Microstructural model for hot strip rolling of high-strength low-alloy steels

Abstract

The microstructural evolution during hot-strip rolling has been investigated in four commercial highstrength low-alloy (HSLA) steels and compared to that of a plain, low-carbon steel. The recrystallization rates decrease as the Nb microalloying content increases, leading to an increased potential to accumulate retained strain during the final rolling passes. The final microstructure and properties of the hot band primarily depend on the austenite decomposition and precipitation during run-out table cooling and coiling. A combined transformation-ferrite-grain-size model, which was developed for plain, lowcarbon steels, can be applied to HSLA steels with some minor modifications. The effect of rolling under no-recrystallization conditions (controlled rolling) on the transformation kinetics and ferrite grain refinement has been evaluated for the Nb-containing steels. Precipitation of carbides, nitrides, and/or carbonitrides takes place primarily during coiling, and particle coarsening controls the associated strengthening effect. The microstructural model has been verified by comparison to structures produced in industrial coil samples.

In situ measurement and modelling of austenite grain growth in a Ti/Nb microalloyed steel

“…However, these TEM studies do not provide measured data for the volume fraction of precipitates. Thus ageing tests in combination with hardness measurements were conducted in the as-received material to provide information on the extent of precipitate strengthening, and also indirectly to some degree on the precipitation kinetics during ageing [40]. For the as-received material only softening was observed, indicating that no substantial formation of new precipitates occurred.…”

Modelling of Microstructure Evolution during Hot Rolling of a 780 MPa High Strength Steel

“…A number of microstructural evolution models have been developed for hot rolling over the last two decades and validated for various steels including HSLA steels with tensile strengths of 400-500 MPa. [1][2][3][4][5][6][7][8] However, the development of these models for higher strength HSLA steels is still in its infancy. A first attempt to extend these model approaches to a 550 MPa HSLA-Nb/Ti steel has been proposed by Militzer et al 8,9) The objective of the present investigation is to extend this microstructure modelling work further to the 780 MPa class of HSLA steels.…”

“…[1][2][3][4][5][6][7][8] However, the development of these models for higher strength HSLA steels is still in its infancy. A first attempt to extend these model approaches to a 550 MPa HSLA-Nb/Ti steel has been proposed by Militzer et al 8,9) The objective of the present investigation is to extend this microstructure modelling work further to the 780 MPa class of HSLA steels. In these higher strength steels with increased alloying additions, recrystallization may be inhibited such that retained strain accumulates during finish rolling.…”

Hot Deformation of 304 Type Austenitic Stainless Steel at High Strain Rates.

“…This may be or may be not realistic since it seems that, up to these days, there is a lack of unequivocal experimental evidence for the hypothesis of calculating loads from extrapolated data. [15][16][17][18] This work presents a simple experimental technique through which strain rates up to 100 s Ϫ1 can be attained during hot torsion testing. Stress-strain curves were obtained for a range of strain rates from 0.1 to 100 s Ϫ1 .…”