There are two types of embrittlement that are of concern
to a fabricator. They are discussed in detail in ASTM A‑143‑74 "Standard
Recommended Practice for Safeguarding Against Embrittlement of Hot‑
Dip Galvanized Structural Steel Products and Procedure for Detecting
Embrittlement." The following is a summary from that specification
of the most common concerns.
Hydrogen
Embrittlement
ASTM
A143, Sec. 3.2 "Hydrogen embrittlement may also occur due to
the possibility of atomic hydrogen being absorbed by the steel.
The susceptibility to hydrogen embrittlement is influenced by the
type of steel, it's previous heat treatment, and degree of previous
cold work. In the case of galvanized steel, the acid pickling reaction
prior to galvanizing presents a potential source of hydrogen. In
practice hydrogen embrittlement of galvanized steel is usually of
concern only if the steel exceeds approximately 150 ksi (1000 MPa)
in ultimate tensile strength, or if it has been severely cold worked
prior to pickling." (The same potential problem exists if high
strength material is electro‑plated as this process uses the same
acid pickling procedure.)
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Accelerated
Strain-age Embrittlement
When
steel is cold bent or cold worked, a process called "Strain‑Age
Embrittlement" commences immediately. The steel's crystal structure
begins to reorganize, and with time, the cold worked area becomes
increasingly brittle and the fracture toughness is decreased. This
process is sped up if the ambient temperature increases, as it does
with galvanizing, and is called "Accelerated Strain‑Age Embrittlement."
Note that the prevention of strain‑age embrittlement is dictated
by proper design and fabrication, regardless of whether or not the
material will be galvanized. Galvanizing does not cause strain‑age
embrittlement.
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Responsibility
For Avoiding Embrittlement
ASTM
A143, Sec. 7.1 "Design of the product and selection of the
proper steel for it's suitability to be fabricated and to withstand
normal galvanizing operations without embrittlement is the responsibility
of the designer and fabricator."
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FORMABILITY
Cold Forming
Plates
and bars of all CSA G40.21M grades can be satisfactorily formed
on a press brake or other conventional cold bending equipment. There
is a considerable difference in the formability of the different
grades due to the strength level and chemical composition differences;
because of this, care must be exercised when forming is required.
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