Hot dip galvanized coatings are achievable on most fabricated ferrous material grades without too much difficulty. These may consist of hot and cold rolled steel sections, cast iron, malleable iron and stainless steel when used in conjunction with other carbon steel. As hot-dip galvanizing is a metallurgical bonding process, when immersed in molten zinc a reaction occurs between the zinc and base steel forming zinc-iron alloy layers with a relatively pure outer zinc layer. Due to this, some susceptible grades of steel may be prone to embrittlement, which is outside our control.
Strain-age embrittlement is caused in certain low-quality steels when areas stressed by cold working are exposed to elevated temperatures, including hole punching and tight radius bending in thicker steel sections. Steels generally have many impurities that gather in high-stress areas. Cracking can occur in certain steels before galvanizing. It is recommended where possible that items be “worked” after galvanizing. Any flaking or cracking will be limited to the zinc coating, which can be repaired using zinc-rich paint.
Hydrogen embrittlement generally occurs in steels with a tensile strength equal to or higher than 100 MPa and harder than 340 DPN. Hydrogen embrittlement rarely affects structural steels. It is likely to be observed when an item is in service and under load. Hydrogen is absorbed during the acid pre-treatment process and then discharged quickly during galvanizing. Specialised steels such as Bisalloy and other susceptible steels should be abrasive blasted immediately before galvanizing to eliminate the requirement for soaking in pre-treatment chemicals.
Liquid embrittlement may occur on high-carbon and stainless steel where susceptible metal absorbs zinc atoms. In critical applications, stainless steel items should not be hot-dip galvanized. When galvanizing non-critical stainless steel items, additional pre-treatment may be required to enable the zinc coating to form.
Other issues related to steel type are generally limited to old ironwork items or castings that are often porous. Castings may have sand embedded, which cannot be removed by pre-treatment processing. Items should be abrasive blasted before delivery.
Of additional note, soft solder and aluminium rivets must not be used in any fabrication, as they will not withstand galvanizing temperatures. Brazed items should be discussed with Hunter Galvanizing staff to confirm suitability.