Exploring Structural Steel

From the buildings we visit, to the homes we live in to the roads we travel, structural steel is a versatile construction material that offers structural strength and fabrication versatility.


WHAT IS STRUCTURAL STEEL?

Structural steel is a regulated category of steel that must meet industry standards for composition and dimensional tolerances. In the United States. Similarly, Canada and Europe have their own regulating bodies and standards.


These and other structural steel grades are primarily used to build frames of buildings and bridges. They are also used in the construction of:

  • Construction equipment

  • Freight cars

  • Machinery

  • Truck parts

  • Transmission towers

  • Crane booms

  • Truck frames

PRODUCING & TESTING STRUCTURAL STEEL

To fully understand how structural steel differs from non-structural steel, such as steel used in aboveground storage tanks, ships or truck beds, we must first look at structural steel’s composition.

Steel can be produced from recycling old steel, or can be made from raw materials. The process of converting recycled steel into new steel involves melting down existing steel and refining it to fit certain specifications. Producing steel from raw materials is a much longer process.


Steel is an alloy comprised of iron and carbon, both of which are abundant, but rarely found in pure form. To produce steel from raw materials, iron is extracted from iron ore, which is rich in iron oxides. In the United States, the majority of iron ore is extracted from taconite, which is found in abundance in Minnesota. The extraction process grinds taconite into a sandy composition, and uses magnets to separate iron ore (in the form of magnetite) from other minerals and substances.


While iron is typically thought of as being hard and strong, raw iron ore is actually soft enough to cut with a knife and some muscle. It is the addition of carbon that gives iron-based alloys their strength.


The most common way of producing an iron-carbon alloy is by mixing coke, a carbon-rich form of coal, with iron ore and applying heat until the coke ignites. This intense heating causes coke to drop carbons and bond to oxygens from the iron oxides, leaving a mixture of iron and carbon. This process known as reduction.


After reduction, the material contains about 4% carbon. It then undergoes additional heating and cooling processes to reduce the amount of carbon, making the material harder and stronger. The material becomes steel once the carbon content falls below 2.1% of the material’s weight. To produce structural steel, carbon must be further reduced until its composition is only 0.05-0.25%.


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