Not all stainless steel is created equal, making many of us question if the added price is worth the difference. Stainless steel was first discovered by Harry Brearly, who lived in Sheffield, United Kingdom. The rustless metal is created by combining chromium and molten iron. Therefore, stainless steel is not pure steel but steel alloy, which is made to increase its strength and resistance to corrosion.
Years after the discovery of stainless steel, it has evolved and now has different formulations. Out of the hundreds, there are four leading families of stainless, namely Austenitic, Ferritic, Duplex, and Martensitic & Precipitation Hardening. Austenitic can be found in stainless steel bracelets and watch cases. This is due to its resistance to corrosion and high strength, making it perfect for timepieces.
There are a number of stainless steel grades within the family of austenitic, plus there are regions and countries with different systems. Besides, some companies developed and patented unique metal combinations for stainless steel. There are wide varieties but three of the primary ASTM grades for Austenitic stainless steel are the following:
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304 – Garden Variety Stainless
This grade is used for almost everything labeled with stainless steel, such as cookware, fridge front, utensils, and pipes. It is due to its easy formability and relatively low price point. Compared to its siblings 316L and 904L, 304 has a higher carbon content making it more prone to pitting, rust, and other corrosion. This makes it a poor choice for your watch since watch cases should withstand corrosive elements like dirt, sweat, seawater, and more. But that doesn’t mean you won’t find it in watches since low-end watch manufacturers use this stainless steel grade.
316L – Stronger, Sexier Stainless
This is considered the industry standard for watch bracelets and cases. It is often referred to as marine or surgical grade stainless steel since it is first used to make marine crafts and surgical instruments. You can expect this alloy to endure considerable bombardment from corrosive materials, including chlorine, seawater, and other chemicals. These are the same reasons why the watch industry used 316L for their dive watches. It can deliver a high-quality stainless steel watch that is anti-magnetic and durable at just the right value to price ratio. The difference between 304 and 316L is the element molybdenum, a silver-grey material that creates a more robust and corrosion-resistant alloy. The L in 316L has a lower carbon content, meaning it is more elastic and less brittle. With increased carbon, the metal becomes more challenging to machine without causing damage or breaking it.
904L – “Superaustenitic” Stainless
This grade is named the king of austenitic stainless steel due to its exceptionally high corrosion resistance. It is used in pollution control, heat piping, and bleaching equipment as it carries more molybdenum, chromium, nickel, and some amount of manganese, silicon, and copper. All these elements increase the anti-corrosive properties of 904L and give it a superior shine and polish. Rolex started using 904L in the 1980s for its SeaDweller and has since made it the standard for all its watches, making them successful in marketing this stainless steel grade as a precious metal. Its price tag is three times more than 316L, which means it is more expensive. Plus, it needs specialized equipment to process it since 904L steel is harder to mold.
Despite these drawbacks, is 904L still worth the extra price? If you want a virtually indestructible and highly polished stainless steel for your watch, then it’s a yes. But you can also settle with the industry standard if you’re okay with the sharpness of 316L stainless steel. One this is for sure no matter what stainless steel material you opt for your watch, always trust an expert watch repair technician like Times Ticking for it.
source: https://www.timesticking.com/grades-of-stainless-whats-in-your-watch-case/
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