Still, even though we would reference such a distinguished authority as Linnert, it is still an arbitrary distinction that would be settled by convention or consensus as opposed to something of a metallurgical foundation.

However, ASME Section IX was not written by Prof. Silva Telles. ;) Ummmm, I truly believe that we can now continue the discussion in here!!! :) :) :)

With respect to 3.2, I believe he's referring to ISO's definition of what is a low alloy steel...

Various attempts have been made to distinguish ‘low’ and ‘high’ alloy steels, but the definitions vary between countries and between standard-setting organizations. As a general indication, low alloy steel can be regarded as alloy steels (by the ISO definition) containing between 1% and less than 5% of elements deliberately added for the purpose of modifying properties... Now ISO isn't the ASME, so Jeff is correct in his observation also.

Now here's an explanation that refers to AISI (The American Iron and Steel Institute) standards from the: "Key to Metals" website and clearly distinguishes the differences between plain carbon, low carbon, and many other carbon steels as well as the differences in various grades of low alloy steels also... Here's the link:

http://www.webcitation.org/5o9SDyEAb

Just in case the link doesn't function, here's the article from "WebCite":

Abstract:
The American Iron and Steel Institute (AISI) defines carbon steel as follows: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.

Steels can be classified by a variety of different systems depending on:

* The composition, such as carbon, low-alloy or stainless steel.
* 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, semi-killed, capped or rimmed steel
* The microstructure, such as ferritic, pearlitic and martensitic
* 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.

Carbon Steels
The American Iron and Steel Institute (AISI) defines carbon steel as follows:

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, semi-killed, or killed steel. Deoxidation practice and the steelmaking process will have an effect on the properties of the steel. However, variations in carbon have the greatest effect on mechanical properties, with increasing carbon content leading to increased hardness and strength. 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 steels. More than 85% of the steel produced and shipped in the United States is carbon steel.

Low-carbon steels contain up to 0.30% C. The largest category of this class of steel is flat-rolled products (sheet or strip), usually in the cold-rolled and annealed condition. The carbon content for these high-formability steels is very low, less than 0.10% C, with up to 0.4% Mn. Typical uses are in automobile body panels, tin plate, and wire products.

For rolled steel structural plates and sections, the carbon content may be increased to approximately 0.30%, with higher manganese content up to 1.5%. These materials may be used for stampings, forgings, seamless tubes, and boiler plate.

Medium-carbon steels are similar to low-carbon steels except that the carbon ranges from 0.30 to 0.60% and the manganese from 0.60 to 1.65%. Increasing the carbon content to approximately 0.5% with an accompanying increase in manganese allows medium carbon steels to be used in the quenched and tempered condition. The uses of medium carbon-manganese steels include shafts, axles, gears, crankshafts, couplings and forgings. Steels in the 0.40 to 0.60% C range are also used for rails, railway wheels and rail axles.

High-carbon steels contain from 0.60 to 1.00% C with manganese contents ranging from 0.30 to 0.90%. High-carbon steels are used for spring materials and high-strength wires.

Ultrahigh-carbon steels are experimental alloys containing 1.25 to 2.0% C. These steels are thermomechanically processed to produce microstructures that consist of ultrafine, equiaxed grains of spherical, discontinuous proeutectoid carbide particles.

High-Strength Low-Alloy Steels
High-strength low-alloy (HSLA) steels, or microalloyed steels, are designed to provide better mechanical properties and/or greater resistance to atmospheric corrosion than conventional carbon steels in the normal sense because they are designed to meet specific mechanical properties rather than a chemical composition.

The HSLA steels have low carbon contents (0.05-0.25% C) in order to produce adequate formability and weldability, and they have manganese contents up to 2.0%. Small quantities of chromium, nickel, molybdenum, copper, nitrogen, vanadium, niobium, titanium and zirconium are used in various combinations.

HSLA Classification:

* Weathering steels, designated to exhibit superior atmospheric corrosion resistance
* Control-rolled steels, hot rolled according to a predetermined rolling schedule, designed to develop a highly deformed austenite structure that will transform to a very fine    equiaxed ferrite structure on cooling
* Pearlite-reduced steels, strengthened by very fine-grain ferrite and precipitation hardening but with low carbon content and therefore little or no pearlite in the microstructure
* Microalloyed steels, with very small additions of such elements as niobium, vanadium, and/or titanium for refinement of grain size and/or precipitation hardening
* Acicular ferrite steel, very low carbon steels with sufficient hardenability to transform on cooling to a very fine high-strength acicular ferrite structure rather than the usual polygonal ferrite structure
* Dual-phase steels, processed to a micro-structure of ferrite containing small uniformly distributed regions of high-carbon martensite, resulting in a product with low yield strength and a high rate of work hardening, thus providing a high-strength steel of superior formability.

