Classification and designation of carbon and Low-Alloy Steel

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Classification and designation of carbon and Low-Alloy Steel

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Classification and designation of carbon and Low-Alloy Steel

Messaggioda Aldebaran » 05/05/2010, 16:03

Introduction
STEELS constitute the most widely used category of metallic material, primarily because they can be manufactured
relatively inexpensively in large quantities to very precise specifications. They also provide a wide range of mechanical
properties, from moderate yield strength levels (200 to 300 MPa, or 30 to 40 ksi) with excellent ductility to yield strengths
exceeding 1400 MPa (200 ksi) with fracture toughness levels as high as 110 MPa m (100 ksi in ).
This article will review the various systems used to classify carbon and low-alloy steels*, describe the effects of alloying
elements on the properties and/or characteristics of steels, and provide extensive tabular data pertaining to designations of
steels (both domestic and international). More detailed information on the steel types and product forms discussed in this
article can be found in the articles that follow in this Section.
Note
* The term low-alloy steel rather than the more general term alloy steel is being used to differentiate the steels
covered in this article from high-alloy steels. High-alloy steels include steels with a high degree of fracture
toughness (Fe-9Ni-4Co), which are described in the article "Ultrahigh-Strength Steels" in this Section of the
Handbook. They also include maraging steels (Fe-18Ni-4Mo-8Co), austenitic manganese steels (Fe-1C-
12Mn), tool steels, and stainless steels, which are described in separate articles in the Section "Specialty
Steels and Heat-Resistant Alloys" in this Volume.
Classification of Steels
Steels can be classified by a variety of different systems depending on:
· The composition, such as carbon, low-alloy, or stainless steels
· The manufacturing methods, such as open hearth, basic oxygen process, or electric furnace methods
· The finishing method, such as hot rolling or cold rolling
· The product form, such as bar, plate, sheet, strip, tubing, or structural shape
· The deoxidation practice, such as killed, semikilled, capped, or rimmed steel
· The microstructure, such as ferritic, pearlitic, and martensitic (Fig. 1)
· The required strength level, as specified in ASTM standards
· The heat treatment, such as annealing, quenching and tempering, and thermomechanical processing
· Quality descriptors, such as forging quality and commercial quality
Fig. 1 Classification of steels. Source: D.M. Stefanescu, University of Alabama, Tuscaloosa
Of the aforementioned classification systems, chemical composition is the most widely used internationally and will be
emphasized in this article. Classification systems based on deoxidation practice and quality descriptors will also be
reviewed. Information pertaining to the microstructural characteristics of steels can be found in the article
"Microstructures, Processing, and Properties of Steels" in this Volume and in Metallography and Microstructures,
Volume 9 of ASM Handbook, formerly 9th Edition Metals Handbook.
Chemical Analysis
Chemical composition is often used as the basis for classifying steels or assigning standard designations to steels. Such
designations are often incorporated into specifications for steel products. Users and specifiers of steel products should be
familiar with methods of sampling and analysis.
Chemical analyses of steels are usually performed by wet chemical analysis methods or spectrochemical methods. Wet
analysis is most often used to determine the composition of small numbers of specimens or of specimens composed of
machine tool chips. Spectrochemical analysis is well-suited to the routine determination of the chemical composition of a
large number of specimens, as may be necessary in a steel mill environment. Both classical wet chemical and
spectrochemical methods for analyzing steel samples are described in detail in Materials Characterization, Volume 10 of
ASM Handbook, formerly 9th Edition Metals Handbook.
Heat and Product Analysis. During the steelmaking process, a small sample of molten metal is removed from the
ladle or steelmaking furnace, allowed to solidify, and then analyzed for alloy content. In most steel mills, these heat
analyses are performed using spectrochemical methods; as many as 14 different elements can be determined
simultaneously. The heat analysis furnished to the customer, however, may include only those elements for which a range
or a maximum or minimum limit exists in the appropriate designation or specification.
A heat analysis is generally considered to be an accurate representation of the composition of the entire heat of metal.
Producers of steel have found that heat analyses for carbon and alloy steels can be consistently held within ranges that
depend on the amount of the particular alloying element desired for the steel, the product form, and the method of making
the steel. These ranges have been published as commercial practice, then incorporated into standard specifications.
Standard ranges and limits of heat analyses of carbon and alloy steels are given in Tables 1, 2, 3, and 4.
Table 1 Carbon steel cast or heat chemical limits and ranges
Applicable only to semifinished products for forging, hot-rolled and cold-finished bars, wire rods, and seamless tubing
Element Maximum of
specified element, %
Range, %
£ 0.12 . . .
>0.12-0.25 incl 0.05
>0.25-0.40 incl 0.06
>0.40-0.55 incl 0.07
>0.55-0.80 incl 0.10
Carbon(a)
>0.80 0.13
£ 0.40 0.15
>0.40-0.50 incl 0.20
Manganese
>0.50-1.65 incl 0.30
Phosphorus >0.040-0.08 incl 0.03
>0.08-0.13 incl 0.05
>0.050-0.09 incl 0.03
>0.09-0.15 incl 0.05
>0.15-0.23 incl 0.07
Sulfur
>0.23-0.35 incl 0.09
£ 0.15 0.08
>0.15-0.20 incl 0.10
>0.20-0.30 incl 0.15
Silicon (for bars)(b)(c)
>0.30-0.60 incl 0.20
Copper When copper is required, 0.20%minimum is commonly used
Lead(d) When lead is required, a range of 0.15-0.35 is generally used
Note: Boron-treated fine-grain steels are produced to a range of 0.0005-0.003% B. Incl, inclusive.
Source: Ref 1
(a) The carbon ranges shown customarily apply when the specified maximum limit for manganese does not exceed 1.10%. When the maximum
manganese limit exceeds 1.10%, it is customary to add 0.01 to the carbon range shown.
(b) It is not common practice to produce a rephosphorized and resulfurized carbon steel to specified limits for silicon because of its adverse effect
on machinability.
(c) When silicon is required for rods the following ranges and limits are commonly used: 0.10 max; 0.07-0.15, 0.10-0.20, 0.15-0.35, 0.20-0.40, or
0.30-0.60.
