Is stainless steel truly impervious to staining?

From bathroom sinks to kitchen appliances, and even iconic structures like the Chrysler Building in New York and the Gateway Arch in St. Louis, stainless steel seems to be everywhere. And with good reason: this material is not only durable and adaptable but also 'stainless.' Or at least, that's what its name suggests [source: Pistor].

Stainless steel refers to a group of materials known for their resistance to corrosion and oxidation, which shields them from rust and unsightly marks. Typically, these steels consist of iron mixed with at least 10.5% chromium (often rounded to 11% by engineers). When chromium interacts with oxygen and moisture, such as when a stainless steel pan gets scratched, it forms a thin oxide layer that coats the surface. This self-healing quality ensures the steel maintains its smooth, shiny appearance [source: International Stainless Steel Forum].

Various European and American metallurgists claim credit for the invention of this remarkable material. However, we know that Krupp Iron Works in Germany developed an acid-resistant steel as early as 1908, which was used for a yacht hull. Two other Germans, P. Monnartz and W. Borchers, discovered that steel containing at least 10.5% chromium has better corrosion resistance [source: British Stainless Steel Association]. Meanwhile, American inventor Elwood Haynes patented a type of stainless steel precursor in 1911, and English researcher Harry Brearley developed a similar material around the same time. After a legal battle in which Haynes successfully opposed Brearley’s patent, the two combined their efforts to market the steel as the American Stainless Steel Company. These and other forms of stainless steel were quickly used in cutlery, airplane components, golf clubs, and more [source: Cobb].

However, not all stainless steel is the same.

Types of Stainless Steel

There are four primary types of stainless steel, classified based on their structure and composition. The most common type is austenitic, which makes up 65 percent of stainless steel production. You'll find austenitic steels in everything from kitchenware and cutlery to automotive details and industrial products. These steels contain at least 16 percent chromium, no more than 0.15 percent carbon, and often include nickel or manganese to enhance their strength [sources: American Welding Society, Styria].

Ferritic stainless steels typically contain up to 27 percent chromium, along with aluminum or titanium, but they have minimal or no nickel. While these materials are highly resistant to corrosion, they lack the durability of austenitic steels. Ferritic steels are more affordable and are commonly used in products like mufflers, exhaust systems, and kitchen countertops and sinks [sources: American Welding Society, Styria].

Martensitic stainless steels, while not as resistant to corrosion as austenitic and ferritic types, are known for their exceptional strength and durability. This material contains 12 to 14 percent chromium, along with small quantities of molybdenum (0.2 to 1 percent) and carbon (0.1 to 1 percent). These steels typically have little to no nickel (less than 2 percent). Martensitic stainless steels are magnetic and are often used in applications where this property is useful, such as in kitchen backsplashes where metal objects can be attached without the need for fasteners [sources: American Welding Society, Styria].

Duplex stainless steels combine the strengths of both austenite and ferrite, offering enhanced resistance to corrosion and improved durability. Metallurgists aim to create a composition that’s approximately half austenitic and half ferritic. The resulting material has higher chromium content and lower nickel levels than pure austenitic steels (around 22 to 25 percent chromium, 5 percent nickel, and high molybdenum content). These steels are mainly used in chemical plants and piping systems [sources: American Welding Society, Styria].

You may have noticed that we refer to these stainless steels as "resistant" when talking about their ability to avoid stains. So, is the material truly stain-resistant or completely stain-proof?

"Stain Less," Not "Stainless"

Despite the tough protection it offers, stainless steel is more "stain less" than "stainless." In other words, while the material is highly resistant to discoloration, stains, and imperfections, it is not entirely impervious. Take the Gateway Arch, for example, which has started showing signs of rust and wear as it nears fifty years of standing tall in St. Louis, welcoming visitors [source: Pistor].

Over time, the protective film covering stainless steel can deteriorate, leading to issues like corrosion and pitting. Additionally, chemicals such as chloride, hydrogen, and hydrogen sulfide can cause the protective film to weaken and crack [sources: International Stainless Steel Forum].

The rust resistance of a particular steel is primarily determined by the materials used in its production. The higher the chromium content, the better the corrosion resistance. More robust stainless steels also contain at least 8 percent nickel, providing additional protection against tarnishing [source: International Stainless Steel Forum].

For household users, it’s essential to understand that many items labeled as stainless steel are actually stainless steel plated. While the plating is resistant to corrosion, it can be damaged if scratched or cut deeply enough to expose the underlying material. Since the plating can wear off over time, buyers should check whether a product is entirely made of stainless steel or merely plated [source: Qiu].

Regardless of whether they’re plated, your stainless steel appliances and products still need to be cleaned. Often, good old soap and water will suffice. For tougher stains, professionals recommend various household solutions. A bit of olive oil or window cleaner can eliminate fingerprints and smudges, while white or cider vinegar can restore shine. Avoid using steel wool pads or harsh powders, as these may scratch the surface. For removing burnt food from your stainless steel pan, soak it in warm water and then clean it with baking soda and a nylon scrub pad [sources: Stainless Online].