Steel Composition

Steels high in silicon and phosphorous will have a normal protective galvanized finish, but may appear duller than usual. This is the result of greater reactivity between the zinc and the steel, producing a thicker coating which we have no control over. This thicker coating will actually provide a longer protective life since durability is directly proportional to coating thickness.

A thicker dull grey finish will occur on steel with silicon content in the range of 0.04 to 0.14%, moderates on steel containing 0.15 to 0.25% silicon but increases again for silicon levels above 0.25%.  In steel containing silicon and phosphorous, the phosphorous can have a disproportionate effect.  Or hot rolled steels, when Si + 2.5 x P ≤ 0.09%, the coated surface will normally be shiny.

If you are aware prior to galvanizing that the composition falls outside the above parameters, contact us for advice. It should be remembered that the initial finish is transitory in nature and will progressively turn to a matt grey with uniform appearance.


For more information on the effect of steel composition refer to the Galvanizers Association of Australia Advisory Note.
Download Advisory Note

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