(d) Lead is reported only as a range of 0.15-0.35% because it is usually added to the mold or ladle stream as the steel is poured.
Table 2 Carbon steel cast or heat chemical limits and ranges
Applicable only to structural shapes, plates, strip, sheets, and welded tubing
Element Maximum of
specified element, %
Range, %
Carbon(a)(b) £ 0.15 0.05
>0.15-0.30 incl 0.06
>0.30-0.40 incl 0.07
>0.40-0.60 incl 0.08
>0.60-0.80 incl 0.11
>0.80-1.35 incl 0.14
£ 0.50 0.20
>0.050-1.15 incl 0.30
Manganese
>1.15-1.65 incl 0.35
Phosphorus £ 0.08 0.03
>0.08-0.15 incl 0.05
£ 0.08 0.03
>0.08-0.15 incl 0.05
>0.15-0.23 incl 0.07
Sulfur
>0.23-0.33 incl 0.10
£ 0.15 0.08
>0.15-0.30 incl 0.15
Silicon
>0.30-0.60 incl 0.30
Copper When copper is required, 0.20%minimum is commonly specified
Incl, inclusive.
Source: Ref 1
(a) The carbon ranges shown in the range column apply when the specified maximum limit for manganese does not exceed 1.00%. When the
maximum manganese limit exceeds 1.00%, add 0.01 to the carbon ranges shown in the table.
(b) Maximum of 0.12% C for structural shapes and plates.
Table 3 Alloy steel heat composition ranges and limits for bars, blooms, billets, and slabs
Element Maximum of Range, %
specified element, %
Open hearth or
basic oxygen steels
Electric
furnace steels
£ 0.55 0.05 0.05
>0.55-0.70 incl 0.08 0.07
>0.70-0.80 incl 0.10 0.09
>0.80-0.95 incl 0.12 0.11
Carbon
>0.95-1.35 incl 0.13 0.12
£ 0.60 0.20 0.15
>0.60-0.90 incl 0.20 0.20
>0.90-1.05 incl 0.25 0.25
>1.05-1.90 incl 0.30 0.30
Manganese
>1.90-2.10 incl 0.40 0.35
£ 0.050 0.015 0.015
>0.050-0.07 incl 0.02 0.02
>0.07-0.10 incl 0.04 0.04
Sulfur(a)
>0.10-0.14 incl 0.05 0.05
£ 0.15 0.08 0.08
>0.15-0.20 incl 0.10 0.10
Silicon
>0.20-0.40 incl 0.15 0.15
>0.40-0.60 incl 0.20 0.20
>0.60-1.00 incl 0.30 0.30
>1.00-2.20 incl 0.40 0.35
£ 0.40 0.15 0.15
>0.40-0.90 incl 0.20 0.20
>0.90-1.05 incl 0.25 0.25
>1.05-1.60 incl 0.30 0.30
>1.60-1.75 incl (b) 0.35
>1.75-2.10 incl (b) 0.40
Chromium
>2.10-3.99 incl (b) 0.50
£ 0.50 0.20 0.20
>0.50-1.50 incl 0.30 0.30
>1.50-2.00 incl 0.35 0.35
>2.00-3.00 incl 0.40 0.40
>3.00-5.30 incl 0.50 0.50
Nickel
>5.30-10.00 incl 1.00 1.00
£ 0.10 0.05 0.05
>0.10-0.20 incl 0.07 0.07
>0.20-0.50 incl 0.10 0.10
>0.50-0.80 incl 0.15 0.15
Molybdenum
>0.80-1.15 incl 0.20 0.20
£ 0.50 0.20 0.20
>0.50-1.00 incl 0.30 0.30
>1.00-2.00 incl 0.50 0.50
Tungsten
>2.00-4.00 incl 0.60 0.60
£ 0.60 0.20 0.20
>0.60-1.50 incl 0.30 0.30
Copper
>1.50-2.00 incl 0.35 0.35
Vanadium £ 0.25 0.05 0.05
>0.25-0.50 incl 0.10 0.10
£ 0.10 0.05 0.05
>0.10-0.20 incl 0.10 0.10
>0.20-0.30 incl 0.15 0.15
>0.30-0.80 incl 0.25 0.25
>0.80-1.30 incl 0.35 0.35
Aluminum
>1.30-1.80 incl 0.45 0.45
Element Steelmaking process Lowest maximum, %(c)
Basic open hearth, basic oxygen, or basic electric furnace steels 0.035(d)
Basic electric furnace E steels 0.025
Phosphorus
Acid open hearth or electric furnace steel 0.050
Sulfur Basic open hearth, basic oxygen, or basic electric furnace steels 0.040(d)
Basic electric furnace E steels 0.025
Acid open hearth or electric furnace steel 0.050
Inc, inclusive.
Source: Ref 2
(a) A range of sulfur content normally indicates a resulfurized steel.
(b) Not normally produced by open hearth process.
(c) Not applicable to rephosphorized or resulfurized steels.
(d) Lower maximum limits on phosphorus and sulfur are required by certain quality
descriptors.
