Credits: Article and images by Joshua Munchow @ Quill & Pad. See the original article here - https://quillandpad.com/2023/09/28/the-science-of-steel-the-stuff-of-cases-mainsprings-hairsprings-pinions-escapements-and-the-backbone-of-watchmaking-reprise/
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The variation among the alloys may be chemically small, but the results are huge. The main changes happen at the atomic level where the alloying elements change how the atoms can move and/or bond to other atoms, altering the macroscopic properties of the bulk material.
Why is this important? What does the process of steel production have to do with watches?
Well, everything.
Importance of grouping
Steel in its many forms is a very versatile material but, due to their specific properties, only a few of the thousands of alloys are practically usable in watches. Some are too soft, too hard, or too brittle; some are magnetic, some rust too quickly, some react with your skin, some corrode in saltwater, and some won’t take a polish.
Steel can be categorized in many ways, but the simplest breakdown based on the chemical compositions results in four categories: carbon steel, alloy steel, stainless steel, and tool steel. Of course all of the categories have alloying elements, but the titles seek to differentiate the basic purpose of each category.
Carbon steels are mainly alloys of iron and carbon with very small amounts of other elements for stability and workability. Tool steels, on the other hand, are usually steels featuring a high carbon content and a specific element added for extreme hardness and rigidity. Stainless steels feature elements (like nickel and chromium) that are resistant to oxidation and produce a less reactive metal.
Finally, alloy steels represent the bulk of the steel alloys (hence the name) and feature a variety of added elements such as manganese, silicon, nickel, titanium, copper, chromium, aluminum, molybdenum, vanadium, tungsten, cobalt, sulfur, phosphorus, and others.
Out of the four general groups, all steels fall into one of nine alloy series, which are given four- (or sometimes five-) digit numbers to differentiate the alloys easily and provide clues to their makeup. Numbering from 1xxx to 9xxx, each category has a primary alloying ingredient, for example 3xxx are nickel-chromium steels, while 1xxx are the plain carbon steels. With regard to the four groups above, different numbered series can fall into the same general categories.
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Credits: Article and images by Joshua Munchow @ Quill & Pad. See the original article here - https://quillandpad.com/2023/09/28/the-science-of-steel-the-stuff-of-cases-mainsprings-hairsprings-pinions-escapements-and-the-backbone-of-watchmaking-reprise/
