Page 7 - Structural Steel Designers Handbook AISC, AASHTO, AISI, ASTM, and ASCE-07 Design Standards

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PROPERTIES OF STRUCTURAL STEELS AND EFFECTS OF STEELMAKING AND FABRICATION

STRUCTURAL STEELS, STEELMAKING, AND FABRICATION 1.5

For methods of estimating the atmospheric corrosion resistance of low-alloy steels based on their
chemical composition, see ASTM Guide G101. The A588 specification requires that the resistance
index calculated according to Guide 101 shall be 6.0 or higher.
A588 and A242 steels are called weathering steels because, when subjected to alternate wetting
and drying in most bold atmospheric exposures, they develop a tight oxide layer that substantially
inhibits further corrosion. They are often used bare (unpainted) where the oxide finish that develops
is desired for aesthetic reasons or for economy in maintenance. Bridges and exposed building fram-
ing are typical examples of such applications. Designers should investigate potential applications
thoroughly, however, to determine whether a weathering steel will be suitable. Information on bare-
steel applications is available from steel producers.
A572 specifies columbium-vanadium HSLA steels in five grades with minimum yield points of
42 to 65 ksi. Grade 42 in thicknesses up to 6 in and Grade 50 in thicknesses up to 4 in are used for
welded bridges. All grades may be used for bolted construction and for welded construction in most
applications other than bridges.
A992 steel, introduced in 1998, is now the main specification for rolled wide flange shapes for
building framing. All other hot-rolled shapes, such as channels and angles, can be furnished to A992.
It provides a minimum yield point of 50 ksi, a maximum yield point of 65 ksi, and a maximum yield
to tensile ratio of 0.85. These maximum limits are considered desirable attributes, particularly for
seismic design. To enhance weldability, a maximum carbon equivalent is also included, equal to
0.47% or 0.45%, depending on thickness. A supplemental requirement can be specified for an aver-
age Charpy V-notch toughness of 40 ft⋅lb at 70°F.

1.1.3 Heat-Treated Carbon and HSLA Steels

Both carbon and HSLA steels can be heat treated to provide yield points in the range of 50 to 75 ksi.
This provides an intermediate strength level between the as-rolled HSLA steels and the heat-treated
constructional alloy steels.
A633 is a normalized HSLA plate steel for applications where improved notch toughness is
desired. Available in four grades with different chemical compositions, the minimum yield point
ranges from 42 to 60 ksi depending on grade and thickness.
A678 includes quenched-and-tempered plate steels (both carbon and HSLA compositions) with
excellent notch toughness. It is also available in four grades with different chemical compositions;
the minimum yield point ranges from 50 to 75 ksi, depending on grade and thickness.
A852 is a quenched-and-tempered HSLA plate steel of the weathering type. It is intended for
welded bridges and buildings and similar applications where weight savings, durability, and good
notch toughness are important. It provides a minimum yield point of 70 ksi in thickness up to 4 in.
The resistance to atmospheric corrosion is typically four times that of carbon steel.
A913 is a high-strength low-allow steel for structural shapes, produced by the quenching and self-
tempering (QST) process. It is intended for the construction of buildings, bridges, and other struc-
tures. Four grades provide a minimum yield point of 50 to 70 ksi. Maximum carbon equivalents to
enhance weldability are included as follows: Grade 50, 0.38%; Grade 60, 0.40%; Grade 65, 0.43%;
and Grade 70, 0.45%. Also, the steel must provide an average Charpy V-notch toughness of 40 ft ⋅
lb at 70°F.

1.1.4 Heat-Treated Constructional Alloy Steels

Steels that contain alloying elements in excess of the limits for carbon steel and are heat treated to
obtain a combination of high strength and toughness are termed constructional alloy steels. Having
a yield strength of 100 ksi, these are the strongest steels in general structural use.
A514 includes several grades of quenched and tempered steels, to permit use of various compo-
sitions developed by producers to obtain the specified strengths. Maximum thickness ranges from
1
1
1 / 4 to 6 in depending on the grade. Minimum yield strength for plate thicknesses over 2 / 2 in is 90 ksi.

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