Papers by Keyword: Niobium Content

Abstract: Effect of niobium content on laminar precipitate and high temperature mechanical properties of 21-2N vavle steel was systematically studied, using specimens contain 0.26%, 0.43%, 0.65% 0.82% and 1.06% Nb. After different solid solution treatment and 750 °C aging heat treatment, experimental results showed that laminar precipitate was suppressed by niobium addition, and with the increasing of niobium content, laminar precipitate content decreased and size, distribution and morphology of laminar precipitate was meliorated. Then creep rupture strength and fatigue strength of experimental steels are improved with increasing of niobium.

Abstract: Compressive deformation behaviors of low carbon steels with different Nb contents were investigated in the temperature range 900oC to 1100oC and strain rates from 0.05s-1 to 2s-1 by single pass deformation. Multi-pass compressive deformation processes were also carried out to examine strain accumulation under different Nb contents. In single pass deformations, dynamic recrystallization (DRX) can be observed in the case of low strain rate and high temperature, and the higher Nb steel exhibits higher deformation activation energy (Qdef) and critical strain value (εc) for the onset of DRX. However during multi-pass compression process (interval time of 3-4s), the higher Nb steel has larger strain accumulation between passes, so it is easier for high Nb steel that DRX happens during hot strip rolling process, which starts at relative high rolling temperature.

Abstract: Effects of niobium content and cooling rate on ferrite and bainite start temperatures (Ar3, Bs) and microstructural features have been studied in niobium bearing ultralow carbon microalloyed steels. The Ar3 and Bs temperatures decrease as niobium content or cooling rate is increased. The dependence of Ar3 on cooling rate is greater than that of Bs in all niobium contents. The bainitic ferrite laths become longer and narrower with increasing niobium content and cooling rate, and niobium also shows a tendency to decrease polygonal ferrite grain size.