Steel & Its Properties
October 9, 2018
What is steel? Steel is an alloy made up of iron and carbon along with various other elements. You’ll notice that definition is pretty lax. The World Steel Organization states that there are over 3,500 grades of steel. The amount of carbon, additional alloying elements, and level of impurities essentially determine what grade of steel it is.
You could write a book about the different grades of steel – people have – lots of books actually. The American Iron & Steel Institute (AISI) asserts that there are four main groups that steel falls into. Today we’ll just cover those very basics.
- Carbon Steel – steel with a carbon content up to 2.1% by weight. You can break down categories carbon steel further by placing them into one of the following categories:
- Low carbon steel (mild steel) – typically 0.04%- 0.30% carbon.
- Medium carbon steel – typically 0.31%-0.60% carbon
- High carbon steel –Typically 0.61%-1.50% carbon
- Alloy Steel – steel that contains alloying elements such as manganese, silicon, nickel, titanium, copper, chromium, and aluminum. These elements are added to the steel to in some way alter its properties – ie. Corrosion resistance, strength, ductility, hardenability etc.
- Stainless Steel – steels that contain between 10%-35% chromium. Chromium offers high corrosion resistance. You can break these down a little further by categorizing them based on their crystalline structure. I won’t be diving into the details of the crystalline structures, but some important attributes of each to note:
- Austenitic – Non-magnetic and non heat-treatable. Typically 18% chromium, 8% nickel, and less than .8% carbon. What you normally see in the food industry.
- Ferritic – Magnetic, non heat-treatable, cold working can strengthen. Typically contain 12%-17% chromium, less than 0.1% carbon.
- Martensitic: Magnetic, and heat-treatable. Contain 11%-17% chromium, less than 0.4% nickel and up to 1.2% carbon. Commonly used for medical equipment and cutting tools.
- Tool steel – Tool steel contains varying amounts of tungsten, cobalt, vanadium and molybdenum. The combination increases heat resistance and durability making tool steels perfect for the manufacturing of tools.
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