It seems that more and more items for boats are being offered in stainless steel and bronze items are becoming increasingly hard to find.
The current aesthetic trend seems to favor the shiny mirror known as stainless steel over the brown patina that will turn green if neglected. While stainless is prettier to look at with its mirrored finish, bronze has many good qualities going for it.
Stainless Steel is an alloy which contains at least 10.5% chromium, this leads to better corrosion resistance for most applications; except in environments that are low in oxygen, high salinity and low air circulation. Sure sounds like the environment below the waterline or encapsulated inside of epoxy! When Stainless Steel is in a low oxygen environment, it begins to suffer what is known as crevice corrosion which is hard to see and detrimental to the metals strength.
Bronze is an older alloy primarily composed of copper, tin, and other corrosion resistant metals. The Bronze Age began around 3000 BCE, and many of the original artifacts are still in relatively good condition. The addition of non-metals, such as silicone, greatly increased the strength, while still retaining the workability and ductility of the alloy.
Stainless Steel will retain its shape while cyclically loaded, showing little sign of distortion or elongation when being pushed near its breaking strength. This cyclic loading in the corrosive marine environment can lead to stress fractures in the metal which will cause catastrophic failure.
Bronze on the other hand is a bit softer and will show signs of elongation and distortion as its limits are reached. This makes it easy to notice during inspection and allows for prompt replacement. Bronze also does not suffer from crevice corrosion, instead it simply forms a light green patina on its surface. This coloring forms a protective barrier called verdigris, which protects the deeper layers from further oxidation.
While most fasteners available in local chandleries tend to all be stainless steel, it is a good idea to know where to get si-bronze fasteners and keep an assortment on board for repairs while underway.