The Influence of Initial Grain Size and Strain Sequence of Slab Hot Rolling on the Austenite Evolution of Peritectic Microalloyed Plate Steels

Abstract

The influence of the strain sequence during slab hot rolling (also known as “roughing”) on the evolution of austenite in plain carbon, C-Mn-V and C-Mn-Nb-Ti-V steels was investigated. Reheating and roughing simulations were conducted in a Bähr deformation dilatometer using a constant austenitising temperature, constant soaking time and various heating rates and roughing strain sequences. Stress analysis was used to quantify the austenite softening behaviour and the prior austenite grain size was measured from quenched specimens. The austenite grains of the plain carbon steel were coarser than those of both microalloyed steels, with the C-Mn-Nb-Ti-V grade being the finest due to effective pinning of the grain boundaries. Pass strains greater than 0.2 were sufficient for initiation of dynamic recrystallisation (DRX) for the C-Mn and C-Mn-V steels and led to uniform austenite microstructure with austenite grain sizes less than 40µm after the roughing stage.

Critical Strain for Complete Austenite Recrystallisation during Rough Rolling of C-Mn Steel and Nb-Ti-V Microalloyed Steel

“…2 and 3 show the austenite grain size a) after reheating, b) after roughing schedule I and c) after roughing schedule III for the C-Mn and Nb-Ti-V steels. The fine D 0 in the Nb-Ti-V steel is due to the grain boundary pinning effect of stable TiN precipitates [10]. Grain refinement is achieved in both steels after roughing in all schedules.…”

“…For a given schedule, the C-Mn steel is the coarsest due to a large D 0 which creates a relatively small S v and a large D rex . Comparison of the measured X f and D rex to predicted values from literature is made elsewhere [10]. Poor correlation was found for X f at ε app less than 0.15.…”

“…Recrystallised Fraction -Physical Simulation. The flow curves in schedules I, II and III, from which the inter-pass recrystallised fractions were measured, are reported elsewhere [10]. Fig.…”