Page 191 - Handbook of Structural Steel Connection Design and Details

Welded Joint Design and Production

176 Chapter Three

Minimum mechanical properties available in the as-rolled condition
vary among the grades and, within most grades, with thickness.
Ranges of properties available in this group of steels are

1. Minimum yield point from 42,000 to 70,000 psi
2. Minimum tensile strength from 60,000 to 85,000 psi
3. Resistance to corrosion, classified as: equal to that of carbon steels,
twice that of carbon steels, or 4 to 6 times that of carbon steels

The high-strength–low-alloy steels should not be confused with the
high-strength quenched and tempered alloy steels. Both groups are
sold primarily on a trade name basis, and they frequently share the
same trade name, with different letters or numbers being used to
identify each. The quenched and tempered steels are full-alloy steels
that are heat-treated at the mill to develop optimum properties. They
are generally martensitic in structure, whereas the HSLA steels are
mainly ferritic steels; this is the clue to the metallurgical and fabri-
cating differences between the two types. In the as-rolled condition,
ferritic steels are composed of relatively soft, ductile constituents;
martensitic steels have hard, brittle constituents that require heat
treatment to produce their high-strength properties.
Strength in the HSLA steels is achieved instead by relatively small
amounts of alloying elements dissolved in a ferritic structure. Carbon
content rarely exceeds 0.28% and is usually between 0.15 and 0.22%.
Manganese content ranges from 0.85 to 1.60%, depending on grade,
and other alloy additions—chromium, nickel, silicon, phosphorus, cop-
per, vanadium, columbium, and nitrogen—are used in amounts of less
than 1%. Welding, forming, and machining characteristics of most
grades do not differ markedly from those of the low-carbon steels.
To be weldable, the high-strength steels must have enough ductility
to avoid cracking from rapid cooling. Weldable HSLA steels must be suf-
ficiently low in carbon, manganese, and all “deep-hardening” elements
to ensure that appreciable amounts of martensite are not formed upon
rapid cooling. Superior strength is provided by solution of the alloying
elements in the ferrite of the as-rolled steel. Corrosion resistance is also
increased in certain of the HSLA steels by the alloying additions.
ASTM specifications. Thirteen ASTM specifications cover the plain-
carbon, high-strength–low-alloy, and quenched and tempered struc-
tural steels. All of the following steels, except those noted, are pre-
qualified according to D1.1-98:

ASTM A36: Covers carbon steel shapes, plates, and bars of struc-
tural quality for use in bolted or welded construction of bridges and
buildings and for general structural purposes. Strength requirements

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