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Technically, every steel is an alloy, but not all of them have the “alloy steel” designation. To be called alloy steel, other elements must be intentionally added to the iron and carbon composition. A small percentage of alloying elements — typically, no more than 5% — is added to the mix, and these metals can improve corrosion resistance, machinability, and many other properties.
What’s the difference between high and low alloy?
Most people say that high alloy is any steel with alloying elements (not including carbon or iron) that make up more than 8% of its composition. These alloys are less common, because most steel only dedicates a few percent to the additional elements. Stainless steel is the most popular high alloy, with at least 10.5% chromium by mass. This ratio gives stainless steel more corrosion resistance, with a coating of chromium oxide to slow down rusting.
Meanwhile, low alloy steel is only modified slightly with other elements, which provide subtle advantages in hardenability, strength, and free-machining. By lowering the carbon content to around 0.2%, the low alloy steel will retain its strength and boast improved formability.
What are some common alloying elements?
- Manganese: Used in tandem with small amounts of sulfur and phosphorus, the steel alloy becomes less brittle and easier to hammer.
- Chromium: A small percentage (0.5% - 2%) can help to harden the alloy; larger percentages (4% - 18%) have the added effect of preventing corrosion.
- Vanadium: With only .15%, this element can boost strength, heat resistance, and overall grain structure. Mixed together with chromium, the steel alloy becomes much harder, but still retains its formability.
- Nickel: Up to 5%, this alloying element will improve the steel’s strength. In excess of 12%, it provides impressive corrosion resistance.
- Tungsten: Boosts heat resistance, so the melting point is higher. Also improves the structural makeup of the steel.