Table 4 Alloy steel heat composition ranges and limits for plates
Element Maximum of Range, %
specified element, %
Open hearth or basic
oxygen steels
Electric
furnace steels
£ 0.25 0.06 0.05
>0.25-0.40 incl 0.07 0.06
>0.40-0.55 incl 0.08 0.07
>0.55-0.70 incl 0.11 0.10
Carbon
>0.70 0.14 0.13
£ 0.45 0.20 0.15
>0.45-0.80 incl 0.25 0.20
>0.80-1.15 incl 0.30 0.25
Manganese
>1.15-1.70 incl 0.35 0.30
>1.70-2.10 incl 0.40 0.35
£ 0.060 0.02 0.02
>0.060-0.100 incl 0.04 0.04
Sulfur
>0.100-0.140 incl 0.05 0.05
£ 0.15 0.08 0.08
>0.15-0.20 incl 0.10 0.10
>0.20-0.40 incl 0.15 0.15
>0.40-0.60 incl 0.20 0.20
>0.60-1.00 incl 0.30 0.30
Silicon
>1.00-2.20 incl 0.40 0.35
£ 0.60 0.20 0.20
>0.60-1.50 incl 0.30 0.30
Copper
>1.50-2.00 incl 0.35 0.35
£ 0.50 0.20 0.20
>0.50-1.50 incl 0.30 0.30
>1.50-2.00 incl 0.35 0.35
>2.00-3.00 incl 0.40 0.40
>3.00-5.30 incl 0.50 0.50
Nickel
>5.30-10.00 incl 1.00 1.00
Chromium £ 0.40 0.20 0.15
>0.40-0.80 incl 0.25 0.20
>0.80-1.05 incl 0.30 0.25
>1.05-1.25 incl 0.35 0.30
>1.25-1.75 incl 0.50 0.40
>1.75-3.99 incl 0.60 0.50
£ 0.10 0.05 0.05
>0.10-0.20 incl 0.07 0.07
>0.20-0.50 incl 0.10 0.10
>0.50-0.80 incl 0.15 0.15
Molybdenum
0.80-1.15 incl 0.20 0.20
Vanadium £ 0.25 0.05 0.05
>0.25-0.50 incl 0.10 0.10
Note: Boron steels can be expected to contain a minimum of 0.0005% B. Alloy steels can be produced with a lead range of 0.15-
0.35%. A heat analysis for lead is not determinable because lead is added to the ladle stream while each ingot is poured. Incl,
inclusive.
Source: Ref 3
Because segregation of some alloying elements is inherent in the solidification of an ingot, different portions will have
local chemical compositions that differ slightly from the average composition. Many lengths of bar stock can be made
from a single ingot; therefore, some variation in composition between individual bars must be expected. The
compositions of individual bars might not conform to the applicable specification, even though the heat analysis does.
The chemical composition of an individual bar (or other product) taken from a large heat of steel is called the product
analysis or check analysis. Ranges and limits for product analyses are generally broader and less restrictive than the
corresponding ranges and limits for heat analyses. Such limits used in standard commercial practice are given in Tables 5,
6, and 7.
Table 5 Product analysis tolerances for carbon and alloy steel plates, sheet, piling, and bars for structural
applications
Element Upper limit or maximum Tolerance, %
specified value, %
Under
minimum limit
Over
maximum limit
Carbon £ 0.15 0.02 0.03
>0.15-0.40 incl 0.03 0.04
£ 0.60 0.05 0.06
>0.60-0.90 incl 0.06 0.08
>0.90-1.20 incl 0.08 0.10
>1.20-1.35 incl 0.09 0.11
>1.35-1.65 incl 0.09 0.12
>1.65-1.95 incl 0.11 0.14
Manganese(a)
>1.95 0.12 0.16
Phosphorus £ 0.04 . . . 0.010
>0.40-0.15 incl . . . (b)
Sulfur £ 0.05 . . . 0.010
£ 0.30 0.02 0.03
>0.30-0.40 incl 0.05 0.05
Silicon
>0.40-2.20 incl 0.06 0.06
Nickel £ 1.00 0.03 0.03
>1.00-2.00 incl 0.05 0.05
Chromium £ 0.90 0.04 0.04
>0.90-2.10 incl 0.06 0.06
£ 0.20 0.01 0.01
>0.20-0.40 incl 0.03 0.03
Molybdenum
>0.40-1.15 incl 0.04 0.04
0.20 minimum only 0.02 . . .
£ 1.00 0.03 0.03
Copper
>1.00-2.00 incl 0.05 0.05
Titanium £ 0.10 0.01(c) 0.01(c)
£ 0.10 0.01(c) 0.01(c)
>0.10-0.25 incl 0.02 0.02
Vanadium
Minimum only specified 0.01 . . .
Boron Any (b) (b)
Niobium £ 0.10 0.01(c) 0.01(c)
Zirconium £ 0.15 0.03 0.03
Nitrogen £ 0.030 0.005 0.005
Incl, inclusive.
Source: Ref 4
(a) Manganese product analyses tolerances for bars and bar size shapes: £ 0.90, ±0.03; >0.90-2.20 incl, ±0.06.
(b) Product analysis not applicable.
(c) If the minimum of the range is 0.01%, the under tolerance is 0.005%.
Table 6 Product analysis tolerances for carbon and high-strength low-alloy steel bars, blooms, billets, and
slabs
Tolerance over the maximum Element Limit or maximum limit or under the minimum limit, %
of specified range, %
£ 0.065 m2
(100 in.2)
>0.065-0.129 m2
(100-200 in.2)
incl
>0.129-0.258 m2
(200-400 in.2)
incl
>0.258-0.516 m2
(400-800 in.2)
incl
Carbon £ 0.25 0.02 0.03 0.04 0.05
>0.25-0.55 incl 0.03 0.04 0.05 0.06
>0.55 0.04 0.05 0.06 0.07
Manganese £ 0.90 0.03 0.04 0.06 0.07
>0.90-1.65 incl 0.06 0.06 0.07 0.08
Phosphorus(a) Over maximum only, £ 0.40 0.008 0.008 0.010 0.015
Sulfur(a) Over maximum only, £ 0.050 0.008 0.010 0.010 0.015
Silicon £ 0.35 0.02 0.02 0.03 0.04
>0.35-0.60 incl 0.05 . . . . . . . . .
Copper Under minimum only 0.02 0.03 . . . . . .
Lead(b) 0.15-0.35 incl 0.03 0.03 . . . . . .
Note: Rimmed or capped steels and boron are not subject to product analysis tolerances. Product analysis tolerances for alloy elements
in high-strength low-alloy steels are given in Table 7. Incl, inclusive.
Source: Ref 2
(a) Because of the degree to which phosphorus and sulfur segregate, product analysis tolerances for those elements are not applicable for
rephosphorized and resulfurized steels.
(b) Product analysis tolerance for lead applies, both over and under the specified range.
