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Rimmed steel is a type of low-carbon steel that has a clean surface and is easily bendable. When steel is normally made, it is deoxidized completely; with rimmed steel, the steel is only partially deoxidized, which allows a rim to form. This rim is almost completely free of other elements and is mostly iron. There is less carbon, so this steel is softer than other types, which makes it ideal for cold-bending and rolling applications. Of all the low-carbon steels, rimmed steel is one of the most common.
When steel is created, the metallurgist uses a deoxidizer to remove the oxygen from the iron and carbon to create steel. If the desired product is rimmed steel, then the deoxidization is only partial, which allows the ingot to remain liquid. During this time, a rim forms around the ingot, which contains fewer impurities than the central area. The impurities, such as carbon and manganese, are held in the center, while the rim is almost completely iron. This means the core has more impurities than most steels, while the outside has fewer impurities than most steels.
Rimmed steel makes use of less carbon than other steel types, so it is much softer than other steels. This means projects that require easily machinable or bendable metals make use of the rimmed metal. It is easily rolled and can be cold-bent and cold-formed. The surface finish also is much cleaner than that of other steels, so it is used for its aesthetic properties and low roughness. Using this steel in hot-bending and other hot processes is actually advised against, though, because the alloying materials and impurities are not uniform, which can cause problems.
While rimmed steel is known for its good surface quality, the quality is usually poor when the steel is being formed. The way in which the rim forms means blowholes will appear on the surface of the steel, because the materials are moving outward and deoxidizing. These holes are removed during the rolling process, to make the metal’s surface uniform and clean.
Rimmed steel is considered a low-carbon steel. Most steels use about 1 percent to 2 percent carbon alloyed with iron. The rimmed variety only uses about 0.15 percent to 0.25 percent carbon. Most steels that are made with 0.15 percent carbon are this type of steel, because it is valued more for being easy to work with than for its strength and durability.
@burcinc-- What are you planning to use the steel rims for?
To add to what @alisha said, deoxidixing agents also make the metal more uniform. That's why rimmed steel has less uniformity and you can't do hot-bending with it.
I don't want to confuse you more, but I think that capped steel is somewhere between rimmed steel and semi-killed steal. It is treated with some deoxidizing agents, but not as much as semi-killed.
Also, the mold is different with capped steel. It's literally capped at the top so you don't get a full rim around the ingot.
@burcinc-- Rimmed steel has little to no deoxidizing agents, whereas killed steel does. Semi-killed is between these two and has some deoxidants added, but not as much as killed steel.
The less the deoxidizing agents added to steel before it is cast, the more blowholes it will get. The blowholes, or bubbles, form because of gas produced in this process. So rimmed steel gets a lot of blowholes and is less dense, light and easily bendable for that reason.
Semi-killed steel has more deoxidizing agents, less blowholes and so is less dense, slightly heavier and less bendable than rimmed steel.
Killed steel has the most deoxidizing agents, no blowholes and is the most dense of this group. It weighs a lot more than rimmed steel and is difficult to bend.
I'm working on a home improvement project and found an ad close by for used steel rims for sale. I want to learn about different steel types so I can figure our which one I need. There are so many different kinds of steel, it's hard not to get confused.
I understand what rimmed steel is, but what about 'killed steel." Is that the opposite of rimmed?
I think there is a third category called "semi-killed' as well and then something called 'capped steel' which is supposed to be close to rimmed steel.
I would love to hear what the differences are between these if anyone can pitch in.