Microalloyed steel

About: Microalloyed steel is a research topic. Over the lifetime, 2183 publications have been published within this topic receiving 33586 citations.

Flow stress behaviour, static recrystallisation and precipitation kinetics in a Nb-microalloyed steel after a strain reversal

Abstract: In the present work, a Nb microalloyed steel has been hot worked in torsion mode following multipass deformation sequences. Some of these sequences involve a reversion of the strain. The effect of this reversion on the mechanical response of the steel on reloading after the pre-straining has been analysed. For pre-strains within the strain hardening deformation range, after a transient, the normal flow curve shape corresponding to austenite exhibiting a single peak dynamic recrystallisation is reached. However, the new position of the peak indicates that the dynamic recrystallisation is clearly delayed by the reversal. Deformation sequences including holding times after different strain paths have been used to study the effect of the reversal on the static softening and the strain induced Nb(C,N) precipitation. A complex relationship between the kinetics of both processes and the strain path is observed.

The influence of inclusion chemical composition on weld metal microstructure

Abstract: The effects of nonmetallic inclusions on weld metal microstructures were investigated. The inclusions were extracted from niobium microalloyed steel weld metal specimens, and examined with light and electron microscopic techniques. An EDS (Energy Dispensive Spectroscopy) system was used to determine the chemical composition of the inclusions. Correlation between weld metal and inclusion composition was established. Aluminum, titanium, sulfur, and iron were the most important elements in the inclusions that affect the final weld metal microstructure. Mn/Si ratio was also found to affect the amount of oxygen and acicular ferrite in the weld. The state of deoxidation, as indicated by the amount of FeO present in the inclusions, actually determines the recovery of alloying elements and the amount of oxygen in the weld pool. It also determines the chemical composition of the nonmetallic inclusions. Inclusions with high aluminum content tend to cluster together forming larger particles while pure silica or silicate particles are small and well disseminated in the weld metal. This explains the different inclusion size distributions observed in the weld specimens of different oxygen concentration. Consequently, the prior austenite grain size will be different resulting in different amounts of acicular ferrite and grain boundary ferrite.

On the Cu precipitation behavior in thermomechanically processed low carbon microalloyed steels

Abstract: The present study concerns determination of activation energies of copper-bearing low carbon microalloyed steels processed under different thermomechanical schedules. Selected samples were subjected to 50% cold deformation to examine the effect of prior strain on precipitation of copper. Activation energies were determined by the Kissinger method using differential scanning calorimetry plots obtained at various heating rates. The results are suitably compared with the published results. In view of the results of differential scanning calorimetry, isothermal ageing treatments have been carried out along with suitable microstructural investigations. An attempt has also been made to correlate the variation of hardness and microstructural evolution during ageing treatment.