The various types of HSLA steels may also have small additions of calcium, rare earth elements, or zirconium for sulfide inclusion shape control.

Low-alloy Steels:
Low-alloy steels constitute a category of ferrous materials that exhibit mechanical properties superior to plain carbon steels as the result of additions of alloying elements such as nickel, chromium, and molybdenum. Total alloy content can range from 2.07% up to levels just below that of stainless steels, which contain a minimum of 10% Cr.

For many low-alloy steels, the primary function of the alloying elements is to increase hardenability in order to optimize mechanical properties and toughness after heat treatment. In some cases, however, alloy additions are used to reduce environmental degradation under certain specified service conditions.

As with steels in general, low-alloy steels can be classified according to:

* Chemical composition, such as nickel steels, nickel-chromium steels, molybdenum steels, chromium-molybdenum steels
* Heat treatment, such as quenched and tempered, normalized and tempered, annealed.

Because of the wide variety of chemical compositions possible and the fact that some steels are used in more than one heat-treated, condition, some overlap exists among the alloy steel classifications. In this article, four major groups of alloy steels are addressed: (1) low-carbon quenched and tempered (QT) steels, (2) medium-carbon ultrahigh-strength steels, (3) bearing steels, and (4) heat-resistant chromium-molybdenum steels.

Low-carbon quenched and tempered steels combine high yield strength (from 350 to 1035 MPa) and high tensile strength with good notch toughness, ductility, corrosion resistance, or weldability. The various steels have different combinations of these characteristics based on their intended applications. However, a few steels, such as HY-80 and HY-100, are covered by military specifications. The steels listed are used primarily as plate. Some of these steels, as well as other, similar steels, are produced as forgings or castings.

Medium-carbon ultrahigh-strength steels are structural steels with yield strengths that can exceed 1380 MPa. Many of these steels are covered by SAE/AISI designations or are proprietary compositions. Product forms include billet, bar, rod, forgings, sheet, tubing, and welding wire.

Bearing steels used for ball and roller bearing applications are comprised of low carbon (0.10 to 0.20% C) case-hardened steels and high carbon (-1.0% C) through-hardened steels. Many of these steels are covered by SAE/AISI designations.

Chromium-molybdenum heat-resistant steels contain 0.5 to 9% Cr and 0.5 to 1.0% Mo. The carbon content is usually below 0.2%. The chromium provides improved oxidation and corrosion resistance, and the molybdenum increases strength at elevated temperatures. They are generally supplied in the normalized and tempered, quenched and tempered or annealed condition. Chromium-molybdenum steels are widely used in the oil and gas industries and in fossil fuel and nuclear power plants.

So just using these two standards alone, one can see clearly the differences in defining various grades of steel...

This is from "Efunda's" website:

Steel is the common name for a large family of iron alloys which are easily malleable after the molten stage. Steels are commonly made from iron ore, coal, and limestone. When these raw materials are put into the blast furnace, the result is a "pig iron" which has a composition of iron, carbon, manganese, sulfur, phosphorus, and silicon.

As pig iron is hard and brittle, steelmakers must refine the material by purifying it and then adding other elements to strengthen the material. The steel is next deoxidized by a carbon and oxygen reaction. A strongly deoxidized steel is called "killed", and a lesser degrees of deoxodized steels are called "semikilled", "capped", and "rimmed".

Steels can either be cast directly to shape, or into ingots which are reheated and hot worked into a wrought shape by forging, extrusion, rolling, or other processes. Wrought steels are the most common engineering material used, and come in a variety of forms with different finishes and properties.

Standard Steels
According to the chemical compositions, standard steels can be classified into three major groups: carbon steels, alloy steels, and stainless steels:

Steels Compositions:

Carbon Steels: Alloying elements do not exceed these limits: 1% carbon, 0.6% copper, 1.65% manganese, 0.4% phosphorus, 0.6% silicon, and 0.05% sulfur.
Alloy Steels: Steels that exceed the element limits for carbon steels. Also includes steels that contain elements not found in carbon steels such as nickel, chromium (up to 3.99%), cobalt, etc.

Stainless Steels: Contains at least 10% chromium, with or without other elements. Based on the structures, stainless steels can be grouped into three grades:

Austenitic: Typically contains 18% chromium and 8% nickel and is widely known as 18-8. Nonmagnetic in annealed condition, this grade can only be hardened by cold working.

