The world of carbon steels can be challenging to wrap your head around. There are many different options to choose from, and each type of steel has different benefits. The main differentiating factor is the amount of carbon that is mixed with iron during production. Other materials, mainly metals, can be added to change the physical properties. Notably, chromium is added to form stainless steel, while other additives can change tensile strength, ductility, or toughness. When looking at the big picture, there are three distinctions between carbon steels: low, medium, and high*.
Carbon Steel Classification Table from Learn Easy
Low carbon steel
Low carbon steels such as 302, 304 or 316 grades of stainless are typically used in applications which require high degrees of corrosion resistance but do not require a hardened surface. The carbon content of these steels typically range between 0.03-0.08%, and consumers typically use these grades of stainless (often without thinking about it) in kitchen equipment, silverware or almost any grade of un-plated steel used in food preparation. It’s great because it can survive the dishwasher without rusting, but it cannot be case hardened due to the very low carbon content.
While it can be used to make linear shafting, it isn’t suitable for loaded ball contact. So if a linear ball bushing were to be used on a soft 304 stainless steel shaft, for example, the balls in the bearing would quickly impact the shaft surface, resulting in visible ball tracking on its surface and a drastic reduction in both bearing and shaft life. It can, however, be used in conjunction with polymer, plain-style bearings which provide great options for both corrosion resistance and self-lubrication. For the right applications, a 300 series stainless steel linear shaft presents a great option for withstanding tough environmental conditions!
Medium carbon steel
Medium carbon steels include grades with carbon contents ranging from 0.25% to 0.60% of the steel mass. Medium carbon grades are typically employed in conjunction with alloys such as chromium, nickel and molybdenum to produce high strength, wear resistance and toughness. Products using medium grades of carbon steel include gears, axles, studs and other machine components that require optimal combinations of strength and toughness.
Medium carbon steels have good machining characteristics, and one of the more popular grades used in machined steel product is AISI 1045. AISI 1045 can also be hardened by heating the material too approximately 820-850C (1508 -1562 F) and held until the material reaches a uniform temperature. It should be soaked for one hour per 25 mm section of material and subsequently cooled in still air.
High carbon steel
High carbon steels are those with carbon contents between 0.60% and 1.4% of the overall weight. The alloys in this particular category constitute the strongest and hardest within the three groups, but they are also the least ductile. These steels are used in a range of different mechanical, cutting and bearing applications as it can be hardened through heat treating and tempering. Additional alloys can be added to this steel category in order to generate different characteristics. Chromium and Manganese, for example, are used in the composition of 52100 steel and aid in the hardening process while enhancing the steel’s resistance to corrosion. Since 52100 is one of the steel grades frequently used to manufacture linear shafting, precise control of the case depth can be critical to generate a shaft with both a hardened surface (for loaded ball contact) and an un-hardened inner core which prevents the shaft from becoming brittle.
Steel alloys are given designators by organizations such as the American Iron and Steel Institute (AISI) and the American Society for Testing and Materials (ASTM) for easier classification and identification. AISI typically follows a four digit system, where the first two digits indicate the alloy, and the second two digits denote the carbon content. ASTM uses an “A” to denote ferrous materials, followed by an arbitrarily assigned number for each alloy.
Regardless of the system used, this standardization allows cross talk between designers, engineers, and builders to ensure the proper material is being selected and used in engineering projects. It also makes looking up physical properties of alloys very easy, as a simple search with the identification number produces the correct information.
As with any selection, there are always advantages and disadvantages to keep in mind when choosing a carbon steel. The main things to consider when choosing carbon steel include final use, required physical properties, and cost. After deciding between low, medium, and high carbon contents, a specific alloy can be chosen from readily available lists to fit your exact needs.
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