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Galvanizing

The galvanizing of HSS is gaining in popularity. One misconception concerning the galvanizing of HSS is that the silicon content of the steel must be .03% or lower.

ASTM A385/385M - Standard Practice for Providing High-Quality Zinc Coatings (Hot-Dip) - provides details on steel selection and other design practices such as venting and draining, welding, etc. to ensure the best quality product after galvanizing. Assemblies should consist of elements of similar chemistry and surface condition. Whenever different analyses of steel or different surfaces of steel are united in an assembly the galvanized finish is not generally uniform in appearance. The recommended limits of silicon are below 0.04% or between 0.15% and 0.22% for silicon content. Steel with a silicon range between .05% to 0.14% should be avoided.

Most steels can be satisfactorily hot-dip galvanized. However, reactive elements in the steel, in particular, silicon (Si) and phosphorus (P), can affect hot-dip galvanizing. An appropriate selection of composition can therefore give more consistent quality of coating with regard to appearance, thickness and smoothness.

During steel production, silicon or aluminum is added to remove oxygen. These steels are known as "killed steels". Steel may also be produced without these additions and are then called "rimming steels". Since the content of silicon (Si) affects the hot dip galvanizing reaction, the silicon content should always be taken into consideration for steels that will be galvanized. Aluminum-killed steels suitable for galvanizing have a low silicon content, below 0.03 weight percent. Silicon killed steels with a silicon content above 0.14 % works well in galvanizing, but give a thicker coating than aluminium- killed steels. Other alloying elements in the steel have no major influence on the coating. Semi-killed steels with a silicon + phosphorus content in the range 0.03-0.14 weight percent are called sandelin steels in galvanizing terminology. These steels should be avoided.

Galvanizing Sandelin Curve

The amount of silicon added during the steel-making process can create differences in the appearance of galvanized products. The Sandelin Curve, as seen in the image to the left, compares zinc coating thickness to the mass percentage of silicon in the steel. The recommended silicon composition is either less than 0.03% or between 0.15% and 0.25%. Any steels not within these ranges are considered reactive steels and can be expected to form thicker than average zinc coatings.

Independence Tube does not galvanize in-house, but can arrange to have your items galvanized prior to shipment to you. Contact your Independence Tube Sales Representative for more details and pricing.