Interrelationship between Hot Ductility and Particle Size in TiNb IF Steel

Abstract

The aim of this work was to observe the relationship between hot ductility and morphology, distribution and size of particles in TiNb IF steel after hot torsion testing at the critical temperatures of deformation with low as well as maximum values of plasticity. Transmission electron microscopy showed that the particles at all temperatures of deformation with minimum number of turns to failure e.g. 1132°C (33.72 rev.), 946°C (6.24 rev.), 637°C (5.54 rev.) as well as with maximum value of plasticity at 844°C (1726 rev.) were of globular, cuboid or elliptical shape. EDX analysis revealed that there were different types of particles such as carbides, sulfides, and carbonitrides of Ti and Nb, Al and Si oxides, Mn sulfides, and phosphides. Quantitative evaluation of particle size in the carbon extracted replicas showed 20% of total number of particles with size 2r = 30-39 nm and an average linear dimension = 42 nm at the deformation temperature of 1132°C. There were 28% of the particles with size 2r = 20-29nm and = 41nm at the temperature of 946°C while at the temperature of 637°C there were 29% of particles with size 2r = 20-29 and 26% with size 2r=10-19 nm and = 41 nm. In the case of maximum plasticity (1726 rev.) at 844°C, the presence of large particles was confirmed with = 105 nm size and 9% distribution in three size categories of 20-29, 30-39, 90-99 nm.