Effects of trace Ce addition on critical cooling rate and Ti (CN) precipitation of ultra high strength steel plate

Abstract It is well-known that issues always occur for local non-hardenability of 1.5 GPa ultra-high strength steel plates during conventional hot forming processes, once the thickness of the plates is more than 2.5 mm. To resolve the issues, our recent research suggests that adding cerium during metallurgical processes is a prospective approach. This paper adopted a novel process to prepare 1.5 GPa ultra-high strength steel plates using a 25 kg smelting furnace. The research team investigated the effects of trace cerium addition on critical cooling rates characterizing the hardenability for the examined steel plates through measuring experimented continuous cooling transformation curves. The results showed the critical cooling rate of the investigated steel plate was about 10 °C s⁻¹ only, which was at least 60% lower than that of traditional 1.5 GPa ultra-high strength steel plate. Cerium addition suppressed the diffusion of Ti atoms in the Fe matrix and improved Ti (CN) precipitation on the matrix of bcc Fe. This paper revealed that cerium addition substantially reduced critical cooling rates of 1.5 GPa ultra-high strength steel plate and significantly improved the hardenability of the processed steel plates.