Investigation of Metallurgical Factors in the Production of High Strength Steel Plate with High Toughness by Controlled Rolling

Abstract

This paper describes a part of the results of a continuing developmental activity to obtain optimun chemical compositions and processing conditions in the production of high strength steel with excellent toughness by controlled rolling. It was noted in the laboratory experiment and mill test that Nb was most effective to improve fracture appearance transition temperature (_υT_s) when a strong controlled rolling was while V was less effective in this respect. Steels containing both Nb and V showed a _υT_s value sianilar to that of Nb bearing steels. Addition of small amounts of Ni, Cr, and Cu to Nb or V bearing steels enhanced precipitation hardening presumably by lowering γ-α: transformation temperature without deterioration of _υT_s-Lowering carbon content below a level of 0.07% in Nb bearing steel considerably improved impact shelf energy without any loss in LYS. Transverse shelf energy was also improved by a decrease in sulfur content and application of cross rolling. However, intensified controlled rolling slightly decreased shelf energy. The improvement of _υT_s by controlled rolling was consistently described by the total rolling reduction below 900°, and was less dependent on rolling reduction of individual pass. A combination of the above knowledges made it possible to produce tough high strength steels, and a few such examples of linepipe plate were shown.