Abstract:
A homogeneous microstructure is required for consistent mechanical properties in
normalised Nb-Ti-V microalloyed plate steels. Frequently, as-hot rolled microalloyed plate
steels have a banded microstructure that is persistent even after normalising heat treatment
(NHT), and this leads to inconsistencies and some scatter in mechanical properties. Therefore,
this work focused on the influence of single-cycle normalising heat treatment (SNHT), doublecycle
normalising heat treatment (DNHT) followed by intercritical annealing normalising heat
treatment (INHT) on the homogenisation and mitigation of a banded microstructure. The study
was conducted on a 0.13C-Nb-Ti-V plate steel grade. The as-hot rolled microstructure was
banded and had a 1.13 Anisotropy Index (AI) value. Results from the three thermal cycles
revealed that the DNHT and INHT mitigated the pearlite microstructural banding and gave a
more homogenized pearlite phase distribution throughout the microstructure, unlike the SNHT
that retained the banding. The DNHT also exhibited the finest ferrite grain size, while the INHT
exhibited the coarsest. From Vickers hardness measurements (153±5.8 HV, 157±3.6 HV and
166±4.5 HV), the UTS was approximately deduced as, 480, 490 and 530 MPa for the SNHT,
DNHT and INHT respectively.
