The corrosion resistance of stainless steel varies depending on the grade.

You might believe that the stainless steel does not rustbut you are wrong.

Stainless steel rusts less easily than other iron-based metals, but it is not literally “stainless.” Like regular steel, it can degrade and develop discoloration and eventually corrode. The difference is resistance, andStainless steel can last much longer before showing signs of wear.

All steels have the basic composition of iron and carbon, but unlike the rest, stainless steel adds a good dose of chromium to its structure (alloy that gives stainless steel its successful corrosion resistance).

Not all stainless steel is the same.

There are multiple grades of stainless steel, each with slightly different compositions and qualities.

Stainless steel must contain minimum 10.5% chrome. Depending on the grade, it may contain much higher levels and additional ingredients such as molybdenum, nickel, titanium, aluminum, copper, nitrogen, phosphorus and selenium.

The most common grades of stainless steel are 304 and 316. The strategic difference is the addition of molybdenum, an alloy that highly improves corrosion resistance, especially for saline or chloride-exposed environments. 316 stainless steel contains molybdenum, while 304 does not.

For exteriors, stainless steel is an ideal corrosion-resistant material, but it will only withstand long-term exposure if the grade is appropriate for the environment. Grade 304 is the economical and practical choice for exposed environments, but does not have the chloride resistance of grade 316.. The slightly higher price of grade 316 is a good investment for areas with higher exposure, especially heavily salted coastlines and roads and An even superior proposal for even more aggressive environments or for a much longer life are steels coated with fluoropolymers such as PTFE..

Each application for stainless steel has its own unique demand and needs a stainless steel that is up to the task, we can assume that when it comes to stainless steel a 304 grade is the cheapest option and with lower quality and shorter life, followed by with better quality grade 316 and even more superior with greater useful life, quality and resistance to highly corrosive environments steel coated with fluopolymers such as PTFE, PFA, PP or PVDF.

Natural Resistance to Corrosion

Corrosion is a natural phenomenon. Pure elements always react with the environment around them, which is why there are so few elements that occur naturally in their pure form. Iron is no exception.

In rainy or humid conditions iron reacts with oxygen in water to form iron oxide (rust), exposing the material to corrosion.

Stainless steel has the innate ability to form a passive layer that prevents corrosion. The secret? Chrome.

Chromium reacts, very similar to how iron does. The difference is that only a very thin layer of chrome will oxidize. Unlike iron, which rust adheres to surfaces; stainless steel is self-renewing.

Once oxidized, stainless steel typically corrodes at a slow rate of less than 0.08 cm per year.