Microalloyed steel

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

Structure-properties relationship of ultra-fine grained V-microalloyed dual phase steels

Abstract: The effect of vanadium microalloying on ultra-high strength dual phase (DP) ferrite-martensite steel microstructure and properties was studied. It was found that the addition of 0.14 wt% V to a Fe-0.18C-1.5Mn-0.3Si-0.008N reference alloy introduced very significant ferrite grain size refinement in the cold rolled and annealed state. During continuous annealing the initial ferrite to austenite transformation kinetics were strongly retarded, however under slow cooling both pearlite and bainite transformations were suppressed indicating increased hardenability. After cold rolling and intercritical annealing at 750 ⁰C intense V(C,N) precipitates (mean radius 3.7 nm) were observed in the ferrite phase whereas precipitates were scarce in martensite (austenite) and much larger (mean radius 6.7 nm). Significant gains in YS, UTS and work hardening rate were observed at low martensite fractions due to a combination of selective precipitation strengthening and grain refinement of ferrite. However, at higher martensite fractions (> 45%) the YS, UTS and work hardening rate became lower than the reference, primarily due to softening of the martensite. The latter was attributed to the fixing of solute carbon by V(C,N). The net increase in tensile strength with martensite content of the vanadium alloy was ~ 4 MPa/%α’ compared to ~ 16 MPa/%α’ for the reference alloy. A recently developed size-sensitive mean field structure-properties model was extended to capture these microalloying effects. At iso-tensile strength both the fracture strain and hole expansion behaviour of the new microalloyed steel showed improved performance over the reference.

Effect of hot deformation parameters on flow stress and microstructure in a low carbon microalloyed steel

Abstract: Hot deformation behavior of low carbon microalloyed steel was investigated by single-pass compression tests using a thermomechanical simulator. After the specimens were subjected to different hot deformation processes, their microstructures were obtained by constant cooling rate and then examined using optical microscopy and electron backscattering diffraction (EBSD) technique. The results showed that the absence of stress peak in the flow stress curves does not necessarily indicate the absence of dynamic recrystallization (DRX) because in some cases the partial DRX phenomenon does occur when the stress peaks are absent in the flow curves. The metallurgical events that occur during hot deformation directly influence the nature of phase transformation products. High dislocation density in the deformed austenite can promote the intragranular nucleation of acicular ferrite, while the DRX austenite grains prefer to form lath bainite/martensite. The EBSD results confirmed that the microstructures that were transformed from prior pancaked austenite grains always contain higher fraction of middle misorientation angle boundaries and larger average local strain as compared to those with prior DRX grain shape.

Effect of controlled rolling on texture development in a plain carbon and a nb microalloyed steel

Abstract: The effect of finish rolling temperature was investigated on texture formation in a plain C and a 0.034% Nb microalloyed steel. When finish rolled at 1020°C (i.e. within the γ recrystallization range), the textures in both steels contain the {001} and {110} components. The sharpness of the {001} component generally increases with decreasing finish rolling temperature down to 630°C, while the {110} component gradually weakens and finally disappears after ferrite rolling. The microalloyed steel displays much sharper texture than the plain C steel when finish rolled at 870°C (i.e. within the γ pancaking range for the Nb steel) and at 730°C (in the γ+α intercritical range). After finish rolling at 870°C, the major texture components in the microalloyed steel are {113} and {332} , in addition to the above two, while the plain C steel texture only contains some low intensity maxima. When finish rolled at 730°C, weak peaks appear at {223} and {554} in the plain C steel and stronger ones at {4411} and {554} in the microalloyed steel. After warm rolling at 630°C, the major texture components in both steels are {223} , {554} and {001} .The {001} and {110} components are obtained, by transformation, from the {100} (cube) and {122} (twinned cube) components of the recrystallized γ. By contrast, the {113} and {332} components originate, respectively, from the {112} (copper) and {110} (brass) components of the unrecrystallized γ. During continued rolling in the γ+α or α range, these transformation texture components are further modified by deformation and ultimately give rise to the stable end orientations which constitute the well-known warm rolling texture in steels.

Effect of manganese on recrystallisation kinetics of niobium microalloyed steel

Abstract: Using hot torsion tests, the influence of Mn on the recrystallisation behaviour of a Nb microalloyed steel was studied. Continuous and interrupted torsion tests were performed in the temperature range 950–1050°C at strain rates of 0.05–5 s-1. The kinetics of static and metadynamic recrystallisation (MRX) were characterised and appropriate expressions were formulated for the effect of Mn and of the other deformation parameters on the kinetics. The rate of MRX increases with strain rate and temperature and is observed to be independent of strain, in contrast to the observations for static recrystallisation (SRX). The strain rate dependence of MRX is about twice that of SRX, whereas the activation energy Q MRX is about Q SRX/2. Thus, results obtained under laboratory conditions must be corrected before application to industrial strain rates. When extrapolated to the much higher mill strain rates (>100 s-1), the present results indicate that SRX is much slower than MRX and is also unlikely to produce...