Abstract:
Grain refinement in a polycrystalline material to micron level is known for its beneficial
effects of enhancing both strength and ductility. Severe plastic deformation (SPD) methods
specially equal-channel angular pressing (ECAP) can be adopted for refinement to ultrafine level
where grain size of the order of ~200-300 nm can be achieved, which is an order of magnitude
higher than that can be obtained by thermomechanical treatment (TMT). Ultra high strength,
ductility and high toughness are required along with reduce mass, improved safety and
performance in transportation equipments. ECAP of alloys enhances yield strength to grain
refinement to ultra high range due to ultrafine level (<1µm) but ductility gets reduced
comparison to their coarse grained counterpart due to limited dislocation activity. The solutions
to these problems are not yet found because of which, the applications of UFG materials are
delayed. Grain refinement of low carbon steel suggests that microstructure of bimodal grain size
distribution where majority of grains are in ultrafine range carrying high stress or load and small
fraction of grains in 1-10 µm range restore ductility can be achieved in metals and alloys of
mixed microstructure. Wang et al. have shown that ductility in electrical grade copper can be
regained while retaining strength to about six times that of coarse grained counterpart by
effecting bimodal grain size distribution through cryorolling followed by short annealing above
secondary recrystallization temperature. Therefore, the solution to the problem is to optimize
strength and ductility by producing mixture of ultrafine grains and micron sized grains in the
microstructure. Such a microstructure can be achieved by combining optimized ECAP
parameters with post ECAP deformation and annealing. Interstitial free (IF) steels are known for
their high formability but their low strength acts as a detriment to their wider applications. There
is a need to improve the strength of the material with maintaining ductility. Therefore, the
present investigation is focused on the refinement of interstitial-free steel to ultrafine-grain level
by ECAP to get ultra high strength and post deformation of UFG IF steel by cold rolling and
cryorolling to refine the material further. One of the other major objectives is to get
bimodal/multimodal grain size distribution in IF steel processed by ECAP and post ECAP
deformation followed by flash annealing. Structure-property correlations are to be established
