In our second part of the Steel Series, we will explore the main types of steel. As we discussed in the first part of the series, steel is an alloy of iron, carbon and other elements. This alloying process is made to introduce new properties to the finished product, which results in more than 3,500 grades of steel. The main types of steel are:
· Plain Carbon Steel
· Stainless Steel
· Alloy Steel
· Low Alloy Steel
Plain Carbon Steel
As the name implies, plain carbon steel contains only carbon as an alloying element, however, it is can be classified based on its carbon content as ultra-low-carbon steel (<0.015% C), extra-low-carbon (ECL) (<0.05%C), low (<0.3% C), medium (0.3-0.5% C) or high (>0.5% C) carbon.
1. Ultra-low-carbon steel has been used since the 1980s in automobile panels.
2. Extra-low-carbon steel is used for welding where the operating conditions are corrosive.
3. Low-carbon steel: is used in manufacturing of gears, cold-forged parts, cold- drawn parts like wires and stamping.
4. Medium-carbon Steel: also named as machinery steel, is used in the making of shafts, seamless tubing and gears.
5. High-carbon Steel: also called spring steel is used in knives, hand-tools and springs.
Stainless Steel
In stainless steel, the main alloying element used is chromium ranging between 10-30%. This provides the alloy with high resistance to both heat and corrosion. This resistance makes it suitable to be used in cookware, surgical instruments, chemical and food storage tanks and industrial buildings. The main categories of stainless steels are austenitic, ferritic, martensitic, duplex and precipitation-hardening.
In addition to chromium, other alloying elements such as nitrogen, aluminum, silicon, nickel, sulfur and copper can be used to introduce certain characteristic. For example, the addition of nickel can increase the corrosion resistance and adding nitrogen increases its mechanical strength as well as pitting corrosion.
Alloy Steel
As we mentioned in our previous article, various elements can be added to improve the properties of steel. The total amount of the added elements can range between 1-50% by weight. The following are examples of the main elements used and their effects on the produced alloy:
Cobalt: increases hot/red hardness.
Manganese: improves surface hardness as well as resistance to strain and shock.
Tungsten: enhances the grains structure and the heat resistance.
Vanadium: adds strength, toughness and corrosion resistance.
Molybdenum: improves the strength and both the heat and shock resistance.
Low Alloy Steel
Low alloy steel is also called High-Strength Low Ally (HSLA). It provides an added strength over plain carbon steel but with the added benefit of lighter weight compared to its normal alloy counterparts. They usually contain between 0.05-0.25% carbon and up to 2% of other alloying elements to alter the microstructure. Low alloy steel is used in cars, cranes, bridges and other high stress sensitive to weight structures. It can be classified as:
· Weathering steels
· Control-rolled steels
· Pearlite-reduced steels
· Acicular ferrite steels
· Dual-phase steels
· Micro-alloyed steels
Summary
In this article, we discussed the four main types of steel and their differences when it comes to carbon content, alloying elements and applications. You can check our articles here.
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