Effect of Zn-Rich Coatings on the Corrosion and Cracking Resistance of High-Strength Armor Steel Available to Purchase

Scribed panel testing under cyclic salt fog conditions indicates that Zn-rich coatings reduce the corrosion damage observed in armor steel as compared to traditional coatings. Constant extension rate and rising step load testing on armor steel were conducted to evaluate the effect of the Zn-rich coating on environmentally assisted crack (EAC) initiation and propagation in a marine environment. It was found that the presence of the Zn-rich coating did moderately degrade the resistance to crack initiation compared to uncoated steel during immersion in artificial seawater. It was also found that the presence of the Zn-rich coating approximately doubled the crack propagation rates compared to uncoated steel in seawater immersion. Adding a chemical agent resistant coating (CARC) topcoat to the Zn-rich coating improved the resistance to crack initiation in the constant extension rate tests, but had no effect on the crack propagation rates. Intergranular and quasi-cleavage fracture modes were noted for the environment-affected test specimens. Seawater exposures followed by a drying time had no residual effect on crack initiation behavior in air as evaluated by the constant extension rate test. In the presence of a precrack, seawater exposure can serve to initiate cracking, and subsequent arrest during the drying period will depend on the mechanical driving force (i.e., applied stress intensity). The subcritical crack growth rates for Zn-coated material during the drying period is slower than under full immersion conditions, and is similar to, or less than, values obtained for the uncoated condition.