Table 7 Product analysis tolerances for alloy steel bars, blooms, billets, and slabs
Tolerance over the maximum limit
or under the minimum limit for size ranges shown, %
Element Limit or maximum of
specified range, %
£ 0.065 m2
(100 in.2)
>0.065-0.129 m2
(100-200 in.2)
incl
>0.129-0.258 m2
(200-400 in.2)
incl
>0.258-0.516 m2
(400-800 in.2)
incl
£ 0.30 0.01 0.02 0.03 0.04
>0.30-0.75 incl 0.02 0.03 0.04 0.05
Carbon
>0.75 0.03 0.04 0.05 0.06
Manganese £ 0.90 0.03 0.04 0.05 0.06
>0.90-2.10 incl 0.04 0.05 0.06 0.07
Phosphorus Over max only 0.005 0.010 0.010 0.010
Sulfur Over max only(a) 0.005 0.010 0.010 0.010
Silicon £ 0.40 0.02 0.02 0.03 0.04
>0.40-2.20 incl 0.05 0.06 0.06 0.07
£ 1.00 0.03 0.03 0.03 0.03
>1.00-2.00 incl 0.05 0.05 0.05 0.05
>2.00-5.30 incl 0.07 0.07 0.07 0.07
Nickel
>5.30-10.00 incl 0.10 0.10 0.10 0.10
£ 0.90 0.03 0.04 0.04 0.05
>0.90-2.10 incl 0.05 0.06 0.06 0.07
Chromium
>2.10-3.99 incl 0.10 0.10 0.12 0.14
£ 0.20 0.01 0.01 0.02 0.03
>0.20-0.40 incl 0.02 0.03 0.03 0.04
Molybdenum
>0.40-1.15 incl 0.03 0.04 0.05 0.06
£ 0.10 0.01 0.01 0.01 0.01
>0.10-0.25 incl 0.02 0.02 0.02 0.02
>0.25-0.50 incl 0.03 0.03 0.03 0.03
Vanadium
Min value specified, check under min limit(b) 0.01 0.01 0.01 0.01
Tungsten £ 1.00 0.04 0.05 0.05 0.06
>1.00-4.00 incl 0.08 0.09 0.10 0.12
£ 0.10 0.03 . . . . . . . . .
>0.10-0.20 incl 0.04 . . . . . . . . .
>0.20-0.30 incl 0.05 . . . . . . . . .
>0.30-0.80 incl 0.07 . . . . . . . . .
Aluminum(c)
>0.80-1.80 incl 0.10 . . . . . . . . .
Lead(c) 0.15-0.35 incl 0.03(d) . . . . . . . . .
Copper(c) £ 1.00 0.03 . . . . . . . . .
>1.00-2.00 incl 0.05 . . . . . . . . .
Titanium(c) £ 0.10 0.01(b) . . . . . . . . .
Niobium(c) £ 0.10 0.01(b) . . . . . . . . .
Zirconium(c) £ 0.15 0.03 . . . . . . . . .
Nitrogen(c) £ 0.030 0.005 . . . . . . . . .
Note: Boron is not subject to product analysis tolerances. Incl, inclusive.
Source: Ref 2
(a) Resulfurized steels are not subject to product analysis limits for sulfur.
(b) If the minimum of the range is 0.01%, the under tolerance is 0.005%.
(c) Tolerances shown apply only to 0.065 m2 (100 in.2) or less.
(d) Tolerance is over and under.
Residual elements usually enter steel products from raw materials used to produce pig iron or from scrap steel used in
steelmaking. Through careful steelmaking practices, the amounts of these residual elements are generally held to
acceptable levels. Sulfur and phosphorus are usually considered deleterious to the mechanical properties of steels;
therefore, restrictions are placed on the allowable amounts of these elements for most grades. The amounts of sulfur and
phosphorus are invariably reported in the analyses of both carbon and alloy steels. Other residual alloying elements
generally exert a lesser influence than sulfur and phosphorus on the properties of steel. For many grades of steel,
limitations on the amounts of these residual elements are either optional or omitted entirely. Amounts of residual alloying
elements are generally not reported in either heat or product analyses, except for special reasons.
Silicon Content of Steels. The composition requirements for many steels, particularly plain carbon steels, contain no
specific restriction on silicon content. The lack of a silicon requirement is not an omission, but instead indicates
recognition that the amount of silicon in a steel can often be traced directly to the deoxidation practice employed in
making it (further information can be found in the section "Types of Steel Based on Deoxidation Practice" in this article).
Rimmed and capped steels are not deoxidized; the only silicon present is the residual amount left from scrap or raw
materials, typically less than 0.05% Si. Specifications and orders for these steels customarily indicate that the steel must
be made rimmed or capped, as required by the purchaser, restrictions on silicon content are not usually given.
The extent of rimming action during the solidification of semikilled steel ingots must be carefully controlled by matching
the amount of deoxidizer with the oxygen content of the molten steel. The amount of silicon required for deoxidation may
vary from heat to heat. Thus, the silicon content of the solid metal can also vary slightly from heat to heat. A maximum
silicon content of 0.10% is sometimes specified for semikilled steel, but this requirement is not very restrictive; for certain
heats, a silicon addition sufficient to leave a residue of 0.10% may be enough of an addition to kill the steel.
Killed steels are fully deoxidized during their manufacture; deoxidation can be accomplished by additions of silicon,
aluminum, or both, or by vacuum treatment of the molten steel. Because it is the least costly of these methods, silicon
deoxidation is frequently used. For silicon-killed steels, a range of 0.15 to 0.30% Si is often specified, providing the
manufacturer with adequate flexibility to compensate for variations in the steelmaking process and ensuring a steel
acceptable for most applications. Aluminum-killed or vacuum-deoxidized steels require no silicon; a requirement for
minimum silicon content in such steel is unnecessary. A maximum permissible silicon content is appropriate for all killed
plain carbon steels; a minimum silicon content implies a restriction that the steel must be silicon killed. Silicon is
intentionally added to some alloy steels, for which it serves as both a deoxidizer and an alloying element to modify the
properties of the steel. An acceptable range of silicon content would be appropriate for these steels.
Users and specifiers of steel mill products must realize that the silicon content of these items cannot be established
independently of deoxidation practice. In ordering mill products, it is often desirable to cite a standard specification (such
as an ASTM specification) where the various ramifications of restrictions on silicon content have already been considered
in preparing the specification. In some instances, such as the forming of low-carbon steel sheet, the choice of deoxidation
practice can significantly affect the performance of the steel; in such cases, it is appropriate to specify the desired practice.
Types of Steel Based on Deoxidation Practice (Ref 3)
Steels, when cast into ingots, can be classified into four types based on the deoxidation practice employed or,
alternatively, by the amount of gas evolved during solidification. These types are killed, semikilled, rimmed, or capped
steels (Fig. 2).
