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| Properties of the Base Steel |
U. S. Steel GALVALUME® Sheet is available in five
designations that provide different levels of formability and
strength to the base sheet.
- Commercial Steel
(CS)
- Forming Steel
(FS)
- Drawing Steel
(DS)
- High Temperature
Steel (HTS)
- Structural Steel
(SS)
These designations
are defined in ASTM Specification A792. The following two tables
provide details about the strength levels and formability
attributes for these designations as presented in ASTM
A792.
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Typical Ranges of
Mechanical Properties*
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Designation
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Yield
Strength
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Elongation
in 2 inches, %
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R
Value
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N
Value
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CS Type B
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>/=20
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A
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A
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FS
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>/=24
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1.0/1.4
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0.16/0.20
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DS
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>/=30
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1.3/1.7
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0.18/0.22
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HTS
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>/=15
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A
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A
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*The typical
mechanical property values presented in this table are nonmandatory. They are intended to provide the purchaser with as
much information as possible to make an informed decision on the
steel to be specified. Values outside of these ranges may
occur.
A - No typical
properties have been established.
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Structural Steel
Mechanical Property Requirements
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Grade
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Yield
Strength
Minimum, ksi
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Tensile
Strength
Minimum, ksi
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Elongation
In 2 inches, Min.
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33
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33
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45
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20
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37
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37
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52
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18
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40
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40
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55
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16
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50 Class1
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50
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65
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12
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50 Class 2
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50
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......
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12
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80A
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80B
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82
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......
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Where an ellipses (...) appears in the table, there is no
requirement.
A - For sheet thicknesses of 0.028 inches and thinner, no
tension test is required if the hardness result is Rockwell B 85 or
higher.
B - As there is no discontinuous yield curve, the yield
strength should be taken as the stress at 0.5% elongation under
load or 0.2% offset.
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Coating Thickness
Coating thickness (measured as ounces of coating per square
foot, total both sides) is an important factor in the effective
application of GALVALUME®
sheet. The most common coating weights
being used today are AZ50 and AZ55. These designations require that
the product have 0.50 oz/sq.ft, triple-spot average - total both
sides, and 0.55 oz/sq.ft, triple-spot average - total both sides,
respectively. Details about the total requirements for these two
designations are contained in ASTM Specification A792. In
applications where formability is an important consideration, AZ50
is recommended for maximum coating adhesion. Where corrosion
resistance is the prime factor, AZ55 is recommended. Other coating
weights can be produced but the specific applications should be
discussed thoroughly with U. S. Steel Technical Service
Representatives to optimize fabric ability and corrosion
resistance.
Surface Finish
GALVALUME® sheet, as produced, exhibits a small, spangled
finish.
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This finish is termed Regular Spangle. The spangle,
or grain, size varies from very small to as large as about 3/8 inch in diameter. For many
applications, this attractive, bright, faceted finish is desired.
From a distance, the sheet exhibits a uniform, reflective
appearance. When the product is intended to be painted, it is often
desirable to order an Extra Smooth finish. The process used to
provide the Extra Smooth finish, temper rolling, imparts a smoother
surface from the standpoint of surface relief; however, the surface
develops a matte appearance and therefore, is less reflective than
the spangled finish.
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Regular Spangle
GALVALUME® Sheet
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Surface Treatment
U. S. Steel
GALVALUME® Sheet can be specified with four variations of
surface treatment:
- Chemical
treatment
- Oil
- Chemical treatment
and oil
- Dry
 Chemical Treatment
When a "Chemical treatment" is specified,
a thin, relatively invisible, corrosion-inhibiting film is applied
at the exit end of the coating line. This film is applied by spraying an aqueous solution of
corrosion-inhibiting chemicals onto the sheet surface. Excess solution is removed by
squeegee rolls located after the application section. After the
squeegee rolls, the strip enters into a small drying oven to remove
the excess water.
Like galvanized sheet, GALVALUME® sheet is susceptible to humid-storage
staining when tightly wrapped coils or lifts get wet through water
intrusion or condensation. Instead of the "white rust" that occurs
on galvanized coatings, humid-storage staining forms a dark gray
surface discoloration on GALVALUME® sheet.
When GALVALUME® sheet is ordered with a chemical treatment,
the coating is much more resistant to humid-storage staining than
an untreated surface. The chemical treatment is particularly
effective in deterring premature darkening and retaining the bright
metallic luster of the GALVALUME® coating for long periods after it is exposed
to the atmosphere (e.g. when used for roofing). Ordering
GALVALUME®
sheet with a chemical treatment is highly recommended for
GALVALUME®
sheet that will be used unpainted.
Oil
Instead of chemical treatment, GALVALUME® sheet can be
ordered with "oil" to minimize the tendency for humid-storage
stain. A thin coat of rust-preventive oil applied at the mill
prevents staining in coils and lifts during transit and short-term
high-humidity storage. Oil is not intended to delay darkening of
the lustrous GALVALUME® surface upon use. It is generally less
effective than a chemical treatment to prevent humid-storage
staining.
 Oil is very effective for preventing roll pickup in
rollforming operations. The usual type of oil applied to
GALVALUME® sheet is a "vanishing" oil. Vanishing oils contain
solvents that evaporate when exposed to air. This helps to minimize
problems associated with handling oiled sheets.
The presence of oil on the sheet can cause the surface to be
slippery. Caution should be exercised when handling or walking on
the sheet.
In the recent past, U. S. Steel has developed a product, ACRYLUME®
sheet that provides sufficient
surface lubricity to rollform without oil. For most rollforming
applications, ACRYLUME® sheet is the preferred product.
Chemical
Treatment and Oil
GALVALUME® sheet is often ordered with a chemical
treatment plus oil. The chemical treatment provides very good
protection against humid-storage staining, while the oil provides
lubricity for operations such as roll-forming. Application of oil
over the chemical treatment generally does not significantly
improve the resistance to humid-storage staining.
Dry
 GALVALUME® sheet is shipped "dry" if neither
chemical treatment nor oil is compatible with the customer's
requirements. Untreated GALVALUME® surfaces are very
susceptible to humid-storage stain from moisture intrusion or
condensation during shipment or storage. GALVALUME® sheet that
is ordered "dry" must be transported and stored with special
precautions to preserve low-humidity conditions.
Because GALVALUME® sheet that is chemically treated can be
painted (this is not true for galvanized sheet except when special
chemical treatments are applied on both the hot-dip coating line
and the coil paint line), there is very little reason to order the
product "dry". The tendency for "dry" product to develop storage
staining is very high.
ACRYLUME® is a registered trademark of United
States Steel.
GALVALUME® is a
registered trademark of BIEC International, Inc.
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