BLOG 7: STEEL PROPERTIES AND JOINTS

 


In today's session, we came across new terms. One such term is the galvanic action.

Galvanic action is when two metals are in contact with each other one metal acts as an anode (more reactive) and the other metal acts as the cathode (less reactive). 

               Here, cathode doesn't get corroded while the anode gets corroded.

To find out the relationship between metals, the galvanic series is used. This series helps us to find out the metal, which is more reactive or not. 

               The anode is high in the galvanic series while the cathode is low in series. 

Moving out to the coefficient of thermal expansion is the rate of material that expands and contracts due to changes in temperature.


               The material is quantified by coefficients. It is the amount of change per length of material per degree of change in temperature. 


              Coming to specific gravity, it is the ratio of the density of a substance( material) to the density of water. 


  Specific gravity = Density of a substance

                         density of water


Reflectivity is nothing, but the light reflected from the material in relation to the amount of light radiated on the material. Reflectivity is denoted by 'P'. Metals have high reflectivity. 

 

              Moving on to oil canning, it occurs in flat areas of metal roofing and metal wall panels. It is seen as visible waviness.

 

 Prevention measures of oil canning

(i) Choice of material is Thicker/ higher quality material

(ii) Light-colored/ low gloss finish

(iii) Thicker/ higher quality material

(iv) Using baker rod

(v) Skilled workers

Welding is a process that joins the metal together. 

Rivet, pin, bolt, mechanical joints, and mechanical fasteners are used as joints in the above process.

 Pin joint mostly works like a lapped joint and it transfers vertical and horizontal shear loads. Pin joints are used in overhead walkways, pavilions. 

Fasteners are mostly used to connect metals, and they are used in bridges, industrial buildings.

Rivets are permanent joinery. Rivet adds more strength to the buildings. Steel plates in construction are assembled using high-strength bolts.

 

               Next moving on to classification of steel,


Steel is classified into four types,


  • Carbon steel - (mild steel, medium carbon steel, high carbon steel)
  • Alloy steel
  • Stainless steel - (Ferrite, martensitic, austenitic, precipitation hardening, duplex)
  • Tool steel

       

       


In stainless steel, be classified into four types


(i)Ferritic - iron-chromium alloy content with body center cubic crystal structure. It cannot be hardened by heat treatment but can be strengthened by the cold working process. 

 

 

(ii)Martensitic - It is strong and tough but not as corrosion-resistant. It is highly machinable, heat treatable, and magnetic.

 

(iii)Austenitic - It has a face-centered cubic structure. It is mostly corrosion-resistant, non-magnetic, highly weldable, and non-heat-treatable.

 

(iv)Duplex stainless steel - It is a two-phase microstructure comprising grains of ferritic and austenitic. 

 

(v)Precipitation hardening - Stainless steel possesses high strength due to precipitation hardening 

To be continued....   

 

Anjanalakshmi M 

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