CEMP-E
TI 809-26
1 March 2000
AISC in developing design methodologies.
(1) ASTM A572, grade 50, manufactured to the supplemental requirements of AISC Technical
Bulletin #3, provides a requirement for a maximum Fy:Fu ratio of 0.85. This same value is a requirement
for ASTM A992 steels. Although not considered critical in low-seismic applications, this requirement is
advisable for members in the lateral load resisting systems in high-seismic applications.
(2) Structural steels providing this maximum Fy:Fu ratio are readily available from mill sources.
Such a requirement can be met by special mill order requirements, the specification of A572, grade 50
meeting AISC Technical Bulletin #3, the specification of A992 shapes, or through the review of mill test
reports of existing steels in inventory that are traceable to the mill heat number. There is currently no
premium in steel mill cost to specify such properties, but some minor delays may be encountered in
purchasing until the inventory of such materials is predominant.
b. Killed Steel. Killed steel has been processed to remove or bind the oxygen that saturates the
molten steel prior to solidification. ASTM A6 / A6M defines killed steel as "steel deoxidized, either by
addition of strong deoxidizing agents or by vacuum treatment, to reduce the oxygen content to such a
level that no reaction occurs between carbon and oxygen during solidification." Semi-killed steel is
incompletely deoxidized, and may also be specified.
(1) The benefit of killing is to reduce the number of gas pockets present in the steel, which can
adversely affect the mechanical properties of the steel, including ductility and toughness, as well as
reduce the number of oxide-type inclusions in the steel.
(2) Most mills provide some form of deoxidation, in the form of semi-killed steel, as a part of
routine production practices. AISC does not require killed steel for any specific applications.
(3) Most commonly, killing is done using additions of silicon, but may also be done with aluminum
or manganese. Killed steels often have silicon levels in the range of 0.10% to 0.30%, but may be higher.
(4) Project requirements for killed steel should be considered when using wide-flange sections in
Groups 4 or 5, and plates when over 50 mm (2 inches) in thickness, in tension applications, which have
special AISC requirements for toughness in AISC Specification section A3.1c. ASTM A992 requires the
steel to be killed.
(5) Specifying killed or semi-killed steel may carry a slight cost premium, except in the case of
A992 steel. Because killed steel is typically a cost-premium mill order item, the inventory of killed
structural steels available at steel service centers and in steel fabricating plants is less than that of
regular steels. Mill orders typically require longer production lead times than service center or stock
items.
c. Fine Grain Practice. Fine grain practice is the method of achieving Fine Austenitic Grain Size,
defined by ASTM A6 / A6M as grain size number 5 or higher, measured using test methods prescribed
by ASTM E112. Aluminum is typically used to achieve fine grain practice, which binds oxygen and
nitrogen. When aluminum content is above 0.20%, by heat analysis, the steel is considered fine-grained,
without the need for testing.
(1) Fine grain practice is beneficial in improving ductility and toughness. Consideration of
requirements for fine grain practice should be made when using wide-flange sections in Groups 4 or 5,
and plates when over 50 mm (2 inches) in thickness, in tension applications, which have special AISC
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