Classification and Joints – Blog 7

Till now we have seen how steel is made, used for different applications, how it behaves as a material, its sustainability and its character in different temperature etc. Let us now see in what ways and how all steel is used in construction. In order to use steel in construction it cannot be used in its pure form it is often composed of contents of other metals to alter it properties and character to suit the purpose and place of construction it is used.

While we come to the use of steel in construction there are a few characteristics which define their usage which are as follows

Galvanic action: It is an electrochemical process where more anodic metal corrodes telling us that the metal used in anode is less resistant to that of the metal used as cathode.

Co-efficient of thermal expansion: The changes occurred in the length of steel due to the effect of temperature is represented by the coefficient of thermal expansion.

Specific Gravity: It is the ratio of the density of the substance to the density of water.

Reflectivity: When light falls on the surface of metals it is either absorbed or reflected. Reflectivity is the ability to scatter the light falling on its surface. More the reflectivity less the absorption of heat.

Oil canning: It is a slight bulging like bubbles or waviness that occurs in steel sheets due to the stresses. This can be prevented by using Thick sheets, backer rod, light colour sheet etc.

As different kind of steel is used for different purpose they are fabricated in one of the following ways:

Welding: In this process the edges are heated and fused together and allowed to cool. It is an easy and strong process. Metal Inert Gas (MIG) and Tungsten Inert Gas (TIG) are used for welding.

Bolting: They are turned tight with cover plate, bracket or gusset plate to prevent slippage.  Bolts are heat treated to gain more strength. It is a quick, easy and cheap process which is reversible.

Riveting: It is a permanent joint similar to nailing. It is used in lap and double joints with cover plate.

Mechanical fastener: It is a mechanical joint which is non-permanent and can be removed or dismantled anytime.

Pin Joint: It is a joint that transfers both horizontal and vertical stresses and constrains the motion. It is used in bridges, walkways etc.

Steel is classified into types like carbon steel (based on carbon content), alloy steel (mixture of other metals) , tool steel ( used in tool making ) and stain less steel so that they can be used where it is most suitable. Stainless steel is further classified as follows.

Ferritic Stainless steel: It has high chromium content having Body Centred Cubic (BCC) structure which is strengthened by cold hardening.

Martensitic Stainless steel: It is strong, tough which is hardened by tempering and heat treatment.

Austenitic Stainless steel: Contains high level of nickel and chromium making it highly corrosion resistance. It is nonmagnetic, non-heat treatable and highly weld able.

Duplex Stainless steel: It is the combination of both Ferritic and Austenitic types and it is twice as hard as the both.

PH steel: Precipitation hardening steel is hardened by a variety of heat treatments.

Check out my next blog to know about how steel is different from other metals.

-Theerthana✌