Grades of Stainless – What’s in Your Watch Case?
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Grades of Stainless – What’s in Your Watch Case?

Contrary to what you might think, all stainless steel is not created equal. The question is, are the differences worth the added price? And the answer depends on who you’re talking to. First off, stainless steel is not pure steel. It’s a steel alloy. An alloy is an element made of two or more metals to increase strength or resistance to corrosion. Harry Brearly of Sheffield, United Kingdom, first discovered stainless steel by adding chromium to molten iron to create a rustless metal. Since that time, stainless steel has evolved to include hundreds of different formulations.
Watch Stainless Grade
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Today, the four leading families of stainless are Austenitic, Ferritic, Duplex, and Martensitic & Precipitation Hardening. You’ll find that most of your stainless steel watch cases and bracelets are of the austenitic family. Of the four groups, austenitic steel is mainly non-magnetic and has high strength and corrosion resistance. Perfect for timepieces. It’s difficult to pin down the number of stainless steel grades within the austenitic family since several countries and regions use their own systems. For instance, the United States uses the American Society for Testing and Materials, while France uses the European Standard (EN). And if that’s not quite enough variety for you, some companies have developed and patented unique combinations of metals, including stainless steel. For instance, Rolex uses grade 904L stainless for its cases and bracelets, but it’s a special form of 904L they refer to as Oystersteel. But we’ll get to all that in a minute. For this article, we’re going to focus on the three primary ASTM grades of Austenitic stainless steel: 304/304L, 316L, and 904L.

304 – Garden Variety Stainless

Your stainless steel fridge front, cookware, utensils, pipes – all these things and many more typically use grade 304 stainless. A relatively low price point and easy formability make 304 the go-to grade for nearly everything with the label ‘stainless steel.’ It also has a higher carbon content than its 316L and 904L siblings, making 304 more prone to rust, pitting, and other corrosion. So, while 304-grade stainless steel is excellent for your kitchen, it can be disastrous for your watch. A quality watch case must stand up to sweat, dirt, seawater, chlorine, and any number of other corrosive elements. ASTM 304 can’t do that, which is why only low-end watch manufacturers still use this grade of stainless steel.

316L – Stronger, Sexier Stainless

Also known as surgical or marine grade stainless steel, 316L is generally considered the industry standard for watch cases and bracelets. As the name suggests, this alloy was first used in making surgical instruments and marine craft, both of which have to withstand considerable bombardment from corrosive materials like seawater, chloride, and other acids. When the watch industry began using 316L in their dive watches, it was for many of the same reasons. Today, you don’t have to be a professional diver to justify having a high-quality stainless steel watch. With just the right value to price ratio, 316L gives you durable, anti-magnetic, and luxurious stainless steel at a non-luxury price. The main difference between 304 and 316L? The addition of an element called molybdenum. Adding two to three percent of this silvery-grey metal created a new alloy considerably more adept than 304 at resisting corrosion and is much stronger at higher temperatures. Grade 316L’s lower carbon content (denoted by the ‘L’) makes the alloy less brittle and more elastic. As carbon increases, so does the metal’s hardness, making it more difficult to machine without breaking it.

904L – “Superaustenitic” Stainless

The king of austenitic stainless steel, 904L, has exceptionally high corrosion resistance, as it’s most often used in piping for heat, pollution control, and bleaching equipment. 904L contains more chromium, molybdenum, and nickel than 316L stainless and amounts of silicon, copper, and manganese. These additions enhance the material’s anti-corrosive properties and give it a superior polish and shine. Rolex began using 904L in its SeaDweller watches in the 1980s and has since made this grade of metal standard in all of its watches. Today, several luxury watchmakers use 904L in their timepieces, but Rolex repair gurus generally agree that Rolex has been the most successful at marketing the grade as a “precious metal.” The Swiss watch icon even created its own patented 904L alloy called Oystersteel. This superaustenitic stainless does have its drawbacks, though. For one, the price for 904L metal can top the price of 316L by almost three times, making watches made out of 904L steel considerably more expensive. Additionally, 904L stainless requires specialized equipment to process it into watch cases and bracelets because it’s much harder to form than 316L. Is the added protection and polish of 904L worth the extra price? If you like the luxurious look of highly-polished stainless steel and the added security of knowing that your watch is virtually indestructible, then yes. However, if you feel a 316L stainless steel Grand Seiko or Omega looks just as sharp and you’re ok with an almost-virtually indestructible watch, then save some money and stick with the industry standard. Whatever stainless steel you choose, you can trust the expert watch repair technicians at Times Ticking to take good care of it for you.

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