Fig. 2 Eight typical conditions of commercial steel ingots, cast in identical bottle-top molds, in relation to the
degree of suppression of gas evolution. The dotted line indicates the height to which the steel originally was
poured in each ingot mold. Depending on the carbon and, more importantly, the oxygen content of the steel,
the ingot structures range from that of a fully killed ingot (No. 1) to that of a violently rimmed ingot (No. 8).
Source:Ref 5
Killed steel is a type of steel from which there is only a slight evolution of gases during solidification of the metal after
pouring. Killed steels are characterized by more uniform chemical composition and properties as compared to the other
types. Alloy steels, forging steels, and steels for carburizing are generally killed.
Killed steel is produced by various steel-melting practices involving the use of certain deoxidizing elements which act
with varying intensities. The most common of these are silicon and aluminum; however, vanadium, titanium, and
zirconium are sometimes used. Deoxidation practices in the manufacture of killed steels are normally left to the discretion
of the producer.
Semikilled steel is a type of steel wherein there is a greater degree of gas evolution than in killed steel but less than in
capped or rimmed steel. The amount of deoxidizer used (customarily silicon or aluminum) will determine the amount of
gas evolved. Semikilled steels generally have a carbon content within the range of 0.15 to 0.30%; they are used for a wide
range of structural shape applications.
Semikilled steels are characterized by variable degrees of uniformity in composition, which are intermediate between
those of killed and rimmed steels. Semikilled steel has a pronounced tendency for positive chemical segregation at the
top-center of the ingot (Fig. 2).
Rimmed Steels. In the production of rimmed steels, no deoxidizing agents are added in the furnace. These steels are
characterized by marked differences in chemical composition across the section and from the top to the bottom of the
ingot (Fig. 2). They have an outer rim that is lower in carbon, phosphorus, and sulfur than the average composition of the
whole ingot, and an inner portion, or core, that has higher levels than the average of those elements. The typical structure
of the rimmed steel ingot results from a marked gas evolution during solidification of the outer rim.
During the solidification of the rim, the concentration of certain elements increases in the liquid portion of the ingot.
During solidification of the core, some increase in segregation occurs in the upper and central portions of the ingot. The
structural pattern of the ingot persists through the rolling process to the final product (rimmed ingots are best suited for
steel sheets).
The technology of manufacturing rimmed steels limits the maximum content of carbon and manganese, and those
maximums vary among producers. Rimmed steels do not retain any significant percentages of highly oxidizable elements
such as aluminum, silicon, or titanium.
Capped steels have characteristics similar to those of rimmed steels but to a degree intermediate between those of
rimmed and semikilled steels. A deoxidizer may be added to effect a controlled rimming action when the ingot is cast.
The gas entrapped during solidification is in excess of that needed to counteract normal shrinkage, resulting in a tendency
for the steel to rise in the mold. The capping operation limits the time of gas evolution and prevents the formation of an
excessive number of gas voids within the ingot.
Mechanically capped steel is cast in bottle-top molds using a heavy metal cap.
Chemically capped steel is cast in open-top molds. The capping is accomplished by adding aluminum or ferrosilicon
to the top of the ingot, causing the steel at the top surface to solidify rapidly. The top portion of the ingot is discarded.
The capped ingot practice is usually applied to steel with carbon contents greater than 0.15% that is used for sheet, strip,
wire, and bars.
Quality Descriptors
The need for communication among producers and between producers and users has resulted in the development of a
group of terms known as fundamental quality descriptors. These are names applied to various steel products to imply that
the particular products possess certain characteristics that make them especially well suited for specific applications or
fabrication processes. The fundamental quality descriptors in common use are listed in Table 8.
Table 8 Quality descriptions of carbon and alloy steels
Carbon steels
Semifinished for forging
Forging quality
Special hardenability
Special internal soundness
Nonmetallic inclusion requirement
Special surface
Carbon steel structural sections
Structural quality
Carbon steel plates
Regular quality
Structural quality
Cold-drawing quality
Cold-pressing quality
Cold-flanging quality
Forging quality
Pressure vessel quality
Hot-rolled carbon steel bars
Merchant quality
Special quality
Special hardenability
Special internal soundness
Nonmetallic inclusion requirement
Special surface
Scrapless nut quality
Axle shaft quality
Cold extrusion quality
Cold-heading and cold-forging quality
Cold-finished carbon steel bars
Standard quality
Special hardenability
Special internal soundness
Nonmetallic inclusion requirement
Special surface
Cold-heading and cold-forging quality
Cold extrusion quality
Hot-rolled sheets
Commercial quality
Drawing quality
Drawing quality special killed
Structural quality
Col-rolled sheets
Commercial quality
Drawing quality
Drawing quality special killed
Structural quality
Porcelain enameling sheets
Commercial quality
Drawing quality
Drawing quality special killed
Long terne sheets
Commercial quality
Drawing quality
Drawing quality special killed
Structural quality
Galvanized sheets
Commercial quality
Drawing quality
Drawing quality special killed
Lock-forming quality
Electrolytic zinc coated sheets
Commercial quality
Drawing quality
Drawing quality special killed
Structural quality
Hot-rolled strip
Commercial quality
Drawing quality
Drawing quality special killed
Structural quality
Cold-rolled strip
Specific quality descriptions are not provided in cold-rolled strip because this product is largely produced for specific end use
Tin mill products
Specific quality descriptions are not applicable to tin mill products
Carbon steel wire
Industrial quality wire
Cold extrusion wires
Heading, forging, and roll-threading wires
Mechanical spring wires
Upholstery spring construction wires
Welding wire
Carbon steel flat wire
Stitching wire
Stapling wire
Carbon steel pipe
Structural tubing
Line pipe
Oil country tubular goods
Steel specialty tubular products
Pressure tubing
Mechanical tubing
Aircraft tubing
Hot-rolled carbon steel wire rods
Industrial quality
Rods for manufacture of wire intended for electric welded chain
Rods for heading, forging, and roll-threading wire
Rods for lock washer wire
Rods for scrapless nut wire
Rods for upholstery spring wire
Rods for welding wire
Alloy steels
Alloy steel plates
Drawing quality
Pressure vessel quality
Structural quality
Aircraft physical quality
Hot-rolled alloy steel bars
Regular quality
Aircraft quality or steel subject to magnetic particle inspection
Axle shaft quality
Bearing quality
Cold-heading quality
Special cold-heading quality
Rifle barrel quality, gun quality, shell or A.P. shot quality
Alloy steel wire
Aircraft quality
Bearing quality
Special surface quality
Cold-finished alloy steel bars
Regular quality
Aircraft quality or steel subject to magnetic particle inspection
Axle shaft quality
Bearing shaft quality
Cold-heading quality
Special cold-heading quality
Rifle barrel quality, gun quality, shell or A.P. shot quality
Line pipe
Oil country tubular goods
Steel specialty tubular goods
Pressure tubing
Mechanical tubing
Stainless and head-resisting pipe, pressure tubing, and mechanical tubing
Aircraft tubing
Pipe
Source: Ref 6
Some of the quality descriptors listed in Table 8 such as forging quality or cold extrusion quality are self-explanatory. The
meaning of others is less obvious: for example, merchant quality hot-rolled carbon steel bars are made for noncritical
applications requiring modest strength and mild bending or forming, but not requiring forging or heat treating. The
descriptor for one particular steel commodity is not necessarily carried over to subsequent products made from that
commodity--for example, standard quality cold-finished bars are made from special quality hot-rolled bars.
