Can Stainless Steel Knives Rust? (Yes, Here's Why)
One of the biggest deciding factors when choosing a Japanese knife is stainless steel v.s. High-carbon steel. Historically, high-carbon steel was superior for many reasons, but today both materials offer incredible performance thanks to modern metallurgy. Both can take a beautiful edge and hold it for a very long time, so choosing between them is simply a matter of personal preference. While I love the edge my carbon steel knives take and how they change colour with use, they can also rust super quickly, so they’re not always a good choice. Stainless steel is much easier to care for, so I often reach for a stainless blade when I’m in a hurry. For home cooks and professionals who just want a high-performance knife without the fuss, stainless is the way to go.
But did you know that stainless steel can rust? That’s right; we’ve been lied to all along! Okay, not really, but stainless steel can absolutely rust under the right conditions. Understanding why this happens and how to prevent it might save you a big headache in the future!
First, a little chemistry: steel is made up of iron and a little bit of carbon, and usually, other elements are added to change the composition of the steel and give it desirable properties. To make steel stainless, a minimum of 10.5% chromium is added. Typically, the iron in steel can react with oxygen and form iron oxide (rust or patina), but in stainless steel, the chromium reacts with oxygen and forms a protective chromium oxide layer. This typically prevents the iron within the steel from reacting and makes the steel stainless! That’s stain-LESS, not stain-NEVER: this oxide layer is quite reliable but not impenetrable. There are a few ways it can fail, and steel can rust.
While stainless steel knives are considered lower maintenance, they still require some care.Why Does Stainless Steel Rust?
Since the chromium oxide layer protects the iron inside, anything that interferes with that layer can result in rust. Here are a few common ways your stainless steel knife could rust:
Lack of oxygen. Because the protective layer is caused by the chromium reacting with oxygen, depriving the steel of oxygen can result in rust. If a part of the steel remains wet for hours or days, or if food is left stuck to the blade for too long, rust spots can develop where the water or food is. To prevent this, simply dry your knife before putting it away!
Putting your knife in the dishwasher. I have a saying: “the dishwasher is a good place for things you don’t like very much”. If you have a favourite knife, piece of cookware, or vintage china, the dishwasher likely isn’t the best place to clean them. In the case of stainless steel, the chlorine in dish detergents can interfere with the protective chromium oxide layer, leaving the delicate iron inside susceptible to rust. When we see rusty stainless steel knives come into the shop, the dishwasher is the culprit a good 90% of the time. To prevent this from happening, just wash your knives by hand.
Contact with other metals in the presence of water. Without getting super technical (and because I don’t 100% understand it), if your knife is next to another metal, such as steel, aluminum, chrome, etc., in the presence of water, the metal can transfer electrons over to your knife. The electrons tunnel into the steel, creating something we’ve called pinhole rust. This can cause small pits in the steel that rust. It usually happens when a knife is left to soak in a metal sink or next to metal or cast-iron cookware, but it could also happen if a knife is put away wet on a knife magnet with a metal face. To prevent this, simply wash your knife right away, don’t leave it to soak, and don’t put it away wet on a metal knife magnet. Metal magnets can chip and scratch knives easily anyway, so we suggest wood magnets.
Low chromium content. Some stainless steels have a lower chromium content than 10.5%, such as SLD and VS1. While these steels are relatively stainless, they can oxidize more easily than typical stainless steel and often patina over time. If you use them to cut acidic foods or leave them wet too long, they can rust more easily than other stainless steel but still much less quickly than high-carbon steel, which can rust in minutes or even seconds.
We call knives like the Tadafusa Hocho Kobo 'Semi-stainless' as they can oxidize more easily than other stainless steel.
Ultimately, keeping your stainless steel knives from rusting is easy. Wash and dry them by hand, and try to do it within a few hours of using them. If they do rust, it’s not a big deal. Bar Keepers Friend is the ultimate rust remover and will get your blades looking good as new! Any good knife requires some care, even a stainless steel one. If you look after your blades, they’ll look after you for decades, even a lifetime!
