3 in.) across

• Concrete-reinforcing bars

The term "shape" includes structural shapes and special shapes Structural shapes are flanged, are 76 mm (3 in.) or greater

in at least one cross-sectional dimension, and are used in structures such as bridges, buildings, ships, and railroad cars Special shapes are those designed by users for specific applications

Dimensions and Tolerances

The nominal dimensions of hot-rolled steel bars and shapes are designated in inches or millimeters with applicable tolerances, as shown in ASTM A 6 and A 29 Bars with certain quality descriptors have size limitations; these are covered

in discussions of individual product qualities later in this article

Bars or shapes can be cut to length in the mill by a number of methods, such as hot or cold shearing or sawing The method used is determined by cross section, grade, and customer requirements Some end distortion is to be expected from most methods When greater accuracy in length or freedom from distortion is required, bars of shapes can be cut overlength, then recut on one or both ends by cold sawing or equivalent means

If a bar or shape requires straightening, prior annealing is sometimes necessary, depending on the grade of steel and the cross-sectional shape of the part The processing necessary to meet straightness tolerances is not intended to improve either the surface finish or accuracy of cross-sectional shape and may result in increased surface hardness Length and straightness tolerances for bars and shapes are found in ASTM A 6 and A 29

Surface Imperfections

Most carbon steel and alloy steel hot-rolled bars and shapes contain surface imperfections with varying degrees of severity In virtually all cases, these defects are undesirable and may in some applications affect the integrity of the finished product

Included in the manufacturing process for hot-rolled bars and shapes are various steps designed to minimize or eliminate surface defects These steps include inspection of both the semifinished and the finished product and either subsequent removal of the defects or rejection of the material if defect removal is not possible Inspection techniques range from visual inspection of the semifinished material to sophisticated electronic inspection of the finished product Defects found

in the semifinished product can be removed by hot scarfing, grinding, or chipping Defects in the finished products are generally removed by grinding, turning, or peeling and, to a lesser degree, by chipping

Currently, it is not technically feasible to produce defect-free hot-rolled bars With the current demand for high-quality bar products, it is becoming increasingly common to subject hot-rolled bars to a cold-finishing operation, such as turning

or grinding, coupled with a sensitive electronic inspection With this process route, it becomes possible to significantly reduce both the frequency and the severity of surface defects

Seams, Laps, and Slivers

Seams, laps, and slivers are probably the most common defects in hot-rolled bars and shapes

Seams are longitudinal defects that can vary greatly in length and depth It is quite common for steel users to refer to any

longitudinal defect as a seam regardless of the true nature of the defect However, there is a classical definition of a seam,

as follows Gas comes out of the solution as the liquid steel solidifies This gas is trapped as bubbles or blowholes by the solidifying steel and appears as small holes under the surface of the steel When the steel is reheated, some areas of the surface may scale off, exposing and oxidizing the interior of these blowholes This oxidation prevents the blowholes from welding shut during rolling This rolling then elongates the steel, resulting in a longitudinal surface discontinuity a seam

As viewed in the cross section, seams are generally characterized as being perpendicular to the surface, completely surrounded by decarburization, and associated with disperse oxides

Laps are mechanical defects that occur during the hot rolling of both semifinished and finished material Laps are

nothing more than a folding over of the material, resulting, for example, from gouging during the rolling process or misalignment of the pass lines or rolls As viewed in the cross section, laps are characterized as being at an angle from the steel surface; they have decarburization on one side only of the defect and often contain entrapped scale

Slivers usually appears as a scablike defect, adhering on one end to the surface of the hot-rolled steel They are normally

pressed into the surface during hot rolling They can originate from short, rolled out defects such as torn corners that are not removed during conditioning They can also result from conditioning gouges or mechanical gouges during rolling Although there is no specific metallographic definition of slivers, metallographic examination can be used to determine the origin of these defects

Decarburization

Another condition that could be considered a surface defect is decarburization This condition is present to some degree

on all hot-rolled steel Decarburization occurs at very high temperatures when the surface carbon of the steel reacts with the oxygen in the furnace atmosphere This loss of surface carbon results in a surface that is softer and unsuitable for any application involving wear or fatigue Because of the existence of this condition, steel ordered for critical applications can

be produced oversize and then ground to desired size

Allowance for Surface Imperfections in Machining Applications

Experience has shown that when purchasers order hot-rolled or heat-treated bars that are to be machined, it is advisable for the purchaser to make adequate allowances for the removal of surface imperfections and to specify the sizes accordingly These allowances depend on the way the surface metal is removed, the length and size of the bars, the straightness, the size tolerance, and the out-of-round tolerance Bars are generally straightened before machining For special quality carbon steel bars and regular quality alloy steel bars, either resulfurized or nonresulfurized (see the article

"Cold-Finished Steel Bars" in this Volume), it is advisable that allowances for centerless-turned or centerless-ground bars

be adequate to permit stock removal of not less than the amount shown below:

Bar diameter Recommended minimum machining

allowance per side, % of specific size

mm in Nonresulfurized Resulfurized

Table 1 Recommended minimum stock removal for steel bars subject to magnetic particle inspection

Hot-rolled size Minimum

stock removal from the surface(a)

mm in mm in

Up to 12.7

Up to 1

20.76 0.030

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

The allowances described above are usually more than sufficient to remove surface imperfections and result in considerable loss of material Therefore, most experienced fabricators remove considerably less stock than recommended