Grain Refinement and Texture Change in Interstitial Free Steels after Severe Rolling and Ultra-short Annealing

Abstract

A Ti-stabilized interstitial free steel was highly cold deformed to a reduction of 95 % and subsequently submitted to extremely short annealing cycles with heating rates varying between 300°C/s and 4 500°C/s followed by water quench at various temperatures. The microstructural and textural development was studied through various consecutive stages: partially recrystallized, fully recrystallized and after a→g→a transformation. It was found that irrespective of the heating rate the recrystallization has completely terminated before the onset of the ferrite to austenite phase transformation. In the fully recrystallized condition, ultrarapid heating gave rise to substantially refined structures with an average ferrite grain size of 6 mm. It was also observed that this grain refinement saturates with heating rates beyond 1 000°C/s.The transformation structures obtained by ultra fast heating to temperatures in the full austenite region exhibited remarkably coarser grains than the ones observed after ferrite annealing. This coarsening effect was attributed to the effects of heterogeneous nucleation during phase transformation as C was initially present as TiC precipitates in the ferrite matrix.With regard to the texture formation, the characteristic {111} deep drawing fibre of cold rolled IF steels was observed, irrespective of the heating rate, in an annealing treatment as short as 0.3 s. After the forward and reverse a→g transformation, the ensuing ferrite texture displayed a strong memory effect, as the {111} fibre was even more intense after the double transformation than before.

Rapid heating effects on grain-size, texture and magnetic properties of 3% Si non-oriented electrical steel

“…Higher stored energy increases the nucleation rate faster than the growth rate. As a result, the annealing by fast heating leads to a smaller grain-size than that by slow heating, which is in agreement with the results of other researchers Reis et al 2003). Figure 4 shows recrystallized texture at ϕ 2 = 45° Euler angle ODF section at different heating rates.…”

“…Nevertheless, during rapid annealing, a high heating rate can reduce the release of stored elastic energy during recovery, increase the driving force for grains nucleation and coarsening and promote high angle grain boundaries migration, which lowers the orientation dependence on the recrystallization nucleation ; recrystallization nuclei can also form in areas with low stored elastic energy orientation (Reis et al 2003;Sidor et al 2007) and finally decreasing the 〈111〉//ND intensity and increasing the intensity of other texture component.…”

The Effect of Different Annealing Strategies on the Microstructure Development and Mechanical Response of Austempered Steels

“…Another promising annealing route towards the new generation of steels is the ultrafast heating (UFH) [8,[14][15][16][17][18][19][20][21]. This strategy represents an optimization of the heat treatment process by employing heating rates ≥100 • C/s, reducing the annealing time from several minutes to a window of 1 to 10 s. Thanks to the development of longitudinal and transverse flux induction heating technologies, the ultrafast heating of steel strips is feasible at small and large scales [17,22,23].…”

Static and dynamic response of ultra-fast annealed advanced high strength steels

“…To this generation among the others, belong steel processed via quenching and partitioning (Q&P), medium Mn steel and steels processed via ultra-fast annealing (UFA) (Also known as rapid heating or "flash" annealing). Although some recent publications show that the UFA steels could be made industrially feasible, still UFA of steel is considered as an "exotic " treatment, mainly applicable on small size samples in laboratory conditions [3][4][5]. However all result for use of ultrafast heating rates in the range between 400 °C/s and 1500 °C/s followed by quenching (or quenching and partitioning) on the existing AHSS showed increase in both the yield strength and tensile strength together with increase in elongation at fracture [6].…”