Welcome to the Online Metals “Materials Talk” series!
My name is Evan, and I am going to walk you through a high-level understanding of steel,
and the four major types designated by the American Iron and Steel Institute (AISI).
To simplify your understanding we will use the acronym CAST:
that includes Carbon, Alloy, Stainless, & Tool Steel
Carbon steel.
As the name indicates, the main alloying ingredient in this type of steel is carbon.
Carbon steel is highly versatile, and its uses and properties vary depending on its
carbon content.
As the carbon content rises, the steel becomes harder and stronger.
However, it does become less ductile, more brittle and harder to weld.
Also, the higher the carbon, the lower the melting point of the steel.
Carbon steel is further broken down into four groups based on its carbon content: low/mild,
medium, high, and ultra-high.
Also known as Mild Steel, Low Carbon Steel contains approximately 0.04–0.3% carbon.
Because of this, it is malleable, ductile, tough, very easy to weld, and one of the cheaper
forms of steel (Ex. 1018 Steel)
Medium carbon, carbon content of this metal ranges from 0.31–0.6%, is stronger and harder
than Mild Steel, but it is more difficult to weld and form.
It is common in large parts, forged parts, and automotive components.
(Ex. 1045)
High or Carbon Tool Steel generally has a range of 0.61-1.5% carbon.
This material is extremely hard and brittle.
But because of this it is very difficult to bend, weld, or cut.
Lastly, Ultra-High Carbon Steel has a carbon content ranging from 1.51-2% and can be heat
treated to exceptional hardness.
Specialist knives, axles, and punches are typically made from ultra-high carbon steel.
Technically every steel is an alloy, but not all steels are called “alloy steels.”
The term refers to steels that have been alloyed with elements in addition to carbon.
The most common elements include manganese, chromium, nickel, silicon, boron, molybdenum,
and vanadium.
Adding other elements to iron and carbon can improve a range of properties including strength,
hardness, toughness, wear resistance, corrosion resistance, and hardenability.
Alloy steels are broken down into two groups: low-alloy and high-alloy.
Low Alloy Steels – 1-5% alloy content, easily weldable with appropriate precautions.
High Strength Low Allow – not made to chemical composition, but to mechanical properties
High Alloy Steels – Alloy Levels in excess of 10%, giving them outstanding properties
Stainless Steel is steel that has a minimum of 10.5% chromium.
The high chromium and carbon content give stainless steel its iconic corrosion resistance,
hardness, and strength.
There are six main types of stainless steel: austenitic, super-austenitic, ferritic, duplex
steel, martensitic and precipitation-hardening martensitic.
These differences are extremely technical and often aren’t very relevant outside of
welding but stay tuned for a Materials Talk video dedicated to Understanding Stainless.
You can generally find an alloy of stainless steel for any project you could imagine.
At present there are over 150 specific alloys of stainless.
This is why stainless steel is used in everything from medical equipment, cheap knives at mall
kiosks, to spacecraft and airplane hulls.
Tool steel is particularly well-suited for making tools because of its distinctive hardness,
resistance to abrasion and ability to hold a cutting edge at elevated temperatures.
The four major alloying elements in tool steel are tungsten, chromium, vanadium and molybdenum.
Tool steel is often used by blade-smiths in making knives, axes, swords, and more.
According to AISI and SAE specifications, there are six major types of tool steel based
around how they are hardened or what they are used for.
Water Hardening, Cold-working, Shock Resistant, High Speed, Hot Working, & Special Purpose.
These grades are also assigned a letter designation to help clarify what they are.
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