Plastic anisotropy of low-carbon, low-manganese steels containing niobium

Abstract

The effect of niobium additions (up to 0.23 pct) on the plastic anisotropy of cold-rolled and annealed low-carbon, low-manganese steels has been studied. When hot-rolling conditions involving coiling temperatures below 1150°F were used, increased concentrations of niobium were deleterious to the development of high plastic anisotropy. Isothermal transformation studies and special hot-rolling studies showed that when transformation from austenite to ferrite and precipitation of carbonitrides occurred at high temperatures (\s>1350°F), excellent plastic anisotropy (•gn about 2) was obtained after cold rolling and annealing. The results are interpreted on the basis of an effect of critical particle sizes or dispersions on the selection of preferred orientations during recrystallization. From electron microscope studies, the critical carbonitride size and interparticle spacing, necessary for the development of high plastic anisotropy, was estimated to be 40 to 500A and 0.04 to 0.5 μm, respectively. However, the presence of a large amount of niobium in solid solution in ferrite is apparently deleterious to the development of high plastic anistropy, even though carbonitrides having the critical size and spacing are present. On the basis of these observations and other published work, it is suggested that second-phase particles influence the development of plastic anisotropy in rimmed and aluminum-killed steels as well as in niobium-and titanium-containing steels. Thus, the degree of plastic anisotropy produced in these steels is influenced by textures developed during annealing, which in turn is dependent on the dispersion characteristics of the particular second-phase particles present.