Precipitation strengthening in high manganese austenitic TWIP steels

Abstract

At low strains (e < 0.25), the precipitation of Ti, Nb, V carbides in austenitic Fe -Mn -C steels which exhibit twinning induced plasticity has no significant effect on work hardening. Strengthening follows the Orowan mechanism and can be described by a simple yield stress offset. However, at higher strains (e > 0.3) the work hardening rate decreased slightly. Synchrotron X-ray diffraction analysis suggested that this was due to a reduction in the kinetics of twin formation. The highest strengthening coefficient in cold strips was obtained with Ti additions £ 0.1 wt.% (+1 380 MPa/ wt.% Ti) but the effect quickly saturated after an increase of *+150 MPa. With Nb additions only modest hardening (+187 MPa/wt.%) could be achieved. The strengthening due to V was > 530 MPa/wt.% for V additions £ 0.4 wt.% Saturation effects are less critical with V additions and yield stress increases of +375 MPa were demonstrated.

Strong and ductile medium Mn steel without transformation-induced plasticity effect

“…Moreover, some large austenite grains also contain the deformation nanotwins (Figure 3(f)). The high thermal stability of deformation nanotwins in present medium Mn steel could be due to V-alloying as it can increase austenite recrystallization temperature [18].…”

Effects of Niobium on Mechanical Twinning and Tensile Properties of a High Mn Twinning-Induced Plasticity Steel

“…5) Microalloying elements such as Ti, Nb and V were deliberately added into Fe(1822)Mn(0.60.9)C TWIP steels to improve the YS by their carbide precipitation. 6) While the increments in YS with additions of Ti, Nb and V to TWIP steels were 1380, 187 and 530 MPa per weight percent, respectively, the strain hardening after yielding was not significantly influenced by the microalloying elements. 6) Considering the crucial effect of mechanical twinning on strain hardening behavior in TWIP steels, the kinetics of mechanical twinning seems to be insignificantly affected by the addition of microalloying elements.…”

Critical Assessment 15: Science of deformation and failure mechanisms in twinning induced plasticity steels

“…19 Besides, twin boundaries can also enhance the workhardening rate by reducing dislocation mean free path. 19,[24][25][26][27] Experimental measurements [28][29][30][31] of the dislocation density by X-ray diffraction and line profile analysis reveal that the dislocation density of TWIP steels at fracture (with a true strain of 0?4-0?5) is usually in the order of 10 15 m…”

“…28 The strengthening coefficients on yield stress of these microalloying elements as carbides are 1380 MPa wt-% 21 for Ti addition <0?1 wt-%, 187 MPa wt-% 21 for Nb and 530 MPa wt-% 21 for V addition <0?4 wt-% respectively. 28 Detailed TEM observation reveals that dislocations (either perfect or partial) can bypass these carbides according to the Orowan mechanism, indicating that the strengthening effect should depend on the average distance of the carbides. 70 Besides, it is also found that the nanometre sized deformation twins can bypass the carbides.…”

“…70 While the carbides do not have significant effect on the workhardening rate at small strain, they may decrease the workhardening rate by suppressing the twinning kinetics at high strain level. 28 The SFE of the austenitic matrix, which depends mainly on the chemical composition and temperature, 38,60,[71][72][73] plays a crucial role in controlling the performance of the deformation mechanisms of TWIP steels. It is generally accepted that deformation twining can occur during plastic ).…”