High strength low alloy structural steels

The development of high strength low alloy structural steel has been a remarkable achievement in the field of metallurgy and is of great interest to both the producers and users of structural steels. Higher strength of the steel permits lighter constructions to be made with thinner sections giving rise to steel economy, increase of payload of transport vehicles and a greater utilisation of the design advantages. Of the various techniques available to enhance the properties of structural steels, addition of grain refining and precipitation hardening elements, niobium, vanadium and titanium, to low carbon steels and their controlled rolling or normalising have been found most advantageous. The alloying element required for making these steels is in micro-quantities and a large part of the strength is derived through grain refinement, which also contributes towards toughness. Various factors that control the properties of structural steels such as the effect on strength of the element in solid solution, ferrite grain size, strengthening by precipitation in ferrite, dislocation strengthening and pearlite volume and its fineness, have been discussed. Results of laboratory scale experiments carried out in NML have been summarised. Results of industrial scale trails on the production and controlled rolling of niobium steels carried out in Rourkela Steel Plant have been discussed. (Dr. S.S. Bhatnagar, Shri B.K. Guha, Shri R.K. Sinha; Scientists, National Metallurgical Laboratory. Dr. N.S. Datar, General Superindentent, Rourkela Steel Plant. Dr. R. Chattopadhyay, former Scientist, National Metallurgical Laboratory)