The various mechanical and physical attributes implied by a quality descriptor arise from the combined effects of several
factors, including:
· The degree of internal soundess
· The relative uniformity of chemical composition
· The relative freedom from surface imperfections
· The size of the discard cropped from the ingot
· Extensive testing during manufacture
· The number, size, and distribution of nonmetallic inclusions
· Hardenability requirements
Control of these factors during manufacture is necessary to achieve mill products having the desired characteristics. The
extent of the control over these and other related factors is another piece of information conveyed by the quality
descriptor.
Some, but not all, of the fundamental descriptors may be modified by one or more additional requirements, as may be
appropriate: special discard, macroetch test, restricted chemical composition, maximum incidental (residual) alloy, special
hardenability or austenitic grain size. These restrictions could be applied to forging quality alloy steel bars, but not to
merchant quality bars.
Understanding the various quality descriptors is complicated by the fact that most of the requirements that qualify a steel
for a particular descriptor are subjective. Only nonmetallic inclusion count, restrictions on chemical composition ranges
and incidental alloying elements, austenitic grain size, and special hardenability are quantified. The subjective evaluation
of the other characteristics depends on the skill and experience of those who make the evaluation. Although the use of
these subjective quality descriptors might seem imprecise and unworkable, steel products made to meet the requirements
of a particular quality descriptor can be relied upon to have those characteristics necessary for that product to be used in
the indicated application or fabrication operation.
References cited in this section
1. "Chemical Compositions of SAE Carbon Steels," SAE J403, 1989 SAE Handbook, Vol 1, Materials, Society
of Automotive Engineers, p 1.08-1.10
2. "Alloy, Carbon and High Strength Low Alloy Steels: Semifinished for Forging; Hot Rolled Bars and Cold
Finished Bars, Hot Rolled Deformed and Plain Concrete Reinforcing Bars," Steel Products Manual,
American Iron and Steel Institute, March 1986
3. "Plates; Rolled Floor Plates: Carbon, High Strength Low Alloy, and Alloy Steel," Steel Products Manual,
American Iron and Steel Institute, Aug 1985
4. "Standard Specification for General Requirements for Rolled Steel Plates, Shapes, Sheet Piling, and Bars for
Structural Use," ASTM A 6/A 6M, American Society for Testing and Materials
5. The Making, Shaping and Treating of Steel, 10th ed., United States Steel Corporation, 1985
6. "Carbon and Alloy Steels," SAE J411, 1989 SAE Handbook, Vol 1, Materials, Society of Automotive
Engineers, p 2.01-2.03
Effects of Alloying Elements (Ref 6)
Steels form one of the most complex group of alloys in common use. The synergistic effect of alloying elements and heat
treatment produce a tremendous variety of microstructures and properties (characteristics). Given the limited scope of this
article, it would be impossible to include a detailed survey of the effects of alloying elements on the iron-carbon
equilibrium diagram. This complicated subject, which is briefly reviewed in the article "Microstructures, Processing, and
Properties of Steels" in this Volume, lies in the domain of ferrous physical metallurgy and has also been reviewed
extensively in the literature (Ref 7, 8, 9, 10, 11). In this section, the effects of various elements on steelmaking
(deoxidation) practices and steel characteristics will be briefly outlined. It should be noted that the effects of a single
alloying elements are modified by the influence of other elements. These interrelations must be considered when
evaluating a change in the composition of a steel. For the sake of simplicity, however, the various alloying elements listed
below are discussed separately.
Carbon. The amount of carbon required in the finished steel limits the type of steel that can be made. As the carbon
content of rimmed steels increases, surface quality becomes impaired. Killed steels in approximately the 0.15 to 0.30% C
content level may have poorer surface quality and require special processing to attain surface quality comparable to steels
with higher or lower carbon contents. Carbon has a moderate tendency to segregate, and carbon segregation is often more
significant than the segregation of other elements. Carbon, which has a major effect on steel properties, is the principal
hardening element in all steel. Tensile strength in the as-rolled condition increases as carbon content increases (up to
about 0.85% C). Ductility and weldability decrease with increasing carbon.
Manganese has less of a tendency toward macrosegregation than any of the common elements. Steels above 0.60% Mn
cannot be readily rimmed. Manganese is beneficial to surface quality in all carbon ranges (with the exception of
extremely low carbon rimmed steels) and is particularly beneficial in resulfurized steels. It contributes to strength and
hardness, but to a lesser degree than does carbon; the amount of increase is dependent upon the carbon content. Increasing
the manganese content decreases ductility and weldability, but to a lesser extent than does carbon. Manganese has a
strong effect on increasing the hardenability of a steel.
