Page 189 - Handbook of Structural Steel Connection Design and Details
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Welded Joint Design and Production
174 Chapter Three
circumstances, it is advisable to proceed with caution, reviewing the
principles outlined in this chapter, and, when necessary, to contact a
welding engineer with expertise in metallurgy to address the
specifics of the situation.
For most applications, however, modern welding codes such as the
American Welding Society’s AWS D1.1 Structural Welding Code—Steel
and the American Institute of Steel Construction’s Steel Construction
Manual list weldable steels suitable for construction. These materials
have a long history of satisfactory performance, and the codes supply
appropriate guidelines as to what precautions or techniques are appro-
priate for certain materials. For example, AWS D1.1 lists “prequalified
steels” that may be used in conjunction with a prequalified welding
procedure. The code requirements for the fabrication of these steels are
sufficiently justified that the contractor is not required to qualify the
welding procedures by test when using this particular material, provided
that all the other prequalified requirements were met.
Codes, however, do not necessarily include new developments from
the steel producers. An inevitable characteristic of codes is that they
will always lag behind industry. Once a particular steel has an accept-
able history of performance, it may be incorporated into the applicable
specifications. Until that time, the engineer must rely upon research
data to determine the suitability of the part for a specific application.
A variety of tests have been devised over the years, each capable of
measuring specific aspects of the weldability of the material under
different conditions. Some tests measure the heat-affected zone prop-
erties, whereas others are more sensitive to weld-metal cracking ten-
dencies. Unproven materials should be carefully reviewed by a com-
petent engineer before being used in actual applications, and actual
consideration of approximate weldability tests is recommended.
Listed in the following section are typical steels that are used for
welded construction today.
3.1.2 Modern base metals for welding
The carbon steels. Classification of the carbon steels is based principally
on carbon content. The groups are low carbon (to 0.30% carbon), medium
carbon (0.30 to 0.45%), and high carbon (more than 0.45%). Mechanical
properties of hot finished steels are influenced principally by chemical
composition (particularly carbon content), but other factors—finishing
temperature, section size, and the presence of residual elements—also
3
affect properties. A ⁄4-in plate, for example, has higher tensile properties
and lower elongation than a 1 ⁄2-in plate of the same composition, resulting
1
3
primarily from the higher rate of cooling of the ⁄ 4 -in plate from the rolling
temperature. Medium- and high-carbon steels are not typically used for
structural operations and therefore will not be discussed further.
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