CEMP-E
TI 809-26
1 March 2000
requirements for toughness in AISC Specification section A3.1c. When specifying steel to fine grain
practice, ASTM Supplementary Requirement S91 should be consulted for the specific steel grade.
(2) Because fine grain practice is typically a cost-premium mill order item, the inventory of
structural steels available at steel service centers and in steel fabricating plants manufactured to fine
grain practice is less than that of regular structural steel. Mill orders typically require longer production
lead times than service center or stock items.
d. Toughness. Steel toughness, also commonly referred to as "notch toughness", is the resistance to
brittle crack initiation and propagation. For this resistance, the steel must have sufficient plastic ductility
to redistribute stresses at the root of a notch to the surrounding material. Toughness may be measured
using a variety of methods, but the steel industry standard is the Charpy V-Notch (CVN) method, as
prescribed by ASTM A370. CVN testing is an added charge by the steel producer, and steel with CVN
testing is not routinely ordered by steel service centers or steel fabricators for inventory. Therefore,
steels with CVN testing are generally available only through mill order, which typically requires longer
production lead times than service center or stock items.
e. Improved Through-thickness Properties. For certain high-restraint applications subject to the risk of
lamellar tearing, steels with improved through-thickness properties may be specified. The most common
method of improving through-thickness properties, to reduce the risk of lamellar tearing, is through the
specification of low-sulfur or controlled sulfur-inclusion steels. By reducing the sulfur content, the number
and size of manganese sulfide (MnS) inclusions is reduced. Typically, low-sulfur steels in plate form can
be ordered to 0.005% sulfur, at a cost premium and with longer lead time. Most steel specifications
permit maximum sulfur in amounts between 0.30% to 0.50%. Shapes are not routinely available with
substantially reduced sulfur levels, and would be available only at substantial cost premium and
considerable delay. However, a mill may be able to select heats of steel with particularly lower levels of
sulfur for rolling specific sections. It is also possible to specify through-thickness tensile testing using
reduction of area as the governing criteria, but this is rarely necessary.
f. Normalizing. Normalizing is defined in ASTM A6 / A6M as "a heat treating process in which a steel
plate is reheated to a uniform temperature above the critical temperature and then cooled in air to below
the transformation range." In practice, steel is heated to approximately 900oC to 930oC (1650oF to
toughness. Few building applications warrant the need for normalized steel. The specification of
normalized steel is a mill order item only, an added expense with added time for delivery from the steel
mill. Normalized steel is not routinely available from steel service centers or stocked by fabricators.
4. SELECTION OF STRUCTURAL STEELS FOR ENVIRONMENTAL EXPOSURE AND SERVICE
APPLICATIONS.
a. High-seismic Applications. The AISC Seismic Provisions, Section 6.3, require steel in the Seismic
Force Resisting System to have a minimum toughness of 27J at 21oC (20 ft.-lb. at 70oF), applicable to
ASTM Group 4 and 5 shapes, Group 3 shapes with flanges 38 mm (1-1/2 in.) or thicker, and to plates in
built-up members 38 mm (1-1/2 in.) or thicker. Studies indicate that a large percentage of domestically
produced structural steel sections lighter or thinner than those mentioned in the previous paragraph will
have a CVN toughness of at least 27J at 21oC (20 ft.-lb. at 70oF), and therefore it does not appear that
CVN testing need be conducted to verify the toughness of all members. It is recommended that
manufacturer's accumulated data be used to verify that the steel routinely produced by that mill meets
the indicated toughness levels. Specification of steel toughness levels, or the specification of A709
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