Columbium-Boron High-Tensile Steel

Abstract

Boron is Seldom used as an alloying element in low carbon steels, although it is recognised to be a potent and cheap alloy to replace sizable quantities of costly elements normally used in harden able steels, to bolster the depth of hardening. Pearlitic steels of commerce encompass a wide range in composition and properties. Amongst these an economically superior class, is the high tensile steels, that are characterised by good strength, high yield-tensile ratio and adequate ductility. In composition, they are of the low carbon low alloy grade, conducive to easy fabri-cation, which is a highly desirable quality. These feat-ures, particularly, the high mechanical properties in the as rolled or normalised condition, is resposible for their special recognition and commercial popularity. The inve-ntion of molybdenum-boron steel1, more popularly known as fortiweld, was a notable addition to this class, as it extended the scope of boron alloying to non martensiti-cally hardenable steels. However attempts to develop a general class of boron-bearing hightensile steel by repla-cement of with molybdenum with a series of common alloying elements were met with rather discouraging results. Based on these observations and the thermal beha-viour of the steel, it was advocated that fortiweld alloy combiation is a unique entity and its superior strength is the out-come of certain delayed phase transformations.Yet, a critical study of the ageing characteristics, mass eff-ect, and response to heat-treatment of the steel gave certain indications that are common to a precipitation hardening phenomenon. If so, substitution of molybdenum by a chemically similar element appeared to be it logical possibility and in view of similarity in structure anti other pbysico-chemical traits, the element columbium was selected for the purpose.