General Metal Information Part-2

Weight
Lbs. per Square Foot

.25000
.26562
.28125
.31250
.34375
.39500

STANDARD AISI and SAE STEELS

Studies have been made in the steel industry for the purpose of establishing certain “standard” steels and eliminating as much as possible the manufacture of other steels which vary only slightly in composition from the standard steels, These standard steels are selected on the basis of serving the significant metallurgical and engineering needs of fabricators and users of steel products.

STANDARD CARBON STEELS

Definition. By common custom. steel is considered to be carbon steel when no minimum content is specified or required for aluminum, boron. chromium, cobalt, columbium, molybdenum. nickel, titanium, tungsten, vanadium or zirconium, or for any other element 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.

Numbering System. In the AISI system of identification. the prefix “B” is used to designate acid bessemer steel. The letter “L’’ within the grade number is used to identify leaded steels.

A four-numeral series is used to designate graduations of chemical composition of carbon steel. The last two numbers of which are intended to indicate the approximate middle of the carbon range. For example, in the grade designation 1035, 35 represents a carbon range of 0.32 to 0.38 per cent.

It is necessary, however. to deviate from this rule and to Interpolate numbers in the case of some carbon ranges and for variations in manganese, phosphorus or sulphur with the same carbon range.

The first two digits of the four-numeral series of the various grades of carbon steel and their meanings are as follows:
10xx Nonresulphurized carbon steel grades
11xx Resulphurized carbon steel grades
12xx Rephosphorized and resulphurized carbon steel grades
I5xx Nonresulphurized high manganese carbon steels.

STANDARD ALLOY STEELS

Definition. Steel is considered to be alloy steel when the maximum of the range given for the content of alloying elements exceeds one or more of the following limits: manganese, 1.65 per cent; silicon, 0.60 per cent; copper, 0.60 per cent; or in which a definite range or a 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 per cent, cobalt, columbium, molybdenum, nickel, titanium, tungsten, vanadium, zirconium or any other alloying element added to obtain a desired alloying effect.

Numbering System. In the AISI numbering system, the prefix letter E is used to designate steels normally made only by the basic electric furnace process. Steels without a prefix letter are normally manufactured by the basic open hearth or basic oxygen processes, but may be manufactured by the basic electric furnace process with adjustments in phosphorus and sulphur limits.

The last two digits of the four-numeral series are intended to indicate the approximate middle of the carbon range. For example, in the grade designation 4142, 42 represents a carbon range of 0.40 to 0.45 per cent. (Where a five-numeral series occurs, the last three digits indicate the carbon content.) It is necessary, however, to deviate from this rule and to interpolate numbers in the case of some carbon ranges, and for variations in manganese, sulphur, chromium, or other elements.

The first two digits indicate the type of alloy according to alloying elements as follows:
13xx Manganese 1.75 per cent
40xx Molybdenum 0.20 or 0.25 per cent
41xx Chromium 0.50, 0.80 or 0.95 per cent — Molybdenum 0.12, 0.20 or 0.30 per cent
43xx Nickel 1.83 per cent — Chromium 0.50 or 0.80 per cent — Molybdenum 0.25 per cent
44xx Molybdenum 0.53 per cent
46xx Nickel 0.85 or 1.83 per cent — Molybdenum 0.20 or 0.25 per cent
47xx Nickel 1.05 per cent Chromium 0.45 per cent
48xx Nickel 3.50 per cent Molybdenum 0.25 per cent
50xx Chromium 0.40 per cent
51xx Chromium 0.80, 0.88, 0.93, 0.95 or 1.00 per cent
5xxxx Carbon 1.04 per cent -- chromium 1.03 or 1.45 per cent
61xx Chromium 0.60 or 0.95 per cent -- Vanadium 0.13 per cent or 0.15 per cent min.
86xx Nickel 0.55 per cent --Chromium 0.50 per cent-- Molybdenum 0.25 per cent
87xx Nickel 0.55 per cent -- Chromium 0.50 per cent -- Molybdenum 0.35
88xx Nickel 0.55 per cent --Chromium 0.50 per cent -- Molybdenum 0.35
92xx Silicon 2.00 per cent

EFFECTS OF COMMON
ALLOYING ELEMENTS IN STEEL

By definition, steel is a combination of iron and carbon. Steel is alloyed with various elements to improve physical properties and to produce special properties, such as resistance to corrosion or heat. Specific effects of the addition of such elements are outlined below:

Carbon (C), although not usually considered as an alloying element, is the most important constituent of steel. It raises tensile strength, hardness and resistance to wear and abrasion. It lowers ductility, toughness and machinability.

Manganese (Mn) is a deoxidizer and degasifier and reacts with sulphur to improve forgeability. It increases tensile strength, hardness, hardenability and resistance to wear. It decreases tendency toward scaling and distortion. It increases the rate of carbon-penetration in carburizing.

Phosphorus (P) increases strength and hardness and improves machinability. However, it adds marked brittleness or cold-shortness to steel.

Sulphur (S) Improves machinability in free-cutting steels, but without sufficient manganese it produces brittleness at red heat. It decreases weldability, impact toughness and ductility.

Silicon (Si) is a deoxidizer and degasifier. It increases tensile and yield strength, hardness, forgeability and magnetic permeability.

Chromium (Cr) increases tensile strength, hardness, hardenability. toughness, resistance to wear and abrasion. resistance to corrosion and scaling at elevated temperatures.

Nickel (Ni) increases strength and hardness without sacrificing ductility and toughness. It also increases resistance to corrosion and scaling at elevated temperatures when introduced in suitable quantities in high chromium (stainless) steels.

Molybdenum (Mo) increases strength, hardness, hardenability and toughness, as well as creep resistance and strength at elevated temperatures. It improves machinability and resistance to corrosion and it intensifies the effects of other alloying elements. In hot-work steels, it increases red-hardness properties.

Tungsten (W) increases strength, hardness and toughness. Tungsten steels have superior hot-working and greater cutting efficiency at elevated temperatures.

Vanadium (V) increases strength, hardness and resistance to shock impact. It retards grain growth, permitting higher quenching temperatures. It also enhances the red hardness properties of high speed metal cutting tools and intensifies the individual effects of other major elements.

Cobalt (Co) Increases strength and hardness and permits higher quenching temperatures. It also intensifies the individual effects of other major elements in more complex steels.

Aluminum (Al) is a deoxidizer and degasifier. It retards grain growth and is used to control austenitic grain size. In nitriding steels it aids in producing a uniformly hard and strong nitrided case when used in amounts 1.00% - 1.25%.

Lead (Pb), while not strictly an alloying element, is added to improve machining characteristics. It is almost completely insoluble in steel, and minute lead particles, well dispersed, reduce friction where the cutting edge contacts the work. Addition of lead also improves chip-breaking formations.