Mild Steel is cheap and easy to form, basically used for remelting, alloying and manufacturing of fabrication of steel structures. Mild steel is often used when large quantities of steel are needed.
The Steel is generally made of low Carbon and Silicon.
Mild steel has a relatively low tensile strength. Therefore it is not used for special purposes such as reinforcement and heavy structure manufacturing.
Where as, HYSD is High Yield Strength Deformed Bars have ribs on the surface and this increases the bond strength at least by 40%. As HYSD steel is stronger, it saves cost. These bars are used as reinforcement steel for construction purposes.
They are graded as Fe415, Fe500 ie fy of 415 and 500 N/mm2 respectively.