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Application Considerations

Properties of the Base Steel
U. S. Steel Electrogalvanized Sheet is processed to provide sheet that possesses differing degrees of formability and strength. The names of these designations are:

• Commercial Steel Type B (CS Type B)
• Drawing Steel Type B (DS Type B)
• Deep Drawing Steel (DDS)
• Extra Deep Drawing Steel (EDDS)
• Dent Resistant BH Steel

The chemical composition ranges and typical mechanical properties associated with the first four designations are presented in the following table.

Notes:
Where an ellipsis (...) appears in the table, there is no requirement but the analysis result shall be reported.

^A The sum of copper, nickel, chromium, and molybdenum shall not exceed 0.50% on heat analysis. When one or more of these elements is specified by the purchaser, the sum does not apply; in which case, only the individual limits on the remaining elements shall apply.

^B Chromium is permitted, at the producer's option, to 0.25% maximum when the carbon content is less than or equal to 0.05%. In such cases the limit on the sum of the four elements in note A does not apply.

^C When copper steel is specified the copper limit is a minimum requirement. When copper steel is not specified the copper limit is a maximum requirement.

^D CS Type B describes the most common product previously described in ASTM A366/A366M

^E When an aluminum deoxidized steel is required for the application, Commercial Steel (CS) may be ordered to a minimum of 0.01% total aluminum.

^F May be furnished as a vacuum degassed and/or chemically stabilized steel at the producer's option.

^G For carbon levels less than or equal to 0.02%, columbium and/or titanium may be used as stabilizing elements at the producer's option. In such cases, the applicable limit for columbium shall be 0.10% max. and the limit on titanium shall be 0.15% max.

^H Shall be furnished as a vacuum degassed steel, and stabilized steel.

^F No typical properties have been established.

As these data show, the major differences are related to increasing degrees of formability from CS through EDDS. As is typical for steel, the yield strength decreases as the level of formability increases. Thus, EDDS can be used to make a part that involves very deep drawing. At the same time, however, the strength of the part may be quite low. (The amount of work hardening associated with deep drawing imparts an increased strength in the areas that are cold worked substantially.) The low initial yield strength of EDDS makes this product very susceptible to damage by denting prior to being formed.

• U. S. Steel Dent Resistant BH Steels include a series of steels that offer a unique combination of as-received formability and final properties after fabrication. These steels have excellent formability and yet they exhibit significantly higher yield strength and superior dent resistance after parts are manufactured. Dent Resistant sheet gains strength from work-hardening during fabrication and from carbon-aging during a subsequent thermal cycle, such as paint-baking. The term BH indicates that these steels are bake-hardenable.

The BH steels that are produced by U. S. Steel include the following designations:

• Dent Resistant BH 25
• Dent Resistant BH 29
• Dent Resistant BH 33
• Dent Resistant BH 36
• Dent Resistant BH 40
• Dent Resistant BH 45

The terminology for the Dent Resistant steels includes the minimal yield strength of the product as produced in our mill. For example, BH 29 means that the yield strength is nominally 29 ksi as produced. The products are manufactured so that, after straining a small amount and then baked at a temperature of about 350°F, the yield strength increases about 10 ksi in the final formed part.

ASTM Requirements
U. S. Steel Electrogalvanized Sheet is produced to the general requirements of ASTM Specifications A568 and A917. A568 is the reference specification for steel tolerances with respect to thickness, width, etc. while A917 covers the general requirements that pertain to the electroplated coating. The dimensional tolerance requirements are the same as those for cold rolled sheet. The reason for this reference is that the product is manufactured identically to cold rolled sheet except that the steel sheet is processed through an electroplating line as a final processing step, an operation that has very little influence on the final product attributes regarding dimensional tolerances and mechanical properties.

Coating Thickness
Coating thickness (measured as coating weight from 10 to 100 grams per square meter per side) is an important factor in the effective application of electrogalvanized sheet. The coating weight that is needed for a specific application depends on the objectives of the part manufacturer, the environment to which the part is exposed, and the quality of the paint system. Obviously, the thicker the coating, the better the life of the product when exposed to a corroding environment. However, items such as stamping and joining need to be considered. Typically, heavier coatings exhibit more powdering and buildup in the dies when formed/stamped. Spot welding is also adversely affected as the coating gets thicker. The coating can be tailored to achieve the appropriate balance of these factors for the intended fabrication and application of the sheet.

U. S. Steel GALVA-ONE^® Sheet is available with a zinc or zinc-iron alloy coating on one side to meet minimum coating weights in a range from 10 to 100 g/sq m in 10-gram increments.

U. S. Steel GALVA-TWO^® Sheet is coated on both sides with zinc or zinc-iron alloy.  It is available in coating weight ranges from 15 to 100 g/sq m (in 10-gram increments) on one side and from 15 to 70 g/sq m on the opposite side. For GALVA-TWO^®, the coating weight must be specified separately for each side of the sheet.

Coating Weight Designator System
The designator system for specifying the coating type and coating weight when ordering one- and two-side electrogalvanized sheet describes the coating weight and coating type for each side individually.  Further, because this product is most often used for parts that have a requirement for one surface to be very high quality, the exposed and unexposed sides (as used by the customer) also are identified.  There are five basic components to the designator:

• Coating weight in g/sq m for the unexposed surface (Numeric).
• Coating type (G or A) unexposed surface (Alpha).
• Coating weight in g/sq m for the exposed surface (Numeric).
• Coating type (G or A) exposed surface (Alpha).
• Exposed or unexposed designation (E or U) for the finished part.

Coating type and finished part classifications:

G=Free Zinc
A=Zinc-Iron Alloy
X=No Coating, i.e., One-Side
E=Exposed Part
U=Unexposed Part

Surface Treatment
U.S. Steel Electrogalvanized Sheet can be ordered with three variations in surface treatment. Those are:

• Oil
• Prelube Coating
• Dry

Oil
When ordered with "oil", a thin layer of a rust preventative oil is applied on top of the zinc or zinc-iron coating to prevent white rust in coils and lifts during transit and storage. It protects the surface so that a high quality surface is maintained for subsequent painting. Prior to painting, it is important to remove all the oil so that good paint adhesion and freedom from paint blistering are achieved.

Prelube Coating
The application of a prelube coating over the metallic zinc or zinc-iron coating is done to provide a sheet that is readily formable without the need to add additional lubricants at the stamping/forming press. The prelube coating is applied at the exit end of the electrogalvanizing line. The excellent lubricating characteristics of this product provide improved forming.

Dry
Electrogalvanized sheet can be shipped "dry" if it is to be painted and minimal or no cleaning capabilities are available. Unprotected surfaces are susceptible to humid-storage stain; moisture intrusion or condensation during shipment or storage will cause white rust.  Electrogalvanized sheet produced dry must be transported and stored with special precautions to prevent moisture condensation on the steel surface.

GALVA-ONE^® and GALVA-TWO^® are  registered trademarks of United States Steel.