Revealing Precipitate Development During Hot Rolling and Cooling of a Ti-Nb Micro-Alloyed High Strength Low-Alloy Steel through X-Ray Scattering

High-energy synchrotron X-ray small-angle scattering (SAXS) is used to study the precipitate development during hot rolling and cooling of a commercial Ti-Nb micro-alloyed, high-strength, low-alloy (HSLA) steel. To study precipitation during hot rolling conditions, Gleeble and dilatometer trials are made. Samples are then studied at room temperature using SAXS in conjunction with transmission electron microscopy (TEM). TEM is used to determine the morphology and composition of the precipitates, whilst both TEM and SAXS are used to study the particle sizes. One major advantage with high-energy SAXS is the ability to make measurements after a minimum of sample preparation and in transmission geometry, as opposed to just at prepared surfaces, plus the possibility to determine volume fractions of the precipitates. The measurements show that after deformation at high temperature, particle coarsening occurs and the volume fraction of precipitates increases after holding for 20 s at 900 degrees C which confirms strain-induced precipitation at finishing rolling conditions. The measurements show that holding at 600 or 650 degrees C for one hour gives a larger volume fraction of nanosized particles. Coiling simulations with slow cooling from 600 to 470 degrees C show coarsening of particles and an increase in the volume fraction of the smaller particles compared to holding at a constant temperature.