Phosphorus segregates, but to a lesser degree than carbon and sulfur. Increasing phosphorus increases strength and
hardness and decreases ductility and notch impact toughness in the as-rolled condition. The decreases in ductility and
toughness are greater in quenched and tempered higher-carbon steels. Higher phosphorus is often specified in low-carbon
free-machining steels to improve machinability (see the article "Machinability of Steels" in this Volume).
Sulfur. Increased sulfur content lowers transverse ductility and notch impact toughness but has only a slight effect on
longitudinal mechanical properties. Weldability decreases with increasing sulfur content. This element is very detrimental
to surface quality, particularly in the lower-carbon and lower-manganese steels. For these reasons, only a maximum limit
is specified for most steels. The only exception is the group of free-machining steels, where sulfur is added to improve
machinability; in this case a range is specified (see the article "Machinability of Steels" in this Volume). Sulfur has a
greater segregation tendency than any of the other common elements. Sulfur occurs in steel principally in the form of
sulfide inclusions. Obviously, a greater frequency of such inclusions can be expected in the resulfurized grades.
Silicon is one of the principal deoxidizers used in steelmaking; therefore, the amount of silicon present is related to the
type of steel. Rimmed and capped steels contain no significant amounts of silicon. Semikilled steels may contain
moderate amounts of silicon, although there is a definite maximum amount that can be tolerated in such steels. Killed
carbon steels may contain any amount of silicon up to 0.60% maximum.
Silicon is somewhat less effective than manganese in increasing as-rolled strength and hardness. Silicon has only a slight
tendency to segregate. In low-carbon steels, silicon is usually detrimental to surface quality, and this condition is more
pronounced in low-carbon resulfurized grades.
Copper has a moderate tendency to segregate. Copper in appreciable amounts is detrimental to hot-working operations.
Copper adversely affects forge welding, but it does not seriously affect arc or oxyacetylene welding. Copper is
detrimental to surface quality and exaggerates the surface defects inherent in resulfurized steels. Copper is, however,
beneficial to atmospheric corrosion resistance when present in amounts exceeding 0.20%. Steels containing these levels
of copper are referred to as weathering steels and are described in the article "High-Strength Structural and High-Strength
Low-Alloy Steels" in this Volume; they are also included in the descriptions of high-strength low-alloy steels given later
in this article.
Lead is sometimes added to carbon and alloy steels through mechanical dispersion during teeming for the purpose of
improving the machining characteristics of the steels. These additions are generally in the range of 0.15 to 0.35% (see the
article "Machinability of Steels" in this Volume for details).
Boron is added to fully killed steel to improve hardenability. Boron-treated steels are produced to a range of 0.0005 to
0.003%. Whenever boron is substituted in part for other alloys, it should be done only with hardenability in mind because
the lowered alloy content may be harmful for some applications. Boron is most effective in lower carbon steels. Boron
steels are discussed in the Section "Hardenability of Carbon and Low-Alloy Steels" in this Volume.
Chromium is generally added to steel to increase resistance to corrosion and oxidation, to increase hardenability, to
improve high-temperature strength, or to improve abrasion resistance in high-carbon compositions. Chromium is a strong
carbide former. Complex chromium-iron carbides go into solution in austenite slowly; therefore, a sufficient heating time
before quenching is necessary.
Chromium can be used as a hardening element, and is frequently used with a toughening element such as nickel to
produce superior mechanical properties. At higher temperatures, chromium contributes increased strength; it is ordinarily
used for applications of this nature in conjunction with molybdenum.
Nickel, when used as an alloying element in constructional steels, is a ferrite strengthener. Because nickel does not form
any carbide compounds in steel, it remains in solution in the ferrite, thus strengthening and toughening the ferrite phase.
Nickel steels are easily heat treated because nickel lowers the critical cooling rate. In combination with chromium, nickel
produces alloy steels with greater hardenability, higher impact strength, and greater fatigue resistance than can be
achieved in carbon steels.
Molybdenum is added to constructional steels in the normal amounts of 0.10 to 1.00%. When molybdenum is in solid
solution in austenite prior to quenching, the reaction rates for transformation become considerably slower as compared
with carbon steel. Molybdenum can induce secondary hardening during the tempering of quenched steels and enhances
the creep strength of low-alloy steels at elevated temperatures. Alloy steels that contain 0.15 to 0.30% Mo display a
minimized susceptibility to temper embrittlement (see the article "Embrittlement of Steels" in this Volume for a
discussion of temper embrittlement and other forms of thermal embrittlement).
Niobium. Small additions of niobium increase the yield strength and, to a lesser degree, the tensile strength of carbon
steel. The addition of 0.02% Nb can increase the yield strength of medium-carbon steel by 70 to 100 MPa (10 to 15 ksi).
This increased strength may be accompanied by considerably impaired notch toughness unless special measures are used
to refine grain size during hot rolling. Grain refinement during hot rolling involves special thermomechanical processing
techniques such as controlled rolling practices, low finishing temperatures for final reduction passes, and accelerated
cooling after rolling is completed (further discussion of controlled rolling can be found in the article "High-Strength
Structural and High-Strength Low-Alloy Steels" in this Volume).
Aluminum is widely used as a deoxidizer and for control of grain size. When added to steel in specified amounts, it
controls austenite grain growth in reheated steels. Of all the alloying elements, aluminum is the most effective in
controlling grain growth prior to quenching. Titanium, zirconium, and vanadium are also effective grain growth
inhibitors; however, for structural grades that are heat treated (quenched and tempered), these three elements may have
adverse effects on hardenability because their carbides are quite stable and difficult to dissolve in austenite prior to
quenching.
Titanium and Zirconium. The effects of titanium are similar to those of vanadium and niobium, but it is only useful in
fully killed (aluminum-deoxidized) steels because of its strong deoxidizing effects.
Zirconium can also be added to killed high-strength low-alloy steels to obtain improvements in inclusion characteristics,
particularly sulfide inclusions where changes in inclusion shape improve ductility in transverse bending.