Ferritic: Contains very little nickel and either 17% chromium or 12% chromium with other elements such as aluminum or titanium. Always magnetic, this grade can be hardened only by cold working.

Martensitic: Typically contains 12% chromium and no nickel. This grade is magnetic and can be hardened by heat treatment.

Tool Steels:
Tool steels typically have excess carbides (carbon alloys) which make them hard and wear-resistant. Most tool steels are used in a heat-treated state, generally hardened and tempered.

There are a number of categories assigned by AISI (American Iron and Steel Institute), each with an identifying letter:

W:   Water-Hardening
S:   Shock-Resisting
O:   Cold-Work (Oil-Hardening)
A:   Cold-Work (Medium-Alloy, Air-Hardening)
D:   Cold-Work (High-Carbon, High-Chromium)
L:   Low-Alloy
F:   Carbon-Tungsten
P:   P1-P19:   Low-Carbon Mold Steels
    P20-P39:   Other Mold Steels
H:   H1-H19:   Chromium-Base Hot Work
    H20-H29:   Tungsten-Base Hot Work
    H40-H59:   Molybdenum-Base Hot Work
T:   High-Speed (Tungsten-Base)
M:   High-Speed (Molybdenum-Base)

http://www.efunda.com/materials/alloys/alloy_home/steels.cfm

Finally, this is from the Former Soviet Union:

Warning! The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.
Alloy Steel

steel that contains—in addition to iron, carbon, and unavoidable impurities—alloying elements, which are added to it to improve its machining or performance properties. Alloying elements are added to steel in various amounts and combinations (two, three, or more elements). Steel with up to 2.5 percent total alloying elements is called low-alloy steel; with 2.5–10.0 percent, medium-alloy steel; with more than 10 percent, high-alloy steel.

Alloy steels are classified according to structure or use. The following structural classes of alloy steel are distinguished:

(1) Steels of the pearlite class, which have the structure of pearlite or its variants (such as sorbite or troostite) or of pearlite with ferrite or hypereutectoid carbides.

(2) Steels of the martensite class, which are characterized by a reduced critical hardening rate and have a martensitic structure after normalizing.

(3) Steels of the austenite class, which have a sharply reduced austenite decomposition temperature, with austenite retained in the structure even at room temperature.

(4) Steels of the ferrite class, which contain elements that narrow the region of existence of austenite; such steels can retain the ferrite structure (sometimes together with carbides) at any temperature up to the melting point and after chilling at any rate.

(5) Steels of the carbide class contain an increased amount of carbon and carbide-forming elements; the structure of such steels is characterized by the presence of carbides (in the cast state, the ledeburite eutectic).

According to use, alloy steels are usually divided into structural steels, tool steels, and special-purpose steels (such as transformer, stainless, and high-temperature steels).

In the USSR, alloy steels are usually designated according to their chemical composition (for example, 18Kh2N4VA). The first number gives the average carbon content. For structural steel, the carbon content is given in hundredths of a percent; for tool steel, in tenths of a percent. The presence of alloying elements is given by the letter N for nickel, Kh for chromium, G for manganese, S for silicon, V for tungsten, F for vanadium, M for molybdenum, D for copper, K for cobalt, B for niobium, T for titanium, Iu for aluminum, R for boron, and A for nitrogen. The numbers after the letters indicate the approximate content of the corresponding element in percent. No number is given if the content of the element is about one percent or less. The letter A at the end of the designation indicates that the steel has a low sulfur and phosphorus content (that is, it is of high quality). The intended use of some steels is indicated by a letter. For example, R18 is high-speed steel with 18 percent tungsten, E3A is transformer steel with 3 percent silicon, and ShKh-15 is ball-bearing steel with 1.5 percent chromium. Some steels are designated by the letters EI or EP with a corresponding number (for example, EI69 or EP220); in most cases these are new steels undergoing testing and adoption in industry.

REFERENCES
Viaznikov, N. F. Legirovannaia stal’. Moscow, 1963.
Mes’kin, V. S. Osnovy legirovaniia stali, 2nd ed. Moscow, 1964.
Houdremont, E. Spetsial’nye stali, 2nd ed., vols. 1–2. Moscow, 1966. (Translated from German.)
Povolotskii, E. Ia., and A. K. Petrov. Proizvodstvo legirovannykh stalei. Moscow, 1967.

A. IA. STOMAKHIN

The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.

http://encyclopedia2.thefreedictionary.com/Alloy+Steel

In summary, it really depends on which standard one is referring to as well as what "neck of the woods" (Part of the world Giavonni. ;) ) one is from also as I only used three examples of many other examples out there in use or were used at one time. ;)

Respectfully,
Henry