Home
/ Sheet / Coated
Sheet / GALVALUME® / Application
Considerations
Coated Sheet
GALVALUME® Sheet
Application Considerations
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.
Typical Ranges of
Mechanical Properties* |
| Designation |
Yield
Strength |
Elongation
in 2 inches, % |
R
Value |
N
Value |
| Ksi
|
MPa |
|
CS Type B
|
35/50
|
245/410
|
>/ = 20
|
A
|
A
|
|
FS
|
25/40
|
170/275
|
>/ = 24
|
1.0/1.4
|
0.16/0.20
|
|
DS
|
20/35
|
140/240
|
>/ = 30
|
1.3/1.7
|
0.18/0.22
|
|
HTS
|
30/65
|
205/450
|
>/ = 15
|
A
|
A
|
*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.
Structural Steel
Mechanical Property Requirements |
| Grade |
Yield
Strength
Minimum, ksi |
Tensile
Strength
Minimum, ksi |
Elongation
in 2 inches, % |
|
33
|
33
|
45
|
20
|
|
37
|
37
|
52
|
18
|
|
40
|
40
|
55
|
16
|
|
50 Class 1
|
50
|
65
|
12
|
|
50 Class 2
|
50
|
. . . . . .
|
12
|
|
80A
|
80B
|
82
|
. . . . . .
|
Where an ellipses (. . . . . ) appears in
the table, there is no requirement.
A - For sheet thickness 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.
Coating Thickness
Coating thickness (measured as ounces of coating per square foot, total both sides) is an
important factor in the effective application of GALVALUMEŽ 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. 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. |
 |
Regular Spangle
GALVALUME® Sheet |
|
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, GALVALUMEŽ 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 GALVALUMEŽ sheet.
When GALVALUMEŽ 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 GALVALUMEŽ coating for long periods after it is exposed to the
atmosphere (e.g. when used for roofing). Ordering GALVALUMEŽ sheet with a chemical
treatment is highly recommended for GALVALUMEŽ sheet that will be used unpainted.
Oil
Instead of chemical treatment, GALVALUMEŽ 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 GALVALUMEŽ 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 GALVALUMEŽ 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, ACRYLUMEŽ sheet that provides sufficient surface
lubricity to rollform without oil. For most rollforming applications, ACRYLUMEŽ sheet
is the preferred product.
Chemical Treatment and Oil
GALVALUMEŽ 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
GALVALUMEŽ sheet is shipped "dry" if neither chemical treatment nor oil is compatible with
the customer's requirements. Untreated GALVALUMEŽ surfaces are very susceptible to
humid-storage stain from moisture intrusion or condensation during shipment or
storage. GALVALUMEŽ sheet that is ordered "dry" must be transported and stored with
special precautions to preserve low-humidity conditions.
Because GALVALUMEŽ 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.
|
