Dispersion strengthening in vanadium microalloyed steels processed by simulated thin slab casting and direct charging Part 2 – Chemical characterisation of dispersion strengthening precipitates

Abstract

The compositions of sub-15 nm particles in six related vanadium high strength low alloy steels, made by simulated thin slab direct charged casting, have been determined using electron energy loss spectroscopy (EELS). Such particles are considered to be responsible for dispersion hardening. For the first time, particles down to 4 nm in size have had their composition fully determined. In all the steels, the particles were nitrogen and vanadium rich and possibly slightly substoichiometric carbonitrides. Equilibrium thermodynamics predicted much higher carbon to metal atomic ratios than observed in all cases so that kinetics and mechanical deformation clearly control the precipitation process. Thus it is important to formulate the steel with this in mind.