If your trained sensibilities have survived the political crassness in this country, then it’s high time we took a pause to appreciate the beauty of our land and in particular the significant contribution by steel and iron in facilitating infrastructure and housing construction that our society depends for the kind of life we live . Apart from being a source of livelihood in the form of welding, metal fabrication and steel rolling mills jobs , steel one of the most widely used metals in buildings construction. It’s used in column bases,concrete columns, in the foundation concrete slab and in walls in the form of binding wires steel bars, wall-pass, door frames and windows ;in roofing it shows up as corrugated iron sheets, steel tiles,ordinarily nails and roofing nails. And that is not all!
So what is steel like
It’s strong and tough like nails and is manufactured from Iron and carbon combo . Whereas Iron is hard heavy metal mined from iron ore or iron stone, Carbon on the other hand is a chemical element found not only in all living things but also in diamond and coal.
As such we are on point, when we say that Steel is a ferrous metal that is relatively cheap, explaining in part why it popular in buildings construction and civil works.It’s cheaper than other metals because of the ingredients – iron ore is like a low hanging fruit-relatively abundant in supply on this planet earth and recyclable.
Up close and personal
Steel being a ferrous metal, it’s various manifestation are classified based on their carbon content .
Wrought iron contains 0.02% carbon. The low carbon content makes it ductile with high melting point making it unsuitable for welding and casting.
Cast iron contain over 2% carbon and with lower melting point making it suitable for welding. Also it is good for casting(i.e. forming an object by pouring molten iron into a moulds, allowing the liquid to become hard and then removing the moulds) and its resistant to corrosion .Hence it is a good material for boiler casting ,street furniture and Manhole covers.
Steel is an alloy of iron and carbon plus a few other element in minor quantities like Nickel. You might find it interesting to learn that 97% of Nickel produced in the world is used in making Steel.
Steel is as tough as nails and is manufactured by smelting iron from iron ores, followed by carbonizing the metal to increase carbon content to a desired level. Then Nickel and other elements in minor quantities are added to it and the molted mix is formed into strips .Finally coils of steel strips are cold rolled into thin sections and profiled sheets.
The carbon content in steel can range from as low as 0.07 % to as high as 1.7%. Higher carbon content in steel increases the strength and wear resistance of the metal but makes it increasingly less elastic or ductile.
Structural steel can be welded and has higher carbon content of about 0.16 to 0.25%.Its normalized by natural cooling in air after hot air rolling.
Hollow section steel
They are made by progressively bending a flat section of steel until it’s almost round. The edges are then fused together at high temperatures. The hollow steel can be circular, oval, square or rectangular.
Profiled steel sheeting
The Pre-coated steel strips are shaped into desired design by passing it through a set of rolls .The continuous profiled sheet is then cut and packaged for hardware store shelves.
- Profiled steel sheets are used make corrugated iron and wall cladding sheets. Corrugated sheets are those sheets that have been moulded into parallel folds or troughs and more often than not,are used as roofing materials. Curved profiled sheets for eaves and the roof hip are manufactured by the brake pressing from the same coated strips.
Steel cable are made by pulling a thin steel rod through a series of tungsten carbide dies which causes the steel rod to increase in length. The pulling process increases the strength of the steel while at same time reducing its ductility. It is because of this phenomena that Steel cable require high carbon content steel as raw materials. For suspended structures the set of individual wires are woven around a core wire to produce a rope. A series of this ropes are then joined to make a cable of required design.
- Weathering steel-This a structural steel alloyed with minor proportions of copper, silicon and manganese. This provide strong resistance to rust and corrosion.
- Stainless steel-It’s an alloy containing 10.5% chromium. The resulting metal-Stainless steel –is resistant to corrosion because of the passive film of chromium oxide that form immediately over the material in the presence of oxygen. When the surface of stainless steel is scratched, the protective layer naturally reforms or as it were heals the damage.
To prevent corrosion steel may be coated with metallic or organic materials. Metallic coating include Zinc, and Zinc aluminium alloys. The coat is applied by dipping steel sheets in hot molten metal. The durability of the coat will depend on the thickness of the coat and the quality of the environment in a given location.
Zinc coating produces galvanized steel sheets and offer protection by acting as a physical barrier between sheet and environment. On the other hand steel coated with Aluminium (55%), Zinc (43.5%) and Silicon (1.5%) is more durable than steel coated by pure Zinc.
Organic coating include liquid paint, powder coating and film.
Steel Tiles are lightweight and made from galvanized steel sheets. They are usually coated with acrylic resin and given a finish that look like grains of sand. These Tiles may give an appearance of traditional tiles but are better because they are lighter and easy to refurbish.
Sources:Materials for Architects and Builders by Arthur Lyons-PhD.