Use of Vanadium in Long Steel Products
Vanadium has been widely used in long steel products such as forging grades, reinforcing bars, sections, tubes, rails, springs and wire rods. Vanadium is the preferred addition in long steel products because of the much higher solubility of its carbonitrides in austenite and lower sensitivity to carbon level compared to niobium and titanium. Vanadium provides precipitation strengthening and grain refinement, resulting in good combinations of strength and toughness. The precipitation strengthening can be maximized by management of nitrogen level and the preferential precipitation of vanadium with nitrogen also minimizes the risk of nitrogen strain aging. In addition, vanadium enables desired strength levels to be attained at lower carbon content, which is beneficial for ductility and weldability. Furthermore, vanadium contributes to temper resistance and provides secondary hardening for quenched and tempered steels. Fine vanadium carbides also act as strong trap sites for diffusible hydrogen, leading to good delayed fracture resistance. The relatively low solution temperature of vanadium carbonitirdes permits the use of energy efficient, low reheating temperatures. Conventional hot rolling or forging with high finish working temperatures, which are inevitable for production of long steel products, can be used for vanadium microalloyed steels to achieve the required mechanical properties and service performance. In addition, the properties of vanadium microalloyed steels are relatively insensitive to changes in processing conditions.
Vanadium microalloyed steel, precipitation strengthening, grain refinement, hydrogen trapping, long steel product .
Yu Li and David Milbourn
Vanitec Ltd., Winterton House, High Street, Westerham, Kent, TN16 1AQ, England.
Proceedings of the 9th China Steel Conference, 22-25 October 2013