A325 type 3 structural bolts are made from weathering steel, but what does this mean in regards to its resistance to corrosion? In other words, does it rust? To put it simply, yes the steel rusts. The steel contains copper, chromium, and nickel which induces the surface to form a heavy oxide coating, which protects the base material from corroding any further. This brownish-red coating seals the material from corrosion much like other external coating options. Basically, the surface rusts, but as a result develops a protective coating and keeps the steel below the surface free from corrosion. Depending on the climate where the bolts are used, such as the Northwest, hot-dip galvanizing is going to provide a more corrosion resistant coating, however if they are used in a more temperate climate, weathering steel bolts may be more prevalent because of their appearance.