References cited in this section
6. "Carbon and Alloy Steels," SAE J411, 1989 SAE Handbook, Vol 1, Materials, Society of Automotive
Engineers, p 2.01-2.03
7. G. Krauss, Steels--Heat Treatment and Processing Principals, ASM INTERNATIONAL, 1989
8. W.C. Leslie, The Physical Metallurgy of Steels, McGraw-Hill, 1981
9. E.C. Bain and H.W. Paxton, Alloying Elements in Steel, American Society for Metals, 1966
10. A.K. Sinha, Ferrous Physical Metallurgy, Butterworths, 1989
11. R.W.K. Honeycombe, Steels--Microstructure and Properties, Edward Arnold Ltd., 1982
Carbon Steels
The American Iron and Steel Institute defines carbon steel as follows (Ref 2, 3):
Steel is considered to be carbon steel when no minimum content is specified or required for
chromium, cobalt, columbium [niobium], molybdenum, nickel, titanium, tungsten, vanadium or
zirconium, or any other element to be added to obtain a desired alloying effect; when the
specified minimum for copper does not exceed 0.40 per cent; or when the maximum content
specified for any of the following elements does not exceed the percentages noted: manganese
1.65, silicon 0.60, copper 0.60.
Carbon steel can be classified, according to various deoxidation practices, as rimmed, capped, semikilled, or killed steel.
Deoxidation practice and the steelmaking process will have an effect on the characteristics and properties of the steel (see
the article "Steel Processing Technology" in this Volume). However, variations in carbon have the greatest effect on
mechanical properties, with increasing carbon content leading to increase hardness and strength (see the article
"Microstructures, Processing, and Properties of Steels" in this Volume). As such, carbon steels are generally categorized
according to their carbon content. Generally speaking, carbon steels contain up to 2% total alloying elements and can be
subdivided into low-carbon steels, medium-carbon steels, high-carbon steels, and ultrahigh-carbon steels; each of these
designations is discussed below.
As a group, carbon steels are by far the most frequently used steel. Tables 9 and 10 indicate that more than 85% of the
steel produced and shipped in the United States is carbon steel. Chemical compositions for carbon steels are provided in
the tables referenced in the section "SAE-AISI Designations" in this article. See Tables 11, 12, 13, 14, 15, 16, 17, 18, 19,
20, 21, and 22.
Table 9 Raw steel production by type of furnace, grade, and cast
Total all grades, net tons × 103 Total production
By grade, % By type of furnace, %
Year Production by type of cast, net tons × 103
Carbon Alloy Stainless Total Carbon Alloy Stainless Open
heart
Basic
oxygen process
Electric Ingots Continuous
castings
Steel
castings
1988 86,823 10,902 2199 99,924 86.9 10.9 2.2 5.1 58.0 36.9 38,615 61,232 77
1987 77,976 9,147 2028 89,151 87.5 10.2 2.3 3.0 58.9 38.1 35,802 53,284 65
1986 71,413 8,505 1689 81,606 87.5 10.4 2.1 4.1 58.7 37.2 36,487 45,064 55
1985 76,699 9,877 1683 88,259 86.9 11.2 1.9 7.3 58.8 33.9 49,035 39,161 63
1984 79,918 10,838 1772 92,528 86.4 11.7 1.9 9.0 57.1 33.9 55,787 36,669 74
Table 10 Net shipments of United States steel mill products, all grades
Steel products 1988 1987
Net tons × 103 % Net tons × 103 %
Ingots and steel for castings 385 0.5 381 0.5
Blooms, slabs, and billets 1,542 1.8 1,212 1.6
Skelp (a) . . . 22 . . .
Wire rods 4,048 4.8 3,840 5.0
Structural shapes ( ³ 75 mm, or 3 in.) 4,860 5.8 4,839 6.3
Steel piling 349 0.4 280 0.4
Plates cut in lengths 5,044 6.0 4,048 5.3
Plates in coils 2,284 2.7 (b) . . .
Rails
standard (>27 kg, or 60 lb) 460 0.5 351 0.5
all other 37 0.0 15 . . .
Railroad accessories 118 0.1 62 0.1
Wheels (rolled and forged) (a) . . . 58 0.1
Axles (a) . . . 29 . . .
Bars
hot rolled 6,460 7.7 6,048 7.9
bar-size light shapes 1,373 1.6 1,190 1.6
reinforcing 5,091 6.1 4,918 6.4
cold finished 1,499 1.8 1,361 1.8
Tool steel 64 0.1 58 0.1
Pipe and tubing
standard 1,238 1.5 969 1.3
oil country goods 1,130 1.3 919 1.2
line 808 1.0 620 0.8
mechanical 901 1.1 767 1.0
pressure 59 0.1 72 0.1
structural 178 0.2 180 0.2
pipe for piling 74 0.1 (c) . . .
stainless 55 0.1 42 0.1
Wire
drawn 1,073 1.3 800 1.0
nails and staples (a) . . . 218 0.3
barbed and twisted (a) . . . 49 0.1
woven wire fence (a) . . . 13 . . .
bale ties and baling wire (a) . . . 25 . . .
Black plate 283 0.3 205 0.3
Tin plate 2,806 3.3 2,765 3.6
Tin free steel 899 1.1 939 1.2
Tin coated sheets 81 0.1 79 0.1
Sheets
hot rolled 12,589 15.0 13,048 17.0
cold rolled 13,871 16.5 13,859 18.1
Sheets and strip
galvanized, hot dipped 8,115 9.7 7,660 10.0
galvanized, electrolytic 2,134 2.5 1,432 1.9
all other metallic coated 1,262 1.5 1,228 1.6
electrical 524 0.6 465 0.6
Strip
hot rolled 1,203 1.4 657 0.9
cold rolled 941 1.1 929 1.2
Total steel mill products 83,840 100.0 76,654 100.0
Carbon 77,702 92.7 68,116 88.9
Stainless and heat resisting 1,586 1.9 1,418 1.8
Alloy (other than stainless) 4,552 5.4 7,120 9.3
Source: Ref 12
Source: Ref 12
(a) Effective 1 January 1988, these products are no longer classified as steel mill products by AISI. Consequently, comparable shipment tonnage is
now included in applicable semifinished forms or drawn wire.
(b) Prior to 1988 included in sheets hot rolled.
(c) Prior to 1988 included in structural pipe and tubing.
Table 11 SAE-AISI system of designations
Table 12 Carbon steel compositions
Applicable to semifinished products for forging, hot-rolled and cold-finished bars, wire rods, and seamless tubing
UNS Cast or heat chemical ranges and limits, %(a)
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