|
Materials Database - Engineering Alloys - Ferrous Alloys
Ferrous alloys are divided into two main categories based on their carbon content. Steel contains between 0.05% and 2.0% carbon and cast iron contains between 2.0% and 4.5% carbon. Steel alloys are further divided into categories based on other alloying contents. Low-alloys steel contain less than 5% noncarbon alloys and high-alloy steels contain greater than 5% noncarbon alloys.
The AISI and SAE numbering systems use the first two digits to define the alloying elements and the last two or three numbers to define the carbon content.
Low Alloy Steels
Carbon Steels [10XX, 11XX, 12XX, 15XX]
Generally, carbon content determines the maximum hardness that can be obtained through heat treatment. A low carbon content (less than 0.3%) is easier to form, weld, and machine. A medium carbon content (0.3-0.5%) balances high toughness and ductility with greater strength and hardness. High carbon content (greater than 0.5%) steels have a high hardness, resist wear, and tend to keep their shape. High carbon content steels are used in tools and blades.
Manganese Steels [13XX]
Manganese is added to achieve a more effective heat treatment with increased strength and toughness over plain carbon steel due to increased hardness depth.
Nickel Steels [23XX, 25XX]
Nickel is added to increase toughness at low temperatures.
Nickel-Chromium Steels [31XX, 32XX, 33XX, 34XX]
Molybdenum Steels [40XX, 44XX]
Molybdenum is added to maintain hardness and strength at high temperatures.
Chromium-Molybdenum Steels [41XX]
Nickel-Chromium-Molybdenum Steels [43XX, 47XX, 81XX, 86XX, 87XX, 88XX, 93XX, 94XX, 97XX, 98XX]
Nickel-Molybdenum Steels [46XX, 48XX]
Chromium Steels [50XX, 51XX, 52XX]
Chromium, like manganese, is added to achieve a more effective heat treatment. Additionally, oxidation is reduced as chromium content is increased. Stainless steels typically have a chromium content over 10.5%.
Chromium-Vanadium Steels [61XX]
Vanadium is added to increase hardenability. This allows the carbon content to remain lower so formability, weldability and toughness can remain higher.
Silicone-Manganese Steels [92XX]
Silicone is added to deoxidize steel.
High Alloy Steels
Three broad categories make up the high alloy steels. Stainless steels use alloys to prevent corrosion, tool steels have a high hardness for fabrication processes, and superalloys are designed to withstand extreme temperatures.
Stainless Steels
This class of steels typically has a chromium content over 10.5%. Stainless steels are categorized as austenitic, ferritic (lower corrosion resistance), martensitic (higher strength and lower ductility), precipitation hardening martensitic (high corrosion resistance and heat treatable), and duplex (combined austenitic and ferretic structures) stainless steels.
Tool Steels
Typically tungsten, molybdenum, and chromium are alloyed with steel to give favorable wear characteritics while maintaining favorable hardenability characteristics.
Superalloys
These high alloy steels are designed to operate at high temperatures. Cobalt, nickel, and chromium are the main alloying elements.
Cast Irons
This ferrous alloy contains iron, carbon, silicon, and manganese. Cast irons are divided into four sections: white iron, gray iron, ductile iron, and malleable iron.
|