Effect of Phosphorus on Mild Steel - From A Structural Engineer’s View

It is generally said that the chemical composition of mild steel is very complex with variation of even 0.01% of any element having an effect on theproperty of steel. From a metallurgy engineer view Phosphorus may be the most undesirable element in stee which makes the steel brittle, from a structural engineers view Phosphorus is an interesting element having beneficial as well as harmful effects. Generally structural engineers understand that addition of phosphorus in steel increases the tensile strength and simultaneously decreases the ductility. The design of Reinforced concrete members is governed by the BIS code IS 456 which was first published in 1953. The code was based on the WSM. The code was further revised in year 2000 where the concept of design was revised to LSD. The important question to think is “DOES THE EARLIER CONCEPT OF DESIGN IS WRONG/ UNSAFE TO USE NOW” the answer is NO, as it is generally considered tha structures designed using older methods NOT COST EFFECTIVE but the design done by tha method is still technically correct. Theoretically PHOSPHORUS should not affect the ductility or strength of steel if the design is still done using the older WORKING STRESS METHOD. Agreed that the design will be uneconomical and costly but considering the present scenario where primary steel manufacturers have started increasing the price of TMT who knows, the equation may change and design using older method with high PHOSPHORUS may come out to be equal of even cheaper