Galvanneal Steel Vs. Galvanized Steel

A question that we get asked frequently is “What is the difference between Galvanneal Steel and Galvanized Steel?”.

ASTM A653 specification covers steel sheet, zinc-coated (galvanized) or zinc-iron alloy-coated (galvanneal) by the hot-dip process. Generally, no significant difference in properties exists between galvanneal and galvanized steel. Both have similar tensile strengths of 48,000 to 50,000psi.

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Surface of galvanneal with zinc-iron crystals (Reference GalvInfoNote 1.3)

Galvanneal A40 includes 0.40 oz/ft2 of zinc iron alloy that gets baked and annealed into the surface of the steel. Galvanize G90 coating equates to 0.90 oz/ft2 of zinc coating. When comparing the amount of zinc, the galvanized G90 has more than the galvanneal steel A40. The annealing process involves a heat process that changes the surface to zinc-iron crystals that mechanically lock to the paint. The corrosion resistance and performance of galvanneal is synergistically improved with the final powder coat finish.

Galvanneal steel also has improved spot welding and formability, which is required to manufacture roof hatches and smoke vents. Galvanized has a soft zinc coating that is easily scratched and removed during the manufacturing processes.

Nystrom’s powder coat painted galvanneal steel product’s corrosion resistance is superior to that of galvanized steel, which relies on field painting for its final ultimate corrosion resistance properties.

Galvanneal Steel

  • ASTM 653A
  • A-40 (.40 oz/ft2) zinc plating
  • Zinc-iron crystal surface is hard
  • Improved spot-welding and formability
  • Ease of painting
  • Improved coating adhesion – paint mechanically locks to crystals
  • Maximum corrosion protection – performance of galvanneal is synergistically improved with powder coat finish
Galvanized Steel

  • ASTM 653A
  • G-90 (.90 oz/ft) zinc plated
  • Pure zinc is a soft finish, easily scratched
  • Typically factory primed only
  • Corrosion protection depends on field painting

For further reference and details see GalvInfoNote 1.3 and GalvInfoNote 3 found at http://www.galvinfo.com/galv_info_notes.htm.