Effect of Initial Austenite Microstructure on the Softening – Precipitation Interaction in a Low Nb Microalloyed Steel

Abstract

The influence of initial grain size on the softening-precipitation interaction in a low niobium microalloyed steel has been investigated. The study has revealed that for the largest initial grain size (1000 μm), the recrystallised fraction remains lower than the softening fraction until relatively long times are reached. In contrast, for the smallest initial grain size (166 μm) both magnitudes are similar. As a result, precipitation interacts with recrystallisation in the case of the finest austenite grain size, whereas for the coarsest one, since recrystallisation is significantly retarded, interaction with recovery process is observed. Apparently, the initial austenite grain size does not affect precipitation kinetics.

Improved Model of Kinetics of Strain Induced Precipitation and Microstructure Evolution of Nb Microalloyed Steels during Multipass Rolling

“…In some cases precipitates are detected on replicas before the onset of precipitation is defined by the "plateau" in the softening curve. 41,42) On the other hand, difficulties arise in separating the hardness increment owing to the precipitates from other mechanisms, such as grain size strengthening, solid solution strengthening and dislocation strengthening. 30) It has been found that microhardness measurements lead to longer periods than in chemical analysis for strain-induced precipitation measurements.…”

Thermo-mechanical modeling of thin slab direct rolling of Nb steels

“…Initial austenite grain size has a great effect on the softening and precipitation interaction in micro-alloyed steels. 3…”

“…Initial austenite grain size has a great effect on the softening and precipitation interaction in micro-alloyed steels. 3 Prediction of material mechanical properties based on thermo-mechanical process parameters will provide the steel industry with a very useful tool. Investigations have proved that the yield and tensile strengths are affected by percentages of micro-alloying elements added to the steels and the final ferrite grain sizes.…”